研究者データベース

研究者情報

マスター

アカウント(マスター)

  • 氏名

    田地川 浩人(タチカワ ヒロト), タチカワ ヒロト

所属(マスター)

  • 工学研究院 応用化学部門 機能材料化学分野

所属(マスター)

  • 工学研究院 応用化学部門 機能材料化学分野

独自項目

syllabus

  • 2020, 応用化学学生実験Ⅰ, Applied Chemistry Laboratory Ⅰ, 学士課程, 工学部, 実験技術、安全、酸化還元滴定、キレート滴定、酸塩基平衡、錯形成平衡、吸光光度法、クラジウス-クラペイロンの式、蒸発エンタルピー、電荷移動錯体、分子間相互作用、電極反応、計測制御、吸収・蛍光スペクトル、分子軌道論、反応速度、アレニウスの式
  • 2020, 化学英語, English for Chemistry, 学士課程, 工学部, 化学,英語,単語,表記法

researchmap

プロフィール情報

学位

  • 工学博士(北海道大学)
  • 工学修士(北海道大学)

プロフィール情報

  • 田地川, タチカワ
  • 浩人, ヒロト
  • ID各種

    200901040826456760

対象リソース

業績リスト

研究キーワード

  • 物性理論   量子化学   反応設計理論   分子設計理論   

研究分野

  • ナノテク・材料 / ナノ材料科学
  • 自然科学一般 / 数理物理、物性基礎
  • 自然科学一般 / 生物物理、化学物理、ソフトマターの物理
  • 自然科学一般 / 半導体、光物性、原子物理
  • ナノテク・材料 / 基礎物理化学

経歴

  • 2007年 - 現在 北海道大学大学院 工学研究院 助教
  • 1989年 - 1990年 スウェーデン・リンシャピン大学博士研究員
  • 1988年 北海道大学 大学院工学研究科 助手

学歴

  •         - 1988年   北海道大学   工学研究科   応用化学専攻博士後期課程
  •         - 1987年   北海道大学   工学研究科   応用化学専攻 修士課程
  •         - 1985年   北海道大学   工学部   応用化学科
  •         - 1985年   北海道大学

論文

  • Tomoya Takada, Hiroto Tachikawa
    Journal of Physics B: Atomic, Molecular and Optical Physics 54 14 145103 - 145103 2021年07月14日 [査読有り]
  • Hiroto Tachikawa
    ACS Omega 6 25 16688 - 16695 2021年06月29日 [査読有り]
  • Hiroto Tachikawa
    The Journal of Physical Chemistry A 125 21 4598 - 4605 2021年06月03日 [査読有り]
  • Hiroto Tachikawa, Yoshiki Izumi, Tetsuji Iyama, Kazuhisa Azumi
    ACS Omega 6 11 7778 - 7785 2021年03月23日 [査読有り]
  • Yu Hashimoto, Kohei Saito, Toshiyuki Takayanagi, Hiroto Tachikawa
    Physical Chemistry Chemical Physics 23 31 16958 - 16965 2021年 [査読有り]
     

    Theoretical calculations that can account for nuclear quantum effects were carried out to interpret the experimentally-measured photoelectron spectra of the O2·H2O anion complex.

  • Hiroto Tachikawa, Tetsuji Iyama
    CHEMICAL PHYSICS 540 2021年01月 [査読有り]
     
    An in-depth understanding of irradiation effects on DNA and enzymes is important in elucidating the effect of radiation exposure on humans and animals. The catalytic triad Ser-His-Glu is composed of amino acids serine (Ser), histidine (His), and glutamic acid (Glu). In the present study, the radiation effects on Ser-His-Glu have been investigated theoretically using ab initio and direct ab initio molecular dynamics (AIMD) methods. In addition, the effects of micro-solvation in Ser-His-Glu were studied, because X-ray diffraction experiments revealed that one water molecule is located near Ser-His-Glu. Based on geometry optimizations, it was determined that the presence of the H2O molecule results in two structures: a structure wherein the H2O molecule is added to the Glu position of Ser-His-Glu (H2O(A)), and the one wherein the molecule is bonded to the Ser position (H2O(B)). The reaction dynamics after hole-capture were calculated for three structures including the unhydrated structure of Ser-His-Glu (no-H2O). For these structures, the proton transfer (PT) from His to Glu occurred after hole-capture. The PT rate of the no-H2O and the H2O(B) was within 10 fs, whereas that of the H2O(A) was 15 fs. This is indicative of the effect of micro-solvation on the PT time in Ser-His-Glu. The reaction mechanism was discussed based on the theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama
    JOURNAL OF PHYSICAL CHEMISTRY A 124 39 7893 - 7900 2020年10月 [査読有り]
     
    Proton transfer (PT) in an interaction system of a hydroxyl-amino group (OH-NH) plays a crucial role in photoinduced DNA and enzyme damage. A phenol-ammonia cluster is a prototype of an OH-NH interaction and is sometimes used as a DNA model. In the present study, the reaction dynamics of phenol-ammonia cluster cations, [PhOH-(NH3)(n)](+) (n = 1-5), following ionization of the neutral parent clusters, were investigated using a direct ab initio molecular dynamics (AIMD) method. In all clusters, PTs from PhOH+ to (NH3)(n) were found postionization, the reaction of which is expressed as PhOH+-(NH3)(n) -> PhOH+ (NH3)(n). The time of the PT was calculated as 43 (n = 1), 26 (n = 2), and 13 fs (n = 3-5), suggesting that the rate of PT increases with an increase in n and is saturated at n = 3-5. The difference in the PT rate originates strongly from the proton affinity of the (NH3), cluster. In the case of n = 3-5, a second PT was found, the reaction of which is expressed as PhO-H+(NH3)(n) -> PhO-NH3-H+(NH3)(n-1), and a third PT occurred at n = 4 and 5. The time of the PT was calculated as 10-13 (first PT), 80-100 (second PT), and 150-200 fs (third PT) in the case of larger clusters ( n = 4 and 5). The reaction mechanism based on the theoretical results is discussed herein.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICAL CHEMISTRY A 124 41 8421 - 8428 2020年10月 [査読有り]
     
    The ice surface provides two-dimensional reaction fields for bimolecular collisions in interstellar space. As H2O molecules on the surface are typically exposed to cosmic rays, H2O in the excited state is easily dissociated into H + OH, where a H atom is released from the surface to the gas phase. In the present study, the reaction dynamics of small-sized water clusters on the triplet-state potential energy (T-1) surface, following the vertical electronic excitation from the ground state (S-0), were investigated using direct ab initio molecular dynamics to provide insights into the generation mechanism of H atoms from an irradiated ice surface. In all clusters, that is, (H2O)(n) (n = 2-6), the H atom was directly dissociated from one of the H2O molecules in the clusters (direct dissociation), whereas the OH radical remained in the cluster. In the branched form of H2O tetramer (n = 4) and the book form of H2O hexamer (n = 6), the dissociated hydrogen atom (H') collided with the neighboring H2O molecule, and the exchange of H atoms occurred as H' + H2O -> H'-H2O (collision) -> H'OH + H (hydrogen exchange). The translational energy of the exchanged H atom decreases significantly (by approximately 50%) because the kinetic energy of the H' atom is efficiently transferred to the vibrational modes of the cluster during the H-exchange reaction. The mechanism of H atom dissociation is discussed based on theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 124 16 3048 - 3054 2020年04月 [査読有り]
     
    Photoirradiation to a hydrogen-bonded system plays an important role in the initial DNA and enzyme damage processes. The formic acid (FA) dimer is a model compound of double proton transfer systems, such as DNA base pairs. In the present study, the reactions of the FA dimer cation, formed upon ionization of the neutral dimer, have been investigated by the direct ab initio molecular dynamics method. Two reaction channels were identified for the FA dimer cation: complex formation and proton transfer (PT). In the complex formation channel, the carbonyl oxygen atoms of the two FA monomers were bound symmetrically, and a face-to-face complex was formed. In the PT channel, the proton of FA(+) was transferred to FA, forming the H+(HCOOH)-HCO2 radical cation as product. At low temperature, the complex channel was dominant, whereas the PT channel increased with increasing temperature. The asymmetric spin distribution on the FA dimer cation exhibited a strong correlation with the PT channel.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 124 10 1903 - 1910 2020年03月 [査読有り]
     
    Ammonia cluster cations are a chemical species that has recently attracted considerable research attention as an ion-molecule reaction species in the planetary atmosphere, surface reaction species in materials chemistry, and super-alkali species. Reactions of the radical cation of an ammonia cluster, [(NH3)(n)](+) (n = 2-6), following the ionization of the parent neutral cluster, were investigated using direct ab initio molecular dynamics to elucidate the reactions of the ammonia cluster cation under astrochemical conditions. The calculations showed that two competing reaction channels-proton transfer (PT) channel and complex formation channel-operate after the ionization of neutral clusters. In the PT channel, a proton of NH3+ was transferred to a neighboring ammonia molecule. The PT channel was found in all clusters (n = 2-6). Reaction via the PT channel became faster with increasing cluster size and saturated around n = 56. In the complex formation channel, a face-to-face complex having a H3N-NH3+ structure (with a N-N bond) was formed. This channel was found only in larger clusters (n = 5-6). Time scales of PT and complex formation channels were calculated to be 20-30 and 40-50 fs, respectively. The reaction mechanism was discussed based on the results of theoretical calculations.
  • Hiroto Tachikawa, Kazuko Haga, Sadayuki Watanabe, Kazuo Yamada
    JOURNAL OF PHYSICAL CHEMISTRY C 124 10 5672 - 5680 2020年03月 [査読有り][通常論文]
     
    Since the accident at the Fukushima Nuclear Power Station, the stabilization of radioactive nuclides such as alkali metals like Cs has become very important. Cementation is a widespread technique for nuclear waste immobilization due to the low leachability of cementitious materials. Calcium silicate hydrate (C-S-H) is the main component of cement and is known to efficiently retain radioactive ions. In the present study, first-principle quantum chemical calculations were conducted for the C-S-H-Na+(H2O)(n) (n = 0-8) hydration system to elucidate the specific adsorption capacity of C-S-H. In addition, nuclear magnetic resonance (NMR) measurement was performed to detect the chemical shift of Na-23 on C-S-H. The calculations showed that Na+ takes two tapped states close to the C-S-H surface. One is the contact form where Na+ is directly bound to the hydroxyl group (OH) of silanol of C-S-H with one or two hydrogen bonds, and subsequently, three or four water molecules are bound to the Na+ ion. The other one is the solvent separated (ss) form where hydrated Na+ interacts with silanol of the C-S-H surface via H2O. The contact form is more stable in energy than the ss form, although the energy difference is small. Both forms are in equilibrium state on C-S-H. The calculated chemical shifts of Na-23 on C-S-H (-5.14 ppm) were in excellent agreement with that measured by NMR spectroscopy (-4.62 ppm). The electronic states and chemical shifts of Na+ on C-S-H were discussed based on theoretical results.
  • Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 59 2 2020年02月 [査読有り]
     
    The functionalization of graphene surfaces by covalent bonds has attracted much attention. Hydrogenated graphene exhibits ferromagnetism, and the degree of hydrogenation on the graphene surface allows for tuning the band gap. In this study, to elucidate the effect of defects in graphene hydrogenation, we investigated defective graphene wherein one carbon atom was removed from the central region of graphene nano-flake, by density functional theory. Hydrogenation of a graphene nano-flake by electrophilic addition in the gas phase is an exothermic reaction only when defects exist. The activation energy of defective graphene nano-flake hydrogenation is approximately 25 kcal mol(-1) lower than that of the normal graphene one due to the involvement of the defect in surface distortion and transition state stabilization. The results obtained suggest that the hydrogenation of a graphene surface can be controlled by carbon defect. (C) 2020 The Japan Society of Applied Physics
  • Hiroto Tachikawa
    SURFACE SCIENCE 691 2020年01月 [査読有り][通常論文]
     
    The efficiency of metal storage in carbon materials directly affects battery performance. Therefore, elucidating the storage mechanism is important for developing high-efficiency and new storage materials. In this study, interatomic interactions between Li species (Li atoms and Li+ ions) and graphene nanoflakes (GRs) have been investigated using the density functional theory method to elucidate the mechanism of Li storage on GRs. Moreover, single, double, and triple Li species were examined. For single Li systems (it = 1), the binding energy and diffusion barrier of Li on GRs were investigated, while the interatomic interactions and packing structures of Li species on GRs were investigated for double and triple Li systems (n = 2 and 3, respectively). The diffusion barriers for Li+ and Li for n = 1 were calculated to be 5.90 and 6.84 kcal/mol, respectively. For n = 2, the diffusion was strongly affected by the counter Li species and was attributed to the repulsive interactions. For n = 2, the close packing configurations of Li species on the surface of the GRs consisted of biphenyl structures where Li species were located inside the benzene rings of the biphenyl-like site of GRs. For n = 3, three Li species were bound to the triphenylene sites (two biphenyl-like sites). The electronic states of the Li species stored on GRs were discussed using the theoretical results.
  • Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 58 12 2019年12月 [査読有り][通常論文]
     
    The functionalization of fullerenes, which are excellent n-type materials, has received much attention. The substituents enable tuning of the electronic state and fixing to the substrate. In this study, to elucidate the hydrofluorination mechanism of C-60 fullerene, reaction mechanisms involving one or two hydrogen fluoride (HF) molecules were investigated by means of density functional theory. The hydrofluorination of C-60 in the gas phase is an electrophilic addition reaction with only the 1,2-addition being an exothermic. The activation energy of hydrofluorination by two molecules of HF is about 30kcalmol(?1) lower than that with one molecule of HF. This is because hydrogen bonds between HF molecules are involved in the stabilization of the reactant and the aromaticity improvement of the transition state. These results suggest that hydrofluorination can be controlled by the size of the HF cluster.
  • Hiroto Tachikawa, Hiroshi Kawabata
    SOLID STATE SCIENCES 97 2019年11月 [査読有り][通常論文]
     
    The electronic states and band gaps of carbon materials such as graphene, fullerene, and carbon nanotubes are strongly affected by radical addition. In the present study, the reactions of graphene nanoflakes with fluorine (F) atoms were investigated by density functional theory (DFT) in order to elucidate the nature of the bonding between the F atoms and the graphene nanoflakes. Graphene nanoflakes composed of 4-37 benzene rings were used as graphene models. The present calculations reveal that F atoms react with graphene surfaces and bind directly to carbon atoms to form strong C-F bonds. The binding sites are locally C delta+-F delta- polarized and have large dipole moments. The binding energy of F to graphene was calculated to be 30 kcal/mol, which is 1.5 times larger than that for the addition of hydrogen. Fluorine atoms also add to these surfaces without activation barriers, which is very different to hydrogen-addition reactions that have barriers of 5-6 kcal/mol. The electronic states of the fluorinated graphenes are discussed on the basis of the theoretical results.
  • Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 58 6 061010 - 061010 2019年06月 [査読有り][通常論文]
     
    Gallium-doped zinc oxide films prepared by atomic layer deposition have received much attention. When triethylgallium is hydrolyzed on the surface of zinc hydroxide, a multi-layered metal oxide film containing a specific amount of gallium at a controlled position is formed. In this study, to elucidate the micro-hydrolysis mechanism of triethylgallium, reaction mechanisms involving one or two water molecules were investigated by molecular orbital calculations. The complete hydrolysis of triethylgallium occurs in three steps with the first partial hydrolysis being the rate limiting step. The activation energy of hydrolysis by two molecules of water is similar to 10 kcal mol(-1) lower than that with one molecule of water for all steps. The addition of further water molecules significantly decreases the activation energy because the transition state is stabilized by hydrogen bonding between the water molecules. These results suggest the hydrolysis reaction proceeds spontaneously under mild conditions by controlling the concentration of water molecules. (C) 2019 The Japan Society of Applied Physics
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 123 22 4743 - 4749 2019年06月 [査読有り][通常論文]
     
    Carbon dioxide (CO2) is one of the stable and inactive molecules that contribute to greenhouse gases. The development of new reactions of CO, activation, chemical fixation, and conversion is a very important issue. In this report, the reactions of CO2-H2O binary clusters were investigated using a direct ab initio molecular dynamics (AIMD) method to find a new reaction of CO, activation. Clusters composed of carbon dioxide and water molecules, CO2 (H2O)(n) (n = 2-5), were utilized as a model of the binary cluster. The reaction dynamics of [CO2 (H2O)(n)](+) following the ionization of parent neutral clusters were also investigated. Two electronic states of [CO2(H2O)(n)](+) were examined for direct AIMD surfaces: [CO2(H2O)(n)](+) (ground state) and (CO2 ) + (H2O)(n) (excited charge transfer (CT) state). After the ionization of the clusters, a proton-transfer (PT) reaction occurred within the (H2O)(n)(+) moiety at the ground state, whereas the reactive HCO3 radical was formed at the CT state for OH addition to CO2+ : + CO2+(H2O)(n) -> HCO3 +H- (+)(H2O)(n-)(1). The mechanisms of the PT process and the HCO3 radical formation were discussed based on the theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama
    JOURNAL OF PHYSICAL CHEMISTRY C 123 14 8709 - 8716 2019年04月 [査読有り][通常論文]
     
    Carbon materials, such as graphene nanoflakes, carbon nanotubes, and fullerenes, can be used for hydrogen storage. Alkali doping of these materials generally increases their H-2-storage density. In this study, the interaction of hydrogen molecules with Li-doped graphene nanoflakes was systematically investigated using density functional theory (DFT). A large polycyclic aromatic hydrocarbon composed of 37 benzene rings (referred to as GR) was used as a model of a graphene nanoflake, and GR-Li-(H-2) and GR-Li+-(H-2)(n), (n = 0-13) clusters were used as hydrogen storage systems. The first and second coordination shells of H2 around GR-Li were saturated at n = 3 and 7, respectively. The binding energy of H-2 to GR-Li decreased with increasing n, reaching a limiting value at n = 10. For GR-Li+-(H-2)(n), similar results were obtained and the Li atom on GR was shown to be activated by electron transfer from Li to GR. The diffusion barrier of Li+ on GR decreased upon addition of H-2 to Li+ from 6.35 (n = 0) to 3.62 kcal/mol (n = 4). The mechanism of H-2 addition is discussed herein based on the calculated results.
  • Hiroto Tachikawa, Ryoshu Iura, Hiroshi Kawabata
    SCIENTIFIC REPORTS 9 2377 - 2377 2019年02月 [査読有り][通常論文]
     
    Single molecule electron devices (SMEDs) have been widely studied through both experiments and theoretical calculations because they exhibit certain specific properties that general macromolecules do not possess. In actual SMED systems, a residual water molecule strongly affects the electronic properties of the SMED, even if only one water molecule is present. However, information about the effect of H2O molecules on the electronic properties of SMEDs is quite limited. In the present study, the effect of H2O on the ON-OFF switching property of benzene-based molecular devices was investigated by means of a direct ab initio molecular dynamics (AIMD) method. T- and H-shaped benzene dimers and trimers were examined as molecular devices. The present calculations showed that a H2O molecule accelerates the pi-stacking formation in benzene molecular electronic systems. The times of stacking formation in a benzene dimer cation (n = 2) were calculated to be 460 fs (H2O) and 947 fs (no-H2O), while those in a trimer cation (n = 3) were 551 fs (H2O) and 1019 fs (no-H2O) as an average of the reaction time. This tendency was not dependent on the levels of theory used. Thus, H2O produced positive effects in benzene-based molecular electronics. The mechanism of pi-stacking was discussed based on the theoretical results.
  • Hiroto Tachikawa
    SURFACE SCIENCE 679 196 - 201 2019年01月 [査読有り][通常論文]
     
    The interaction and reaction of methyl radical (CH3) with polycyclic aromatic hydrocarbons (PAHs) have been investigated by means of density functional theory (DFT) to systematically elucidate the binding nature of CH3 to graphene nanoflakes. PAHs with n = 4-37, where n indicates the number of benzene rings, were chosen as graphene nanoflakes. The activation energies for the addition of CH3 to the graphene surface were found to be almost constant, with values in the range 13.0-15.0 kcal/mol at the CAM-B3LYP/6-311G(d,p) level, for all PAHs. The binding energies between CH3 and the graphene surfaces were slightly dependent on the size (n): 1.0-4.2 kcal/mol. The absorption spectra showed that a long tail is generated in the low-energy region after CH3 addition to the graphene surfaces. The electronic states of the CH3-added graphenes were discussed on the basis of theoretical results
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 122 16 4121 - 4129 2018年04月 [査読有り][通常論文]
     
    The benzene radical cation (Bz(+)) is a typical model molecule of the Jahn-Teller (J-T) active species. Bz(+) has two structural forms due to the J-T effect. These are the compressed and elongated forms, expressed as Bz(+)(comp) and Bz(+)(elong), respectively. In Bz(+)(comp), the hexagonal structure of the benzene ring is compressed up and down, and in Bz+(elong), it is pulled up and down. From electron spin resonance experiments, it was found that Bz(+) takes a compressed form in low temperature Freon matrices (CF3CI and CF2ClCFCl2), whereas the elongated form was found in argon matrices. However, the selectivity of these structural forms is still unclear. In this study, the ionization dynamics of isolated benzene (Bz) and benzene-M complexes (where M denotes counter-molecules, M = NH3, H2O, CF3Cl, CH4, CH3OH, Ar, SH2, ammonia dimer, or water dimer) have been investigated by means of the direct ab initio molecular dynamics (AIMD) method in order to shed light on the Bz(+) formation mechanism. The static ab initio calculations showed that Bz(+)(comp) is slightly more energetically stable than Bz(+)(elong), although the energy difference was only 0.1 kcal/mol at the CCSD/6-311++G(d,p) level. The direct AIMD calculations indicated that Bz(+)(comp) was formed from the Bz-M complexes when M was NH3, CF3Cl, or an ammonia dimer, whereas the ionization of Bz-M when M was H2O, CH4, CH3OH, SH2, or a water dimer formed Bz(+)(elong). In the case of complexes with an argon dimer, Bz(Ar)(2), both forms were obtained from a slight orientation change of Ar on Bz. A selective rule is discussed on the basis of the calculated results.
  • Hiroto Tachikawa, Yoshiyuki Miyazawa, Ryoshu Iura
    CHEMISTRYSELECT 3 4 1113 - 1119 2018年01月 [査読有り][通常論文]
     
    The pi-stacking interaction plays a crucial role in structural arrangements and molecular assemblies in several molecular systems. In the present study, pi-stacking formation in the benzene trimer cation, (Bz)(3)(+), following ionization of the parent neutral benzene trimer, (Bz)(3), was investigated using direct ab initio molecular dynamics to elucidate the timescale of pi-stacking formation and reaction mechanism in the ionized state. Cyclic (Bz)(3) was chosen as the benzene cluster. After ionizing (Bz)(3), the structure drastically changed to a double pi-stacking form. The (Bz)(3)(+) product vibrated between two structural forms, (Bz-Bz(c))(+)Bz Bz(Bz(c)-Bz)(+), where Bz(c) is a benzene molecule located in the central position of (Bz)(3)(+) and (Bz(c)-Bz)(+) represents a dimer core composed of the benzene dimer cation. The timescale of pi-stacking formation was calculated as 300-380 fs. The absorption spectrum of (Bz)(3)(+) was blue-shifted as a function of time. We discuss the reaction mechanism based on the theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 17 12 8835 - 8841 2017年12月 [査読有り][通常論文]
     
    Functionalized fullerene, graphene, and carbon nanotubes are known as high-performance molecular devices. In this work, the electronic structures and formation mechanism of hydrogen-functionalized fullerene were investigated by means of density functional theory. The mechanism of the addition of a hydrogen atom to the fullerene surface was mainly investigated. Both pure and boron-nitrogen-substituted fullerenes (denoted by C-60 and BNC58, respectively) were examined. We found that the addition of hydrogen atom to B (boron atom) and C (carbon atom) sites of BNC58 proceeded without an activation barrier, whereas the hydrogenation of N (nitrogen atom) sites required activation energy. The electronic states of hydrogen-functionalized C-60 and BNC58 are discussed on the basis of these theoretical results.
  • Hiroto Tachikawa, Kazuko Haga, Kazuo Yamada
    COMPUTATIONAL AND THEORETICAL CHEMISTRY 1115 175 - 178 2017年09月 [査読有り][通常論文]
     
    Since the accident at the Fukushima nuclear power plant, the removal of radioactive cesium ions (Cs-137(+)) from wastewater has become an important topic. Nickel ferrocyanide (Ni-FeCN) is known to adsorb Cs-137(+) preferentially from radioactive waste solutions. However, the mechanism underlying the selectivity of Ni-FeCN is not clearly understood. In the present study, the ion selectivity of Ni-FeCN was investigated by means of density functional theory (DFT) calculations to determine why Ni-FeCN selectively adsorbs Cs+. Models of the interactions of Cs+ and K+ with Ni-FeCN were examined via DFT calculations, which revealed that the hydration energy of Cs+ plays an important role in its selective adsorption by Ni-FeCN. The electronic states of Cs+/K+ in Ni-FeCN are discussed based on the theoretical results. (C) 2017 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 121 28 5237 - 5244 2017年07月 [査読有り][通常論文]
     
    Reactions of the microhydrated hydrogen chloride radical cation, [HCl-(H2O)(n)](+) (n = 1-5), following the ionization of,the parent neutral cluster were investigated by the direct ab initio molecular dynamics (AIMD) method to elucidate the cluster size dependence of the proton transfer (PT) rate in the ionized state. The ionization occurred from the HCl moiety of the clusters. The proton of HCl+ was transferred to the neighboring water molecule in the cluster. The time of PT was strongly dependent on the cluster size (n); the time of PT decreased with increasing n and reached a limiting value at n = 4-5 (the time of PT was ca. 7 fs). The acceleration of the PT rate was mainly caused by the shortness of the hydrogen bond between HCl+ and H2O in larger clusters, that is, a short hydrogen bond causes fast PT. The electrostatic effects of the water cluster further accelerated the rate of PT. After the first PT from HCl+ to H2O, the second PT (H3O+ + H2O -> H2O + H3O+) was detected for n = 3-5. The times of the first and second PTs were calculated as 7-15 and 30-40 fs, respectively.. The reaction mechanism was discussed based on the theoretical results.
  • Hiroshi Kawabata, Hiroto Tachikawa
    C-JOURNAL OF CARBON RESEARCH 3 2 2017年06月 [査読有り][通常論文]
     
    The smallest fullerene C-20 with positive electron affinity is considered to be a new organic nano-electronic material. The binding structures and electronic states of lithium ions and atoms (Li+ and Li) trapped on the surface of C-20 have been investigated by means of density functional theory (DFT) calculation to elucidate the nature of their interaction. It was found that a Li+ can bind to only one site of C-20. This is, specifically, on top of the site where Li+ binds to the carbon atom of C-20. On the other hand, in the case of a Li atom, two structures were obtained besides the on-top structure. One was pentagonal structure which included a Li atom on a five-membered ring of C-20. The other was a triangular structure in which the Li atom bind to the the carbon-carbon bond of C-20. Finally, the nature of the interactions between Li ions or atoms and the C-20 cluster was discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF COMPUTATIONAL CHEMISTRY 38 17 1503 - 1508 2017年06月 [査読有り][通常論文]
     
    Reactions of water dimer cation (H2O)(2)(1) following ionization have been investigated by means of a direct ab initio molecular dynamics method. In particular, the effects of zero point vibration and zero point energy (ZPE) on the reaction mechanism were considered in this work. Trajectories were run on two electronic potential energy surfaces (PESs) of (H2O)(2)(+) : ground state ((2) A ''-like state) and the first excited state ((2)A '-like state). All trajectories on the ground- state PES lead to the proton- transferred product: H2O+(Wd)center dot H2O(Wa) -> OH(Wd)center dot H3O+(Wa), where Wd and Wa refer to the proton donor and acceptor water molecules, respectively. Time of proton transfer (PT) varied widely from 15 to 40 fs (average time of PT=30.9 fs). The trajectories on the excited- state PES gave two products: an intermediate complex with a face- to- face structure (H2O-OH2)(+) and a PT product. However, the proton was transferred to the opposite direction, and the reverse PT was found on the excited- state PES: H2O(Wd)center dot H2O+ (Wa) -> H3O+ (Wd)center dot OH( Wa). This difference occurred because the ionizing water molecule in the dimer switched between the ground and excited states. The reaction mechanism of (H2O)(2)(+) and the effects of ZPE are discussed on the basis of the results. (C) 2017 Wiley Periodicals, Inc.
  • Hiroto Tachikawa
    CHEMICAL PHYSICS 490 12 - 18 2017年06月 [査読有り][通常論文]
     
    Biphenyl (Bp) and its related compounds are widely applied in single-molecule electronic devices. In this study, the effects of micro-solvation on the hole capture (ionization) dynamics of Bp were investigated by means of direct ab initio molecular dynamics (AIMD) simulations. The micro-solvation of Bp was simulated using one and two water molecules (i.e., Bp(H2O)(n) (n = 0-2)). The reaction dynamics of Bp(+)(H2O)(n)). following hole capture were investigated via direct AIMD simulation. In the case without H2O (n = 0), the twist angle of Bp(+) periodically vibrated without decay. In contrast, when water molecules were near Bp(+), the amplitude of the twist angle vibration decayed periodically. The formation of hydrogen bonds between Bp(+) and water molecules prevents periodic vibration by generating friction. The electronic states and reaction mechanism were investigated based on the theoretical results. (C) 2017 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    APPLIED SURFACE SCIENCE 396 1335 - 1342 2017年02月 [査読有り][通常論文]
     
    Polycyclic aromatic hydrocarbons (PAHs) provide a 2-dimensional (2D) reaction surface in 3-dimensional (3D) interstellar space and have been utilized as a model of graphene surfaces. In the present study, the reaction of PAHs with atomic hydrogen was investigated by means of density functional theory (DFT) to systematically elucidate the binding nature of atomic hydrogen to graphene nanoflakes. PAHs with n = 4-37 were chosen, where n indicates the number of benzene rings. Activation energies of hydrogen addition to the graphene surface were calculated to be 5.2-7.0 kcal/mol at the CAM-B3LY13/6-311G(d,p) level, which is almost constant for all PAHs. The binding energies of hydrogen atom were slightly dependent on the size (n): 14.8-28.5 kcal/mol. The absorption spectra showed that a long tail is generated at the low-energy region after hydrogen addition to the graphene surface. The electronic states of hydrogenated graphenes were discussed on the basis of theoretical results. (C) 2016 Published by Elsevier B.V.
  • Saori Yoshizawa, Shigeaki Abe, Mami Mutoh, Teruo Kusaka, Mariko Nakamura, Yasuhiro Yoshida, Junichiro Iida, Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 56 1 2017年01月 [査読有り][通常論文]
     
    Oligosilane-functionalized C-60 fullerenes [namely, C-60-(SiH2)(n)-H, n = 1-4] have been investigated by the density functional theory (DFT) method to elucidate the structures and electronic states of oligosilane-radical added fullerene. The DFTcalculation showed that oligosilane radicals bind to the carbon atom of C60 in the on-top site, and a strong Si-C heterojunction is formed. The binding energies of oligosilane radicals to C-60 were calculated to be 24.6-28.2 kcal/mol at the CAM-B3LYP/6-311G(d, p) level. The electronic states of oligosilane-functionalized fullerenes C-60-(SiH2)(n)-H are discussed on the basis of theoretical results. (C) 2017 The Japan Society of Applied Physics
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 120 37 7301 - 7310 2016年09月 [査読有り][通常論文]
     
    The ice surface provides an effective two-dimensional reaction field in interstellar space. However, how the ice surface affects the reaction mechanism is still unknown. In the present study, the reaction of an ammonia dimer cation adsorbed both on water ice and cluster surface was theoretically investigated using direct ab initio molecular dynamics (AIMD) combined with our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) method, and the results were compared with reactions in the gas phase and on water clusters. A rapid proton transfer(PT) from NH3+ to NH3 takes place after the ionization and the formation of intermediate complex NH2(NH4+) is found. The reaction rate of PT was significantly, affected by the media connecting to the ammonia dimer. The time of PT was calculated to be SO fs (in the gas phase), 38 fs (on ice), and 28-33 fs (on water clusters). The dissociation of NH2(NH4+) occurred on an ice surface. The reason behind the reaction acceleration on an ice surface is discussed.
  • Hiroto Tachikawa, Tomoya Takada
    COMPUTATIONAL AND THEORETICAL CHEMISTRY 1089 13 - 20 2016年08月 [査読有り][通常論文]
     
    The proton transfer (PT) reaction after water cluster ionization is known to be a very fast process occurring on the 10-30 fs time scale. In the present study, the ionization dynamics of the branched water tetramer (H2O)(4) were investigated by means of a direct ab initio molecular dynamics (AIMD) method to elucidate the time scale of PT in the water cluster cation. A long-lived non-proton-transferred intermediate was found to exist after the ionization of the branched-type water cluster. The lifetimes of the intermediate were calculated to be ca. 100-150 fs. PT occurred after the formation of the intermediate. The structure of the intermediate was composed of a symmetric cation core: H2O-H2O+-H2O. The broken symmetry of the structure led to PT from the intermediate. The reaction mechanism is discussed based on the theoretical results. (C) 2016 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICAL CHEMISTRY A 120 33 6596 - 6603 2016年08月 [査読有り][通常論文]
     
    The mechanism by which CO2 is formed in the interstellar space remains a mystery. The most likely reaction is collision between CO and OH; however, previous theoretical works have shown that the activation barrier for CO2 formation is high enough to prevent the reaction at the low thermal conditions of space (similar to 10 K). The effects of single water molecule on the reaction barrier of CO, formation from reaction between CO and OH have been investigated here by means of ab initio calculation. The barrier height along the lowest-energy pathway in the reaction between CO and OH in the absence of the H2O molecule was calculated to be 2.3 kcal/mol when CCSD(T) energy corrections are combined with the MP2 basis set limit. In the case of the hydrated (H2O-CO-OH) system, the inclusion of a single H2O molecule into the system significantly decreased the barrier height to 0.2 kcal/mol. This suggests that CO2 can be formed when CO and OH react in the presence of H2O, even under thermal conditions as low as 10 K.
  • Hiroto Tachikawa, Tomoya Takada
    CHEMICAL PHYSICS 475 9 - 13 2016年08月 [査読有り][通常論文]
     
    The surfaces of icy planets and comets are composed of frozen water (H2O), carbon dioxide (CO2), and methane (CH4). These surfaces are irradiated by solar wind and cosmic rays from the interstellar space and they cause ionization of surface molecules. In this report, the effects of ionization of cold water clusters have been investigated using a direct ab initio molecular dynamics (AIMD) method to elucidate the rate of proton transfer (PT) in cations of small water clusters (H2O)(n) (n = 2-7). After ionization of the water clusters, PT occurred in all the cluster cations, and dissociation of the OH radical occurred for n = 4-7. The time of PT decreased with increasing the cluster size at n = 2-5 and reached a limiting value at n = 6 and 7. The mechanism of the PT process in ionized water clusters was discussed based on the theoretical results. (C) 2016 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 6 2016年06月 [査読有り][通常論文]
     
    Functionalized graphenes are known as a high-performance molecular device. In the present study, the structures and electronic states of the aryl radical functionalized graphene have been investigated by the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of graphene (GR). Also, the mechanism of aryl radical reaction with GR was investigated. The benzene, biphenyl, p-terphenyl, and p-quaterphenyl radicals [denoted by (Bz)(n) (n = 1-4), where n means numbers of benzene rings in aryl radical] were examined as aryl radicals. The DFT calculation of GR-(Bz)(n) (n = 1-4) showed that the aryl radical binds to the carbon atom of GR, and a C-C single bond was formed. The binding energies of aryl radicals to GR were calculated to be ca. 6.0 kcal mol(-1) at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists in the aryl radical addition: the barrier heights were calculated to be 10.0 kcal mol(-1). The electronic states of GR-( Bz) n were examined on the basis of theoretical results. (C) 2016 The Japan Society of Applied Physics
  • Hiroto Tachikawa
    SURFACE SCIENCE 647 1 - 7 2016年05月 [査読有り][通常論文]
     
    The solid surface provides an effective two-dimensional reaction field because the surface increases the encounter probability of bi-molecular collision reactions. Also, the solid surface stabilizes a reaction intermediate because the excess energy generated by the reaction dissipates into the bath modes of surface. The ice surface in the universe is one of the two dimensional reaction fields. However, it is still unknown how the ice surface affects to the reaction mechanism. In the present study, to elucidate the specific property of the ice surface reaction, ionization dynamics of water dimer adsorbed on the ice surface was theoretically investigated by means of direct ab-initio molecular dynamics (AIMD) method combined with ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) technique, and the result was compared with that of gas phase reaction. It was found that a proton is transferred from H2O+ to H2O within the dimer and the intermediate complex H3O+ (OH) is formed in both cases. However, the dynamic features were different from each other. The reaction rate of the proton transfer on the ice surface was three times faster than that in the gas phase. The intermediate complex H3O+(OH) was easily dissociated to H3O+ and OH radical on the ice surface, and the lifetime of the complex was significantly shorter than that of gas phase (100 fs vs. infinite). The reason why the ice surface accelerates the reaction was discussed in the present study. (C) 2015 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    SOLID STATE SCIENCES 55 138 - 143 2016年05月 [査読有り][通常論文]
     
    Electronic structures and formation mechanism of hydrogen functionalized carbon nanotube (CNT) have been investigated by means of density functional theory (DFT) method. The mechanism of hydrogen addition reaction to the CNT surface was also investigated. Pure and boron-nitrogen (BN) substituted CNT (denoted by CNT and BN-CNT, respectively) were examined as the carbon nanotubes. It was found that the additions of hydrogen atom to B (boron atom) and C (carbon atom) sites of BN-CNT proceed without activation barrier, whereas the hydrogenation of N (nitrogen atom) site needs the activation energy. The electronic states of hydrogen functionalized CNT and BN-CNT were discussed on the basis of theoretical results. (C) 2016 Elsevier Masson SAS. All rights reserved.
  • Mami Mutoh, Shigeaki Abe, Teruo Kusaka, Mariko Nakamura, Yasuhiro Yoshida, Junichiro Iida, Hiroto Tachikawa
    ATOMS 4 1 2016年03月 [査読有り][通常論文]
     
    The ternary interaction system composed of fluorinated ethylene carbonate, denoted by EC(F), lithium ion (Li+) and a model of nano-structured graphene has been investigated by means of the density functional theory (DFT) method. For comparison, fluorinated vinylene carbonate, denoted by VC(F), was also used. The model of graphene consisting of 14 benzene rings was examined as a nano-structured graphene. The effects of fluorine substitution on the electronic state and binding energy were investigated from a theoretical point of view. It was found that both EC(F) and VC(F) bind to a hexagonal site corresponding to the central benzene ring of the model of the graphene surface. The binding energies of Li+EC(F) and Li+VC(F) to the model of graphene decreased with increasing number of fluorine atoms (n).
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICAL CHEMISTRY A 120 9 1529 - 1535 2016年03月 [査読有り][通常論文]
     
    To design theoretically the high-performance proton switching element based on DNA base pair, the effects of fluorine substitution on the rate of proton transfer (PT) in the DNA model base pair have been investigated by means of direct ab initio molecular dynamics (AIMD) method. The 2-amino-pyridine dimer, (AP)(2), was used as the model of the DNA base pair. One of the hydrogen atoms of the AP molecule in the dimer was substituted by a fluorine (F) atom, and the structures, of the dimer, expressed by F-(AP)(2), were fully optimized at the MP2/6-311++G(d,p) level. The direct AIMD calculations showed that the proton is transferred within the base pair after the vertical ionization. The rates of PT in F-(AP)(2)(+) were calculated and compared with that of (AP)(2)(+) without an F atom. It was found that PT rate is accelerated by the F-substitution. Also, the direction of PT between F-AP and AP molecules can be clearly controlled by the position of F-substitution (AP)(2) in the dimer.
  • Shigeaki Abe, Shimpei Kawano, Yu Toida, Mariko Nakamura, Satoshi Inoue, Hidehiko Sano, Yasuhiro Yoshida, Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 3 2016年03月 [査読有り][通常論文]
     
    The structures and electronic states of alkyl-radical-functionalized C-20 fullerenes (denoted by C-20-R) have been investigated using density functional theory (DFT). The different alkyl radicals investigated were methyl, ethyl, propyl, and butyl radicals. The DFT calculation indicated that the alkyl radical binds to the carbon atom of C-20 in the on-top site, thus forming a strong C-C single bond. The binding energies of the alkyl radicals to C-20 were calculated to be 83.9-86.6 kcal/mol at the CAM-B3LYP/6-311G(d,p) level. The electronic states of the C-20-R complex are discussed on the basis of the theoretical results. (C) 2016 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Hiroshi Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 2 2016年02月 [査読有り][通常論文]
     
    Functionalized fullerenes are known as a high-performance molecules. In this study, the alkyl-functionalized fullerenes (denoted by R-C-60) have been investigated by means of the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of fullerene. Also, the reaction mechanism of alkyl radicals with C-60 was investigated. The methyl, ethyl, propyl, and butyl radicals (denoted by n = 1-4, where n means the number of carbon atoms in the alkyl radical) were examined as alkyl radicals. The DFT calculation showed that the alkyl radical binds to the carbon atom of C-60 at the on-top site, and a strong C-C single bond is formed. The binding energies of alkyl radicals to C-60 were distributed in the range of 31.8-35.1 kcal mol(-1) at the CAM-B3LYP/6-311G(d, p) level. It was found that the activation barrier exists before alkyl addition, the barrier heights were calculated to be 2.1-2.8 kcal mol(-1). The electronic states of R-C-60 complexes were discussed on the basis of the theoretical results. (C) 2016 The Japan Society of Applied Physics
  • Hiroto Tachikawa
    THEORETICAL CHEMISTRY ACCOUNTS 135 3 1 - 9 2016年02月 [査読有り][通常論文]
     
    Ionizing radiation to DNA induces sometimes the DNA damage. In this report, the ionization dynamics of uracil dimer (U)(2) and its water complex (U)(2)-H2O have been investigated by means of direct ab initio molecular dynamics (AIMD) method in order to elucidate the effects of single water molecule on the reaction rate of proton transfer (PT) in DNA model base pair. The (U)(2) dimer is widely used as a simplified mimetic model of Watson-Crick base pair. The static ab initio calculation showed that two conformers exist as neutral complex of (U)(2)-H2O. The direct AIMD calculation of ionization process of (U)(2)-H2O showed that the rate of PT is affected even by a single water molecule, while it was dependent on the position of H2O around (U)(2). The interaction of water molecule with (U)(2) affected the potential energy curve for PT. Especially, the activation barrier along the PT coordinate was significantly changed by the interaction with one H2O molecule. The effects of one H2O molecule on the PT process were discussed on the basis of theoretical results.
  • Tachikawa Hiroto, Kawabata Hiroshi
    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 116 2 123 - 129 2016年01月15日 [査読有り][通常論文]
  • Hiroto Tachikawa, Hiroshi Kawabata
    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 116 2 123 - 129 2016年01月 [査読有り][通常論文]
     
    High energy irradiation to the hydrogen bonded system is important in relevance with the initial process of DNA and enzyme damages. In the present study, the effects of radiation to catalytic triad have been investigated by means of direct ab-initio molecular dynamics (AIMD) calculation. As a model of the catalytic triad, Ser-His-Glu residue, which is one of the important enzymes in the acylation reaction, was examined. The ionization and electron attachment processes in Ser-HisGlu were investigated as the radiation effects. The direct AIMD calculation showed that a proton of His is spontaneously transferred to carbonyl oxygen of Glu after the ionization. However, the whole structure of catalytic triad was essentially kept after the ionization. On the other hand, in the case of the electron capture in the model catalytic triad Ser-His-Glu, the dissociation of Glu residue from [Ser-His](2) was found as a product channel. The mechanism of ionization and electron capture process in the catalytic triad was discussed on the basis of theoretical results. (C) 2015 Wiley Periodicals, Inc.
  • Hiroto Tachikawa, Tetsuji Iyama
    SOLID STATE SCIENCES 50 91 - 96 2015年12月 [査読有り][通常論文]
     
    Halogen-functionalized graphenes are utilized as electronic devices and energy materials. In the present paper, the effects of halogen-termination of graphene edge on the structures and electronic states of graphene flakes have been investigated by means of density functional theory (DFT) method. It was found that the ionization potential (Ip) and electron affinity of graphene (EA) are blue-shifted by the halogen termination, while the excitation energy is red-shifted. The drastic change showed a possibility as electronic devices such as field-effect transistors. The change of electronic states caused by the halogen termination of graphene edge was discussed on the basis of the theoretical results. (C) 2015 Elsevier Masson SAS. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    SOLID STATE SCIENCES 48 141 - 146 2015年10月 [査読有り][通常論文]
     
    Structures and electronic states of organic inorganic compound of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) with alkali metals, M-n(NTCDA) (M=Li and Na, n = 0-2), have been investigated by means of hybrid density functional theory (DFT) calculations. From the DFT calculations, it was found that the electronic state of the complex at the ground state is characterized by a charge-transfer state expressed by (M)(+)(NTCDA)(-). The alkali metals were bound equivalently to the carbonyl oxygen and ether oxygen atoms of NTCDA. The C=O double bond character of NTCDA was changed to a C-O single bond like character by the strong interaction of M to the C=O and O sites. This change was the origin of the red-shift of the IR spectrum. The UV-vis absorption spectra of M-n(NTCDA) were theoretically predicted on the basis of theoretical results. (C) 2015 Elsevier Masson SAS. All rights reserved.
  • Hiroto Tachikawa
    JOURNAL OF CHEMICAL PHYSICS 142 6 064301-064301-8  2015年02月 [査読有り][通常論文]
     
    Metal catalyzed carbon-carbon (C-C) bond formation is one of the important reactions in pharmacy and in organic chemistry. In the present study, the electron and hole capture dynamics of a lithium-benzene sandwich complex, expressed by Li(Bz)(2), have been investigated by means of direct ab-initio molecular dynamics method. Following the electron capture of Li(Bz)(2), the structure of [ Li(Bz)(2)](-) was drastically changed: Bz-Bz parallel form was rapidly fluctuated as a function of time, and a new C-C single bond was formed in the C-1-C-1' position of Bz-Bz interaction system. In the hole capture, the intermolecular vibration between Bz-Bz rings was only enhanced. The mechanism of C-C bond formation in the electron capture was discussed on the basis of theoretical results. (C) 2015 AIP Publishing LLC.
  • Hiroto Tachikawa, Tomoya Takada
    RSC ADVANCES 5 9 6945 - 6953 2015年 [査読有り][通常論文]
     
    A proton transfer process is usually dominant in several biological phenomena such as the energy relaxation of photo-excited DNA base pairs and a charge relay process in Ser-His-Glu. In the present study, the rates of proton transfer along a hydrogen bond in a water cluster cation have been investigated by means of a direct ab initio molecular dynamics (AIMD) method. Three basic clusters, water dimer, trimer and tetramer, (H2O)(n) (n = 2-4), were examined as the hydrogen bonded system. It was found that the rate of the first proton transfer is strongly dependent on the cluster sizes: average time scales of proton transfer for n = 2, 3, and 4 were 28, 15, and 10 fs, respectively, (MP2/6-311++G(d,p) level) suggesting that proton transfer reactions are very fast processes in the three clusters. The second proton transfer was found in n = 3 and 4 (the average time scales for n = 3 and 4 were 120 fs and 40 fs, respectively, after the ionization). The reaction mechanism was discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama
    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 12, NO 6 12 6 659 - 663 2015年 [査読有り][通常論文]
     
    The addition reaction of methyl radical (CH3) to fullerene (C-60) surface has been investigated by means of density functional theory (DFT) method. The DFT calculation showed that the CH3 radical binds directly to the carbon atom of C-60 and a strong C-C single bond is formed. The binding energy of CH3 to C-60 was calculated to be 35.1 kcal/mol at the CAM-B3LYP/6-311G(d,p) level. The potential energy curve plotted as a function of a distance of CH3 from the C-60 surface showed that the CH3 radical can approach to the carbon atom with very low activation barrier: the barrier height was calculated to be 2.8 kcal/mol. The electronic states of CH3-C-60 complex were discussed on the basis of theoretical results.
  • Yoshinori Aoyama, Toshihiro Yamanari, Takurou N. Murakami, Tatsuya Nagamori, Kazuhiro Marumoto, Hiroto Tachikawa, Junji Mizukado, Hiroyuki Suda, Yuji Yoshida
    POLYMER JOURNAL 47 1 26 - 30 2015年01月 [査読有り][通常論文]
     
    We investigated the initial photooxidation mechanism leading to reactive radical formation of polythiophene derivatives by focusing on the differences in the photochemical behaviors of photounstable poly(3-hexylthiophene) (P3HT) and photostable poly (3-octyloxythiophene) (P3OOT). Electron spin resonance measurements revealed that the [P3HT](+center dot) (formed by oxygen doping) decayed, whereas no change was observed in the photostable [P3OOT](+center dot) after light irradiation. Furthermore, the absorption decrease of the [P3HT](+center dot) (P3HT) was suppressed by superoxide dismutase. Therefore, the oxygen dopant is superoxide, which might also initiate the oxidation of P3HT. The photochemical difference between P3HT and P3OOT can be explained by the reaction of an a-proton with superoxide in the case of P3HT.
  • Tetsuya Hama, Hirokazu Ueta, Akira Kouchi, Naoki Watanabe, Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 5 21 3843 - 3848 2014年11月 [査読有り][通常論文]
     
    Despite the rapid accumulation of structural information about organic materials, the correlation between the surface structure of these materials and their chemical properties, a potentially important aspect of their chemistry, is not fully understood. Here, we show that the amorphous or crystalline structure of a solid benzene surface controls its chemical reactivity toward hydrogen. In situ infrared spectroscopy revealed that cold hydrogen atoms can add to an amorphous benzene surface at 20 K to form cyclohexane by tunneling. However, hydrogenation is greatly reduced on crystalline benzene. We suggest that the origin of the high selectivity of this reaction is the large difference in geometric constraints between the amorphous and the crystalline surfaces. The present findings can lead us to a more complete understanding of heterogeneous reaction systems, especially those involving tunneling, as well as to the possibility of nonenergetic surface chemical modification without undesired side reactions or physical processes.
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    JOURNAL OF SOLUTION CHEMISTRY 43 9-10 1676 - 1686 2014年10月 [査読有り][通常論文]
     
    Structures and electronic excitation energies of the benzophenone-water (Bp-H2O) and benzophenone-methanol (Bp-CH3OH) complexes have been investigated by means of density functional theory calculations. The CAM-B3LYP/6-311++G(d,p) and higher level calculations were carried out for the system. The calculations indicate that free Bp has a nonplanar structure with twist angle of 54.2A degrees for two phenyl rings (referred to as I center dot). In the case of the Bp-H2O system, the twist angle of the phenyl rings and structure of the Bp skeleton were hardly changed by hydration (I center dot = 55.1A degrees for Bp-H2O). However, the excitation energies of Bp were drastically changed by this solvation. The time-dependent density functional calculations show that the n-IEuro* transition (S-1 state) is blue-shifted by the solvation, whereas two pi-pi* transitions (S-2 and S-3) were red-shifted. The origin of the specific spectral shifts is discussed on the basis of the theoretical results.
  • Hiroto Tachikawa, Takahiro Fukuzumi
    JOURNAL OF SOLUTION CHEMISTRY 43 9-10 1519 - 1528 2014年10月 [査読有り][通常論文]
     
    Electron detachment dynamics of the hydrated superoxide anion (n = 2) have been investigated by means of the direct ab initio molecular dynamics method. Two electronic states (triplet and singlet states) were examined for the neutral oxygen molecule after the electron detachment. In both electronic states, the dissociation products O-2 + water cluster, were obtained. However, the internal states are essentially different from each other. On the triplet state surface, the O-O stretching mode of O-2(I-3 ) pound is excited as a vibrational mode. On the other hand, the internal mode of the product on the singlet state surface is silent. The reaction mechanism is discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    CHEMPHYSCHEM 15 8 1604 - 1610 2014年06月 [査読有り][通常論文]
     
    The mechanism of dissolution of the Li+ ion in an electrolytic solvent is investigated by the direct ab initio molecular dynamics (AIMD) method. Lithium fluoroborate (Li+BF4-) and ethylene carbonate (EC) are examined as the origin of the Li+ ion and the solvent molecule, respectively. This salt is widely utilized as the electrolyte in the lithium ion secondary battery. The binding of EC to the Li+ moiety of the Li+BF4- salt is exo-thermic, and the binding energies at the CAM-B3LYP/6-311++G(d,p) level for n= 1, 2, 3, and 4, where n is the number of EC molecules binding to the Li+ ion, (EC) n(Li+BF4-), are calculated to be 91.5, 89.8, 87.2, and 84.0 kcalmol(-1) (per EC molecule), respectively. The intermolecular distances between Li+ and the F atom of BF4- are elongated: 1.773 angstrom (n= 0), 1.820 angstrom (n= 1), 1.974 angstrom (n= 2), 1.942 angstrom (n= 3), and 4.156 angstrom (n= 4). The atomic bond populations between Li+ and the F atom for n= 0, 1, 2, 3, and 4 are 0.202, 0.186, 0.150, 0.038, and 0.0, respectively. These results indicate that the interaction of Li+ with BF4- becomes weaker as the number of EC molecules is increased. The direct AIMD calculation for n= 4 shows that EC reacts spontaneously with (EC) 3(Li+BF4-) and the Li+ ion is stripped from the salt. The following substitution reaction takes place: EC+(EC)(3)-(Li+BF4-)->(EC)(4)Li+-(BF4-). The reaction mechanism is discussed on the basis of the theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 118 18 3230 - 3236 2014年05月 [査読有り][通常論文]
     
    Ionization dynamics of water microsolvated sulfur dioxide SO2(H2O)(n) (n = 1-3 and 6) have been investigated by means of direct ab initio molecular dynamics (AIMD) method to elucidate the hydration effects of OH addition reaction to SO2 following the ionization. The calculations showed that the neutral 1:1 complex SO2-H2O has a C-s symmetry and the sulfur of SO2 interacts with the oxygen of H2O with an eclipsed form. In the case of ionization of SO2-H2O 1:1 complex (n = 1), the cation complex composed of [H2O-SO2](+) with a face-to-face form was obtained as the product. The OH addition reactions to SO2 were found in larger systems (n = 2, 3, and 6) following the ionization. The reaction was expressed as SO2+(H2O)(n) -> SO2(OH)center dot center dot center dot H+(H2O)(n-1) (n = 2, 3, and 6). The proton generated as (SO2-H2O)(+) -> (HSO3) + H+ was stabilized by the second water molecule as the reaction: H+ + H2O -> H3O+. These processes occurred and were completed within the cluster. The OH addition mechanism in SO2+(H2O)(n) cluster was discussed on the basis of the present results.
  • Hiroto Tachikawa, Tetsuji Iyama
    THIN SOLID FILMS 554 148 - 153 2014年03月 [査読有り][通常論文]
     
    Electronic structures and band gaps of hydrogenated fullerenes have been investigated by means of density functional theory method. The mechanism of hydrogen addition reaction to the fullerene (C-60) surface was also investigated. Addition of one and two hydrogen atoms was examined in the calculations. The binding energies of the second hydrogen atom to C60H were widely distributed in the range 1.5-3.6 eV. It was found that the bonding energy is strongly dependent on the spin density of carbon atom of C60H. The second hydrogen atom preferentially binds to the neighbor site of the first addition site. The electronic states and excitation energies of C-60-H were discussed on the basis of theoretical results. (C) 2013 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    THIN SOLID FILMS 554 199 - 203 2014年03月 [査読有り][通常論文]
     
    The effects of hydrogenation on the band gap of graphene have been investigated by means of density functional theory method. It is generally considered that the band gap increases with increasing coverage of hydrogen atom on the graphene. However, the present study shows that the band gap decreases first with increasing hydrogen coverage and reaches the lowest value at finite coverage (gamma = 0.3). Next, the band gap increases to that of insulator with coverage from 0.3 to 1.0. This specific feature of the band gap is reasonably explained by broken symmetry model and the decrease of pi-conjugation. The electronic states of hydrogenated graphene are discussed. (C) 2013 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Tetsuji Iyama
    SOLID STATE SCIENCES 28 41 - 46 2014年02月 [査読有り][通常論文]
     
    Functionalized graphenes have been utilized as electronic devices and energy materials. In the present paper, the effects of fluorine-termination of graphene edge on the structures and electronic states of graphene have been investigated by means of density functional theory (OFT) method. It was found that the ionization potential (Ip) and electron affinity of graphene (EA) are blue-shifted by the F-substitution. On the other hand, the excitation energy was red-shifted. The drastic change shows a possibility as electronic devices such as field-effect transistors. The drastic change of electronic states caused by the F-substitution of graphene edge was discussed on the basis of the theoretical results. (C) 2013 Elsevier Masson SAS. All rights reserved.
  • Koichi Kato, Tetsuji Iyama, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 53 2 02BD02.1-02BD02.4  2014年02月 [査読有り][通常論文]
     
    The interactions, of magnesium species (Mg, Mg+, and Mg2+) with a graphene surface have been investigated by the density functional theory (OFT) method. The distances of Mg atoms from the graphene surface were calculated to be 1.80 angstrom (Mg2+), 2.16 angstrom (Mg+), and 4.17 angstrom (Mg) at the Coulomb-attenuating method (CAM)-B3LYP/6-31G(d) level. The binding nature of Mg ions (Mg2+ and Mg+) is caused by the charge transfer interaction; and the Mg atom interacts with the surface via van der Weals (vdW) force. The Mg ions can diffuse via the C-C bond center between hexagonal sites. The barrier heights for the diffusion of Mg2+ and Mg+ on the graphene surface were calculated to be 14.6 and 2.8 kcal/mol, respectively. On the other hand, the diffusion of Mg atoms proceeds with a very low barrier. The mechanism of the interaction of Mg with the graphene surface was discussed on the basis of theoretical results. (C) 2014 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Shigeaki Abe
    ELECTROCHIMICA ACTA 120 57 - 64 2014年02月 [査読有り][通常論文]
     
    Solvent dissociation dynamics from solvated lithium ion solvated by ethylene carbonates (EC) have been investigated by means of direct ab-initio molecular dynamics (AIMD) Method. The lithium ion was solvated by four EC molecules as the first solvation shell. It was found that the solvation number of lithium ion is drastically changed from 4 to 1 when the solvated lithium ion accepts an excess electron. The binding energy of Li-EC decreased to a one-tenth. Finally, the contact ion pair composed of Li+ and EC- was formed as the product. The mechanism of solvent dissociation was discussed on the basis of theoretical results. (C) 2013 Elsevier Ltd. All rights reserved.
  • Hiroto Tachikawa
    RSC ADVANCES 4 1 516 - 522 2014年 [査読有り][通常論文]
     
    Electron detachment dynamics of the hydrated superoxide anion O-2(-)(H2O) have been investigated by means of direct ab initio molecular dynamics (AIMD) methods. Two potential energy surfaces were examined as electronic states of oxygen molecule after the electron detachment of the hydrated superoxide anion: O-2((3)Sigma)(H2O) and O-2((1)Delta)(H2O). In both electronic states, the dissociation products, O-2 + H2O, were obtained. However, the internal states of O-2 were essentially different from each other. On the triplet state surface, the O-O stretching mode of O-2((3)Sigma) was excited, whereas that of O-2((1)Delta) was silent. The reaction mechanism was discussed on the basis of theoretical results.
  • Hiroshi Yoshida, Akitoshi Tomizawa, Hiroto Tachikawa, Shin-ichiro Fujita, Masahiko Arai
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 16 35 18955 - 18965 2014年 [査読有り][通常論文]
     
    The catalytic hydrogenation of 2,4-dinitroaniline using a 0.5 wt% Pt/TiO2 catalyst was investigated in a multiphase medium of tetrahydrofuran (THF) pressurized by CO2 at different pressures and at 323 K. When CO2 pressure was increased, the overall rate of hydrogenation simply decreased but the selectivity to the desired product of 4-nitro-1,2-phenylenediamine increased. The noticeable enhancement of the selectivity to 4-nitro-1,2-phenylenediamine can be explained by chemical reactivities of CO2 molecules. In situ high-pressure FTIR and molecular simulations demonstrate that the dissolved CO2 molecules may interact with amino groups of the substrate and weaken the intra-hydrogen bonding between the amino and 2-nitro groups, which results in the change in the relative reactivity of the two nitro groups, yielding the desired product in a higher selectivity. The change in the intra-and inter-molecular interactions between the substrate and CO2 molecules was theoretically examined by DFT calculations.
  • Tetsuji Iyama, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 579 1 10 - 16 2013年09月 [査読有り][通常論文]
     
    The interaction of carbon free radicals (CH and CCH) with a graphene surface has been investigated by means of density functional theory (DFT) method in order to elucidate the radical scavenge mechanism of graphene surface. These radicals are highly reactive and the radical plays an important part of materials chemistry. The DFT calculation showed that the CH and CCH radicals bind to the bond center of C-C carbon atoms as a carbon bridge and a strong C-CH-C bond (or C-C2H-C bond) is formed. The binding energies of CH and CCH radicals to the graphene were calculated to be 48.2 and 46.2 kcal/mol at the B3LYP/6-31G(d) level of theory. The mechanism of CH radical addition was discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    THEORETICAL CHEMISTRY ACCOUNTS 132 7 2013年07月 [査読有り][通常論文]
     
    Mechanism of pi-pi double stacking process of benzene trimer cation has been investigated by means of direct ab initio molecular dynamics method. It was found that H-shaped form of neutral benzene trimer is drastically changed to the pi-pi double stacking form composed of benzene trimer cation following the ionization. Absorption spectrum of charge resonance band of (Bz)(3)(+) was gradually blueshifted as a function of time. Time scale of the double stacking process (the formation of trimer cation from the H-shaped form) was calculated to be 0.7-1.5 ps, which is comparable to that of dimer cation formation. After the ionization of benzene trimer, (Bz)(Bz)c(Bz'), the hole is distributed around three benzene molecules with a branching ratio of (Bz)(+0.3) (Bz)c(+0.4) (Bz')(+0.3), and the structure of (Bz)c(+) was rapidly deformed due to the Jahn-Teller effect. Next, the molecular rotation of central benzene (Bz)c(+) occurred gradually. Immediately, both benzene molecules in the wing positions were also rotated synchronicity. Finally, the pi-pi double stacking form composed of benzene trimer cation was formed. The formation mechanism of benzene trimer cation was discussed on the basis of theoretical results.
  • Yoshinori Aoyama, Toshihiro Yamanari, Nagatoshi Koumura, Hiroto Tachikawa, Masaru Nagai, Yuji Yoshida
    POLYMER DEGRADATION AND STABILITY 98 4 899 - 903 2013年04月 [査読有り][通常論文]
     
    The photooxidation of poly(3-hexylthiophene) (P3HT) has previously been investigated and it is known that the sulfur atom of the thiophene ring is oxidized into sulfur oxides by a hydroxyl radical that arises through hydrogen abstraction at the hexyl side chain at the alpha-position. In this study, in order to further investigate the photooxidation mechanism of the polymer, the side chain at alpha-position was varied and three different polythiophene derivatives with phenyl (P3PhT), tert-pentyl (P3DMPT), and alkoxy (P3OOT) groups were synthesized with no alpha-hydrogens. We observed the differences in the photochemical behavior of the polythiophene derivatives by UV-vis-NIR and FT-IR (ATR) spectroscopy during simulated solar light irradiation. It was found that the photooxidation of P3PhT and P3DMPT progressed in the same way as P3HT, whereas the analogous decomposition of P3OOT was not observed. (C) 2013 Elsevier Ltd. All rights reserved.
  • Hiroto Tachikawa, Tomoya Takada
    CHEMICAL PHYSICS 415 76 - 83 2013年03月 [査読有り][通常論文]
     
    Ionization dynamics of the cyclic water trimer (H2O)(3) have been investigated by means of direct ab initio molecular dynamics (AIMD) method. Two reaction channels, complex formation and OH dissociation, were found following the ionization of (H2O)(3). In both channels, first, a proton was rapidly transferred from H2O+ to H2O (time scale is similar to 15 fs after the ionization). In complex channel, an ion-radical contact pair (H3O+-OH) solvated by the third water molecule was formed as a long-lived H3O+(OH)H2O complex. In OH dissociation channel, the second proton transfer further takes place from H3O+(OH) to H2O (time scale is 50-100 fs) and the OH radical is separated from the H3O+. At the same time, the OH dissociation takes place when the excess energy is efficiently transferred into the kinetic energy of OH radical. The OH dissociation channel is significantly minor, and almost all product channels were the complex formation. The reaction mechanism was discussed on the basis of theoretical results. (C) 2012 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS 52 1 2013年01月 [査読有り][通常論文]
     
    The interaction of a hydroxyl OH radical with a graphene surface has been investigated by the density functional theory (DFT) method in order to elucidate the radical scavenge mechanism of the graphene surface. The DFT calculation showed that the OH radical binds directly to the carbon atom of the graphene surface and a strong C-O bond is formed. The binding energies were dependent on the cluster size and were distributed in the 4.1-9.5 kcal/mol range at the B3LYP/6-31G(d) level of theory. The potential energy curve plotted as a function of the distance of OH from the surface carbon showed that the OH radical can bind to the carbon atom with a low activation barrier: the barrier heights for n = 7 and 14 were calculated to be 3.9 and 1.9 kcal/mol, respectively. Also, it was found that the structural change from sp(2) to sp(3)-like hybridization occurs by the approach of the OH radical. (C) 2013 The Japan Society of Applied Physics
  • Hirokazu Tamai, Martina Hafner, Achim Walter Hassel, Hiroto Tachikawa, Kazuhisa Azumi
    PLASMA PROCESSING 19 50 46 85 - 91 2013年 [査読有り][通常論文]
     
    Microplasma was formed in a gap hole made in a quartz plate immersed in various kinds of electrolyte solutions at different concentrations. High-voltage AC was applied to the solution by using a pair of contact-or non-contact electrodes at both sides of the gap hole to ignite microplasma generation. Spectra of the light emitted from the microplasma showed elemental emission lines of the species contained in the solution, and their intensities depended on not only their concentration but also plasma conditions such as plasma temperature. A non-equilibrium plasma state was confirmed from estimated temperature of electrons and OH center dot radicals in the order of thousand and 10 thousand Kelvins. Deformation of the gap hole was observed depending on the polarization condition and species, probably due to high-temperature plasma and also dielectric loss in the gap hole.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 720 60 - 65 2012年12月 [査読有り][通常論文]
     
    Hole capture dynamics of phenyl-capped thiophene (DPT) have been investigated by means of density functional theory (DFT) and direct ab-initio molecular dynamics (AIMD) calculations. DPT has been utilized as a part of organic solar cells. The direct AIMD calculations showed that the twist angle of DPT vibrates periodically after hole capture. (C) 2012 Elsevier B.V. All rights reserved.
  • Shigeaki Abe, Fumio Watari, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 10 2012年10月 [査読有り][通常論文]
     
    The interaction between fluorinated ethylene carbonate denoted by EC(F) and a graphene surface was investigated using of density functional theory (DFT) method. The interaction system examined was a complex composed of graphene (consisting of 14 benzene rings) and one EC(F) molecule. Ten binding sites of EC(F) binding site on the surface and edge regions of the graphene, were identified as stable points. EC(F) bound to a hexagonal position corresponding to the central of benzene ring on the graphene surface and can also bind to the edge of the graphene. The EC(F) binding energies on the surface and edge sides were 0.5 and 2.8 kcal/mol, respectively. The activation barrier for the diffusion of EC(F) on the graphene surface was significantly low (less than 0.3 kcal/mol), indicating that EC(F) can move freely on the graphene surface. (C) 2012 The Japan Society of Applied Physics
  • Takahiro Fukuzumi, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 10 2012年10月 [査読有り][通常論文]
     
    The interaction of hydroperoxyl radical (OOH) with a graphene surface has been investigated by means of density functional theory (DFT) method in order to elucidate the radical scavenge mechanism of graphene surface. The OOH radical is highly reactive and the radical plays an important part of materials chemistry. The DFT calculation showed that the OOH radical binds to the carbon atom of graphene surface and a strong C-O bond is formed. The binding energies were dependent on the cluster size and were distributed in the range 18-25 kcal/mol at the B3LYP/6-31G(d) level of theory. The potential energy curve plotted as a function of C-OOH bond distance showed that the OOH radical approaches to the carbon atom with an activation barrier (the barrier height is distributed in 20-25 kcal/mol). Also, it was found that structural change from sp(2) to sp(3)-like hybridization occurs by the approach of OOH. (C) 2012 The Japan Society of Applied Physics
  • Tomoya Takada, Hiroshi Kawabata, Hiroto Tachikawa
    JOURNAL OF MOLECULAR STRUCTURE 1020 1 - 5 2012年08月 [査読有り][通常論文]
     
    Hydrogen transfer reactions at the ground and excited states of tert-butyl radical to form iso-butyl radical have been investigated by means of ab initio calculation and electron spin resonance (ESR) spectroscopy. It was found that tert-butyl radical irradiated with 254 nm ultraviolet light converts quite efficiently to iso-butyl radical. Also, it was suggested that this conversion occurs as an intramolecular hydrogen transfer from a methyl group of tert-butyl radical to a radical site (central carbon atom). The theoretical calculations showed that barrier height of hydrogen transfer at the excited state is significantly lower than that of ground state. The mechanism of internal hydrogen atom conversion from tert-butyl to iso-butyl radicals was discussed. (C) 2012 Elsevier B.V. All rights reserved.
  • Takeshi Sakamoto, Hiroto Tachikawa, Kazuhisa Azumi
    APPLIED SURFACE SCIENCE 258 18 6785 - 6792 2012年07月 [査読有り][通常論文]
     
    Density functional theory (DFT) calculation was applied to acetylene (AC) and 2-butyne-1,4-diol (BD) adsorbed on an Ni(1 1 1) or Ni(1 0 0) model cluster surface in order to elucidate the relationship between their electronic states and geometry in the adsorption process. Adsorption energy of AC calculated using BSSE correction and binding structure were in good agreement with the experimental data. The geometry and adsorption energy of AC or BD on the Ni(1 1 1) surface in the optimized adsorption condition differ from those on the Ni(1 0 0) surface. Analysis of a natural electron configuration of adsorbates before and after adsorption on Ni clusters clarified that the 2s orbital rather than other orbitals such as 2p contributed mainly to the adsorption energy. (C) 2012 Elsevier B. V. All rights reserved.
  • Shigeaki Abe, Fumio Watari, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 1 2012年01月 [査読有り][通常論文]
     
    Density functional theory (DFT) calculations have been applied to complexes composed of ethylene carbonate (EC) with a graphene chip to theoretically elucidate the interaction of EC with the graphene. A graphene chip consisting of 14 benzene rings and one EC molecule were examined as the interaction system. Ten binding sites of EC were examined as binding e points around the graphene chip. EC binds to a hexagonal position corresponding to the central of benzene ring of graphene surface. In addition, EC can bind to the edge region of graphene. The energy of EC in the edge region was 4.2 kcal/mol more stable than that of the hexagonal position. The activation barriers for diffusion of EC on the graphene surface were significantly low (less than 0.2 kcal/mol), indicating that EC, put on the surface, can move freely on the graphene surface and then down into the edge region. (C) 2012 The Japan Society of Applied Physics
  • Tetsuji Iyama, Shigeaki Abe, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 567 200 - 206 2012年 [査読有り][通常論文]
     
    The radical addition to the smallest fullerene C-20 has been investigated by means of density functional theory (DFT) method in order to elucidate the radical scavenge mechanism of fullerene. The OH radical was examined as an organic radical because the radical has a high reactivity. The DFT calculation showed that the OH radical binds directly to the carbon atom of C-20 and a strong C-O bond is formed. The binding energies of the first addition of OH radical were calculated to be 85.2 kcal/mol at the B3LYP/6-311G(d,p) level of theory. In the second radical addition, the binding energy of OH to C-20(OH) was 91.5 kcal/mol. The unpaired electron was distributed widely over the C-20 surface in the C-20(OH) complex.
  • Hiroto Tachikawa
    RSC ADVANCES 2 17 6897 - 6904 2012年 [査読有り][通常論文]
     
    The ionization dynamics of a benzene dimer have been investigated by means of a direct ab initio molecular dynamics (MD) method in order to elucidate the reaction mechanism. Following the ionization, the T-shaped neutral benzene dimer was gradually changed to a p-stacked benzene dimer cation. The structural change and time evolution of the electronic absorption spectrum were completely visualized for the first time. The time scale of the dimer formation was estimated to be 1.0-1.5 ps. First, the benzene molecule at the stem position (Bz(')) was ionized, and the structure of Bz'(+) was rapidly deformed due to the Jahn-Teller effects. Next, the rotation of (Bz')(+) gradually occurred relative to Bz. Finally, a pi-stacked benzene dimer cation was formed. TD-DFT calculations indicated that the absorption spectrum of (Bz)(2)(+) is blue-shifted as a function of time. The formation mechanism of the benzene dimer cation was discussed on the basis of the theoretical results.
  • Hiroto Tachikawa
    RSC ADVANCES 2 32 12346 - 12354 2012年 [査読有り][通常論文]
     
    Direct ab initio molecular dynamics (MD) has been applied to the electron detachment dynamics of Cu-(H2O)(n) (n = 1-3). The initial structures of Cu(H2O)(n) were generated randomly around the equilibrium point of anionic complex Cu-(H2O)(n) and then trajectories were run from the vertical electron detachment points of Cu-(H2O)(n). It was found that three reaction channels compete with each other when n = 1: dissociation channel (the product is Cu + H2O) and complex formation channel (the product is neutral CuH2O complex). The complex channel is further classified to two kind of complexes: a strongly bound (I) complex and a weakly bound (II) complex. The dissociation channel occurred from an inner Franck-Condon (FC) region where the distance Cu--H2O is shorter than the equilibrium point. On the other hand, the complex formation channel occurred from the wide FC region. In case of n = 2 and 3, dissociation channels were the main products. The mechanism of the electron detachment dynamics was discussed on the basis of the theoretical results.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 44 20 2011年10月 [査読有り][通常論文]
     
    Structures and electronic states of graphene flakes (finite and small sized graphenes) have been investigated by means of the density functional theory method. Sizes of graphene flakes examined in this study were n = 7, 10, 14, 19, 29 and 44, where n is the number of benzene rings in the graphene flake. The excitation energies of graphene flakes decreased gradually as a function of the number of the ring (n). The orbitals of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) are localized in the edge region of the graphene flake. It was found that the edge region can react with a water molecule and H2O is dissociated into OH radical and hydrogen atom (H) without an activation barrier. A lithium ion can bind strongly to the edge region. The ability of the edge region in the graphene flakes was discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY C 115 42 20406 - 20411 2011年10月 [査読有り][通常論文]
     
    The interaction of the Li+ ion with fullerene (C-60) surface has been investigated by means of density functional theory (DFT) and direct molecular orbital-molecular dynamics (MO-MD) methods. It was found that the Li+ ion can bind two stable binding sites, hexagonal and pentagonal sites where Li+ binds to six- and five-membered rings composed of carbon atoms, respectively. The saddle points between binding sites were found: activation energies for (5-6) and (6-6) saddle points were calculated to be 2.7 and 3.6 kcal/mol at the B3LYP/6-311G(d,p) level, respectively, where (5-6) means a saddle point between pentagonal and hexagonal sites. The dynamics calculations showed that the Li+ ion diffuses between stable points near the saddle points at 250 K. The electronic states of Li+ ion along the diffusion path on C-60 were discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    CHEMICAL PHYSICS LETTERS 513 1-3 94 - 98 2011年09月 [査読有り][通常論文]
     
    Density functional theory (DFT) and direct ab initio molecular dynamics (MD) calculations have been applied to a hydrogen atom trapped in diamond cluster. The DFT calculation showed that spin density of hydrogen atom in diamond (hyperfine coupling constant, hfcc) is lower than that of free hydrogen atom in vacuo. This result was in good agreement with that of muon-spin-rotation experiment. The MD calculation showed that the hfcc of hydrogen atom decreases with increasing temperature because the hydrogen atom behaves as electron donor in diamond lattice. The electronic states of hydrogen atom trapped in the diamond were discussed on the basis of theoretical results. (C) 2011 Elsevier B. V. All rights reserved.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 115 33 9091 - 9096 2011年08月 [査読有り][通常論文]
     
    Electron capture dynamics of SO2-H2O (Ar)(n) complexes (n = 0-2) have been investigated by means of direct ab initio molecular dynamics (MD) method in order to elucidate the effects of solvent argon on the reaction dynamics of SO2-H2O. The neutral complex of SO2-H2O has a C-s symmetry, and the sulfur of SO2 interacts with the oxygen of H2O with an eclipsed form. In the SO2-H2O(Ar)(n) complexes, the dipole of H2O interacts with the argon atoms in the most stable structure. Following the electron capture of the complex SO2-H2O, the complex anion SO2-(H2O) is dissociated directly into SO2- + H2O. On the other hand, the electron capture of SO2(H2O)(Ar)(n) argon complex (n = 1-2) leads to the anion-water complex SO2- (H2O) because the collision of H2O with the Ar atom causes a rebound of H2O from Ar atom to the SO2- anion. The argon solvent enhanced the SO2-(H2O) complex formation. The reaction mechanism of SO2(H2O) in the participation of argon atoms was discussed on the basis of the present results.
  • Shigeaki Abe, Yoshinori Nagoya, Fumio Watari, Hiroto Tachikawa
    COMPUTATIONAL MATERIALS SCIENCE 50 9 2640 - 2643 2011年07月 [査読有り][通常論文]
     
    The evaporation processes of water molecules adsorbed in the edge region of graphene have been investigated by means of direct MO-MD method. A large system composed of 29 water molecules and a graphene sheet (C(96)H(24)) was used as a model system. The edge carbon atom of graphene was terminated by hydrogen atom. The geometry optimization showed that the water molecules interact with the hydrogen atoms in the edge region of graphene. At low temperature (300 K), the water molecules were dissociated as water clusters from the graphene. On the other hand, in addition to the dissociation of water clusters, the isolated water molecule was also found as dissociation product at high temperature (500 K). The mechanism of water evaporation was discussed on the basis of theoretical results. (C) 2011 Elsevier By. All rights reserved.
  • Shigeaki Abe, Yoshinori Nagoya, Fumio Watari, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 50 1 2011年01月 [査読有り][通常論文]
     
    The structures and electronic states of graphene-water interaction systems have been investigated by means of density functional theory (DFT) method to elucidate the effects of water clusters on the electronic states of graphene chip. Solvation caused by five to eight water molecules (n = 5-8) was examined as the interaction systems. A graphene chip composed of 14 benzene rings was used as a model of finite-sized graphene (C42H16). The water clusters interact with the graphene chip with hydrogen bonds. The band gap of graphene was slightly red-shifted by the solvation and the first excitation energy was saturated around n = 5. The electronic states of graphene-water systems were discussed on the basis of theoretical results. (c) 2011 The Japan Society of Applied Physics
  • Shigeaki Abe, Rika Komine, Yoshinori Nagoya, Fumio Watari, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 538 258 - 264 2011年 [査読有り][通常論文]
     
    The interaction of carbon nanotubes (CNTs) and peptide molecule has been investigated by means of experiment and theoretical calculations. For comparison, the graphene-peptide system was investigated with the same manner. It was found that peptide interacts strongly with the CNTs, whereas the interaction of graphene with the peptide is negligibly small. The theoretical calculation supports strongly these findings.
  • Yoshimichi Ami, Hiroto Tachikawa, Naoki Takano, Norihisa Miki
    JOURNAL OF MICRO-NANOLITHOGRAPHY MEMS AND MOEMS 10 1 2011年01月 [査読有り][通常論文]
     
    We demonstrate the fabrication of polymer microneedle arrays using soft lithography. A photomask was designed to use Fresnel diffraction of UV light to create sharp, tapered hollows in SU-8, a negative photoresist, after development. Polymer microneedles were formed using these SU-8 structures as a mold. These polymer needles may be applicable as flexible electrodes in brain-machine interfaces because they are more likely to survive movement of the skin than conventional brittle silicon needles. Similar needles, made from medicinal substances, could be used for transdermal drug administration. For these applications, the needles must be long, sharp, and stiff enough to penetrate the stratum corneum (similar to 20 mu m in thickness) and reach the viable epidermis (200-300 mu m in thickness), but must not reach the dermis, which contains sensitive nerve endings. We successfully manufactured 20x20 microneedle arrays of polydimethylsiloxane with a needle length of 200 mu m. We experimentally verified that these manufactured electrodes successfully penetrated the stratum corneum of a cultured skin. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3553393]
  • Takahiro Fukuzumi, Hiroto Tachikawa, Kazuhisa Azumi
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 538 61 - 66 2011年 [査読有り][通常論文]
     
    The binding structures and electronic states of sodium ion and atom (Na(+) and Na) trapped on the smallest fullerene surface (C(20)) have been investigated by means of density functional theory (DFT) calculation to elucidate the nature of interaction. It was found that the Na(+) ion can bind two sites of C(20): one is on-top site where Na(+) ion binds to the carbon atom of C(20), while the other is a pentagonal site where the Na(+) ion binds to five membered ring of C(20). In case of sodium atom, the similar binding structures were obtained on C(20) surface. The nature of the interaction between Na(+) (Na) and the C(20) cluster was discussed on the basis of theoretical results.
  • Koichi Kato, Tetsuji Iyama, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 50 1 2011年01月 [査読有り][通常論文]
     
    The interaction of magnesium atom (Mg) and ionic species (Mg+ and Mg2+) with graphene chip (finite sized graphene) have been investigated by means of density functional theory (DFT) method. The B3LYP/6-31G(d) calculation showed that the Mg atom does not make a chemical bind to the graphene chip. On the other hand, the ionic species can bind srongly to a hexagonal site of graphene chip. Time-dependent (TD)-DFT calculation of Mg+ doped graphene showed that the first excitation band is assigned to a charge transfer band from a pi-orbital of graphene chip (HOMO: highest occupied molecular orbital) to a singly occupied molecular orbital (SOMO) composed of Mg+(3s) orbital, whereas the second excitation band is composed of a pi-pi(center dot) transition corresponding to the HOMO-lowest unoccupied molecular orbital (LUMO) excitation of free graphene chip. The nature of the interaction between the Mg ions and the graphene chip was discussed on the basis of theoretical results. (c) 2011 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Hiroshi Kawabata
    THEORETICAL CHEMISTRY ACCOUNTS 128 2 207 - 213 2011年01月 [査読有り][通常論文]
     
    Solvent re-orientation process of triplet acetone/methanol complex and intermolecular hydrogen atom abstraction reaction on the triplet state energy surface, (CH3)(2)C=O (T-1) + CH3OH -> (CH3)(2)C-OH + CH2OH in gas phase, have been investigated by means of density functional theory (DFT) and direct ab initio molecular dynamics (MD) methods. The static DFT calculation of hydrogen abstraction reaction at the T-1 state showed that the transition state is 16.4 and 30.9 kcal/mol lower than the energy levels of S-1 and S-2 states, respectively, and 9.2 kcal/mol higher than the bottom of T-1 state. The product state, (CH3)(2)C-OH center dot center dot center dot CH2OH, is 8.4 kcal/mol lower in energy than the level of T-1 state. The direct ab initio MD calculation showed that the product is rapidly formed within 150 fs and the separated products (CH3)(2)C-OH + CH2OH were formed. The mechanism of reaction dynamics of the triplet acetone/methanol complex was discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama, Kazuhisa Azumi
    JAPANESE JOURNAL OF APPLIED PHYSICS 50 1 2011年01月 [査読有り][通常論文]
     
    The structures and electronic states of boron- and nitrogen-substituted graphene chips ( B-, N-, and BN-doped graphene chips) have been investigated by means of the density functional theory (DFT) method in order to shed light on the mechanism of change in the electronic properties of graphene chips caused by heteroatoms. The atomic charge of nitrogen atoms in N- graphene was a negative value, whereas that of boron atoms in B-graphene was positive. In the case of the BN-doped graphene chip, a charge polarization such as B delta+-N delta- was found. It was also found that the B-N bond pair is preferentially formed because of the large heat of formation of the B-N bond. The BN-doped graphene chips showed a large red shift of the band gap compared with that of normal graphene. The electric states of BN-graphenes were discussed on the basis of theoretical results. (c) 2011 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Takahiro Fukuzumi
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 13 5881 - 5887 2011年 [査読有り][通常論文]
     
    The ionization dynamics of an aminopyridine dimer (AP)(2) has been investigated by means of the direct ab initio molecular dynamics (MD) method. It was found that the reaction process was composed of three steps after the vertical ionization of (AP)(2): dimer approach, proton transfer and energy relaxation. The timescales of these processes were 50-100, 10-20, and 200 fs, respectively. The timescale of the dimer approach was dependent on the initial separation between AP(+) and AP. After the ionization, AP approached gradually the ionized AP(+). The proton of AP(+) was transferred to AP at the nearest intermolecular distance, while the potential energy was quickly dropped according to the proton transfer. The energy relaxation of the dimer cation was significantly faster than that of the monomer cation. The mechanism of ionization dynamics of (AP)(2) was discussed on the basis of the theoretical results.
  • Hiroto Tachikawa
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 23 11206 - 11212 2011年 [査読有り][通常論文]
     
    Ionization dynamics of a water dimer have been investigated by means of a direct ab initio molecular dynamics (MD) method. Two electronic state potential energy surfaces of (H2O)(2)(+) (ground and first excited states, (2)A '' and (2)A') were examined as cationic states of (H2O)(2)(+). Three intermediate complexes were found as product channels. One is a proton transfer channel where a proton of H2O+ is transferred into the H2O and then a complex composed of H3O+(OH)was formed. The second is a face-to-face complex channel denoted by (H2O-OH2)(+) where the oxygen-oxygen atoms directly bind each other. Both water molecules are equivalent to each other. The third one is a dynamical complex where H2O+ and H2O interact weakly and vibrate largely with a large intermolecular amplitude motion. The dynamics calculations showed that in the ionization to the (2)A '' state, a proton transfer complex H3O+(OH) is only formed as a long-lived complex. On the other hand, in the ionization to the (2)A' state, two complexes, the face-to-face and dynamical complexes, were found as product channels. The proton of H2O+ was transferred to H2O within 25-50 fs at the (2)A '' state, meaning that the proton transfer on the ground state is a very fast process. On the other hand, the decay process on the first excited state is a slow process due to the molecular rotation. The mechanism of the ionization dynamics of (H2O)(2) was discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Akihiro Yabushita, Masahiro Kawasaki
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 46 20745 - 20749 2011年 [査読有り][通常論文]
     
    A direct ab initio molecular dynamics method has been applied to a water monomer and water clusters (H2O)(n) (n = 1-3) to elucidate the effects of zero-point energy (ZPE) vibration on the absorption spectra of water clusters. Static ab initio calculations without ZPE showed that the first electronic transitions of (H2O)(n), B-1(1) <- (1)A(1), are blue-shifted as a function of cluster size (n): 7.38 eV (n = 1), 7.58 eV (n = 2) and 8.01 eV (n = 3). The inclusion of the ZPE vibration strongly affects the excitation energies of a water dimer, and a long red-tail appears in the range of 6.42-6.90 eV due to the structural flexibility of a water dimer. The ultraviolet photodissociation of water clusters and water ice surfaces is relevant to these results.
  • Hiroto Tachikawa, Tetsuji Iyama, Shigeaki Abe
    9TH INTERNATIONAL CONFERENCE ON NANO-MOLECULAR ELECTRONICS 14 2011年 [査読有り][通常論文]
     
    The interaction of OH radical with C-60 has been investigated by means of DFT method in order to elucidate the radical scavenge mechanism of fullerene. The OH radical was examined as an organic radical because the radical has a high reactivity. The DFT calculation showed that the OH radical binds to the carbon atom of C-60 and a strong C-O bond is formed. The binding energies were calculated to be 36.4 and 35.2 kcal/mol at the B3LYP/6-31G(d) and 6-311G(d,p) levels of theory. The potential energy curve plotted as a function of C-O distance showed that the OH radical approaches to the carbon atom without activation barrier. Also, it was found that structural change from sp(2) to sp(3)-like hybridization occurs easily by the approach of OH. The unpaired electron is distributed widely over the C-60 surface in the C-60(OH) complex. (C) 2010 Published by Elsevier B.V.
  • Takeshi Sakamoto, Kazuhisa Azumi, Hiroto Tachikawa, Kei Iokibe, Masahiro Seo, Nobuya Uchida, Yasunaga Kagaya
    ELECTROCHIMICA ACTA 55 28 8570 - 8578 2010年12月 [査読有り][通常論文]
     
    Structures of Ni films electrodeposited from a Watts-type bath containing 2-buthyne-1 4-diol (BD) were investigated using SEM cross-sectional SIM XRD measurement with a pole profiling technique and electrochemical methods for controlling properties of Ni electrodeposits Preferred orientation of Ni electrodeposits was assigned to potential domains for electrodeposition Preferred orientation in the higher potential region was (1 1 0) or (1 00) that in the middle potential region were (1 1 1) and (3 1 1) and that in the lower potential region was (1 0 0) The growing axis of Ni electrodeposits seems to agree with the speculation from Pangarov s model based on the two-dimensional nuclei theory in the lower overpotential region in which the dominant growing plane is fundamentally determined by crystallization overpotential related to supersaturation of adatom although the growth axes of Ni deposits do not always agree with the preferred orientation For example preferred orientation of (1 1 0) was assigned to growing (1 1 1) plane which tilts at 55 degrees to the substrate Adsorption of BD affects the structure and morphology of electrodeposits via an inhibitory effect related to its surface coverage depending on surface orientation growth rate and BD concentration in the plating bath (C) 2010 Elsevier Ltd All rights reserved
  • Hiroto Tachikawa, Takahiro Fukuzumi, Kazushige Inaoka, Inosuke Koyano
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 12 47 15399 - 15405 2010年12月 [査読有り][通常論文]
     
    The ion-molecule reaction, CH3CN+ + CH3CN -> CH3CNH+ + CH2CN, has been investigated using the threshold electron-secondary ion coincidence (TESICO) technique. Relative reaction cross sections for two microscopic reaction mechanisms, i.e., proton transfer (PT) from the acetonitrile ion CH3CN+ to neutral acetonitrile CH3CN and hydrogen atom abstraction (HA) by CH3CN+ from CH3CN, have been determined for two low-lying electronic states, E-2 and (2)A(1) of the CH3CN+ primary ion. The cross section for PT of the (2)A(1) state was smaller than that of the E-2 state, whereas that of HA are almost the same in the two states. Ab initio calculations showed that the dissociation of the C-H+ bond of CH3CN+ is easier in the E-2 state than that in the (2)A(1) state. The direct ab initio molecular dynamics (MD) calculations showed that two mechanisms, direct proton transfer and complex formation, contribute the reaction dynamics.
  • Hiroto Tachikawa, Yoshinori Nagoya, Takahiro Fukuzumi
    JOURNAL OF POWER SOURCES 195 18 6148 - 6152 2010年09月 [査読有り][通常論文]
     
    The electronic structures of a lithium ion (Li+) doped-graphene at the ground and low-lying excited states have been investigated by means of density functional theory (DFT) method. A graphene composed of 19 benzene rings was used as a model of graphene, while the edge carbon atom was terminated by hydrogen atom (expressed by C54H18). The geometry optimization showed that the Li+ ion binds to a hexagonal site where six carbon atoms interact equivalently to the Li+ ion. When the Li+ ion interacts with the graphene surface, the electronic configuration of the Li+ ion is changed from (1s)(2)(2s)(0) to (1s)(2)(2s)(0.01)(2p)(0)(3p)(0.02), suggesting that the sp-hybridization of lithium ion is important in the adsorption to the graphene surface. The band gap of graphene is slightly red-shifted by the doping of Li+ ion due to the interaction with the sp-hybrid orbital. The effects of Li+ on both the ground and excited electronic states of graphene were discussed on the basis of theoretical results. (C) 2010 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 114 37 10309 - 10314 2010年09月 [査読有り][通常論文]
     
    Electron capture dynamics of the water tetramer (H2O)(n) (n = 4) have been investigated by means of a full-dimensional direct ab initio molecular dynamics (MD) method at the MP2/6-311++G(d,p) level. Two structural conformers (branched and cyclic forms of the water tetramer) were examined as neutral water tetramers. The structure of the branched form is that a dangling water molecule binds to the ring composed of a cyclic water trimer. In the case of electron capture of the branched form, first, an excess electron was trapped by the dangling water molecule. Next, rotation of the water molecule located in the ring occurred rapidly, while a hydrogen bond of the ring was broken. The branched structure was gradually changed to a linear one. This change was caused by the increase of the dipole moment of the neutral water tetramer oriented toward the excess electron. The time scale of hydrogen bond breaking and solvation of the excess electron were estimated to be 100 and 400 fs, respectively. In the case of the cyclic water tetramer, a planar structure was only changed to a slight bent form. The mechanism of electron capture of the water tetramer (mainly the branched form) was discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 114 14 4951 - 4956 2010年04月 [査読有り][通常論文]
     
    The electron capture dynamics of hydroperoxy radical-water complexes have been investigated by means of direct density functional theory (DFT) molecular dynamics (MD) method to elucidate the solvation (hydration) effect on the reaction mechanism. The complexes composed of HOO and one to four water molecules, HOO(H2O)(n) (n = 1-4), were considered to be the hydrated HOO system. After the electron capture of n = 1, only solvent reorientation of H2O around HOO- occurred, and a stable complex (HOO--H2O) was formed within 100-300 fs. In the case of n = 2-4, a proton of H2O was transferred from H2O to OOH-, whereas H2O2 and OH-(H2O)(n-1) were found as products. It was suggested that the MOO radical adsorbed on water cluster is efficiently converted in the H2O2 without activation barrier after the electron capture of HOO. Time scales of proton transfer were calculated to be 200-300 fs. The mechanism of electron capture of HOO in polar stratospheric cloud was discussed on the basis of theoretical results.
  • Shigeaki Abe, Yoshinori Nagoya, Fumio Watari, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 6 2010年 [査読有り][通常論文]
     
    Effects of water molecules on the electronic states of graphene have been investigated by means of density functional theory (DFT) and time-dependent DFT methods at the PW91PW91 and B3LYP/6-31G(d) levels of theory. Solvation caused by one to four water molecules (n = 1-4) was examined in the present study. A graphene composed of 14 benzene rings was used as a model of finite-sized graphene (C42H16). The water molecules interact with the graphene surface via hydrogen bonding. The band gap of graphene was slightly red-shifted by the solvation. This shift was caused by the formation of hydrogen bonds between H2O and the graphene surface. The electronic states of the graphene-water system were discussed on the basis of theoretical results. (C) 2010 The Japan Society of Applied Physics
  • Shigeaki Abe, Yoshinori Nagoya, Fumio Watari, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 1 2010年 [査読有り][通常論文]
     
    The evaporation processes of water from the edge region of graphene sheets was investigated by means of the direct molecular orbital-molecular dynamics (MO-MD) method at the AM1 level. Five graphenes with n = 1, 7, 19, 37, and 61 (where n is the number of benzene rings in the graphene) were examined as models of graphene sheets. The edge carbons of each graphene were terminated by hydrogen atoms. In the H2O-graphene interaction system, the oxygen atom of the water molecule binds to one or two C-H hydrogen atoms of the edge carbons. The binding energy of H2O increased gradually as a function of n and was saturated around n = 61. At low temperature (10-100 K), the water molecule was still connected to the graphene sheet, whereas the evaporation of H2O was found above 300 K. The mechanism of water evaporation is discussed on the basis of theoretical results. (C) 2010 The Japan Society of Applied Physics
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    SYNTHESIS AND REACTIVITY IN INORGANIC METAL-ORGANIC AND NANO-METAL CHEMISTRY 40 5 306 - 311 2010年 [査読有り][通常論文]
     
    Effects of point charges on the excitation energies of protonated Schiff base of retinal (PSBR) in gas phase have been investigated by means of time-dependent density functional theory (TD-DFT) method in order to shed light on the electrostatic effects on the absorption spectra of PSBR. The positive and negative charges around PSBR were tested for 11-cis of PSBR. The TD-DFT calculations indicated that the first and second excitation energies are blue-shifted by the existence of the negative charge around the N-H site of PSBR, whereas those are red-shifted by positive charge. On the other hand, the spectral feature in -ionone ring was much different from that of the N-H site: the first and second excitation energies are red-shifted by the negative charge. The spectral feature is drastically changed at the polyene part of PSBR. It was found that the excitation energies of PSBR are affected strongly by the electrostatic environment. The effects of electrostatic interaction on the absorption spectra of PSBR are discussed on the basis of theoretical results.
  • Shigekazu Ohmori, Hiroshi Kawabatay, Ken Tokunaga, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 1 2010年 [査読有り][通常論文]
     
    The electronic structure and density distribution in the poly-fused furans were investigated using density functional theory (DFT) calculations. Differential electron density (DED) distribution analysis of the neutral and charged states of oligomer species were calculated to visualize spatial charge modulation in the molecular. Polymers of fused furans [p-F(n)] were also investigated using one-dimensional periodic boundary conditions (PBC) for comparison. A difference in the electronic structure and density distribution of p-F(n) was found between electron and hole transport processes. The electronic states of F(n) and p-F(n) were discussed on the basis of the differential electron density distribution, density of states (DOS) around the frontier states, and crystal orbital overlap population (COOP) analysis. (C) 2010 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Shigeaki Abe
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 12 15 3904 - 3909 2010年 [査読有り][通常論文]
     
    Structures and electronic states of the HOO radical interacting with water molecules, expressed by HOO(H2O)(n) (n = 1 and 2), have been investigated by means of a direct ab initio molecular dynamics (MD) method. From the static ab initio calculation of HOO-H2O complex, two types of HOO radical were found: i.e., the HOO radical acts as a hydrogen donor or acceptor in the complex (n = 1). The binding energies of former and latter complexes were calculated to be 8.7 and 3.3 kcal mol(-1), respectively, at the QCISD/6-311 + + G(2d, 2p) level. In the case of 1 : 2 complex HOO(H2O)(2), a cyclic structure with a hydrogen donor of HOO was obtained as the stable form. Effects of zero point vibration on the structures and hyperfine coupling constants of the HOO radical were also investigated. The structures and electronic states of HOO(H2O)(n) (n = 1 and 2) were discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 6 2010年 [査読有り][通常論文]
     
    The structures and electronic states of hydrogenated graphenes with a finite size have been investigated by a density functional theory (DFT) method. Five graphenes of various sizes (n = 2, 4, 7, 14, and 19, where n indicates the number of benzene rings in graphene) were examined as models of a hydrogenated graphene system. The harmonic vibrational frequency corresponding to a C-H stretching mode showed a linear relationship between the frequency and the C-H bond length. The C-H bond formed by the addition of hydrogen atoms was completely polarized as C delta--H delta+ in an equilibrium structure. It was found that the activation barrier is formed by hybridization from sp(2) to sp(3) in the transition region. The mechanism of C-H bond formation on a graphene surface was discussed on the basis of theoretical results. (C) 2010 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 1 2010年 [査読有り][通常論文]
     
    Direct molecular orbital-molecular dynamics (MO-MD) method has been applied to diffusion processes of the Li+ ion on a modified graphene surface. A graphene sheet composed of carbon, fluorine and hydrogen atoms were used as a model graphene (Li+C150H3F27, denoted by FH-graphene). The edges of graphene were terminated by fluorine (F-edge region) and hydrogen atom (H-edge region). Simulation temperatures were chosen in the range 250-350 K. It was found that the lithium ion diffuses freely on the surface, but the ion does not approach the F-edge region of the surface. This is due to the repulsive interaction with a positive charged carbon atom where C-F bond is polarized as C delta+-F delta-. On the other hand, the Li+ ion approached to the H-edge region and it exited from the H-edge region. The diffusion mechanism of Li-was discussed on the basis of theoretical results. (C) 2010 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 1 2010年 [査読有り][通常論文]
     
    Geometrical and electronic structures of a hydrogen-added graphene have been investigated by means of density functional theory (DFT) and direct molecular dynamics (MD) methods. A graphene composed of 19 benzene rings was examined as a model of finite-sized graphene. The hyperfine coupling constants (hfcc's) of hydrogen atoms on graphene were calculated to be similar to 63 G in the bulk region and 20-5 G in the edge region of graphene, indicating that the hfcc of hydrogen atoms is strongly dependent on the bonding site. The excitation energies of hydrogen added graphene were calculated to be 1.28, 1.54, and 1.60 eV, which were lower than that of graphene without hydrogen atoms (2.24 eV). The first electronic transition was assigned to an excess electron transfer band from a defect hydrogen site to the bulk region of graphene. The electronic states and thermal behavior of hydrogen atoms interacting with graphene are discussed on the basis of theoretical results. (C) 2010 The Japan Society of Applied Physics
  • Shigekazu Ohmori, Hiroshi Kawabata, Ken Tokunaga, Hiroto Tachikawa
    THIN SOLID FILMS 518 2 901 - 905 2009年11月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for oligomer species of a fused porphyrin, denoted by P(n), where n represents the number of porphyrin rings in the oligomer, to elucidate the electronic structures at ground and excited states. A polymer of fused porphyrin (p-Por) was also investigated using one-dimensional periodic boundary conditions (PBC) for comparison. It was found that the lowest energy band is located below 0.6 eV in the case of oligomers larger than n = 8, which corresponds to a band gap of p-Por. Carrier transport pathways in p-Por were discussed on the basis of theoretical results. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    THIN SOLID FILMS 518 2 877 - 879 2009年11月 [査読有り][通常論文]
     
    The interaction of magnesium (Mg) with a graphene surface has been investigated by means of density functional theory (DFT) method. Also, the direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa, J. Phys. Chem. C, 112 (2008) 101931 have been applied to the dynamics of Mg on the graphene surface. The B3LYP/LANL2MB calculations showed that the Mg atom is bound to a hexagonal site and is located in 2.02 angstrom from the graphene surface. The direct MO-MD calculations showed that the Mg atom vibrates in the hexagonal site and diffusion does not occur even at 1000 K. The nature of the interaction between the Mg atom and the graphene sheet was discussed on the basis of theoretical results. (C) 2009 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    THIN SOLID FILMS 518 2 873 - 876 2009年11月 [査読有り][通常論文]
     
    The structures and electronic states of sodium ion (Na(+)) trapped on the graphene have been investigated by means of density functional theory (DFT) calculation to elucidate the nature of interaction between Na(+) and the graphenes. In addition, direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa, J. Phys. Chem. C, 112 (2008) 101931 was applied to diffusion processes of the Na(+) ion on graphene. The graphene composed of 37 benzene rings was used as a model of graphene. The B3LYP/LANL2MB calculation showed that the sodium ion is stabilized in hexagonal site and is located at ca. 2.230 angstrom from the graphene surfaces. The direct MO-MD calculation showed that the Na(+) ion diffuses freely on the graphene surface, but the ion did not approach the edge region due to the fact that a high potential barrier exists near the edge region. The nature of interaction between Na(+) and graphene was discussed on the basis of theoretical results. (C) 2009 Elsevier B.V. All rights reserved.
  • Tomoya Takada, Hiroto Tachikawa
    JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL 311 1-2 54 - 60 2009年09月 [査読有り][通常論文]
     
    Methyl radicals interacting with silica gel surfaces have been investigated by means of DFT and direct ab-initio molecular dynamics (MD) methods using cluster models. Four typical binding sites of CH3 on the cluster models were found in the geometry optimization from several initial geometries of CH3 around the silica gel clusters. These were two silanol Si-OH sites and two siloxane Si-O-Si sites. In both sites, magnitude of hyperfine coupling constants of the methyl radical (a(H)) was smaller than that of free CH3 (a(H) = 23.04 G). Temperature effects on aH of the methyl radical were investigated by means of the direct ab-initio MD method. The hyperfine coupling constant of CH3 interacting with the SiOH group decreased with increasing temperature. The methyl radical interacting with alkali metal supported silica gel was also investigated for comparison. The electronic states of methyl radicals on silica gel were discussed on the basis of theoretical results. (C) 2009 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Yoshinori Nagoya, Hiroshi Kawabata
    JOURNAL OF CHEMICAL THEORY AND COMPUTATION 5 8 2101 - 2107 2009年08月 [査読有り][通常論文]
     
    Electronic states of graphenes, whose carbon atoms are terminated by hydrogen atoms (hydrogenated graphene, denoted H-graphene) and defective graphene (one carbon atom was removed from H-graphene, denoted D-graphene) have been investigated by density functional theory. The sizes of graphenes examined in the present study were n = 7, 14, 19, 29, 37, 44, and 52; where n is the number of benzene rings in the graphene. The excitation energies of H-graphenes were gradually decreased as a function of the number of rings. In D-graphene, new energy levels for the first and second excited states appeared as low-lying excited states. It was found that the formation of defect sites in graphene produces large decreases in the excitation energies for third and higher excited states. The highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO) in H-graphene were widely delocalized over the graphene surface. On the other hand, LUMO in D-graphene was localized only in the defect sites. The effects of vacancy defects on both the ground and excited electronic states of graphene were discussed on the basis of theoretical results.
  • SN2反応を実時間で見る!
    田地川浩人
    化学 64 697 62 - 63 2009年06月 [査読無し][通常論文]
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICAL CHEMISTRY C 113 18 7603 - 7609 2009年05月 [査読有り][通常論文]
     
    Electronic states of normal graphene, the defective graphene (one carbon atom is removed from the normal graphene), the defective graphene anion (defective graphene plus an excess electron), and the defective graphene cation (defective graphene plus one hole) have been investigated by means of density functional theory (DFT) and direct molecular orbital-molecular dynamics (MO-MD) methods in order to elucidate the effect of vacancy defect on the electronic states of graphene. The HOMO and LUMO of normal graphene were widely delocalized as pi-conjugated orbitals over the graphene surface in the normal graphene. On the other hand, the excess electron in defective graphene anion was localized in the defect site, indicating that the excess electron on the graphene circuit is,efficiently trapped and stabilized by the vacancy defect site of graphene. The direct MO-MD calculations showed that the trapped electron in the defect site is stable at low temperature. Around room temperature (300 K), the structural change of the graphene backbone was found and the vacancy defect was reconstructed by thermal activation. The excess electron escaped from the defect site of the reconstructed graphene, while the spin density delocalized the graphene.
  • 阿部 薫明, 赤坂 司, 宇尾 基弘, 亘理 文夫, 田地川 浩人
    歯科材料・器械 28 2 82 - 82 (一社)日本歯科理工学会 2009年03月
  • Tetsuji Iyama, Kohichi Kato, Hiroshi Kawabata, Hiroto Tachikawa, Kazuhisa Azumi
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 504 140 - 146 2009年 [査読有り][通常論文]
     
    The structures and electronic states of sodium atom (Na) trapped on the graphene surfaces have been investigated by means of density functional theory (DFT) calculation to elucidate the nature of interaction between Na and the graphenes. In addition, direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa, J. Phys. Chem. C, 112 (2008) 10193] was applied to diffusion processes of the Na atom on graphene surfaces. Seven graphenes (n = 7, 14, 19, 29, 37, 44 and 52, where n means numbers of rings in each carbon cluster) were examined in the present study. The B3LYP/LANL2MB calculation showed that the sodium atom is located at ca. 3.0 angstrom from the graphene surfaces. The direct MO-MD calculation showed that diffusion of Na atom is slower than that of Na+ ion on graphene surface. The nature of the interaction between Na atom and the carbon clusters was discussed on the basis of theoretical results.
  • Hiroshi Kawabata, Tetsuji Iyama, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 504 147 - 154 2009年 [査読有り][通常論文]
     
    Electronic states of lithium ion (Li+) interacting with a chlorinated graphene surface (Cl- graphene) have been investigated by means of hybrid density functional theory (DFT) to elucidate the effect of chlorination of graphene on the diffusion of lithium ion. Also, direct molecular orbital-molecular dynamics (MO-MD) calculation [H. Tachikawa, J. Phys. Chem. C, 112 (2008) 10193] was applied to diffusion processes of the Li+ ion on Cl- graphene. The potential barrier height for movement of Li+ was estimated to be 2.95 kcal/mol on Cl- graphene. The direct MO-MD calculations showed that the Li+ ion diffuses freely on bulk and edge region of Cl- graphene at 300 K. The nature of the interaction between Li+ and Cl- graphene was discussed on the basis of theoretical results.
  • Yasunori Yamamoto, Shingo Takada, Norio Miyaura, Tetsuji Iyama, Hiroto Tachikawa
    ORGANOMETALLICS 28 1 152 - 160 2009年01月 [査読有り][通常論文]
     
    Cross-coupling between bromoarenes and [(E)-CH3CH=CHCH2BF3]K (2a) by a catalyst prepared from Pd(OAc)(2) and D-t-BPF selectively provided gamma-coupling products via S(E)2' substitution. Mechanistic study of transmetalation revealed a heretofore unknown process, namely, formation of a highly electrophilic [Pd(Ar)(D-t-BPF)](+) before transmetalation with 2a. Thus, kinetic data in coupling of 4-substituted bromoarenes with 2a showed a linear positive correlation (rho = -1.1) accelerated by donating substituents. This rate-determining role of transmetalation was further confirmed by kinetic data between oxidative adducts [Pd(Ar)(Br)(D-t-BPF)] and 2a that exhibited an analogous correlation with a negative rho-value (-0.50). Theoretical study by density functional theory (DFT) calculation showed that transmetalation between [Ar-Pd](+) and 2a via an S(E)2' (open) transition state is a slightly lower energy process than an S(E)2' (closed) process. Allylic substitutions with chiral catalysts are the current topics for enantioselective C-C bond fort-nation, but the catalysts that are effective for allylic nucleophiles have remained unexplored. Among the ligands screened, (R,S)-CyPF-t-Bu was found to achieve 77-90% ee for representative para-and meta-substituted bromoarenes and 2-bromo-l-alkenes in refluxing aqueous tetrahydrofuran (THF) or MeOH. To obtain mechanistic information on enantioselection, the mode of substrate coordination to a cationic phenylpalladium intermediate was calculated, that is, the reaction stage directly preceding the stereodetermining insertion step by DFT calculation. A stable adduct between [Pd(CyPF-t-Bu)(Ph)](+) and 2a located at the C-C double bond from its re-face yielding the experimentally observed R-product is preferred thermodynamically rather than the corresponding si-coordination.
  • KAWABATA Hiroshi, IYAMA Tetsuji, TACHIKAWA Hiroto
    Mol. Crst. Liq. Crst. 504 147 - 154 2009年 [査読有り][通常論文]
  • Shigeaki Abe, Fumio Watari, Tomoya Takada, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 505 289 - 296 2009年 [査読有り][通常論文]
     
    The interaction of manganese (II) ion (Mn2+) with graphene surfaces have been investigated by means of density functional theory (DFT). Also, the molecular dynamics (MD) calculations using molecular mechanics-2 (MM2) potential functions have been applied to the diffusion dynamics of Mn2+ on the graphene surface. Two graphene sheets (n = 19 and 52, where n means numbers of rings in each carbon cluster) were considered as models of graphene surface in the present study. The B3LYP/LANL2MB calculations showed that the Mn2+ ion is located in the ranges 2.28-2.46 angstrom from the graphene surface. Also, classical MD calculation was applied to diffusion processes of the Mn2+ on the graphene surface (n - 52). The classical MD calculations showed that the Mn2+ ion diffuses from bulk to edge region at 300-600 K and is trapped in the edge region. The nature of the interaction between the Mn2+ ion and the graphene sheet was discussed on the basis of theoretical results.
  • IYAMA Tetsuji, KATO Kohichi, KAWABATA Hiroshi, TACHIKAWA Hiroto, AZUMI Kazuhisa
    Mol. Crst. Liq. Crst. 504 140 - 146 2009年 [査読有り][通常論文]
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    PHYSICS AND CHEMISTRY OF LIQUIDS 47 1 103 - 109 2009年 [査読有り][通常論文]
     
    Hydrogen molecules inserted into water clusters have been investigated by means of both density functional theory and ab initio calculations in order to determine a limit to the hydrogen storage capacity of water clusters. Three water clusters, (H2O)m (m = 20, 24 and 28), were examined as the water cages, while the guest hydrogen molecules up to nine were tested in the calculations. The maximum capacities of hydrogen storage for m = 20, 24 and 28 were determined to be n = 3, 6 and 8, respectively, at the MP2/6-311G(d, p)//B3LYP/6-311G(d, p) level of theory. In order to elucidate thermal behaviour of the hydrogen hydrate, direct molecular orbital-molecular dynamics calculations were carried out for (H2)n(H2O)m (n = 6 and 8, m = 28). It was found that the hydrogen molecule escapes from the hexagonal site without large deformation to the water lattice. The electronic states of the hydrogen molecules in the water clusters were discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama, Kohichi Kato
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 11 28 6008 - 6014 2009年 [査読有り][通常論文]
     
    Direct ab initio molecular dynamics (MD) method has been applied to a benzophenone-water 1 : 1 complex Bp(H2O) and free benzophenone (Bp) to elucidate the effects of zero-point energy (ZPE) vibration and temperature on the absorption spectra of Bp(H2O). The n-pi* transition of free-Bp (S-1 state) was blue-shifted by the interaction with a water molecule, whereas three pi-pi* transitions (S-2, S-3 and S-4) were red-shifted. The effects of the ZPE vibration and temperature of Bp(H2O) increased the intensity of the n-pi* transition of Bp(H2O) and caused broadening of the pi-pi* transitions. In case of the temperature effect, the intensity of n-pi* transition increases with increasing temperature. The electronic states of Bp(H2O) were discussed on the basis of the theoretical results.
  • Hiroto Tachikawa, Andrew J. Orr-Ewing
    JOURNAL OF PHYSICAL CHEMISTRY A 112 46 11575 - 11581 2008年11月 [査読有り][通常論文]
     
    Electron capture dynamics of protonated methane (CH5+) have been investigated by means of a direct ab initio molecular dynamics (MD) method. First, the ground and two low-lying state structures of CH5+ with eclipsed C-s, staggered C-s and C-2v symmetries were examined as initial geometries in the dynamics calculation. Next, the initial structures of CH5+ in the Franck-Condon (FC) region were generated by inclusion of zero point energy and then trajectories were run from the selected points on the assumption of vertical electron capture. Two competing reaction channels were observed: CH5+ + e(-) -> CH4 + H (I) and CH5+ + e(-) -> CH3 + H-2 (II). Channel II occurred only from structures very close to the s-C-s geometry for which two protons with longer C-H distances are electronically equivalent in CH5+. These protons have the highest spin density as hydrogen atoms following vertical electron capture of CH5+ and are lost as H-2. On the other hand, channel I was formed from a wide structural region of CH5+. The mechanism of the electron capture dynamics of CH5 is discussed on the basis of the theoretical results.
  • Shinichi Enami, Yosuke Sakamoto, Takashi Yamanaka, Satoshi Hashimoto, Masahiro Kawasaki, Kenichi Tonokura, Hiroto Tachikawa
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 81 10 1250 - 1257 2008年10月 [査読有り][通常論文]
     
    The yields of IO radical from the reaction of CH3I with Cl atom in the presence of O-2 were determined as functions of total pressure from 5 to 250 Torr of N-2 diluent and temperature over the range of 278 to 328 K using cavity ring-down spectroscopy. The yields are pressure and temperature dependent. The rate constants and product branching ratios of the reaction of CH2I radical with O-2 were investigated. We determined a rate constant of (1.28 +/- 0.22) x 10(-12) cm(3) molecule(-1) s(-1) at 298 K (2 sigma uncertainty) for this reaction. Theoretical calculations were performed to determine energetics of the reactions of CH2I + O-2, and CH2Br + O-2. The present results suggest that non-negliggible IO radicals will be formed from the reactions of CH3I/CH2I2 + OH/Cl/NO3 at atmospheric conditions.
  • Hiroto Tachikawa, Hiroshi Kawabata
    CHEMICAL PHYSICS LETTERS 462 4-6 321 - 326 2008年09月 [査読有り][通常論文]
     
    DNA repair reactions of the thymine dimer ( T) 2 following the hole capture have been investigated by means of direct ab initio molecular dynamics ( MD) method in order to elucidate the mechanism of repair processes of thymine dimer interacting with a photo-enzyme. The thymine dimer has two C-C single bonds between thymine rings at neutral state expressed by (T=T). After the hole capture of (T=T), one of the C-C bonds was preferentially broken, while the structure of (T=T)(+) was spontaneously changed to an intermediate having a C-C single bond expressed by (T-T)(+). Time scale of the C-C bond breaking and formation of the intermediate was estimated to be 60-180 fs. The mechanism of repair reactions of the thymine dimer was discussed on the basis of theoretical results. (C) 2008 Elsevier B.V. All rights reserved.
  • Yukio Nakano, Hiromi Ukeguchi, Takashi Ishiwata, Yugo Kanaya, Hiroto Tachikawa, Atsushi Ikeda, Shigeyoshi Sakaki, Masahiro Kawasaki
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 81 8 938 - 946 2008年08月 [査読有り][通常論文]
     
    The rate constants of the reaction of NO3 With CH3I, which can affect iodine chemistry in the atmosphere, were measured in the temperature range of 298-323 K with cavity ring-down spectroscopy. The reaction has a rate constant of k = (4.1 +/- 0.2) x 10(-13) cm(3) molecule(-1) s(-1) at 298 K. Uncertainties reported herein are one standard deviation. On the basis of an Arrhenius plot in the region of 298-323 K, the reaction has an activation energy (E-a = 13 +/- 3 kJ mol(-1)). Density functional and coupled-cluster calculations suggest that the reaction proceeds via a transition state in which the hydrogen atom is nearly located at the middle position between the carbon atom of CH3I and the oxygen atom of NO3 to give HNO3 + CH2I. On the atmospheric implications, box model simulations indicate that the present reaction has an important effect on the levels and diurnal patterns of the mixing ratios of NO3 and CH3I, and also on the activation of iodine chemistry in the atmosphere.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY C 112 27 10193 - 10199 2008年07月 [査読有り][通常論文]
     
    A direct molecular orbital-molecular dynamics (MO-MD) method has been applied to diffusion processes of the Li+ ion on a fluorinated graphene surface. A graphene sheet composed Of C96F24 (denoted by F-graphene) was used as a model of the fluorinated graphene surface. The total energy and energy gradient on the full dimensional potential energy surface of the Li+C96F24 system were calculated at each time step in the trajectory calculation. The calculations were carried out at the AM I level. Simulation temperatures were chosen in the range 200-1000 K. At low temperatures, below 200 K, the diffusion of lithium ion did not occur, and the ion vibrates around an equilibrium point. At around room temperature (similar to 300 K), the lithium ion diffused freely on the surface, but the ion did not approach to the edge region of the surface. This is due to the repulsive interaction with positively charged carbon atom connecting to the fluorine atom where the C-F bond is polarized as C delta+-F delta-. The repulsive interaction strongly dominates the diffusion path of the Li+ ion on the F-graphene. However, the order of magnitude of diffusion coefficient for the Li+ ion moving on the F-graphene surface was close to that of the normal graphene surface (H-graphene). At higher temperatures, the Li+ ion moves freely on the F-graphene, and it fell in the edge region. On the basis of theoretical results, we designed a molecular device composed of F-graphite sheets.
  • Hiroshi Kawabata, Shigekazu Ohmori, Kazumi Matsushige, Hiroto Tachikawa
    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 9 2 24405 - 24411 2008年06月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for neutral and radical cation species of a fused selenophene oligomer, denoted by Se(n), where n represents the number of selenophene rings in the oligomer, to elucidate the electronic structures at ground and low-lying excited states. A polymer of fused selenophene was also investigated using one-dimensional periodic boundary conditions (PBC) for comparison. It was found that the reorganization energy of a radical cation of Se(n) from a vertical hole trapping point to its relaxed structure is significantly small. Also, the reorganization energy decreased gradually with increasing n, indicating that Se(n) has an effective intramolecular hole transport property. It was found that the radical cation species of Se(n) has a low-energy band in the near-IR region, which is strongly correlated to hole conductivity. The relationship between the electronic states and intramolecular hole conductivity was discussed on the basis of theoretical calculations.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICAL CHEMISTRY B 112 24 7315 - 7319 2008年06月 [査読有り][通常論文]
     
    The interaction between the fully reduced flavin-adenine dinucleotide (FADH(-)) and thymine dimer (T)(2) has been investigated by means of density functional theory (DFT) calculations. The charges of FADH(-) and (T)(2) were calculated to be -0.9 and -0.1, respectively, at the ground state. By photoirradiation, an electron transfer occurred from FADH(-) to (T)(2) at the first excited state. Next, the reaction dynamics of electron capture of (T)(2) have been investigated by means of the direct ab initio molecular dynamics (MD) method (HF/3-21G(d) and B3LYP/6-31G(d) levels) in order to elucidate the mechanism of the repair process of thymine dimer caused by the photoenzyme. The thymine dimer has two C-C single bonds between thymine rings (C(5)-C(5') and C(6)-C(6') bonds) at the neutral state, which is expressed by (T)(2). After the electron capture of (T)(2), the C(5)-C(5') bond was gradually elongated and then it was preferentially broken. The time scale of the C-C bond breaking and formation of the intermediate with a single bond (T)(2)(-) was estimated to be 100-150 fs. The present calculations confirmed that the repair reaction of thymine dimer takes place efficiently via an electron-transfer process from the FADH(-) enzyme.
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    THIN SOLID FILMS 516 9 2611 - 2614 2008年03月 [査読有り][通常論文]
     
    The electronic states of sodium ion (Na+) trapped on the model surfaces of amorphous carbon have been investigated by means of hybrid density functional theory (DFT) calculations to elucidate the nature of interaction between Na+/Na and the amorphous carbon surfaces. Also, direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa and Shimizu, J. Phys. Chem. 13, 110 (2006) 20445] was applied to diffusion processes of the Na+ ion on the model surface of amorphous carbon. Seven models of graphene sheets (n = 7, 14, 19, 29, 3 7, 44 and 52, where n means numbers of rings in each carbon cluster) were considered in the present study. The B3LYP/LANL2MB calculations showed that the sodium ion is located at 2.24-2.26 angstrom from the graphene surfaces. The direct MO-MD calculations showed that the Na+ ion diffuses freely on the surface above 300 K. At higher temperature (1100 K), the Na+ ion moved from the center to edge region of the model surface. The nature of the interaction between Na+ and the amorphous carbon surfaces was discussed on the basis of theoretical results. (c) 2007 Elsevier B.V. All rights reserved.
  • Hiroshi Kawabata, Shigekazu Ohmori, Kazumi Matsushige, Hiroto Tachikawa
    THIN SOLID FILMS 516 9 2421 - 2425 2008年03月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for neutral and radical cation of fused furan oligomer, denoted by F(n) where n means number of furan rings in the oligomer, to elucidate the electronic structures at ground and low-lying excited states. A polymer of fused furan was also investigated using one-dimensional periodic boundary condition (PBC) for comparison. It was found that the reorganization energy of radical cation of F(n) from vertical hole trapping point to its relaxed structure is significantly small. Also, the reorganization energy decreased gradually with increasing n, indicating that F(n) has an effective hole transport property. It was found that the cation radical of F(n) has a low energy band at near IR region, which is strongly correlated to hole conductivity. The relation between the electronic states and hole conductivity was discussed on the basis of theoretical calculations. (C) 2007 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    THIN SOLID FILMS 516 10 3287 - 3293 2008年03月 [査読有り][通常論文]
     
    Hybrid density functional theory calculations have been carried out for the organic-inorganic hybrid complex of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) with an indium atom (In) to elucidate the degradation mechanism of thin films of molecular organic semiconductors by water molecules. This compound has been used as an organic semiconductor. The band gap of NTCDA was calculated to be as high as 3.39 eV as a single molecule, whereas a new band of NTCDA was formed as low-lying excited state (1.64 eV) after the interaction with the In atom. The water molecule attacked preferentially the In atom of In-NTCDA, and the solvation structure was formed around the In atom (solvation). Further addition of a water molecule to the system, the In atom is stripped off from NTCDA by water molecules, and solvation shell around the In atom is formed (separated solvation). The hydrogen-bond network was broken by the formation of solvation shell. The mechanism of degradation of the electron conductivity has been discussed on the basis of theoretical results. (c) 2007 Elsevier B.V All rights reserved.
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 1 803 - 805 2008年01月 [査読有り][通常論文]
     
    The electronic states of potassium ion and atom (K(+) and K) adsorbed on the amorphous carbon surfaces have been investigated by means of hybrid density functional theory (DFT) calculation to elucidate the nature of interaction between K(+)/K and the amorphous carbon. Seven graphene sheets (n = 7, 14, 19, 29, 37, 44, and 52, where n means numbers of rings in each carbon cluster) were considered as models of amorphous carbon in the present study. The B3LYP/LANL2MB calculations showed that the potassium ion is located at ca. 2.80 angstrom from the graphene surfaces and the charge of K+ is not dependent on the cluster size of the graphene sheets. On the other hand, the charge of potassium atom (K) increased with increasing cluster size (n), and it reached a constant value (ca. +0.70) at n = 29-52. Also, direct molecular orbital-molecular dynamics (MO-MD) calculation [H. Tachikawa and A. Shimizu: J. Phys. Chem. B 110 (2006) 204451 was applied to diffusion processes of the K(+) ion and K atom on the model surfaces of amorphous carbon. The direct MO-MD calculations showed that the K(+) ion and K atom diffuse freely on the surface at 800K. The nature of the interaction between K(+)/K and the carbon clusters was discussed on the basis of theoretical results.
  • Nobuhito Kurono, Tadahiro Kondo, Masanori Wakabayashi, Hirohito Ooka, Tsutomu Inoue, Hiroto Tachikawa, Takeshi Ohkuma
    CHEMISTRY-AN ASIAN JOURNAL 3 8-9 1289 - 1297 2008年 [査読有り][通常論文]
     
    Enantiomer-selective carbamoylation of racemic alpha-hydroxy gamma-lactones with half equivalents of isocyanates in the presence of chiral Cu-II catalysts was studied. Among a series of catalyst bearing chiral bis(oxazoline) (box) and pyridine(bisoxazoline) ligands, [Cu(tBu-box)]X-2 [X=OSO2CF3 (3a), SbF6 (3b)] showed the highest enantioselectivity in the reaction of pantolactone (1a). Use of n-C3H7NCO, a small alkyl isocyanate, in CH2Cl2 solution was important to achieve a high level of enantiomer selection. The tBu-box-Cu-II catalyst efficiently differentiated two enantiomers of beta-substituted alpha-hydroxy gamma-lactones under the optimized reaction conditions, resulting in a stereoselectivity factor (s = k(fast)/k(slow)) of up to 209. Furthermore, this catalyst is highly active, so that the carbamoylation can be conducted with a substrate-to-catalyst molar ratio of 2000-3000. A catalytic cycle of this reaction is also proposed.
  • Shigeaki Abe, Takahiro Fukuzumi, Hiroto Tachikawa
    SYNTHESIS AND REACTIVITY IN INORGANIC METAL-ORGANIC AND NANO-METAL CHEMISTRY 38 1 105 - 110 2008年 [査読有り][通常論文]
     
    Ab initio and density functional theory (DFT) calculations have been applied to hydration processes of dimethylsulfide (DMS), which plays an important role in cloud condensation nuclei (CCN) in marine boundary layer. The molecular complexes composed of water and dimethylsulfide, DMS(H(2)O)(n) (n = 0-3), were examined in the present calculations. The MP4SDQ/6311G(2d, p)//B3LYP/6-311G(d, p) calculations indicated that the binding energy of H(2)O to DMS is calculated to be 7.7 kcal/mol for n = 1. The second water molecule is bound to H(2)O of DMS(H(2)O) by a hydrogen bond, and then a 1: 2 complex is formed. The binding energy of the second water molecule to DMS(H(2)O) was calculated to be 10.4 kcal/mol. This energy is larger than that of water dimer (the corresponding binding energy was 6.6 kcal/mol in water dimer). Direct molecular orbital-molecular dynamics (MO-MD) calculations were carried out for the hydration reactions DMS(H(2)O) + H(2)O --> DMS(H(2)O)(2) (1) and H(2)O + H(2)O --> (H(2)O)(2) (2) at thermal collision energy. The calculations showed that water dimer formation reaction on DMS, reaction (1), is efficiently occurred, whereas half of the trajectories for reaction (2) gave dissociation products (H(2)O + H(2)O). The mechanism of hydration of DMS was discussed on the basis of theoretical results.
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    SYNTHESIS AND REACTIVITY IN INORGANIC METAL-ORGANIC AND NANO-METAL CHEMISTRY 38 1 101 - 104 2008年 [査読有り][通常論文]
     
    Gas phase structures and electronic states of micro-solvated biomolecule clusters composed of water clusters and protonated Schiff Base Retinal (PSBR) have been investigated by means of hybrid density functional theory (DFT) method. Up to three-water molecules were considered as the water clusters, denoted by PSBR(H2O)(n) (n = 0-3). We focused our attention mainly on the effects of microsolvation on the infrared (IR) spectrum of PSBRs in the gas phase. The calculations showed that the water molecules bind strongly the N-H+ site of PSBR. The calculated IR spectra showed that the N-H stretching mode of PSBR is largely red-shifted by the interaction with water molecules. The similar calculations were carried out for methanol-PSBR clusters. The effects of microsolvation on the structure and electronic states were discussed on the basis of theoretical results.
  • Hiroshi Kawabata, Ken Tokunaga, Shigekazu Ohmori, Kazumi Matsushige, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 1 420 - 424 2008年01月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for neutral and radical cation species of a fused thiophene oligomer, denoted by T(n), where n represents the number of thiophene rings in the oligomer, to elucidate the electronic structures at ground and low-lying excited states. A polymer of fused thiophene was also investigated using one-dimensional periodic boundary conditions (PBCs) for comparison. It was found that the reorganization energy of a radical cation of T(n) from a vertical hole trapping point to its relaxed structure is significantly small. Also, the reorganization energy decreased gradually with increasing n, indicating that T(n) has an effective hole transport property. It was found that the radical cation species of T(n) has a low energy band in the near-IR region, which is strongly correlated to hole conductivity. The relationship between the electronic states and hole conductivity was discussed on the basis of theoretical calculations.
  • Hiroshi Kawabata, Tetsuji Iyama, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 1 800 - 802 2008年01月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for the lithium adsorbed on a fluorinated graphene surface (F-graphene, C(96)F(24)) to elucidate the effect of fluorination of amorphous carbon on the diffusion mechanism of lithium ion. Also, direct molecular orbital-molecular dynamics (MO-MD) calculation [H. Tachikawa and A. Shimizu: J. Phys. Chem. B 109 (2005) 13255] was applied to diffusion processes of the Li(+) ion on F-graphene. The B3LYP/LANL2MB calculation showed that the Li(+) ion is most stabilized around central position of F-graphene, and the energy was gradually instabilized for the edge region. The direct MO-MD calculations showed that the Li+ ion diffuses on the bulk surface region of F-graphite at 300 K. The nature of the interaction between Li+ and F-graphene was discussed on the basis of theoretical results.
  • Akira Miura, Shiro Shimada, Masaaki Yokoyama, Hiroto Tachikawa, Toshio Kitamura
    CHEMICAL PHYSICS LETTERS 451 4-6 222 - 225 2008年01月 [査読有り][通常論文]
     
    We investigated the properties of heavily oxygen-doped single GaN crystals and proposed their electronic structure based on first-principle calculations. The crystals were grown by carbothermal reduction and nitridation of Ga2O3 at 1180 degrees C for 2-8 h. The crystal were found to have high-crystallinity and high-concentration oxygen (4-9 x 10(20) atoms/cm(3)). Cathodoluminescence measurements of the 8-h-grown crystals showed a shift of band-edge-related luminescence peak toward higher energy (ca. 120 meV). Density of state of oxygen-doped GaN supercell was calculated using the first-principle to support this upward shift of luminescence energy. (C) 2007 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 10 16 2200 - 2206 2008年 [査読有り][通常論文]
     
    Dissociative electron capture dynamics of halocarbon absorbed on water cluster anion, caused by internal electron transfer from the water trimer anion to the halocarbon, have been investigated by means of the direct density functional theory (DFT)-molecular dynamics (MD) method. The CF2Cl2 molecule and a water trimer anion e(-)(H2O)(3) were used as a halocarbon and a trapped electron, respectively. First, the structure of trapped electron state, expressed by e(-)(H2O)(3)-CF2Cl2, was fully optimized. The excess electron was trapped by a dipole moment of water trimer. Next, initial geometries were randomly generated around the equilibrium point of the trapped electron state, and then trajectories were run. The direct DFT-MD calculations showed that the spin density distribution of excess electron is gradually changed from the water cluster (trapped electron state) to CF2Cl2 as a function of time. Immediately, the Cl- ion was dissociated from CF2Cl2- adsorbed on the water cluster. The reaction was schematically expressed bye(-)(H2O)(3)-CF2Cl2 ->[(H2O)(3)-CF2Cl2](-) -> (H2O)(3) + CF2Cl + Cl- (1)where [(H2O)(3)-CF2Cl2](-) indicates a transient intermediate state in which the excess electron is widely distributed on both the water cluster and CF2Cl2. The mechanism of the electron capture of halocarbon from the trapped electron in water ice was discussed on the basis of the theoretical results. Also, the dynamics feature was compared with those of the direct electron capture reactions of CF2Cl2 and CF2Cl2-(H2O)(3), i.e.e(-) + CF2Cl2, and e(-) + CF2Cl2-(H2O)(3), investigated in our previous paper [Tachikawa and Abe, J. Chem. Phys., 2007, 126, 194310].
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 692 25 5541 - 5548 2007年12月 [査読有り][通常論文]
     
    Structures and electronic states of paramagnetic species in co-deposit film composed of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) and aluminum (Al) have been investigated by means of hybrid density functional theory (DFT) calculations to determine the species in detail. Al-NTCDA 1:1 complex, 1:3 Al-3-NTCDA complex and an Al metal bridged dimer Al-(NTCDA)(2) were examined as paramagnetic species of Al-NTCDA complexes. The simulated electron paramagnetic resonance (EPR) spectra of the 1:3 complex and the dimer were in reasonable agreement with experiment reported previously by Tachikawa et al. [Tachikawa et al., J. Phys. Chem. B 109 (2005) 3139]. It was found that the contribution from the 1: 1 complex to the EPR spectra was very small. From the comparison with theoretical and experimental UV and EPR spectra, it was found that several paramagnetic and diamagnetic species exist in the co-deposit film of Al/NTCDA. The structures and electronic states were discussed on the basis of theoretical results. (C) 2007 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 111 40 10134 - 10138 2007年10月 [査読有り][通常論文]
     
    The mechanism of excess electron and hole localizations in radical ions of poly(dimethylsilane) (PDMS) has been investigated by means of molecular dynamics (MD) and extended Huckel methods. Oligo(dimethylsilane) composed of 100 monomer units of dimethylsilane, CH3(Si(CH3)(2))(n)CH3 (n = 100), were used as a model of PDMS. Both wings of the oligomer were capped by a methyl group. First, the geometry of PDMS with a regular all-trans form was fully optimized by MM2(+) energy gradient method. Next, the MD calculation was carried out for PDMS at 300 K. The structure of PDMS was gradually deformed as a function of simulation time, especially the dihedral angle of Si-Si-Si-Si backbone that was randomized. At time zero when the structure has the regular all-trans form, both the excess electron and hole were completely delocalized on the Si backbone of PDMS. After thermal activation, the localization of the electron and hole was found. The mechanism of the localization was discussed on the basis of theoretical results.
  • Shinichi Enami, Takashi Yamanaka, Satoshi Hashimoto, Masahiro Kawasaki, Kenichi Tonokura, Hiroto Tachikawa
    CHEMICAL PHYSICS LETTERS 445 4-6 152 - 156 2007年09月 [査読有り][通常論文]
     
    Formation of the iodine monoxide radical (IO) was observed during the reaction of iodoalkyl radicals (RCHI) or cyclo-C6H10I radical with O-2 at 298 K using cavity ring-down spectroscopy, where R stands for CnH2n+l (n = 0-3). The yields of IO from the reactions of various RCH2I species with Cl atom in the presence of O-2 were determined. The energy level diagrams derived from theoretical calculations for each individual reaction support the formation of IO radicals via a direct RCHI radical oxidation pathway. (C) 2007 Elsevier B.V. All rights reserved.
  • Kei Iokibe, Kazuhisa Azumi, Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY C 111 36 13510 - 13516 2007年09月 [査読有り][通常論文]
     
    The adsorption and diffusion of a Zn atom on a Zn(001) surface has been investigated theoretically by using first-principles periodic boundary condition calculations to elucidate the mechanism of crystal growth of zinc in a Zn surface. Three surface models, terrace, step, and kink, of the Zn(001) surface were considered as adsorption sites in the present study. The most stable site in the terrace model was the on-top site, where the zinc adatom is bound to only one zinc atom of the surface. The activation barrier between the on-top site and the next on-top site was negligibly low (the activation energy is 44 meV at the PW91/LANL2DZ level), suggesting that the Zn adatom diffuses easily on the Zn(001) surface. The Zn adatom was more stabilized at the step site (752 meV) and kink site (935 meV) with respect to the on-top site. It was found that the magnitude of 4s-4p orbital mixing of the Zn adatom (hybridization) is strongly related to the binding energy. The mechanism of the adsorption of Zn on Zn(001) surfaces was discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY C 111 35 13087 - 13091 2007年09月 [査読有り][通常論文]
     
    The diffusion dynamics of the Li+ ion on fullerene (C-60) have been investigated by means of the direct molecula-orbital-molecular dynamics (MO-MD) method. The total energy and energy gradient on the full dimensional potential energy surface of the Li(+)C60 system were calculated at each time step in the trajectory calculation. The optimized structure, where the Li+ ion is located at the hexagonal Site Of C60, was used as an initial itructure at time zero. Simulation temperatures were chosen in the range of 10-300 K. The dynamics calculations showed that the Li+ ion vibrates around the initial equilibrium point below 40 K, while the ion can move above 50 K. At low temperature (below 300 K), the diffusion coefficients for the Li+ ion on the C60 surface are larger than those of the graphite surface. The diffusion coefficients on both C60 and the graphite surface were almost equivalent at medium temperatures around 300 K. At higher temperatures (T > 300 K), the coefficients for the graphite surface were significantly larger than those Of C60. On the basis of theoretical results, A e designed an ion-switching molecular device composed Of C60 and graphite sheet.
  • Hong-Yan Xiao, Jun Cao, Ya-Jun Liu, Wei-Hai Fang, Hiroto Tachikawa, Masaru Shiotani
    JOURNAL OF PHYSICAL CHEMISTRY A 111 24 5192 - 5200 2007年06月 [査読有り][通常論文]
     
    The s-cis and s-trans isomer radical cations of hexafluoro-1,3-butadiene (s-cis-HFBD+ and s-trans-HFBD+) were generated by a gamma-irradiated solid solution of the neutral HFBD molecule in solid matrix at 77 K and observed by means of electron spin resonance (ESR) and electronic spectroscopies. In comparing the experimental isotropic and anisotropic F-19 hyperfine splittings with the computational ones by the DFT B3LYP and MP2 methods, the generated s-cis-HFBD+ and s-trans-HFBD+ radical cations were confirmed to be (2)A(2) and B-2(g) electronic ground states in C-2v and C-2h symmetries, respectively. The present spectroscopic study revealed that the relative abundance of s-cis-HFBD+ to s-trans-HFBD+ was 4.0 immediately after being formed by gamma-irradiation, and subsequently most s-cis-HFBD+ was isomerized to s-trans-HFBD+ by visible-light illumination with 500-600 nm wavelength. The process of nonplanar HFBD ionizing to form stable planar s-cis- and s-trans-HFBD+ and the reaction mechanism of the cis-to-trans photoisomerization were discussed by (MS-)CASPT2//CASSCF calculated vertical excitation energies (T-v) and torsional potential energy curves (TPECs) of HFBD and HFBD+.
  • Hiroto Tachikawa, Shigeaki Abe
    JOURNAL OF CHEMICAL PHYSICS 126 19 2007年05月 [査読有り][通常論文]
     
    The electron capture dynamics of halocarbon and its water complex have been investigated by means of the full dimensional direct density functional theory molecular dynamics method in order to shed light on the mechanism of electron capture of a halocarbon adsorbed on the ice surface. The CF2Cl2 molecule and a cyclic water trimer (H2O)(3) were used as halocarbon and water cluster, respectively. The dynamics calculation of CF2Cl2 showed that both C-Cl bonds are largely elongated after the electron capture, while one of the Cl atoms is dissociated from CF2Cl2- as a Cl- ion. Almost all total available energy was transferred into the internal modes of the parent CF2Cl radical on the product state, while the relative translational energy of Cl- was significantly low due to the elongation of two C-Cl bonds. In the case of a halocarbon-water cluster system, the geometry optimization of neutral complex CF2Cl2(H2O)(3) showed that one of the Cl atoms interacts with n orbital of water molecules of trimer and the other Cl atom existed as a dangling Cl atom. After the electron capture, only one C-Cl bond (dangling Cl atom) was rapidly elongated, whereas the other C-Cl bond is silent during the reaction. The dangling Cl atom was directly dissociated from CF2Cl2-(H2O)(3) as Cl-. The fast Cl- ion was generated from CF2Cl2-(H2O)(3) on the water cluster. The mechanism of the electron capture of halocarbon on water ice was discussed on the basis of the theoretical results. (C) 2007 American Institute of Physics.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 692 7 1511 - 1518 2007年03月 [査読有り][通常論文]
     
    The electronic states of radical cations of oligo[methyl(phenyl)silane] (OMPSi+) with all trans form (n = 2-8, where n is number of monomer unit of OMPSi) have been investigated by means of density functional theory (DFT) calculation to shed light on the mechanism of hole-transport in oligosilanes with phenyl group in the side chain. For the shorter oligomers (n < 3), the hole (unpaired electron) was widely distributed equivalently in both the Si main and side chains (55% for the Si main chain and 45% for the side chain). The distribution of hole on the chains was largely changed as a function of chain lengths (n). Ratios of the hole distribution on the main and side chains became almost constant at n = 7-8: 70% of spin density was distributed on the Si-main chain and 30% on the side-chain, which is much different from that of oligo(dimethyl)silane (the spin density on the methyl side chain was less than 3% of spin density). From these results, it was concluded that the hole in OMPSi+ can transfer by the mechanism for both intermolecular and the intrachain hole-transfer processes. (c) 2006 Elsevier B.V. All rights reserved.
  • Hiroshi Kawabata, Kazumi Matsushige, Shigekazu Ohmori, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 472 687 - 695 2007年 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for neutral and radical cation of permethyl-oligogermane, Ge-n(CH3)(2n+2) (n=4-28), to elucidate the electronic structures at ground and low-lying excited states. It was found that a hole is distributed in both the Ge-Ge skeleton (main chain) and methyl group (side chain) in the case of shorter chain-lengths below n = 8, whereas the spin density (hole) in the methyl group becomes significantly smaller in longer chain-lengths (n > 10). The IR-band of radical cation were assigned on the basis of theoretical calculations.
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 472 697 - 704 2007年 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for the lithium ion-carbon cluster model systems to elucidate the nature of lithium-carbon surface interaction. Also, direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa and Shimizu, J. Phys. Chem. B, 109 (2005) 13255] was applied to diffusion processes of the Li ion on the model surfaces of amorphous carbon. Seven cluster models (n = 7, 14, 19, 29, 37, 44 and 55, where n means numbers of rings in the carbon cluster models) were considered in the present study. The B3LYP/LANL2MB calculations showed that the lithium ion is located at ca. 1.60 angstrom from the carbon surface. The direct MO-MD calculations showed that the Li ion diffuses freely on the surface above 250 K. At higher temperature (1100 K), the Li ion moves from the center to edge region of the model surface and leaves from the surface. The nature of the interaction between Li+ and the carbon clusters was discussed on the basis of theoretical results.
  • Kei Iokibe, Hiroto Tachikawa, Kazuhisa Azumi
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 40 2 427 - 436 2007年01月 [査読有り][通常論文]
     
    Ab-initio and density functional theory (DFT) calculations have been carried out for zinc clusters Zn-n (n = 2-32, n is the number of atoms to form a cluster) to elucidate the structure and electronic charge states of the clusters and the mechanism of clustering. The binding energies of Zn atoms were negligibly small at n = 2-3, whereas the energy increased significantly at n = 4 (the first transition). The second transition occurred at n = 8-16. In the larger clusters (n = 16-32), the binding energy increased slightly with increasing cluster size (n). The cluster size dependence of the binding energy and bond length between zinc atoms agreed well with that of the natural population of electrons in the 4p orbital of the zinc atom. In the larger clusters (n > 20), it was found that the zinc atoms in the surface region of the cluster have a positive charge, whereas those in the interior region have a negative charge with a large population in the 4p orbital. The formation mechanism of zinc clusters was discussed on the basis of the theoretical results.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF CHEMICAL THEORY AND COMPUTATION 3 1 184 - 193 2007年01月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for the radical cation and anion of permethyloligosilane Si-n(CH3)(2n+2)(+/-) (n = 2-6) to elucidate the electronic structures at ground and low-lying excited states, and the results were compared with the corresponding experimental values. In particular, the assignment of electronic transition appeared at near-IR and visible regions, which is strongly correlated to hole and electron conductivity, and was carried out on the basis of time-dependent DFT calculation. The structure of oligosilane was generated at 300 K by direct PM3 molecular dynamics calculations, and then the geometry was fully optimized at the DFT(B3LYP)/6-311+G(d,p) level. It was found that the hole in the radical cation and the electron in the radical anion of oligosilane are delocalized over the Si skeleton. The proton-hyperfine coupling constants calculated were in good agreement with those obtained by an electron spin resonance experiment. It was also found that the g-anisotropy of the radical anion was significantly larger than that of the radical cation. The IR bands of radical ions were assigned on the basis of theoretical calculations.
  • Hiroto Tachikawa, Kei Iokibe, Kazuhisa Azumi, Hiroshi Kawabata
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 9 30 3978 - 3984 2007年 [査読有り][通常論文]
     
    Ab initio and Density Functional Theory (DFT) calculations have been carried out for zinc-water clusters Zn-n-(H2O)m (n = 1-32 and m = 1-3, where n and m are the numbers of zinc atoms and water molecules, respectively) to elucidate the structure and electronic states of the clusters and the interaction of zinc cluster with water molecules. The binding energies of H2O to zinc clusters were small at n = 2-3 (2.3-4.2 kcal mol(-1)), whereas the energy increased significantly in n = 4 (9.0 kcal mol(-1)). Also, the binding nature of H2O was changed at n = 4. The cluster size dependency of the binding energy of H2O accorded well with that of the natural population of electrons in the 4p orbital of the zinc atom. In the larger clusters (n > 20), it was found that the zinc atoms in surface regions of the zinc cluster have a positive charge, whereas those in the interior region have a negative charge with the large electron population in the 4p orbital. The interaction of H2O with the zinc clusters were discussed on the basis of the theoretical results.
  • Hiroshi Kawabata, Shigekazu Ohmori, Kazumi Matsushige, Hiroto Tachikawa
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 691 26 5525 - 5530 2006年12月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for neutral, radical cation and dication of permethyloligosilane, Si-n(CH3)(2n+2) (n=4-30), to elucidate the electronic structures at ground and low-lying excited states. It was found that a hole is distributed in both the Si-Si skeleton (main chain) and methyl group (side chain) in the case of shorter chain-lengths below n=6, whereas the spin density (hole) in the methyl group becomes significantly smaller in longer chain-lengths (n > 7). The IR-band of radical cation were assigned on the basis of theoretical calculations. (c) 2006 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Shigeaki Abe
    CHEMICAL PHYSICS LETTERS 432 4-6 409 - 413 2006年12月 [査読有り][通常論文]
     
    The excitation energies of O-3-H2O complex have been calculated by means of SAC-Cl method to elucidate the spectral shifts of excitation energies of O-3 caused by the complex formation with a water molecule. The eclipsed form, where the center oxygen of O-3 and water oxygen are located on the C, molecular plane, was examined in the present study. The first and third excitation energies of O-3 were slightly blue-shifted by the complex formation with H2O. The oscillator strength for the third excitation was not affected by the complex formation, indicating that the photo-dissociation of the O-3-H2O Complex occurs efficiently as well as free ozone molecule. The electronic states of the complex was discussed on the basis of theoretical results. (c) 2006 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 691 23 4843 - 4849 2006年11月 [査読有り][通常論文]
     
    The electronic structures at the ground and low-lying excited states of permethyloligosilane radical cations, Si-n(CH3)(2n+2)(+) (n = 4-7), have been investigated using DFT and ab initio calculations. The calculations showed that positive charge (hole) is delocalized along the Si-Si main chain at the ground and first excited states. On the other hand, the hole is transferred to the methyl side-chain at the second and higher excited states. From these results, it was concluded that hole can move along the Si-Si main chain at thermal conditions. Also, it was predicted that intermolecular hole hopping takes place by photo-irradiation to the permethyloligosilane radical cation. The mechanism of hole transfer was discussed on the basis of the results. (c) 2006 Elsevier B.V. All rights reserved.
  • KONDO Satomi, HASHIMOTO Kenro, TACHIKAWA Hiroto
    Chem. Phys. Lett. 431 1-3 45 - 50 2006年11月 [査読有り][通常論文]
     
    The dynamics of Na(H2O) following electron detachment from Na-(H2O) in a zero-point vibrational state was investigated using an ab initio direct molecular-dynamics method. In 96% of the trajectories of Na(H2O), the reorientations of water occurred on the similar to 120 fs time scale. Na-O bond formation was observed in more than 80% of the neutral trajectories. The photodetachment-photoionization spectra using 4.3-5.3 eV photons delayed from electron detachment were calculated for 5 ps. (c) 2006 Elsevier B.V. All rights reserved.
  • Takahiro Itoh, Toshiaki Mase, Takashi Nishikata, Tetsuji Iyama, Hiroto Tachikawa, Yuri Kobayashi, Yasunori Yarnamoto, Norio Miyaura
    TETRAHEDRON 62 41 9610 - 9621 2006年10月 [査読有り][通常論文]
     
    An enantioselective synthesis of acyclic beta-diaryl ketones and esters via 1,4-addition of arylboronic acids to beta-aryl-alpha,beta-unsaturated ketones or esters is described. The complex in situ prepared from [Rh(nbd)(2)]BF4 and chiraphos was found to be an excellent catalyst to achieve high enantioselectivities in a range of 83-89% ee for the ketone derivatives and 78-94% ee for tert-butyl beta-arylacrylate derivatives. The protocol provided a catalytic method for the enantioselective synthesis of selective endothelin A receptor antagonists (7, 8) reported by SmithKline Beecham and Merck-Banyu. The enantioselection mechanism and efficiency of the chiraphos ligand for beta-aryl-alpha,beta-unsaturated ketones and esters are discussed on the basis of results of DFT computational studies on the modes of coordination of the enone substrates to the phenylrhodium(I)-(S,S)-chiraphos complex. (c) 2006 Elsevier Ltd. All rights reserved.
  • Shinichi Enami, Takashi Yamanaka, Satoshi Hashimoto, Masahiro Kawasaki, Simone Aloisio, Hiroto Tachikawa
    JOURNAL OF CHEMICAL PHYSICS 125 13 133116 - 133122 2006年10月 [査読有り][通常論文]
     
    The broad absorption of Cl-3 radical was observed between 1150 and 1350 nm using cavity ring-down spectroscopy at 213-265 K and 50-200 Torr with He, N-2, Ar, or SF6 diluents. The absorption intensity of Cl-3 increased at lower temperature and higher pressure. SF6 was the most efficient diluent gas. The temperature dependent equilibrium constants for Cl-3 formation from Cl+Cl-2 were theoretically calculated at the MP4SDQ/6-311+G(d) level. Observed decay time profiles of Cl-3 and the pressure dependence of Cl-3 formation are explained by the equilibrium reaction and a decay reaction of Cl+Cl-3. (c) 2006 American Institute of Physics.
  • Hiroto Tachikawa
    JOURNAL OF CHEMICAL PHYSICS 125 13 133119 - 133129 2006年10月 [査読有り][通常論文]
     
    Reaction dynamics for a microsolvated S(N)2 reaction OH-(H2O)+CH3Cl have been investigated by means of the direct ab initio molecular dynamics method. The relative center-of-mass collision energies were chosen as 10, 15, and 25 kcal/mol. Three reaction channels were found as products. These are (1) a channel leading to complete dissociation (the products are CH3OH+Cl-+H2O: denoted by channel I), (2) a solvation channel (the products are Cl-(H2O)+CH3OH: channel II), and (3) a complex formation channel (the products are CH3OH center dot center dot center dot H2O+Cl-: channel III). The branching ratios for the three channels were drastically changed as a function of center-of-mass collision energy. The ratio of complete dissociation channel (channel I) increased with increasing collision energy, whereas that of channel III decreased. The solvation channel (channel II) was minor at all collision energies. The selectivity of the reaction channels and the mechanism are discussed on the basis of the theoretical results. (c) 2006 American Institute of Physics.
  • Hiroto Tachikawa, Akira Shimizu
    JOURNAL OF PHYSICAL CHEMISTRY B 110 41 20445 - 20450 2006年10月 [査読有り][通常論文]
     
    Direct molecular orbital-molecular dynamics (MO-MD) calculation was applied to diffusion processes of the Li atom on a model surface of amorphous carbon and compared with the diffusion mechanism of Li+ ion. A carbon sheet composed of C96H24 was used as the model surface. The total energy and energy gradient on the full dimensional potential energy surface of the LiC96H24 system were calculated at each time step in the trajectory calculation. The optimized structure, where the Li atom is located at the center of mass of the model surface, was used as the initial structure at time zero. Simulation temperatures were chosen in the range of 200-1250 K. The dynamics calculations showed that the Li atom vibrates around the initial position below 250 K, and it moves above 300 K. At middle temperature, the Li atom translates freely on the surface. At higher temperature (1000 K), the Li atom moves from the center to edge region of the model surface and is trapped in the edge. The activation energy calculated for the Li atom is larger than that for the Li+ ion. This difference is due to the fact that the Li atom diffuses together with an unpaired electron on the carbon surface. The diffusion mechanism of the Li atom was discussed on the basis of the theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF CHEMICAL PHYSICS 125 14 144307 - 144315 2006年10月 [査読有り][通常論文]
     
    Electron attachment dynamics of excess electron in water cluster (H2O)(n) (n=2 and 3) have been investigated by means of full-dimensional direct ab initio molecular dynamics (MD) method at the MP2/6-311++G(d,p) level. It was found that the hydrogen bond breaking due to the excess electron is an important process in the first stage of electron capture in water trimer. Time scale of electron localization and hydrogen bond breaking were determined by the direct ab initio MD simulation. The initial process of hydration in water cluster is clearly visualized in the present study. In n=3, an excess electron is first trapped around the cyclic water trimer with a triangular form, where the excess electron is equivalently distributed on the three water molecules at time zero. After 50 fs, the excess electron is concentrated into two water molecules, while the potential energy of the system decreases by -1.5 kcal/mol from the vertical point. After 100 fs, the excess electron is localized in one of the water molecules and the potential energy decreases by -5.3 kcal/mol, but the triangular form still remained. After that, one of the hydrogen bonds in the triangular form is gradually broken by the excess electron, while the structure becomes linear at 100-300 fs after electron capture. The time scale of hydrogen bond breaking due to the excess electron is calculated to be about 300 fs. Finally, a dipole bound state is formed by the linear form of three water molecules. In the case of n=2, the dipole bound anion is formed directly. The mechanism of electron hydration dynamics was discussed on the basis of theoretical results. (c) 2006 American Institute of Physics.
  • Hiroto Tachikawa, Manabu Igarashi
    CHEMICAL PHYSICS 324 2-3 639 - 646 2006年05月 [査読有り][通常論文]
     
    Direct ab initio molecular dynamics (MD) calculations have been applied to a S(N)2 reaction OH- + CH3Cl -> CH3OH + Cl-. The collision dynamics with non-zero impact parameters were treated in the present study, and the results are compared with the near collinear collision dynamics previously reported by us [H. Tachikawa, M. Igarashi, T. Ishibashi, J. Phys. Chem. A 106 (2002) 10977]. The collision energy was fixed to 25 kcal/mol. The product state distribution obtained for the non-zero impact parameter collision dynamics was slightly different from that of the collinear collision. The distribution of relative translational energy between products Cl- and CH3OH in the non-zero impact parameter collision dynamics was shifted to higher energy region from that of collinear collision. Also, it was found that the mean translational energy of the product has a maximum at non-zero impact parameter (b = 0.6-1.2 angstrom). The reaction mechanism is discussed on the basis of theoretical results. (c) 2005 Elsevier B.V. All rights reserved.
  • H Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 110 1 153 - 159 2006年01月 [査読有り][通常論文]
     
    Ionization processes of chlorobenzene-ammonia 1:1 complex (PhCl-NH3) have been investigated by means of full dimensional direct ab initio molecular dynamics (MD) method, static ab initio calculations, and density functional theory (DFT) calculations. The static ab initio and DFT calculations of neutral PhCl-NH3 complex showed that one of the hydrogen atoms of NH3 orients toward a carbon atom in the para-position of PhCl. The dynamics calculation for ionization of PhCl-NH3 indicated that two reaction channels are competitive with each other as product channels: one is an intramolecular S(N)2 reaction expressed by a reaction scheme [PhCl-NH3](+) -> S(N)2 intermediate complex -> PhNH3+ + Cl, and the other is ortho-NH3 addition complex (ortho complex) in which NH3 attacks the ortho-carbon of PhCl+ and the trajectory leads to a bound complex expressed by (PhCl-NHS3)(+). The mechanism of the ionization of PhCl-NH3 is discussed on the basis of the theoretical results.
  • T Takada, H Tachikawa
    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 105 1 79 - 83 2005年10月 [査読有り][通常論文]
     
    The hyperfine coupling constants of hydrogen atom (H-hfcc's, a(H)) of methyl radical (CH3) in matrices have been calculated by means of the hybrid density functional theory (DFT) and ab initio methods in order to elucidate the effect of matrices on the H-hfcc of CH3. Three typical matrices (X = CH4, H-2, and Ar) were examined in the calculations. The systems calculated in the present work, denoted by CH3(X)(n), are CH3(H-2)(n) (n = 12 and 20), CH3(Ar)(n) (n = 12 and 18), and CH3(CH4)(n) (n = 12 and 18). The Moller-Plesset type 2 (MP2) and B3LYP methods were applied to the H-hfcc calculation. The H-hfcc of methyl radical was slightly perturbed by the interaction with matrices lattice, and it was shifted from that of free methyl radical (a(H) = -23.03 G). The mechanism of the shift of H-hfcc of CH3 in matrices lattice was discussed on the basis of theoretical results. (c) 2005 Wiley Periodicals, Inc.
  • Hiroto Tachikawa
    Canadian Journal of Chemistry 83 9 1597 - 1605 2005年09月01日 [査読有り][通常論文]
     
    Direct ab initio molecular dynamics (MD) calculations have been carried out for the reaction of cyclopropenyl chloride with halide ion (F–) (F– + (CH)3Cl → F(CH)3 + Cl–) in gas phase. Both SN2 and SN2′ channels were found as product channels. These channels are strongly dependent on the collision angle of F– to the target (CH)3Cl molecule. The collision at one of the carbon atoms of the C=C double bond leads to the SN2′ reaction channel; whereas the collision at the methylene carbon atom leads to the SN2 reaction channel. The reactions proceed via a direct mechanism without long-lived complexes. The reaction mechanism is discussed on the basis of the theoretical results.Key words: SN2 reaction, direct ab initio molecular dynamics, halogen exchange, reaction mechanism.
  • H Tachikawa, A Shimizu
    JOURNAL OF PHYSICAL CHEMISTRY B 109 27 13255 - 13262 2005年07月 [査読有り][通常論文]
     
    Diffusion processes of the Li+ ion on a model surface of amorphous carbon (Li+C96H24 system) have been investigated by means of the direct molecular orbital (MO) dynamics method at the semiempirical AMI level. The total energy and energy gradient on the full-dimensional AMI potential energy surface were calculated at each time step in the dynamics calculation. The optimized structure, where Li+ is located in the center of the cluster, was used as the initial structure at time zero. The dynamics calculation was carried out in the temperature range 100-1000 K. The calculations showed that the Li+ ion vibrates around the equilibrium point below 200 K, while the Li+ ion moves on the surface above 250 K. At intermediate temperatures (300 K < T < 400 K), the ion moves on the surface and falls in the edge regions of the cluster. At higher temperatures (600 K < T), the Li+ ion transfers freely on the surface and edge regions. The diffusion pathway of the Li+ ion was discussed on the basis of theoretical results.
  • H Tachikawa, H Kawabata
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 79 3 191 - 195 2005年06月 [査読有り][通常論文]
     
    Effects of the residues on the excitation energies of protonated Schiff base of retinal (PSBR) in bacteriorhodopsin have been investigated by means of time-dependent density functional theory. The residues around PSBR are replaced by the point charges on atoms. The structures of PSBR and residues are referred from X-ray data. The atomic charges on the each residue were calculated the B3LYP/6-311 G(d,p) level. The excitation energy of PSBR perturbed by the point charges on atoms of each residue was calculated at the B3LYP/6-31 G(d,p) level. A total of 23 residues and five water molecules around PSBR were considered in the calculations. The large spectral shifts were caused by the Asp212 and Asp85. The origin of the spectral shifts was discussed on the basis of theoretical results. © 2005 Elsevier B.V. All rights reserved.
  • H Tachikawa, H Kawabata, K Ishida, K Matsushige
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 690 12 2895 - 2904 2005年06月 [査読有り][通常論文]
     
    The structures and electronic states of phenyl-capped terthiophene (denoted by P3T) and the ionic species of P3T have been investigated by means of density functional theory (DFT) and direct MO dynamics calculations. P3T is one of the high-performance molecular devices, which has been utilized as a semi-conductor. The calculations indicated that the neutral P3T has a non-planar structure whose the phenyl rings in both ends of thiophene chain are largely deviated from the molecular plane. The cation and anion radicals, dication and dianion were considered as its ionic states. The structure for cation radical of P3T is close to more planar than that of neutral P3T. The structures for anion radical, dication and dianion take a pure planar structure. The first excitation energy of neutral P3T is calculated to be 2.90 eV at the TD-B3LYP/6-31G(d)HB3LYP/6-311+G(d) level, while the P3T cation and anion radicals have lower excitation energies (1.22 and 1. 10 eV, respectively). The direct MO dynamics calculation showed that neutral, cation and anion hold near planar structure at 300 K. On the other hand, oligothiophene (n = 5) and its ionic species are strongly deformed from the planar structure, and thiophene rings in both ends of chain rotate rapidly by thermal activation. The mechanism of the electron conductivity in P3T was discussed on the basis of theoretical results. (c) 2005 Elsevier B.V. All rights reserved.
  • H Tachikawa, H Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 6A 3769 - 3773 2005年06月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for high-performance molecular devices, complexes of naphthalene tetracarboxylic dianhydride (NTCDA) and halogen-substituted NTCDA with aluminum (denoted by Al-4(X)(4)NTCDA, where X denotes H, F, Cl or Br). The four hydrogen atom of NTCDA were substituted with X atoms. It was found that the electronic state of the complex in the ground state is composed of a charge-transfer state expressed by (Al-4)(delta)+((X)(4)NTCDA)(delta-). Also, it was predicted that the binding energy of the Al atom was enhanced by the halogen substitution, indicating that the complex of (X)(4)NTCDA (X = halogen atoms) is more stable in terms of energy than that of pure NTCDA (X = H). The large binding energy results in the high material stability in atmosphere. By photoirradiation of the complex, the interaction between Al and NTCDA was changed from ionic to covalent. This electronic excitation was assigned to the back donation of an electron from NTCDA to Al, and it was predicted theoretically that the absorption spectrum appears as a charge-transfer (CT) band in the near infrared region. The effects of halogen-substitution on the electronic states of NTCDA are discussed on the basis of theoretical results.
  • H Tachikawa, M Igarashi, J Nishihira, T Ishibashi
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 79 1 11 - 23 2005年04月 [査読有り][通常論文]
     
    Ab initio molecular orbital (MO) and hybrid density functional theory (DFT) calculations have been applied to the initial step of the acylation reaction catalyzed by acetylcholinesterase (AChE), which is the nucleophiric addition of Ser200 in catalytic triads to a neurotransmitter acetylcholine (ACh). We focus our attention mainly on the effects of oxyanion hole and Glu327 on the potential energy surfaces (PESs) for the proton transfer reactions in the catalytic triad Ser200-His440-G1027. The activation barrier for the addition reaction of Ser200 to ACh was calculated to be 23.4 kcal/mol at the B3LYP/6-31G(d)//HF/3-21G(d) level of theory. The barrier height under the existence of oxyanion hole, namely, Ser200-His440-Glu327-ACh-(oxyanion hole) system, decreased significantly to 14.2 kcal/mol, which is in reasonable agreement with recent experimental value (12.0 kcal/mol). Removal of Glu327 from the catalytic triad caused destabilization of both energy of transition state for the reaction and tetrahedral intermediate (product). PESs calculated for the proton transfer reactions showed that the first proton transfer process is the most important in the stabilization of tetrahedral intermediate complex. The mechanism of addition reaction of ACh was discussed on the basis of theoretical results. (c) 2004 Elsevier B.V. All rights reserved.
  • H Tachikawa, H Kawabata, R Miyamoto, K Nakayama, M Yokoyama
    JOURNAL OF PHYSICAL CHEMISTRY B 109 8 3139 - 3145 2005年03月 [査読有り][通常論文]
     
    Electronic absorption, Fourier transform-infrared (FT-IR), and electron spin resonance spectra of aluminium-naphthalene tetracarboxylic dianhydlide (Al-NTCDA) co-deposited film have been measured at room temperature, and hybrid density functional theory (DFT) calculations have been carried out in order to elucidate the electronic states for the ground and low-lying excited states of the complexes. After the interaction of NTCDA with Al atom, the new electronic transition bands were appeared at near-IR region. The C=O stretching modes of NTCDA are red-shifted by the interaction with Al. From the DFT calculations, it was found that the electronic state of the complex at the ground state is characterized by a slight charge-transfer state expressed by (Al-4)(delta+)(NTCDA)(delta-). The binding of Al to NTCDA is strong. The C=O double-bond character of NTCDA is changed to C-O single-bond-like character by the strong interaction of Al to the C=O bond. This is the origin of the red-shift of the FT-IR spectrum. The electronic states of organic-inorganic hybrid material were discussed on the basis of theoretical results.
  • H Tachikawa, T Iyama
    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 102 2 230 - 238 2005年03月 [査読有り][通常論文]
     
    Density Functional Theory (DFT) and direct ab initio molecular dynamics (MD) calculations were applied to the hydrogen molecule trapped in a water cluster composed of 12 water molecules (H2O)(12). The static DFT calculation showed that the H-2 molecule is trapped in the center of mass of (H2O)(12). The vibrational frequency of the H-H stretching mode of the H-2 molecule trapped in the water cluster was blueshifted from that in vacuo. On the other hand, the vibrational frequency of H, in water-hydrogen 1:1 complex (H2O-H-2)was redshifted. A direct ab initio MD calculation of H-2(H2O)(12) at 50 K indicated that the H-2 molecule is rotated freely around the center of mass of the water cluster. The origin of the spectral shift of H-2 in water ice is discussed on the basis of the theoretical results. (C) 2004 Wiley Periodicals, Inc.
  • H Tachikawa, T Iyama, H Kawabata
    JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM 718 1-3 117 - 122 2005年03月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for the nitric oxide NO molecule on the Cu model cluster in order to shed light on the diffusion mechanism of the NO molecule on the Cu(100) cluster model surface. The metal surface was represented approximately by a finite metal cluster Cu-9. Three binding sites, 'two-fold site', 'four-fold site', and 'on-top site', were considered in the present study. In two-fold site, NO binds to two Cu atoms in the shorter Cu-Cu bond of the surface, whereas NO in four-fold site was bound in the longer Cu-Cu bond and interacts with four Cu atoms. The binding energies of NO were larger in the order, on-top < two-fold < fourfold sites. Also, it was found that on-top site is transition state for the diffusion of NO. The activation energy along the diffusion path from two-fold site to next neighboring two-fold site via on-top site was calculated to be 4.8 kcal/mol, while the diffusion was a symmetry-allowed adiabatic process. On the other hand, the barrier height for the diffusion path from four-fold site to four-fold site was as high as 8.90 kcal/mol, and the diffusion needs non-adiabatic process (symmetry-forbidden). The mechanism of the adsorption of NO on Cu was discussed on the basis of theoretical results. (c) 2005 Elsevier B.V. All rights reserved.
  • Takayuki Kumada, Hiroto Tachikawa, Toshiyuki Takayanagi
    Physical Chemistry Chemical Physics 7 5 776 - 776 2005年 [査読有り]
  • H Tachikawa, S Abe
    INORGANICA CHIMICA ACTA 358 2 288 - 294 2005年01月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been carried out for ozone-water clusters O-3(H2O)(n) (n = 1-4) in order to obtain hydration effects on the absorption spectrum of ozone. The first water molecule in n = I is bound to the ozone molecule by an oxygen orientation form in which the oxygen atom of H2O orients the central oxygen atom of O-3. In n = 2, the water dimer is bound to O-3 and then the cyclic structure is formed as the most stable structure. For n = 3 (or n = 4), the cyclic water trimer (or tetramer) is bound by a hydrogen bond to the ozone molecule. The TD-DFT calculations of O-3(H2O)(n) (n = 0-4) show that the first and second excitation energies of O-3 are blue-shifted by the interaction with the water clusters. The magnitude of the spectral shift is largest in n = 2, and the shifts of the excitation energies are +0.07 eV for S-1 and +0.13 eV for S-2 states. In addition to the spectral shifts (SI and S2 states), it is suggested that a charge-transfer band is appeared as a low-lying excited state above the S-1 and S-2 states. The origin of the spectrum shifts was discussed on the basis of theoretical results. (C) 2004 Elsevier B.V. All rights reserved.
  • Hiroshi Kawabata, Yoshitaka Matsui, Ken-Ichi Nakayama, Masaaki Yokoyama, Hiroto Tachikawa
    Molecular Simulation 30 13-15 923 - 928 2004年11月15日 [査読有り][通常論文]
     
    Density functional theory (DFT) calculation at the B3LYP/6-311++ G(d, p) level has been applied to one of the high-performance molecular devices, magnesium-naphthalene tetracarboxylic dianhydlide (NTCDA) complex expressed by Mg4NTCDA. The electronic state of the complex at the ground state is consisted of a slight ion-pair state expressed by (Mg4)δ+(NTCDA)δ. The magnitude of the charge transfer (CT) is estimated to be δ = 0.56e. The first and second excitation energies of free NTCDA were calculated to be 3.40 and 3.42 eV, respectively. By the interaction of NTCDA with the Mg atom, a new energy band is generated at low energy region: the excitation energies of Mg4NTCDA are calculated to be 0.17 and 1.37 eV, respectively. These bands are assigned to a CT band. The mechanism of the electron conductivity was discussed on the basis of theoretical results.
  • T. Iyama, H. Tachikawa
    Molecular Simulation 30 13-15 917 - 921 2004年11月15日 [査読有り]
  • H Tachikawa, T Iyama
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 76 1-3 55 - 60 2004年10月 [査読有り]
     
    One-dimensional potential energy curves for the isomerization of protonated Schiff base of retinal (PSBR) in bacteriorhodopsin (bR), i.e., isomerization from all-trans- to 13-cis-forms, have been calculated by means of time-dependent density functional theory (TD-DFT) calculations, in order to elucidate the mechanism of initial step in photo-absorption. The transition state of the isomerization in the first excited state is located at theta(13-14) = 58degrees, where theta(13-14) means twist angle around the C-13=C-14 double bond of PSBR The potential barrier is formed by the avoided crossing between S-1 (B-u-like) and S-2 (A(g)-like) states. The mechanism of the isomerization was discussed on the basis of theoretical results. (C) 2004 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    Journal of Physical Chemistry A 108 39 7853 - 7862 2004年09月30日 [査読有り]
     
    The ionization dynamics of the water clusters (H2O)n (n = 3-6) have been investigated by means of the full-dimensional direct ab initio trajectory method. The static ab initio and DFT calculations were carried out at the HF/6-311G(d,p) and B3LYP/6-311G(d,p) levels, whereas the direct ab initio trajectory calculations were performed at the HF/6-31 G(d) and 6-311 G(d,p) levels of theory. The static ab initio and DFT calculations showed that the most stable structure is the cyclic form for all cases (n = 3-6). In the ionization of the water trimer, the complex (H3O+OH)H 2O was obtained as a product (complex formation channel). In the larger clusters (n = 4-6), the OH dissociation was only found after the ionization of (H2O)n (OH dissociation channel). The OH dissociation occurs via two-step processes: the first step is a proton-transfer process from H2O+ to H2O along the hydrogen bond in the cluster, and then the (H3O+OH) complex is formed as a core in the cluster, expressed by (H2O +)-H2O-H2O → (OH)(H3O +)-H2O. The next step is the second proton-transfer process from H3O+OH to the neighboring water molecule, which is expressed by (OH)-H3O+-H2O → (OH)-H2O-H3O+. It was found that the OH dissociation takes place immediately after the second proton transfer. The lifetimes of the intermediate complexes are distributed in the range 50-200 fs for n = 4-6. The reaction mechanism was discussed on the basis of theoretical results.
  • A Yabushita, Y Hashikawa, A Ikeda, M Kawasaki, H Tachikawa
    JOURNAL OF CHEMICAL PHYSICS 120 11 5463 - 5468 2004年03月 [査読有り][通常論文]
     
    The TOF spectra of photofragment hydrogen atoms from the 193 run photodissociation of amorphous ice at 90-140 K have been measured. The spectra consist of both a fast and a slow kcomponents that are characterized by average translational energies of 2k(B)T(trans)= 0.39 +/- 0.04 eV (2300 +/- 200 K) and 0.02 eV (120 +/- 20 K), respectively. The incident laser power dependency of the hydrogen atom production suggests one-photon process. The electronic excitation energy of a branched cluster, (H2O)(6+1), has been theoretically calculated, where (H2O)(6+1) is a (H2O)(6) Cyclic cluster attached by a water molecule with the hydrogen bond. The photoabsorption of this branched cluster is expected to appear at around 200 nm. The source of the hydrogen atoms is attributed to the photodissociation of the ice surface that is attached by water molecules with the hydrogen bond. Atmospheric implications are estimated for the photodissociation of the ice particles (Noctilucent clouds) at 190-230 nm in the region between 80 and 85 km altitude. (C) 2004 American Institute Of Physics.
  • Trans-Cis Isomerization of Protonated Schiff Base of Retinal at the Ground and Triplet States: A Hybrid DFT Study
    Iyama, T, Tachikawa, H
    Int. Elec. J. Molec. Design 3 37 - 44 2004年 [査読有り][通常論文]
  • A Shimizu, H Tachikawa
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 64 12 2397 - 2402 2003年12月 [査読有り][通常論文]
     
    For inspection of thermal behaviors of sodium (Na) atom in the bulk and on the surface of two layered hydrogen terminated cluster model, 2C(150)H(30), the molecular dynamics calculation was taken place at molecular mechanics 2 level. From the requirement of structural optimization, interlayer distance of 2C(150)H(30) is 3.38 Angstrom which is consistent with the observed value. In the cluster models intercalated and adsorbed by one Na atom, C150H30.Na.C150H30 and Na.2C(150)H(30), respectively, the Na atom is stabilized beneath and above the nearest central carbon atom, C-0, in the upper layer where the distances, Na-C-0, are 2.76 and 3.16 Angstrom, respectively. Adsorption of the Na atom to the surface has no influence on the geometrical structure of cluster model, whereas, intercalation to two layers expands the interlayer distance maximally to 5.01 Angstrom which will be responsible for the carbon expansion of graphite electrode in cryolite melt-alumina slurries. Diffusion processes are observed above 200 K for the Na atoms stabilized in both sites. Although the Na atom migrates parallel to the layers in the range between 200 and 300 K in C150H30.Na.C150H30, it moves above the carbon layer from the center to the circumference periodically below 250 K and gets out at 300 K for Na.2C(150)H(30). The migration rates of Na atom are almost the same irrespective of the diffusion areas. (C) 2003 Elsevier Ltd. All rights reserved.
  • A Shimizu, H Tachikawa
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 64 11 2235 - 2243 2003年11月 [査読有り][通常論文]
     
    As the preliminary step to elucidate the charge-discharge mechanism in the glassy carbon cathode of lithium (Li) secondary battery, the molecular dynamics (MD) calculation was applied at molecular mechanics 2 (MM2) level for three Li atoms stabilized in the form of regular triangle in the central area of the hydrogen terminated planar cluster, C150H30. The stabilized Li sites are given on the basis of the structural optimization. Up to 10 K, the triangular Li aggregate kept at almost the same figure as that formed by three stabilization sites, rotating parallel to the cluster plane, goes around the central area of it, whereupon interatomic vibrational stretching is observed. Below 75 K, the aggregate of three Li atoms separates to a pair of two atoms and one Li atom arbitrarily, however, reformation of the pair occurs periodically among three atoms with the lapse of simulation time. Then, three Li atoms move correlatively irrespective of the long interatomic distance of 18 Angstrom at maximum. However, at 100 K one Li atom goes out of the cluster model directly and the rest of two atoms continues the revolutional movement with the rotation as a pair in the central area of the cluster model. Thus, three Li atoms show the appreciably stable movements in the glassy carbon by forming the aggregate or the atomic pair, which will be responsible for the hysteresis in the charge-discharge cycle of lithium secondary battery. (C) 2003 Elsevier Ltd. All rights reserved.
  • H Tachikawa, M Igarashi, T Ishibashi
    JOURNAL OF PHYSICAL CHEMISTRY A 107 38 7505 - 7513 2003年09月 [査読有り][通常論文]
     
    Ionization dynamics of trans-formanilide-water 1:1 complexes FA(H2O) have been investigated by means of direct ab initio trajectory method. From the static ab initio calculations, three conformers of the FA(H2O) complexes were obtained as stable structures: namely, these are the N-H site, the C=O carbonyl site and the bridge site, which are different in the positions of H2O around FA. In the N-H and C=O sites, a water molecule binds to the hydrogen and oxygen atoms of the peptide (-NH-CO), respectively. In the bridge site, the hydrogen and oxygen atoms of H2O bind to the C=O carbonyl and a hydrogen of benzene ring (o-position) of FA, respectively. The trajectories from the vertical ionization points of these three structures were calculated by means of full dimensional direct ab initio trajectory method. It was found that the H2O molecule in the N-H site is still remained in its site after ionization, i.e., the strong complex cation where H2O binds to the N-H site of FA(+) is directly formed. On the other hand, in the cases of the ionization from both CO and bridge sites, the water molecule was moved easily around both the benzene ring and the C=O carbonyl group. The mechanism of the ionization of FA(H2O) was discussed on theoretical results.
  • H Tachikawa, H Kawabata
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 678 1-2 56 - 60 2003年07月 [査読有り][通常論文]
     
    The structures and electronic states of acetone-metal complexes (Ac-M, where M = Ga, Al, and 13) have been calculated by means of ab-initio DFT and configuration interaction (CI) calculations in order to shed light on the mechanism of the electron conductivity and doping effects. It was found that the electronic states of Ac-Ga and Ac-Al at the ground state are composed of ion-pair state expressed approximately by (Acdelta-)(Mdelta+): the electron is transferred from metal to the carbonyl group, suggesting that the carbonyl compound interacting with Ga and At behaves as an n-type semiconductor. In the case of the Ac-B complex, on the other hand, the electron on Ac is significantly transferred to the boron atom, expecting that hole is transferred in the boron-doped carbonyl compound (p-type semiconductor). In these complexes, the first electronic transition is a charge-transfer band between metal and carbonyl group. The mechanism of the electronic conductivity was discussed on the basis of theoretical results. (C) 2003 Elsevier Science B.V. All rights reserved.
  • T Seki, H Tachikawa, T Yamada, H Hattori
    JOURNAL OF CATALYSIS 217 1 117 - 126 2003年07月 [査読有り][通常論文]
     
    An efficient, economical, and environmentally benign method for the synthesis of phthalide-skeleton using heterogeneous catalytic intramolecular Tishchenko reaction with solid bases is described. Among the solid base catalysts examined, MgO, CaO, and SrO, exhibited high catalytic performances for the; intramolecular Tishchenko reaction of o-phthalaldehyde to yield phthalide exclusively in excellent yields at 313 K in the short time span of 0.25 h. Application of gamma-alumina to the intramolecular Tishchenko reaction of o-phthalaldehyde was also successful; phthalide was obtained selectively in excellent yields at 313 K in 4 h. The employment of KF/alumina and KOH/alumina at 313 K for 4 h resulted in the selective formation of phthalide in moderate yields. The heterogeneous catalytic systems realized by the use of CaO, and gamma-alumina were also successfully applicable to the selective intramolecular Tishchenko reaction of 2,3-naphthalenedicarbaldehyde to give the corresponding five-membered lactone in excellent yields at 333 K for 2 and 20 h, respectively. Based on the reaction results, the infrared spectra of adsorbed a-phthalaldehyde, and the quantum chemical calculations conducted at the PM3-MO level of theory for elucidation of the molecular and electronic structures of o-phthalaldehyde and the potential intermediates, a plausible reaction mechanism for the intramolecular Tishchenko reaction of o-phthalaldehyde to phthalide over MgO and gamma-alumina was proposed. The catalytically active species should be o-PAOCH(2)C(6)H(4)CHO (M = Mg or Al). (C) 2003 Elsevier Science (USA). All rights reserved.
  • Akira Shimizu, Hiroto Tachikawa
    Journal of Physics and Chemistry of Solids 64 5 807 - 811 2003年05月 [査読有り][通常論文]
     
    In order to investigate the thermal behaviors of lithium (Li) atom intercalated in and adsorbed on the graphite intercalated compound, the molecular dynamics procedure at molecular mechanics 2 level was applied to the hydrogen terminated cluster model composed of two layers of C150H30 plane. On the basis of the optimized structure, one intercalated Li atom was stabilized at the mass center and adsorbed Li was done above the center of upper plane. Both Li atoms initiate to migrate at 50 K parallel to the plane with almost the same migration rate in the temperature range from 50 to 200 K. However, their migration processes are clearly different. The former gets out of the cluster model, drawing the increasing curves accompanied by the induction period in the coordinate axes of the migration distance vs. the simulation time at every temperature. The latter, however, cannot be released from the cluster model below 150 K where it remains on the side face of the cluster model. At 50 and 100K, it migrates from the center to the circumference periodically cannot escape from the surface of cluster model. Thus, the potential well is considered to be deeper on the surface than in the layers.
  • A Shimizu, H Tachikawa
    ELECTROCHIMICA ACTA 48 12 1727 - 1733 2003年05月 [査読有り][通常論文]
     
    As the preliminary step to elucidate the ion transfer mechanism of lithium (Li) species in the cathode electrode of glassy carbon material, molecular dynamics (MD) simulation was taken place describing the initial thermal movement of two Li atoms in the simulation time range of 10 ps maximally in the hydrogen terminated cluster model, C150H30, at molecular mechanics 2 (MM2) level. The formation of Li-2 atom pair is specified in the central area of the cluster model as the result of the structural optimization. In the low temperature range from 4 to 10 K, accompanied by the rotational and stretching vibrational motions, it goes around the central area of the cluster model. Diffusion process of the atom pair is simulated dynamically for the first time in the present study. Decomposition of the atom pair occurred at 50 K and it produces two Li atoms which go and back independently from the center to the edge of the cluster model crossing the C-C bonds orthogonally. Formation and diffusion processes of Li-2 atom pair may be responsible for the charge-discharge cycles in the glassy carbon electrode in the lithium secondary battery. (C) 2003 Elsevier Science Ltd. All rights reserved.
  • H Tachikawa, S Abe
    INORGANIC CHEMISTRY 42 7 2188 - 2190 2003年04月 [査読有り][通常論文]
     
    Ab initio MO calculations have been carried out for the ozone-water 1:1 complexes in order to elucidate the structures and electronic state of the complexes. The QCISD calculations indicated that three structures are obtained as stable forms Of O-3-H2O. The most stable structure Of O-3-H2O has C, symmetry where the central oxygen Of O-3 and all atoms of H2O are located on the molecular C, plane. The dipole of H2O orients toward the central oxygen atom Of O-3 (i.e., dipole orientation form). The other two forms are cis and trans forms Of O-3-H2O where all atoms are located on the molecular plane, and a hydrogen of H2O binds to one of the terminal oxygen atoms Of O-3 by a hydrogen bond. The binding energies Of O-3 to H2O for dipole, cis, and trans forms are calculated to be 2.39, 2.27, and 2.30 kcal/mol, respectively, at the QCISD(T)/6-311++G(3df,3pd)//QCISD/6-311++G((d,p) level. The dipole orientation form is more stable in energy than the cis and trans forms. Rotational constants for the dipole orientation form are calculated to be A = 11.897, B = 4.177, and C = 3.318 GHz which are in good agreement with the experimental values (A = 11.961, B = 4.174, and C = 3.265 GHz). The electronic states Of O-3-H2O were discussed on the basis of theoretical results.
  • H Tachikawa
    CHEMICAL PHYSICS LETTERS 370 1-2 188 - 196 2003年03月 [査読有り][通常論文]
     
    The electron capture dynamics in water dimer (H2O)(2) has been investigated by means of direct ab initio trajectory method. It was found that the solvent reorientation of the water cluster anion occurs spontaneously following the vertical electron capture of the neutral water dimer: namely, the linear form water dimer which is the most stable structure of neutral water dimer, was drastically changed by accepting an excess electron to a dipole orientation form in which the two dipoles of the water molecules coordinate equivalently to the excess electron. The electron was located around the center of two water molecules at the final structure. The water dimer's solvation time was calculated to be about 150-400 fs. The mechanism of the solvent reorientation was discussed on the basis of theoretical results. (C) 2003 Elsevier Science B.V. All lights reserved.
  • A Shimizu, H Tachikawa
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 64 3 419 - 423 2003年03月 [査読有り][通常論文]
     
    For investigation of thermal behaviors of hydrogen (H) atom in a graphite intercalated compound (GIC), the molecular dynamic (MD) procedure at the molecular mechanics 2 (MM2) level was applied to a hydrogen terminated cluster model composed of two layers of C150H30 plane. On the basis of the optimized structure, one intercalated H atom was stabilized at the mass center of the cluster model. According to the trajectory of the intercalated H atom, the diffusion is initiated at 100 K towards lower potential energy area in the periphery of the cluster model. The diffusion rate increased with the increase in the simulation temperature from 100 to 500 K. According to the extended Huckel calculation, the band gap of graphite is broadened by 0.1 eV with the intercalation. Thus, the present MD simulation proposed that the semiconductivity of GIC is promoted due to the development of the ionic conductivity. However, H atom adsorbed on the surface of C150H30 plane formed the stable covalent bond with a host carbon atom and made little contribution to the conductivity. (C) 2002 Elsevier Science Ltd. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    Journal of Physical Chemistry B 107 5 1113 - 1119 2003年02月06日 [査読有り][通常論文]
     
    Direct ab initio trajectory calculations have been applied to the ionization (i.e., hole-capture) processes of biphenyl (Bp) in order to shed light on hole-capture processes of Bp and poly(4-vinylbiphenyl) (PVB). The static ab initio calculations at several levels of theory showed that the neutral Bp has a nonplanar structure with a twist angle between benzene rings in the range φ = 38-50°. The potential energy curve for the twist rotation of benzene rings was shallow for Bp. This twist angle was changed to 18-21° in biphenyl cation (Bp+), which has a more planar structure and a more tight potential shape than those of Bp. Full, dimensional direct ab initio trajectory calculations showed that the structure of Bp is spontaneously changed after the ionization: the nonplanar structure was changed to planar one after 120 fs, and then the twist angle vibrated between -40° and +40° with a time period of about 500 fs. The C-C bond distance in the connection site between two benzene rings was immediately shortened after the hole capture of Bp, and it vibrated in the range 1.375-1.481 Å. Direct PM3 dynamics calculations for the model compound composed of two-monomer units of PVB indicated that a hole is localized on one of the biphenyl groups at time zero, and then it is delocalized over the two side?groups after the structural relaxation. The mechanism of hole capture in Bp and in PVB was discussed on the basis of theoretical results.
  • H Tachikawa, H Kawabata
    JOURNAL OF PHYSICAL CHEMISTRY B 107 5 1113 - 1119 2003年02月 [査読有り][通常論文]
     
    Direct ab initio trajectory calculations have been applied to the ionization (i.e., hole-capture) processes of biphenyl (Bp) in order to shed light on hole-capture processes of Bp and poly(4-vinylbiphenyl) (PVB). The static ab initio calculations at several levels of theory showed that the neutral Bp has a nonplanar structure with a twist angle between benzene rings in the range phi = 38-50degrees. The potential energy curve for the twist rotation of benzene rings was shallow for Bp. This twist angle was changed to 18-21degrees in biphenyl cation (Bp(+)), which has a more planar structure and a more tight potential shape than those of Bp. Full dimensional direct ab initio trajectory calculations showed that the structure of Bp is spontaneously changed after the ionization: the nonplanar structure was changed to planar one after 120 fs, and then the twist angle vibrated between -40degrees and +40degrees with a time period of about 500 fs. The C-C bond distance in the connection site between two benzene rings was immediately shortened after the hole capture of Bp, and it vibrated in the range 1.375-1.481 Angstrom. Direct PM3 dynamics calculations for the model compound composed of two-monomer units of PVB indicated that a hole is localized on one of the biphenyl groups at time zero, and then it is delocalized over the two side-groups after the structural relaxation. The mechanism of hole capture in Bp and in PVB was discussed on the basis of theoretical results.
  • H. Tachikawa, T. Iyama, T. Fukuzumi
    Astronomy and Astrophysics 397 1 1 - 6 2003年 [査読有り][通常論文]
     
    Ab-initio MO calculations have been carried out for hydrogen-dissociation reactions HCNH, i.e. HCNH → H + HCN (I) and HCNH → HNC+H(II), in order to elucidate the branching ratio of HCN/HNC on the ground state potential energy surface. The calculations showed that the transition state for reaction I is lower in energy than that of reaction II. The "bare" barrier heights for channel I and II were calculated to be 33.5-34.8 kcal/mol and 38.5-40.7 kcal/mol, respectively. The energy difference between transition states I and II was calculated to be 3.7-6.9 kcal/mol, meaning that reaction I preferentially occurs in the threshold energy region. Rice-Ramsperger-Kassel-Marcus (RRKM) theory including the tunneling effect indicated that reaction I is more favorable than reaction II at lower energy region, if tunneling effects are included in the rate calculations. On the other hand, the higher energy region above ca. 50 kcal/mol, channel II became dominant. The branching ratio (HCN/HNC) was calculated to be 0.3 at E = 4.4 eV, which corresponds to the electron affinity of HCNH+. The mechanism of the reaction is discussed on the basis of theoretical results.
  • Hiroshi Kawabata, Hiroto Tachikawa
    Phys. Chem. Chem. Phys. 5 17 3587 - 3590 2003年 [査読有り]
  • H Tachikawa, H Kawabata
    JOURNAL OF MATERIALS CHEMISTRY 13 6 1293 - 1297 2003年 [査読有り][通常論文]
     
    Ab-initio DFT and configuration interaction (CI) calculations have been carried out for indium-carbonyl compounds, such as acetone-In (Ac-In), 1,8-naphthalic anhydride-In (In(2)NA) and 3,4,9,10-perylene-tetracarboxylic dianhydride-indium (In(4)PTCDA), in order to shed light on the mechanism of electronic conductivity in the molecular devices. It was found that the electronic state of these complexes at the ground state is composed of ion-pair states expressed approximately by (Acdelta-)(Indelta+), (In-2)(delta+)(NA)(delta-) and (In-4)(delta+)(PTCDA)(delta-), respectively. On the other hand, the interaction at the first excited state was changed to a van der Waals interaction. Namely, the electron returned again to the In atom by electronic excitation. The second excited state is attributed to internal excitation within the carbonyl anion, while the charge on the indium was close to neutral. The mechanism of the electronic conductivity was discussed on the basis of theoretical results.
  • Energetics of Catalytic Reaction of Acetylcholinesterase (AChE) with Acetylcholine (ACh): Role of the Oxyanion Hole
    Igarashi, M, Ishibashi, T, Nishihira, J, Tachikawa, H
    Int. Elec. J. Mol. Design 2 712 - 722 2003年 [査読有り][通常論文]
  • Hiroto Tachikawa, Tetsuji Iyama
    Physical Chemistry Chemical Physics 4 23 5806 - 5812 2002年11月14日 [査読有り]
  • Hiroto Tachikawa, Manabu Igarashi, Teruo Ishibashi
    The Journal of Physical Chemistry A 106 46 10977 - 10984 2002年11月 [査読有り]
  • Manabu Igarashi, Teruo Ishibashi, Hiroto Tachikawa
    Journal of Molecular Structure: THEOCHEM 594 1-2 61 - 69 2002年10月11日 [査読有り]
  • Hiroto Tachikawa, Manabu Igarashi, Teruo Ishibashi
    Chemical Physics Letters 363 3-4 355 - 361 2002年09月 [査読有り][通常論文]
  • H Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 106 30 6915 - 6921 2002年08月 [査読有り][通常論文]
     
    Ionization processes of a water dimer have been investigated by means of full dimensional direct ab-initio trajectory method. The structure of (H2O)(2) before the ionization was simulated at 10 K up to 2 ps by means of a direct ab-initio molecular dynamics (MD) method. Sixty geometrical configurations were selected from the MD calculation, and then the dynamics of (H2O)(2)(+) were calculated by means of a direct ab-initio trajectory method under a constant energy condition. The trajectories on two electronic state potential energy surfaces of (H2O)(2)(+), i.e., the (2)A" and 2A' states, were full-dimensionally calculated under the C-s symmetry. For the (2)A" state, a complex composed of H3O+ and OH, which is expressed by (H3O+)OH, was only formed as a long-lived complex. On the other hand, in the ionization to the (2)A' state, two reaction channels, the complex formation (H3O+)OH ((2)A') and direct dissociation (H3O+ + OH) were open as product channels. The dynamics calculations indicated that the proton of H2O+ transferred to H2O within 100-150 fs for the (2)A" state, whereas the proton transfer at the (2)A' state occurs faster (30-50 fs) than that of the (2)A" state. The mechanism of the ionization dynamics of (H2O)(2) was discussed on the basis of theoretical results.
  • Akira Shimizu, Hiroto Tachikawa
    Journal of Physics and Chemistry of Solids 63 5 759 - 763 2002年05月 [査読有り]
  • Akira Shimizu, Hiroto Tachikawa
    Journal of Physics and Chemistry of Solids 63 4 619 - 624 2002年04月 [査読有り]
  • Hiroto Tachikawa
    Physical Chemistry Chemical Physics 4 7 1135 - 1140 2002年03月15日 [査読有り]
  • Hiroto Tachikawa
    Chemical Physics 276 3 257 - 262 2002年02月 [査読有り][通常論文]
  • Hiroto Tachikawa
    Journal of Physics B: Atomic, Molecular and Optical Physics 35 1 55 - 60 2002年01月14日 [査読有り][通常論文]
  • Hiroto Tachikawa, Manabu Igarashi, Teruo Ishibashi
    Chemical Physics Letters 352 1-2 113 - 119 2002年01月 [査読有り]
  • Kenji Komaguchi, Yuko Ishiguri, Hiroto Tachikawa, Masaru Shiotani
    Phys. Chem. Chem. Phys. 4 21 5276 - 5280 2002年 [査読有り]
  • H. Konno, K. Shiba, H. Tachikawa, T. Nakahashi, H. Oka, M. Inagaki
    Synthetic Metals 125 2 189 - 196 2001年11月 [査読有り]
  • H Tachikawa
    CHEMICAL PHYSICS 273 2-3 149 - 157 2001年11月 [査読有り][通常論文]
     
    The ionization dynamics of the complexes composed of CF4 and H2O, which plays an important role in plasma dry-etching processes on semi-conductor surface, have been investigated by means of full dimensional direct ab initio trajectory calculations in order to shed light on mechanism of plasma dry etching of silicon surface by CF4. Effect of a water molecule existing near CF4 on the ionization dynamics of CF4 was examined. The trajectory calculations showed that the water molecule affects strongly the reaction mechanism: namely, H2O molecule reacts with CF4+ to form [CF3OH2](+) complex after the ionization of CF4. The reaction is expressed by [CF4-H2O] --> (hv)(-e) [CF4-H2O](ver)(+) --> [CF3OH2](+) + F where [CF4-H2O](ver)(+) means a vertical ionized point of the complex. The fraction of the kinetic energy of F atom is 40% of the total available energy, which is significantly smaller than that of the dissociation of free CF4 (65%). The reaction energy is dissipated mostly as the internal energy of the [CF3OH2](+) complex. Also, we found the other reaction channel expressed by [CF4-H2O] (-e)--> (hv) [CF4-H2O](ver)(+) --> CF3+ + F + H2O This channel is three-body dissociation channel. The reaction mechanism was discussed on the basis of the present calculations. (C) 2001 Elsevier Science B.V. All rights reserved.
  • A Shimizu, H Tachikawa
    JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM 544 173 - 180 2001年07月 [査読有り][通常論文]
     
    For simulation on thermal behavior of the migrating species, Li+ ion and Li atom, at the circumference of graphite in lithium battery, direct molecular orbital (MO) dynamics calculation was carried out at AM I level, using the hydrogen terminated planar cluster model C54H18. According to the static MO calculation, both species stabilize above the segment joining two terminating hydrogen atoms, H1 and H2, which are bonded by the corner edge and the side edge carbon atoms, respectively. Although Li+ ion is located 1.8425 Angstrom above the middle point of the segment, Li atom 1.620 Angstrom above the point shifted to H2 on the same segment. As results of the dynamics calculation at 300 K for these stabilized species, Li+ ion shows the elliptic movement under the equilibrium coulombic potential energy ascribed to both the side edge and corner edge carbon atoms, however, Li atom circulates around the side carbon atom keeping the covalent bond composed of sp(3) hybrid orbitals. Migration trajectories of the species are reflected by the electronic density maps. (C) 2001 Elsevier Science BN. All rights reserved.
  • A Shimizu, H Tachikawa
    CHEMICAL PHYSICS LETTERS 339 1-2 110 - 116 2001年05月 [査読有り][通常論文]
     
    For the diffusion species of Li+ ion and Li atom stabilized at the same site of the circumference of the graphite, migration processes are simulated using the direct molecular orbital (MO) dynamics calculation on the hydrogen terminated cluster model, C54H18, at AM1 level. Although Li+ forms ionic bond with two carbon atoms in the circumference. Li bonds covalently with one atom through sp3 hybrid orbital at 0 K. At 700 K, Li+ dissociated goes across the bulk and escapes from the cluster model after 0.6 ps. On the other hand, Li circulates only around the carbon atom, keeping the covalent bond. (C) 2001 Elsevier Science B.V. All rights reserved.
  • H. Tachikawa, S. Abe, T. Iyama
    Journal of Molecular Structure: THEOCHEM 538 1-3 261 - 266 2001年03月30日 [査読有り][通常論文]
     
    Accurate ab-initio MO calculations were carried out for the decay processes of HFCO on the triplet energy surface (T1). Two reaction pathways, HFCO(T1) → H + FCO and HFCO(T1) → F + HCO, are concerned with the decay processes of HFCO(T1). The former and latter are denoted by channels I and II, respectively. The structures at the stationary points along the reaction coordinates were fully optimized at the MP4SDQ/6-311 + +G(d,p) level, and the total energies were calculated at the several levels of theory up to the MP4SDQ/cc-pVTZ level. The activation barriers were found in both channels. All calculations show that the barrier height for channel I is slightly lower than that for channel II, while the reaction energies for channel I (i.e. the products are H + FCO) is about 10 kcal/mol lower than that of channel II (i.e. F + HCO). The reaction rates, calculated on the basis of the RRKM theory, indicate that channel I is dominant in all excitation energy regions. The reaction mechanism is discussed on the basis of theoretical results. © 2001 Elsevier Science B.V.
  • H Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 105 8 1260 - 1266 2001年03月 [査読有り][通常論文]
     
    Collision energy dependence on the microsolvated S(N)2 reaction of F-(H2O) with CH3Cl has been investigated by means of direct ab initio dynamics method. A full dimensional ab initio potential energy surface including all degrees of freedom was used in the dynamics calculations; i.e., total energies of the reaction system and gradient of all atoms were calculated at each time step. Three energies, E-coll = 10.0, 17.7, and 25.0 kcal/mol were chosen as center of mass collision energies between F-(H2O) and CH3Cl. The present dynamics calculations indicated that in all collision energies three reaction channels were open as products. These are expressed by F-(H2O) + CH3Cl --> CH3F + H2O + Cl- (channel I); F-(H2O) + CH3Cl --> CH3F + Cl-(H2O) (channel II); and F-(H2O) + CH3Cl --> CH3F-H2O + Cl- (channel III). Channel I is three-body dissociation of each product, whereas Cl- and CH3F are solvated by H2O in channels II and LU, respectively. The dynamics calculations also showed that branching rations of channels I:II:III at E-coll = 10.0, 17.7, and 25.0 kcal/mol are calculated to be 0.55:0.04:0.41, 0.46:0.18:0.36, and 0.35:0.43:0.22, respectively. These results indicate that channels I and III are more favored at lower collision energies and channel II is minor, whereas channel II becomes dominant at higher collision energies. The mechanism of the reaction and the effects of water were discussed on the basis of the present calculations.
  • H Tachikawa, S Abe, T Iyama
    INORGANIC CHEMISTRY 40 6 1167 - 1171 2001年03月 [査読有り][通常論文]
     
    At, initio molecular orbital (MO) calculations have been carried out for base-hydrogen fluoride (HF) complexes (base = O-3 and SO2) in order to elucidate the structures and energetics of the complexes. The ab initio calculations were performed up to the QCISD(T)/6-311++G(d,p) level of theory. In both complexes, hydrogen-bonded structures where the hydrogen of HF orients toward one of the oxygen atoms of bases were obtained as stable forms. The calculations showed that cis and trans isomers exist in both complexes. All calculations for the SO2-HF complex indicated that the cis form is more stable in energy than the trans form. On the other hand, in Os-HF complexes, the stable structures are changed by the ab initio levels of theory used, and the energies of the cis and trans forms are close to each other. From the most sophisticated calculations (QCISD(T)/6-311++G(d,p)//QCISD/6-311+G(d) level), it was predicted that the complex formation energies for cia SO2-HF, trans SO2-HF, cis O-3-HF, and trans O-3-HF are 6.1, 5.7, 3.4, and 3.6 kcal/mol, respectively, indicating that the binding energy of HF to SO2 is larger than that of O-3. The harmonic vibrational frequencies calculated for cia O-3-HF and cis SO2-HF complexes were in good agreement with the experimental values measured by Andrews et al. Also, the calculated rotation constants for cis SO2-HF agreed with the experiment.
  • Hiroto Tachikawa, Tadaomi Yamano
    Chemical Physics 264 1 81 - 89 2001年02月01日 [査読有り][通常論文]
     
    The dynamics of electron capture by sulfur hexafluoride (SF6) have been investigated by means of full dimensional direct ab initio dynamics calculations at the HF/6-311 G(d)+sp (a diffuse sp-function is further added to sulfur atom) level. A rigid SF6 structure and narrow Franck-Condon region for electron capture was assumed in choosing initial conditions for the trajectories. The direct ab initio dynamics calculations for the electron capture processes by SF6 indicated that the SF6/- ion formed by the vertical electron attachment to SF6 decomposes into SF5/- and F via short-lived complex formation (SF6/-). The lifetime of SF6/- was distributed from 0.1-0.2 ps, which is quite short as lifetime of the intermediate complex. The dynamics calculations showed that 12% of the total available energy is partitioned into the relative translational mode between SF5/- and F. The effect of solid phase on the dynamics has been examined by introducing a model bath-relaxation time for energy dispersion. There was a possibility that the SF6/- anion exists in solid phase. The mechanism of the electron capture by SF6 in gas phase and in solid phase was discussed on the basis of the results. © 2001 Elsevier Science B.V.
  • Akira Shimizu, Michio Inagaki, Hiroto Tachikawa
    Journal of Chemical Engineering of Japan 34 2 207 - 210 2001年02月 [査読有り][通常論文]
     
    In order to represent the thermal motion of a hydrogen atom and a proton trapped inside a diamond lattice, trajectories of these oscillators around the trapping site were simulated using a C26H32 cluster model on the basis of the semi-empirical PM3-MO method combined with the direct molecular orbital (MO) dynamics calculation. Trapping occurs in the tetrahedral (T) interstitial site for both the hydrogen atom and the proton. With increasing temperature from 0 to 600 K the hydrogen and proton show an increase in amplitude of vibration due to the thermal activation. The hydrogen atom vibrates only around the trapping site up to 600 K, which leads to a decrease in the spin density for the atom from 0.971 at 0 K to 0.963 at 600 K. On the other hand, the proton is observed to transfer to the next tetrahedral site, exceeding the potential energy barrier at 600 K. No other trapping sites can be found in this process.
  • H Tachikawa, T Yamano
    CHEMICAL PHYSICS LETTERS 335 3-4 305 - 310 2001年02月 [査読有り][通常論文]
     
    Hyperfine coupling constants of hydronium radical H3O and methyl radical CH3 were calculated by means of ab initio molecular orbital calculations. All calculations showed that hydrogen-hyperfine coupling constant of H3O (a(H)) is positive, whereas that of methyl radical is negative. The absolute value of hydrogen-hyperfine coupling constant of the H3O radical \a(H)(H3O)\ was slightly smaller than that of CH3\a(H)(CH3)\ In the case of CH3, the hyperfine coupling interaction is induced by spin-polarization mechanism, whereas that of H3O is caused by direct overlap between Rydberg 3s orbital of the oxygen and Is orbital of the hydrogen. From the present calculations, it is predicted that both H3O and CH3 radicals are distinguishable from each other by means of electron nuclear double resonance spectroscopy. (C) 2001 Published by Elsevier Science B.V.
  • Tsunetake Seki, Hajime Kabashima, Kazumasa Akutsu, Hideshi Hattori, Hiroto Tachikawa
    Journal of Catalysis 204 2 393 - 401 2001年 [査読有り][通常論文]
     
    Catalytic behaviors of solid base catalysts for mixed Tishchenko reactions were investigated to elucidate the activity- and selectivity-determining factors in active sites of the catalysts and molecular structures of the reactants. A mixture containing equal amounts of two kinds of aldehydes was allowed to react at 353 K. The aldehydes used were benzaldehyde, pivalaldehyde, and cyclopropanecar-baldehyde. For all the reactions, the catalytic activity of alkaline earth oxides increased in the order of BaO ≪ MgO < CaO < SrO. As far as the alkaline earth oxides are concerned, it is suggested that a catalyst possessing strong basic sites and high surface area exhibits a high activity. Other solid base catalysts, such as La2O3, ZrO2, ZnO, γ-alumina, hydrotalcite, KF/alumina, and KOH/alumina, were all inactive for the mixed Tishchenko reaction of benzaldehyde and pivalaldehyde not only crossed-condensation products but also self-condensation products hardly formed. Quantum chemical calculations of the positive charges on the carbonyl carbon atoms of aldehydes and the structure parameters of the active species for the ester formations account for the observed selectivities to four Tishchenko dimers. The selectivities to four Tishchenko dimers over MgO and CaO are determined primarily in the step of the nucleophilic addition of the active species (PhCH2O−, tBuCH2O−, and C3H5CH2O−) to the carbonyl carbon atoms of aldehydes. The reaction of the aldehyde having a more positively charged and sterically less-hindered carbonyl carbon atom with the active species having a less-hindered oxygen atom proceeds faster. © 2001 Elsevier Science.
  • Y. Aoki, H. Konno, H. Tachikawa
    Journal of Materials Chemistry 11 4 1214 - 1221 2001年 [査読有り][通常論文]
     
    The electric conductivity of monazite-type LaCrO4 and zircon-type Nd1-xCaxCrO4 (x = 0-0.2) were characterized by measurements of dc electric conductivity and the Seebeck coefficient in the 300-600 K range. The LaCrO4 and NdCrO4 were found to be n-type semiconductors, while commonly known monazite- or zircon-type oxides are insulators. In mixed valence compounds of CrV and CrVI, Nd1-xCaxCrO4 (x = 0.1, 0.2), hole hopping conduction arising from the mixed valency was also observed. The Nd1-xCaxCrO4 (x = 0.1, 0.2) compounds obeyed Curie-Weiss behavior above the Neel temperature, and the observed magnetic moments for the CrV ions were in good agreement with the theoretical values. Experimental results and the calculated spin densities by the UHF method indicated that most of the unpaired electrons from CrV were localized on Cr atoms. The ab initio MO calculations for CrO4 3- clusters in NdCrO4 revealed that the SOMO is the degenerate dπ* state and that the LUMO is the pσ* state (O 2p origin): the SOMO forms the degenerate states at the top of the valence band and the LUMO forms a wide conduction band. For NdCrO4 and LaCrO4 the electronic conduction mechanism as semiconductors was explained by the band model. For Nd1-xCaxCrO4 (x = 0.1, 0.2) electronic conduction was described by the band model combined with hopping conduction of holes in degenerate dπ* states. It is concluded that the electronic conductivity of these compounds is caused by an intermixing of the ligand-to-metal charge-transfer (LMCT) state into the ionic configuration.
  • H Tachikawa, M Igarashi, T Ishibashi
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 3 15 3052 - 3056 2001年 [査読有り][通常論文]
     
    Structure and vibrational frequencies of the benzene-water complex cation [BzH(2)O](+) have been calculated by means of density functional theory (B3LYP calculation). A planar structure with a C-s symmetry, in which all heavy atoms are located on a molecular plane, was obtained as the most stable form of the [BzH(2)O](+) cation. Hydrogen atoms of the water molecule are located above and below the molecular plane. From the present calculations, it was predicted that vibrational frequencies of symmetric and asymmetric O-H stretching modes of H2O (nu (1) and nu (3) modes, respectively) are red-shifted from those of a free H2O by the formation of a complex, whereas the H-O-H bending mode (nu (2) mode) is blue-shifted. Infrared intensities of the three modes of H2O were significantly increased by the complex formation. Similar features were obtained for the ethylene-H2O complex cation [C2H4-H2O](+). The origin of the frequency-shifts is discussed on the basis of theoretical results. The hydrogen-hyperfine coupling constants of the complex cations were also predicted theoretically.
  • H Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 104 33 7738 - 7743 2000年08月 [査読有り]
     
    Electron capture pdrocesses of H-4(+), that is, H-4(+) + e(-) --> H-2 + H-2, have been studied by means of direct ab initio dynamics calculations to elucidate the reaction mechanism. The ab initio molecular orbital calculations showed that the structure of H-4(+) is flexible and its intermolecular motion H-H-3(+) is composed of a low-frequency mode. The H-4(+) ion has a wide Franck-Condon (FC) region for the direction of the low-frequency mode. In dynamics calculations, we assumed that all trajectories run on the ground state of H-4 and that auto-ionization does not take place once the H-4(+) ion captures an electron. A total of 120 trajectories were run from the initial geometries of H-4 chosen from the FC region. Each trajectory gave two kinds of hydrogen molecules: a vibrationally excited hydrogen molecule (hot-H-2) and a vibrationally ground-state H-2 (cold-H-2) The vibrational quantum number of cold-H-2 was populated only in nu = 0, whereas that of hot-H-2 was widely distributed in nu = 4-8. About 30% of the total available energy was partitioned into the relative translational mode between hot-H-2 and cold-H-2 The reaction mechanism of the electron capture processes of H-4(+) is discussed On the basis of the theoretical results.
  • Hiroto Tachikawa
    Journal of Physics B: Atomic, Molecular and Optical Physics 33 12 2367 - 2376 2000年06月28日 [査読有り]
  • Akira Shimizu, Hiroto Tachikawa
    Chemical Physics Letters 323 5-6 448 - 453 2000年06月 [査読有り]
  • Hiroto Tachikawa
    Journal of Physics B: Atomic, Molecular and Optical Physics 33 9 1725 - 1733 2000年05月14日 [査読有り]
  • Y Aoki, H Konno, H Tachikawa, M Inagaki
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 73 5 1197 - 1203 2000年05月 [査読有り][通常論文]
     
    Single phase LnCrO(4) (Ln = La-Nd) compounds were attempted to synthesize by the pyrolysis of precursors prepared from Ln(III)-Cr-VI mixed solutions. Only LaCrO4 and NdCrO4 were obtained as a single phase. LaCrO4 was monazite type (monoclinic, P2(1)/n), as reported, and the cell parameters were refined to be a = 0.70369, b = 0.72348, c = 0.66918 nm and beta = 104.950 degrees by an X-ray Rietveld method. NdCrO4 was zircon type (tetragonal, I4(1)/amd) and the eel parameters were a = 0.73107 and c = 0.66999 nm. It was found that CrO43- tetrahedra in LaCrO4 have C-1 symmetry and the four Cr-O bond lengths are different, whereas those in NdCrO4 have D-2d symmetry and all Cr-O bond lengths are 0.1702 nm. Detailed Raman spectra of LaCrO4 and NdCrO4 were measured and assigned to the vibrational modes of the CrO(4)(3-)tetrahedra. Molecular orbital calculations indicated that the charge density on the chromium ions in the tetrahedra is much less than the nominal 5+ due to the migratory electrons from oxygen atoms, and nearly the same irrespective of the symmetry of tetrahedron, suggesting that the Cr-O bonds are strongly covalent in nature.
  • Hiroto Tachikawa
    Physical Chemistry Chemical Physics 2 4 839 - 845 2000年02月15日 [査読有り]
  • M Igarashi, H Tachikawa
    INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 197 1-3 243 - 252 2000年02月 [査読有り][通常論文]
     
    Direct ab initio dynamics calculations on the photoelectron detachment processes of H3O- anion have been carried out by using HF/6-311G** full dimensional potential energy surface (PES). Total energy and the energy gradient of atoms were calculated in each time step. The excess energy was assumed to be zero at the starting point of the trajectory. The H3O- anion is composed of two isomers, H-(H2O) and OH-(H-2) in which H- and OH- anions are solvated by H2O and H-2 molecules, respectively. The present calculations indicated that the available energy, yielded by the electron detachment of H-(H2O), is almost distributed into the relative translational energy between fragments. On the other hand, the available energy in an OH-(H-2) isomer is Partitioned into both the relative translational mode and internal modes of the fragments, although the latter energy is minor. The excitation of internal modes of the products were observed for only the detachment process of the OH-(H-2) complex. These are due to the fact that the structure of solvent molecules (H2O and H-2) in each complex is significantly close to that of free molecules whereas the PES of the neutral state is always repulsive. The mechanism of the electron detachment process of H3O- is discussed on the basis of theoretical results. (C) 2000 Elsevier Science B.V.
  • A. Shimizu, H. Tachikawa
    Journal of Physics and Chemistry of Solids 61 12 1895 - 1899 2000年 [査読有り][通常論文]
     
    In order to investigate the diffusion process of Li atom in graphite, molecular dynamics simulation was achieved on the basis of molecular mechanics 2 (MM2) method using four layers cluster model one of which is composed of C150H30 with terminating hydrogen atoms. According to the simulations at 500 K, Li atom stabilizes initially around the center of mass, gets out of the graphite layers after 3.0 ps through diffusion, which is different from the movement of Li+ ion captured by the dangling bonds of the edge carbon atoms. The diffusion process of Li atom is found to be composed of following four steps in series: (1) vibration around the stabilization point (2) bulk diffusion (3) vibration under influence of the dangling bonds of edge carbon atoms and (4) escape from the graphite layers. The diffusivity for step (3) is smaller than that for step (2).
  • Akira Shimizu, Hiroto Tachikawa, Michio Inagaki
    Solid State Ionics 127 1-2 157 - 162 2000年01月01日 [査読有り][通常論文]
     
    In order to elucidate the thermal vibrations of hydrogen and normal muonium atoms trapped inside diamond lattice, the potential energy and trapping site were determined on the basis of semi-empirical PM3 MO method combined with the direct dynamics calculation. The calculation shows that these atoms are trapped deeply in the tetrahedral site. Reduction of the spin density from 0.977 at 0 K to 0.975 at 300 K suggests that the donors are enhanced due to increase in both amplitude and frequency of thermal vibrations of the trapped atoms.
  • H Tachikawa
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 2 19 4327 - 4333 2000年 [査読有り][通常論文]
     
    Dynamics of H3O following the electron capture by H3O+, which plays an important role in the H2O formation in interstellar cloud, have been investigated by means of ab-initio direct dynamics calculations. The full dimensional potential energy surface, calculated at the HF/6-311+G(d,p) level, was used in the dynamics calculation throughout. The reaction proceeds on the ground state of H3O with zero excess energy at time zero, while H3O is formed by vertical electron capture by H3O+ without structural change. A total of 200 trajectories were run from an initial geometrical configuration generated by ab-initio molecular dynamics calculation for H3O+ at 300 K. The dynamics calculations for H3O showed that two reaction channels are involved in the decay processes of H3O, formed by electron capture by H3O+: one is a dissociation channel in which the reaction proceeds via a short-lived complex, H3O* (channel 1), and the other channel is one of complex formation in which the reaction proceeds via a long-lived complex, H3O* (channel 2). The lifetimes of the complexes for channels 1 and 2 are calculated to be about 5-60 fs and > 200 fs, respectively, although the branching ratio for channel 2 is negligibly small. The relative translational energy between H2O and H is distributed in the range 150-200 kJ mol(-1) with an average of 185 kJ mol(-1), which is 90% of the total available energy. The mechanism of the reaction has been discussed on the basis of the theoretical results.
  • Hiroto Tachikawa
    The Journal of Physical Chemistry A 104 3 497 - 503 2000年01月 [査読有り]
  • Hiroto Tachikawa
    Physical Chemistry Chemical Physics 2 20 4702 - 4707 2000年 [査読有り]
  • A Shimizu, H Tachikawa
    CHEMICAL PHYSICS LETTERS 314 5-6 516 - 521 1999年12月 [査読有り][通常論文]
     
    For the proton trapped in the C26H32 diamond cluster model, the effect of temperature on the trajectory activated by thermal energy has been simulated on the basis of newly developed direct molecular orbital dynamics calculations at the semi-empirical PM3 molecular orbital (MO) level. The static PM3-MO calculations showed that the proton is stabilized in the tetrahedral site of the cluster model. The simulation temperatures were chosen as 0, 100, 300 and 600 K. Up to 300 K, the amplitude of thermal vibration of the proton increases remarkably around the tetrahedral trapping site with increasing temperature. However, at 600 K it was found that the proton transfers to the next tetrahedral site through the hexagonal site at a time interval of 0.2 ps. (C) 1999 Elsevier Science B.V. All rights reserved.
  • A Shimizu, M Inagaki, H Tachikawa
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 60 11 1811 - 1815 1999年11月 [査読有り][通常論文]
     
    In order to estimate the spin densities of hydrogen atom trapped inside the diamond lattice, thermal vibrations around the tetrahedral trapping site were simulated for C26H32 cluster model on the basis of semi-empirical PM3-MO method combined with direct molecular orbital (MO) dynamics calculation. The calculations show that the hydrogen atom behaves as a shallow spin donor in the diamond lattice. Increase of temperature brings about increase in the amplitude of vibration of trapped atom due to the thermal activation, which leads to decrease in the spin densities of the atom from 0.971 at 0 K to 0.958 at 900 K. It is predicted that the effect of temperature on the hyperfine coupling constant of the hydrogen can be detectable experimentally by means of EPR spectroscopy. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • T Ichikawa, K Kagei, H Tachikawa, Y Ishitani
    JOURNAL OF PHYSICAL CHEMISTRY A 103 32 6288 - 6294 1999年08月 [査読有り][通常論文]
     
    ESR study on alkyl radicals generated in deuterated organic matrixes at 77 K by hydrogen atom tunneling from alkane molecules to free deuterium atoms has been carried out for elucidating control actors for the tunneling. For small alkane molecules, the tunneling rate is determined by the height of the potential energy barrier for the tunneling. For larger molecules in glassy matrixes, the rate decreases with increasing number and length of alkyl chains bonded to a carbon atom to be hydrogen abstracted. The tunneling rate from antepenultimate tertiary carbon is much slower than that from penultimate secondary carbon, even the potential energy barrier is lower. This abnormal effect is explained as being due to the steric hindrance by matrix molecules to the deformation of alkane molecules during the reaction. The alkyl chains surrounded by matrix molecules prevent the deformation of the chemical bonds of the carbon atom from the initial sp(3) to the final sp(2) configuration, which may cause the increase of the thickness of the potential energy barrier and thereby decrease of the tunneling rate. Free deuterium atoms in a crystalline adamantane matrix selectively abstract hydrogen atoms from the antepenultimate tertiary carbon, probably due to less steric hindrance to the deformation.
  • H Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 103 34 6873 - 6879 1999年08月 [査読有り][通常論文]
     
    Direct ab initio dynamics calculations have been carried out for the ionization processes of the benzene-HF (Bz-HF) complex in order to elucidate its mechanism and dominant factor on the reaction channels. The full dimensional potential energy surface (PES) including all degrees of freedom and its gradient were calculated at each time step in the dynamics calculation. The dynamics calculations of the neutral complex were carried out at constant temperatures 10 and 50 K in order to obtain the relevant structures at finite temperatures. It was found that the angle between a dipole moment of HF and the benzene C-6 axis (theta) fluctuates largely due to the thermal energy. The Bz-HF complex has a nonrigid structure and a wide Franck-Condon region for the ionization. Using the geometrical configurations selected randomly from the neutral structures of Bz-HF, the trajectories for Bz(+)-HF system following the vertical ionization were calculated. Two reaction channels were obtained as products: one is the complex formation channel in which the complex composed of Bz(+)-FH is formed, while the other one is dissociation channel in which the trajectory directly leads to the dissociation product Bz(+) + HF. In the latter,channel, the rotational quantum number of the dissociating HF molecule is calculated to be J = 1-3. The ionization from C-6v structure of neutral Bz-HF complex, calculated for comparison directly leads to the dissociation products Bz+ + HF without the rotational excitation of the HF molecule. The calculations indicated that the ionization from the geometrical configuration with a large angle theta leads to the complex formation Bz(+)-FH, whereas the trajectory with a small angle theta leads to the dissociation products (Bz(+) + HF). The present calculations indicated that the angle theta dominants strongly the preference of the reaction channels in the photoionization of Bz-HF complex. The mechanism was discussed on the basis of the theoretical results.
  • T Ichikawa, K Kagei, Y Ishitani, H Tachikawa, H Koizumi
    RADIATION PHYSICS AND CHEMISTRY 55 5-6 529 - 534 1999年08月 [査読有り][通常論文]
     
    Hydrogen-atom transfer from organic molecules to free deuterium atoms and to methyl radicals in cryogenic organic solids due to quantum-mechanical tunneling of C-H hydrogen was studied for elucidating the control factors for the reaction. The following differences were found in comparison with regular thermal reactions: (1) The rate of hydrogen-atom tunneling decreases with increasing number and length of alkyl chains attaching to C-H carbon to be hydrogen-abstracted. This is due to the increase of steric hindrance to the deformation of the chemical bonds of the C-H carbon. The abstraction accompanies the change of the chemical bonds for the C-H carbon from sp(3) to sp(2), SO that prevention of the deformation by the alkyl chains causes the increase of the thickness of the potential barrier for the tunneling. The tunneling rate therefore decreases. (2) The rate of abstraction increases with the energy released by the reaction. The energy is used to excite the vibrational states of product molecules, which accelerates the tunneling from the initial reactant state to the final product state. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • H Tachikawa, Y Yamada, T Iyama
    CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE 77 8 1419 - 1423 1999年08月 [査読有り][通常論文]
     
    Dynamics of photoreaction of permethylcycloheptasilane (Me2Si)(7) on the triplet state surface, (Me2Si)(7) (T-1) --> (Me2Si)(6) + Me2Si (T-1), has been investigated by means of the direct MO dynamics method in order to elucidate mechanism of silylene extrusion from the Si-ring following the triplet energy transfer from a carbonyl compound. Full dimensional potential energy surface calculated at the PM3 method was employed in the dynamics calculation: the total energy and energy gradient on each atom were calculated at each time step during the reaction. The calculations showed that the seven-membered Si-ring is spontaneously changed to the six-membered ring without activation barrier on T-1 surface. The photoreaction of (Me2Si)(7) is significantly fast (reaction is completed within 1.0 ps), although heavy molecule (silylene radical) is dissociated. This is due to the fact that the T-1 surface is strongly repulsive for the coordinate between the silylene and the Si-ring. The mechanism of the silylene extraction from the Si-ring was discussed on the basis of theoretical results.
  • Toshiyuki Takayanagi, Yuzuru Kurosaki, Hiroto Tachikawa
    Radiation Physics and Chemistry 55 4 367 - 371 1999年07月11日 [査読有り][通常論文]
     
    Ab initio molecular orbital (MO) calculations have been carried out for the ground-state potential energy surface of the CCl4 molecule. It has been found that there is no local minimum corresponding to a C(2v) contact ion CCl3+···Cl- structure, which was previously reported to be an isomer of the most stable T(d)-CCl4 molecule at the restricted Hartree-Fock level of theory. The primary failure of the previous study is that harmonic vibrational analyses as well as a check on instability for Hartree-Fock wavefunctions were not carried out. Configuration interaction calculations with single and double substitutions have been carried out to obtain qualitative features of excited-state potential energy surfaces and a local minimum corresponding to the ion pair structure has been found on the singlet excited-state surface.
  • T Ichikawa, H Tachikawa, T Kumada, J Kumagai, T Miyazaki
    CHEMICAL PHYSICS LETTERS 307 3-4 283 - 286 1999年07月 [査読有り][通常論文]
     
    Theoretical support for the recent finding of the formation of electron bubbles (excess electrons trapped in vacancies) in crystalline H-2 containing a small amount of D-2 has been given. Quantum-mechanical calculations have shown that the addition of D-2 lowers the energy of the electron bubbles by expanding the volume of the vacancies, which prevents the conversion of the electron bubbles to H-2(-) anions. (C) 1999 Elsevier Science B.V. All rights reserved.
  • H Tachikawa, A Shimizu
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 72 7 1491 - 1496 1999年07月 [査読有り][通常論文]
     
    Direct ab-initio dynamics calculations have been carried out for hydrogen and muonium (Mu) trapped in a C10H16 cluster model in order to elucidate qualitatively the finite temperature effect on f-value ( = \Phi(H)(0)\(2)/\Phi(vac)(0)\(2), where \Phi(vac)(0)\(2) is the contact spin density on H nuclei in vacuum and \Phi(H)(0)\(2) is one in the model cluster). In the dynamics calculations, a split-valence type basis set (31G) was used for the central hydrogen atom and a minimal basis set STO3G for the cluster model. All atoms were treated as classical particles moving on the ab-initio full dimensional surface including all degrees of freedom calculated at the Hartree-Fock level. Three temperatures, 300, 600, and 1000 K, are chosen as simulation temperatures. The averaged f-values are obtained for each temperature by using MP2/3-21G* level. In addition, the f-value corresponding to 0 K is calculated by the static ab-initio MO calculation (i.e., without dynamics effect). The f-values for 0, 300, 600, and 1000 K were calculated to be 1.224, 1.211, 1.200, and 1.185, respectively, indicating that the f-value linearly decreases with increasing temperature. The f-value was simply expressed by the equationf(T) = f(T = 0 K) [1 - 0.325 x 10(-5) T]. The present calculations indicated that the f-value is slightly affected by the thermal activation, the shift off-value is small. This work is the first attempt to calculate the finite-temperature effect on the f-value at the ab-initio dynamics level.
  • RN Dixon, H Tachikawa
    MOLECULAR PHYSICS 97 1-2 195 - 203 1999年07月 [査読有り][通常論文]
     
    New ab initio potential energy functions for collinear OHF- and OHF have been used with time-dependent wavepacket studies in a simulation of the photodetachment spectrum of the OHF- anion. Franck-Condon excitation of OHF- lies within the transition state region for the bimolecular reaction F + OH <-> O + HF on the lowest triplet surface. The branching ratios for fragmentation of the excited OHF are such that the peaks in this spectrum may each be correlated with dissociation to a single vibrational state of the O + HF(v) or OH(v) + F products. The possible influence of vibrational excitation of the anion has been explored also. This is predicted to lead to marked changes in the spectra. Experimental observations of such spectra could be used in refinement of the potential as could an experiment in which the electron kinetic energy is detected in coincidence with the vibrational states of the molecular products or with the kinetic energy of the atomic products. The calculations revealed a number of metastable resonances on the OHF surface, although these are all at higher energies than are relevant to the photodetachment spectrum from the ground state anion.
  • Hiroto Tachikawa
    Chemical Physics 244 2-3 263 - 272 1999年06月 [査読有り][通常論文]
     
    Direct ab initio dynamics calculations have been applied to the ionization process of methanol dimer (CH3OH)(2). Full dimensional ab initio potential energy surface including all degrees of freedom was used in the dynamics calculation. Total energies and gradients were calculated at each time step. The initial geometrical configurations at time zero were randomly selected from the geometries calculated for the neutral dimer at 10 K. It was found that the ionization of neutral methanol dimer leads directly to a long-lived complex formation (methanol. dimer cation) which is composed of CH3O and CH3OH2+. The proton transfer was completed within 10-100 fs after several vibrations of the proton between the heavy molecules as expressed by CH3O...H+... O(H)CH3. For comparison, the bimolecular collision reaction, CH3OH+ + CH3OH, was studied by the same dynamics calculations. Two reaction channels are concerned with the reaction. In addition to the long-lived complex formation channel, the proton transfer-dissociation channel (CH3OH2+ + CH3O) was open as a product channel. (C) 1999 Elsevier Science B.V. All rights reserved.
  • Hiroto Tachikawa
    Physical Chemistry Chemical Physics 1 11 2675 - 2679 1999年06月 [査読有り]
  • Hiroto Tachikawa
    Journal of Physical Chemistry A 103 15 2501 - 2505 1999年04月15日 [査読有り][通常論文]
     
    The localization mechanism for the excess electron and positive hole in the polysilane radical anion and cation has been investigated by means of both molecular dynamics (MD) and extended Hückel molecular orbital (EHMO) calculations. A linear oligosilane (SinH2n+2) (n = 32 and 64) was chosen as the model of polysilane. The geometry optimization of the polysilane at the MM2 level gave a regular all-trans form as the most stable structure. The MD calculations, started from the optimized structure, showed that the conformation of the polysilane skeleton was gradually randomized as a function of time by thermal activation at 300 K. The conformations at 0.0, 0.05, 1.0, 1.5, and 2.0 ps were chosen as sampling points, and spin densities on the silicon atoms were calculated by the EHMO calculations at each sampling point. An excess electron and a positive hole were fully delocalized along the Si chain in the regular all-trans form (time = 0.0 ps), whereas in the disordered conformations (time ≠ 0) both electron and hole were completely localized on a few Si atoms (10 - 20 monomer units). The present calculations suggested that a continuous disorder of the Si main chain randomized by thermal energy (i.e., disordered dihedral angle of Si skeletons) is dominant in both electron and hole localization. The localization mechanism was discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Manabu Igarashi
    Chemical Physics Letters 303 1-2 81 - 86 1999年04月 [査読有り]
  • Hiroto Tachikawa
    Journal of Physics B: Atomic, Molecular and Optical Physics 32 6 1451 - 1458 1999年03月28日 [査読有り]
  • Yoshihisa Yamada, Hiroto Tachikawa
    Journal of Photochemistry and Photobiology A: Chemistry 122 3 145 - 149 1999年03月 [査読有り]
  • H Tachikawa
    CHEMICAL PHYSICS LETTERS 300 5-6 577 - 582 1999年02月 [査読有り][通常論文]
     
    A direct molecular orbital (MO) dynamics method was applied to the hydrogen atom trapped in a crystalline silicon model cluster. The cluster Si26H32 was considered as a model of a silicon lattice. The full dimensional PM3-MO potential energy surface was used for the dynamics calculations. Two trapping sites for the hydrogen in the Si lattice, the interstitial tetrahedral (T) site and the Si-Si bond-center (BC) site (i.e., Si ... H ... Si), were examined. The calculations have shown that the hydrogen can be trapped in a T-site at low temperatures, whereas the hydrogen trapped in the T-site is easily transferred to the BC site by thermal activation at a higher temperature (similar to 30 K). The reaction of H atoms trapped in a silicon lattice is discussed on the basis of the theoretical results. (C) 1999 Elsevier Science B.V. All rights reserved.
  • Jun Nishihira, Hiroto Tachikawa
    Journal of Theoretical Biology 196 4 513 - 519 1999年02月 [査読有り]
  • H Konno, H Oka, K Shiba, H Tachikawa, M Inagaki
    CARBON 37 6 887 - 895 1999年 [査読有り][通常論文]
     
    Two types of boron containing polyimide (Kapton type) film were prepared either by adding dihydroxyphenylborane (DPB) to polyamic acid [mixing method] or by using diaminodiphenyl ether having a boron containing functional group (DDE-B) to prepare polyamic acid [substitution method]. Formed polyimide films containing boron were carbonized at 600 - 1200 degrees C, By doping boron into the precursor polyimide, preferential formation of B-N bonds in carbonized films was observed and appreciable amounts of nitrogen were chemically trapped in the carbon film even after carbonization at 1200 degrees C, The polyimide prepared by the substitution method gave uniform carbon films in composition and structure, though DDE-B is not simply synthesized and didn't polymerize to high degree. The polyimide prepared by the mixing method gave non-uniform carbon films. but the process was very simple and possible to increase boron content by using different boron compounds. (C) 1999 Elsevier Science Ltd. All rights reserved.
  • Christof Maul, Christoph Dietrich, Tobias Haas, Karl-Heinz Gericke, Hiroto Tachikawa, Stephen R. Langford, Mitsuhiko Kono, Claire L. Reed, Richard N. Dixon, Michael N. R. Ashfold
    Physical Chemistry Chemical Physics 1 5 767 - 772 1999年 [査読有り][通常論文]
     
    The time-of-flight spectrum of the H atoms resulting from photodissociation of gas phase HFCO molecules at 243.12 nm indicates a role for secondary photolysis of HCO(X) fragments arising via the F + HCO(X) dissociation channel. Analysis of this spectrum, and of earlier photofragment translational spectroscopy results obtained at a number of neighbouring wavelengths in the range 218.4-248.2 nm, allow estimation of an upper limit for the C - F bond dissociation energy: D0(F - CHO) ≤ 482 kJ mol-1. HCO(X) fragments are deduced to be amongst the primary products of HFCO photolysis at all wavelengths λ ≤ 248.2 nm, indicating that any energy barrier in the F - C bond fission channel [measured relative to the asymptotic products F(2P) + HCO(X)] must be small. This observation is considered in the light of available knowledge regarding the potential energy surfaces for the ground (X1A') and first excited singlet (A 1A'') and triplet (a 3A'') states of HFCO the available evidence all points to radiationless transfer and subsequent dissociation on the triplet surface as the mechanism for the deduced F - C bond fission.
  • Hiroto Tachikawa
    Physical Chemistry Chemical Physics 1 21 4925 - 4930 1999年 [査読有り]
  • Manabu Igarashi, Hiroto Tachikawa
    International Journal of Mass Spectrometry 181 1-3 151 - 157 1998年12月 [査読有り]
  • H Tachikawa, M Igarashi
    JOURNAL OF PHYSICAL CHEMISTRY A 102 45 8648 - 8656 1998年11月 [査読有り][通常論文]
     
    Ionization processes of benzene-water cluster Bz(H2O)(n) (n = 1 and 2) have been studied by means of direct ab initio dynamics calculations. The ab initio calculations for the BzH(2)O 1:1 neutral complex show that in the minimum energy structure the water hydrogens point toward the center of mass of the benzene ring (the dipole orientation form). The potential energy curve calculated as a function of the benzene-H2O center of mass distance (R-cm) indicates that the H2O molecule is weakly bound to the benzene ring. The potential energy curve for the cationic system BzH(2)O(+) constrained to the dipole orientation form is purely repulsive, whereas the curve calculated for the oxygen orientation form has a fairly deep well. The complex has a wide Franck-Condon (FC) region for the ionization. Dynamics of the ionization process of the BzH(2)O complex was studied by means of direct ab initio dynamics calculations. A total of 11 points in the FC region were chosen as initial points. The trajectories started from both the equilibrium point of BzH(2)O (R-cm 3.395 Angstrom) and the outer classical turning point in the FC region (R-cm = 3.60 Angstrom) gave a strongly bound BzH(2)O(+) complex as a product, whereas the trajectory from the inner classical turning point (R-cm = 2.95 Angstrom) leads to the dissociation product (Bz(+) + H2O). The reaction mechanism of the ionization processes of the BzH(2)O complex was discussed on the basis of these theoretical results.
  • Hiroto Tachikawa, Takayuki Hamabayashi, Manabu Igarashi
    Journal of Molecular Structure: THEOCHEM 453 1-3 191 - 196 1998年10月30日 [査読有り][通常論文]
     
    Quenching probabilities (PQ values) in the energy transfer reaction S(1D) + CO → S(3P) + CO(v,J) have been calculated as functions of both center of mass collision energy (Ecoll) and spin-orbit coupling (H12) by means of the surface-hopping trajectory method using ab initio fitted potential energy surfaces (PESs). Two ab initio fitted potential energy surfaces (singlet and triplet PESs) obtained at the MP2/6-31G* level were employed in the quenching process. The surface hopping was treated as the Landau-Zener model in the crossing seam between the singlet and triplet PESs. The calculations showed that the reaction is composed of three reaction channels: one is a complex channel in which the reaction proceeds via a long-lived complex [SCO], and the second one is a direct channel in which the reaction proceeds without the long-lived complex. The third one is a mixed channel composed of direct and complex channels. The PQ decreases with increasing Ecoll and increases linearly with increasing spin-coupling value H12. The collision energy dependence of PQ is due to the fact that branching ratio of direct channels to complex ones is varied as a function of collision energy. © 1998 Elsevier Science B.V. All rights reserved.
  • Hiroto Tachikawa, Emiko Komatsu
    Inorganica Chimica Acta 281 1 85 - 89 1998年10月30日 [査読有り][通常論文]
     
    Ab initio MO and direct dynamics calculations of the electron donor-acceptor (EDA) complex composed of trimethylamine (Me)3N and F2 molecules (D and A) have been carried out in order to elucidate the interaction between D and A molecules. The electronic states and structures of the EDA complex were determined for both ground and excited states by means of the singly excited configuration interaction (SE-CI) and MP2 calculations. The ab initio calculations indicated that the interactions between D and A are composed of weak charge-transfer (CT) interaction at the ground state, whereas this becomes a strong CT interaction at the first excited state. The structure of the EDA complex was largely distorted at the first excited state, which strongly supports a model proposed previously by us (Tachikawa, Komatsu, Inorg. Chem. 34 (1995) 6546). The direct dynamics calculations for R3N...F2 system (R = H and Me) were carried out in order to include the temperature effect on the structures of the complexes. The large substitution effect of methyl group was found in the structure of the EDA complex. The geometric structures and the electronic states of the EDA complexes are discussed on the basis of the present results. © 1998 Elsevier Science S.A. All rights reserved.
  • Hiroto Tachikawa, Manabu Igarashi, Kenji Komaguchi
    International Journal of Mass Spectrometry 177 1 17 - 21 1998年08月 [査読有り]
  • Hiroto Tachikawa
    The Journal of Physical Chemistry A 102 35 7065 - 7069 1998年08月 [査読有り]
  • Application of direct dynamics method to ionization and enectron capturing of CF3Cl
    Takayanagi, M., Kurosaki, Y. , Tachikawa, H.
    Int. J. Mass Spectrom. 176 227 - 235 1998年07月 [査読有り][通常論文]
  • Hiroto Tachikawa
    Journal of Molecular Structure: THEOCHEM 427 1-3 191 - 198 1998年03月16日 [査読有り][通常論文]
     
    Solvation dynamics of the fluorenone radical anion by the methanol molecule have been studied by direct MO dynamics calculations. A cluster composed of the fluorenone radical anion and a methanol molecule, [Fl-...MeOH], was considered as a model of the solvation system. The solvation process after vertical electron attachment to the neutral system, [Fl-...MeOH]unrelaxed → [Fl-...MeOH]relaxed, was treated by direct MO dynamics calculation. The absorption spectrum of the anionic system was monitored as a function of solvation time. The theoretical calculation shows that the potential energy is slightly decayed as a function of time due to the slight structural relaxation of Fl-, whereas the conspicuous spectral shift was not observed. This is due to the fact that the solvation structure of [Fl-...MeOH] resembles that of the neutral system. The solvation mechanism of the fluorenone radical anion is discussed and compared with that of the benzophenone radical anion. © 1998 Elsevier Science B.V.
  • H Tachikawa
    JOURNAL OF CHEMICAL PHYSICS 108 10 3966 - 3973 1998年03月 [査読有り][通常論文]
     
    The collisional energy transfer reaction, S(D-1) + CO --> S(P-3) + CO(upsilon, J), has been studied by means of the al, initio MO (molecular orbital) and surface-hopping trajectory calculations. The potential-energy surfaces (PESs) calculated by the nb initio MO calculations showed that the singlet and triplet PESs [S(D-1) + CO and S(P-3) + CO] are composed of the attractive and repulsive potential curves, respectively. The strongly bond intermediate corresponding to SCO((1) Sigma) is found on the collision region on the singlet PES, The singlet and triplet PESs are crossed each other at region of around r(S - C) = 2.4 Angstrom with the seam of the conical intersection. By using the fitted ab initio PESs, three-dimensional surface-hopping trajectory calculations are performed under the Landau-Zener approximation. The calculated rotational and vibrational state distributions of the product CO(upsilon, J) are composed of two components due to the contributions from both direct and complex channels. The calculations show-that the quenching probability decreases gradually with increasing collision energy, This decrease is due to the fact that the branching ratio of direct to complex channels is varied as a function of collision energy, The mechanism of the energy transfer was discussed on the basis of the theoretical results. (C) 1998 American Institute of Physics. [S0021-9606(98)00210-4].
  • Hiroto Tachikawa
    Journal of Organometallic Chemistry 555 2 161 - 166 1998年03月 [査読有り]
  • Akira Shimizu, Hiroto Tachikawa
    Journal of Physics and Chemistry of Solids 59 6-7 929 - 936 1998年 [査読有り][通常論文]
     
    The interaction between alkali metals (Li and Na) and Si(111) surface cluster models has been investigated by means of an ab-initio MO method including electron correlation for both ground state and low-lying excited states. Three cluster models composed of Si4H9, Si7H15 and Si10H15 were chosen as the models of a dangling bond in a Si(111) surface. Potential energy curves, calculated as a function of Si-M distance for two alkali metal systems (M = Li and Na), showed that the alkali metals can form a strong chemical bond with the surface dangling bond. The bonding nature between the metal and the surface dangling bond at the ground state is composed of charge interaction in which an electron is transferred from the metal to the surface. At the first exited state, the bonding is varied to a strong repulsive interaction between the metal and the dangling bond due to a σ* interaction. According to the calculation of excitation energies and charge populations, the interaction generates different levels from those of the cluster alone. The first electronic excitation for the interaction systems is attributed to a charge transfer band from the Si dangling bond to the alkali metal. The absorption band appearing at a higher energy region was attributed to a local excitation within the Na atom (3s → 3p). The bonding natures at the ground and low-lying excited states are discussed on the basis of the theoretical results. © 1998 Elsevier Science Ltd. All rights reserved.
  • Toshiyuki Takayanagi, Yuzuru Kurosaki, Hiroto Tachikawa
    International Journal of Mass Spectrometry 176 3 227 - 235 1998年 [査読有り][通常論文]
     
    Ab initio direct dynamics calculations have been carried out for the ionization and electron attachment processes for the CCl3F molecule in order to obtain dynamical information on these processes. CCl3F+ produced via vertical ionization directly dissociates into CCl2F+ + Cl within a very short time. It has been found that 80% of the available energy is partitioned into the relative translational energy. It has been also found that CCl3F- formed by vertical electron attachment dissociates to CCl2F + Cl- however, the energy partitioning was very different from the CCl3F+ case. This difference in the dissociation dynamics has been discussed on the basis of the potential energy curves. © 1998 Elsevier Science B.V.
  • Michio Inagaki, Hiroto Tachikawa, Tamaki Nakahashi, Hidetaka Konno, Yoshihiro Hishiyama
    Carbon 36 7-8 1021 - 1025 1998年 [査読有り]
  • Electronic- to- Vibrational and -Rotational Energy Transfer in S(1D) + CO quenching reaction: Ab-initio MO and classical Trajectory Studies
    1998年 [査読有り][通常論文]
  • Hiroto Tachikawa
    Chemical Physics Letters 281 1-3 221 - 225 1997年12月19日 [査読有り]
  • Tsuneki Ichikawa, Hiroto Tachikawa, Jun Kumagai, Takayuki Kumada, Tetsuo Miyazaki
    The Journal of Physical Chemistry A 101 40 7315 - 7317 1997年10月 [査読有り]
  • Hiroto Tachikawa
    The Journal of Physical Chemistry A 101 40 7454 - 7459 1997年10月 [査読有り][通常論文]
  • H Tachikawa, K Komaguchi
    International Journal of Mass Spectrometry and Ion Processes 164 1-2 39 - 44 1997年06月 [査読有り]
  • Jun Nishihira, Hiroto Tachikawa
    Journal of Theoretical Biology 185 2 157 - 163 1997年03月 [査読有り]
  • Hiroto Tachikawa, Koichi Ohnishi, Takayuki Hamabayashi, Hiroshi Yoshida
    The Journal of Physical Chemistry A 101 12 2229 - 2232 1997年03月 [査読有り]
  • Hiroto Tachikawa
    Chemical Physics Letters 265 3-5 455 - 459 1997年02月07日 [査読有り][通常論文]
     
    The electronic structures of linear polysilane radical cations in ground and low-lying excited states have been studied by means of the semi-empirical PM3-CI method. The permethyl-oligosilane radical cation [Sin(Me)2n + 2]+ (n = 4-18) was chosen as a model compound of the polysilane. Molecular dynamics calculations and geometry optimizations suggested that the regular all-trans chain was the most stable for the polysilane radical cations. From the CI calculations, it was concluded that the ground state can be expressed by a single Slater determinant (single configuration of the Hartree-Fock solution) with a hole (or unpaired electron) occupied in the HOMO of the parent neutral polysilane (i.e. SOMO), whereas the first excited state is composed of two configurations: the hole is occupied in (SOMO - 1) and (SOMO + 1) states, where SOMO + i means that an unpaired electron is occupied in the i-th molecular orbital relative to the SOMO. The ratio of the weights, (SOMO - 1)/(SOMO + 1), is strongly dependent on the number of chain Si atoms n. The electronic states of the oligosilane (n = 4-18) and polysilane radical cations with a large chain (n = ∞) are discussed on the basis of the theoretical results.
  • Y Itagaki, M Shiotani, H Tachikawa
    ACTA CHEMICA SCANDINAVICA 51 2 220 - 223 1997年02月 [査読有り][通常論文]
     
    An EPR and MO study has been carried out to elucidate the electronic structure of methylacetylene (MA) radical anion generated in glassy 2- methyltetrahydrofuran matrix by ionization radiation at 77 K. The EPR spectrum was dominated by a large and slightly anisotropic H-1 hf splitting of ca. 4.53 mT due to one ethynyl proton. With the help of a selectively deuteriated methylacetylene, MA-d(3), the anisotropic hf and g-values were determined: the principal hf ((A) over tilde) and (g) over tilde values are A(xx) = 5.36 mT, A(yy) = 4.39 mT, A(zz) = 3.85 mT for, the ethynyl proton, a = 0.50 mT for the methyl protons, and g(xx) = 2.0005, g(yy) = 2.0020, g(zz) = 2.0021, respectively. From a comparison of the experimental values with the theoretical ones calculated by ab initio MO and INDO methods, a trans-bent structure was concluded for MA(-). The formation of MA(-) was also confirmed by an electron absorption spectroscopic study.
  • H. Tachikawa, T. Iyama, T. Hamabayashi
    Electronic Journal of Theoretical Chemistry 2 1 263 - 267 1997年 [査読有り]
  • Hiroto Tachikawa
    Chemical Physics 211 1-3 305 - 312 1996年11月 [査読有り][通常論文]
  • J Kumagai, H Tachikawa, H Yoshida, T Ichikawa
    JOURNAL OF PHYSICAL CHEMISTRY 100 42 16777 - 16778 1996年10月 [査読有り][通常論文]
     
    The measurements of the ESR and optical absorption spectra of polysilane radical ions revealed that the hole in the radical cation is delocalized onto the side chains, whereas the excess electron in the radical anion is confined within the silicon main chain. This observation suggests that the side chains hinder the interchain hopping of the charge for the anion but not the cation. Therefore the hole is the primary charge carrier in polysilanes.
  • Hiroto Tachikawa
    Chemical Physics Letters 260 5-6 582 - 588 1996年10月 [査読有り][通常論文]
     
    The geometrical structure, electronic states and g-tensor values of the hydrated Cu2+ ion, [Cu(H2O)(6)](2+) complex, have been studied by means of ab initio MO and MRSDCI methods. The ground State potential energy surface calculated as Functions of the axial and equatorial Cu-O bond distances (r(ax) and r(eq)) show two energy minima which correspond to elongated and compressed structures of the [Cu(H2O)(6)](2+) complex. For the elongated structure, the optimized geometry and ratio of the bond lengths (r(ax)/r(eq)) were in good agreement with the structure determined by ESR and the EXAFS experiments. On the basis of second-order perturbation theory, g-tensor components of the complexes were calculated with the natural orbitals obtained by an MRSDCI calculation. For the elongated structure, the g(parallel to) value is larger than g(perpendicular to) (g(parallel to) = 2.400 and g(perpendicular to) = 2.098) which is in agreement with the ESR experiment.
  • H Tachikawa, H Yoshida
    JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM 363 3 263 - 268 1996年04月 [査読有り][通常論文]
     
    Potential energy curves (PECs) for the dissociation of the MgN2+ complex have been calculated by means of the ab initio MO method for the ground (X(2) Sigma) and low-lying excited ((II)-I-2 and 2(2) Sigma) states. The PECs for the ground and the first excited states were bound with respect to both dissociation limits, Mg+(S-2) + N-2 and Mg+(P-2) + N-2, respectively. A linear structure was obtained as the most stable form of the complex on the ground state PEG. The Cl calculations showed that the first excitation energy ((II)-I-2 <-- X(2) Sigma) was red-shifted relative to that for free Mg+(P-1 <-- S-2) transition owing to the formation of an excited state complex with a pi interaction between Mg+(3p) and N-2(pi(NN)) The PEC for the second excited state (2(2) Sigma) has a strongly repulsive shape because of a sigma* interaction between Mg+(3p) and N-2(n sigma). The photodissociation and N-N bond activation mechanisms of the MgN2+ complex are discussed on the basis of the PEC characteristics.
  • Hiroto Tachikawa
    The Journal of Physical Chemistry 100 43 17090 - 17093 1996年01月 [査読有り]
  • H Tachikawa, E Komatsu
    INORGANIC CHEMISTRY 34 26 6546 - 6549 1995年12月 [査読有り][通常論文]
     
    The geometrical structures and the electronic states of the electron donor-acceptor (EDA) complexes for both ground and excited states have been studied by means of the ab-initio MO method. As models of the EDA complex, sigma-type EDA complexes composed of ammonia and halogen molecules NH3-X(2) (X = F and Cl) were chosen. For comparison, the NH3-X(2) complexes (X = Br and I) were also studied with only a small basis set. Geometry optimization of the complexes gave the van der Waals (vdW) structure whose the ammonia molecule is weakly interacting to the halogen molecule for the ground state and the distorted structure whose ammonia molecule is largely deformed for the excited charge-transfer (CT) state. This large distortion at the CT state is due to the fact that a dipole induced by bending deformation of the ammonia cation coordinates the halogen anion. Potential energy curves (PECs) for the formation of the EDA complexes were calculated by singly excited CI and MP2 methods for both the ground and CT states. The first excitation band of the intramolecular transition in X(2) of the CT complex showed a considerably large blue shift relative to that of the monomer molecule. This result was in qualitative agreement with the experimental feature. For the CT state, the transition energy is largely red-shifted due to the complex formation if the geometrical distortion is permitted. The structural model for the CT state was proposed on the basis of the theoretical results.
  • H TACHIKAWA, T HAMABAYASHI, H YOSHIDA
    JOURNAL OF PHYSICAL CHEMISTRY 99 45 16630 - 16635 1995年11月 [査読有り][通常論文]
     
    The collisional energy transfer reaction, O(D-1) + N-2 --> O(P-3) + N-2(v,J), has been studied by means of the ab initio MO and quasi-classical trajectory calculations. The ab initio MO calculations showed that the singlet surface [O(D-1)+N-2] is composed of the attractive potential curve where a strongly bound intermediate complex N2O is formed in the potential basin, whereas the triplet surface [O(P-3)+N-2] is composed of the repulsive shape. Both surfaces were crossed at region of around r(O-N) = 1.9 Angstrom and formed the seam of the conical intersection. By using the fitted ab initio PESs, three-dimensional surface-hopping trajectory calculations are performed. The calculated rotational and vibrational state distributions of the product N-2-(v,J) were composed of two components due to the contributions from both direct and complex channels. The branching ratio of direct channel to complex one increased linearly with collision energy. This is due to the fact that number of trajectories via complex channels is significantly diminished with collision energy because of less contribution from complex channels at higher collision energy. The mechanism of the energy transfer was discussed on the basis of the theoretical results.
  • Y INAGAKI, M ABE, Y MATSUMI, M KAWASAKI, H TACHIKAWA
    JOURNAL OF PHYSICAL CHEMISTRY 99 34 12822 - 12828 1995年08月 [査読有り][通常論文]
     
    Vibrational and rotational distributions of CO excited by collisions with either S(D-1) atoms (average collision energy, [E(coll)] = 4 kcal/mol) or S(P-3) atoms ([E(coll)] = 10 kcal/mol) have been studied by monitoring the products using vacuum ultraviolet laser induced fluorescence. Ab initio potential energy surfaces (PESs) of (1)A' and (3)A' states of OCS have been calculated. Quasiclassical trajectory (QCT) calculations using LEPS-PESs fitted to the ab initio PESs were performed. For the S(D-1) + CO system, the intermediate complex channel model in which the collision proceeds via the (1)A' state intermediate complex predicts the formation of the vibrationally excited CO(v=0,1,2). On the other hand, the direct channel model in which the collision directly proceeds without the intermediate step predicts the formation of vibrationless state CO. The experimental vibrational and rotational distributions agree with the QCT results for the intermediate complex channel model of the S(D-1) + CO system.
  • Hiroto Tachikawa, Nobuyuki Hokari, Hiroshi Yoshida
    Chemical Physics Letters 241 1-2 7 - 12 1995年07月14日 [査読有り]
     
    The hydrogen atom abstraction reaction, CH3 + CH3CN → CH4 + CH2CN has been studied by means of both the ab initio MO and the reaction dynamics methods in order to shed light on the reaction mechanism at low temperature. The potential energy surface (PES [for the reaction was calculated by means of the MR-SD-CI method. By using the PES obtained, the canonical rate constants from high- to low-temperature regions were calculated by means of the convenient transition state theory along the transition state and the short-cut paths on two-dimensional (2D) PES. The dynamics calculations lead to the conclusion that the quantum mechanical tunneling effect strongly affects the reaction rate and that the short-cut path plays an important role in the reaction dynamics at low temperature. The deuterium abstraction reaction, CH3 + CH3CN → CH4 + CH2CN was also investigated for comparison. The deuterium substitution caused a large isotope effect on the reaction rate below 100 K. The ratio of the reaction rates (kH kD) was estimated to be ≈ 103 at 77 K. The present results were in good agreement with the experimental feature obtained at low temperature. © 1995.
  • H TACHIKAWA, A MURAKAMI
    JOURNAL OF PHYSICAL CHEMISTRY 99 28 11046 - 11050 1995年07月 [査読有り][通常論文]
     
    Using crystal field (CF) theory and ab initio MO calculations, the g-tensor components of the [Ti(H2O)(6)](3+) complex have been computed in order to elucidate the reason that the [Ti(H2O)(6)](3+) complex has a large g-factor anisotropy in the alum crystal (g(parallel to) = 1.25 and g(perpendicular to) = 1.14). Ab initio MO calculations show that the H-O-H plane is parallel to the C-3 molecular axis at the most stable paint, suggesting that the complex has D-3d symmetry. The g-tensor components of the complex with the D3d symmetry are in good agreement with experimental results obtained in the amorphous solid (g(parallel to) = 2.00 and g(perpendicular to) = 1.86). A simple model in which the H-O-H plane is rotated from the C-3 axis is considered to explain the large anisotropy in the alum crystal. It is found that the rotation of the H-O-H plane relative to the C-3 axis causes both the energy shift of low-lying doublet states and the large anisotropy of the g-tensor components. This is due to the fact that the repulsive interaction between the d-orbital and the nonbonding orbital of the ligand H2O molecule causes the energy shift. The g-tensor components calculated for the rotated structure are in reasonable agreement with those in the alum crystal. It is concluded that the rotation of the H-O-H plane relative to the C-3 axis is the origin of the large anisotropy of the g-factor in the alum crystal.
  • H TACHIKAWA, T TSUCHIDA
    JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL 96 3 277 - 282 1995年03月 [査読有り][通常論文]
     
    The electronic states of the surface and bulk aluminum ions in gamma-Al2O3 have been determined by using ab initio molecular orbital (MO) method. As bulk and surface models of gamma-Al2O3, [Al(OH)(n)](3-n) and [Al(OH)(n-1)](4-n) (n = 4, 6) clusters for one-unit model and [Al2O(OH)(m)](4-m) and [Al2O(OH)(m-2)](6-m) (m = 6, 10) clusters for two-unit model are chosen. Lewis Acidity of central aluminum ion in each model cluster is characterized by means of both electron density on Al and the energy level of the lowest unoccupied MO (LUMO). Geometry optimization of the model cluster leads to the conclusion that reactivity of surface aluminum is governed by the location of A1 relative to oxygen layer as well as the electronic state of surface A1 site.
  • H TACHIKAWA
    JOURNAL OF PHYSICAL CHEMISTRY 99 1 255 - 261 1995年01月 [査読有り][通常論文]
     
    The selectivity of the vibrational and rotational states of products in the gas-phase proton-transfer reaction F- + HCl (X(1) Sigma(+)) --> HF(nu,J) + Cl- has been studied by means of the ab initio MO method and quasi-classical trajectory calculations. A strongly bound intermediate complex [FHCl](-) is found on the ground-state potential energy surface (PES) obtained by the ab initio MO method. The intermediate complex is most stable at the collinear form. By using a fitted ab initio PES, three-dimensional quasi-classical trajectory calculations are performed. The calculated rotational- and vibrational state distributions of the product HF(nu,J) are composed of two components. On the basis of the theoretical results, we propose a reaction model composed of two reaction channels: one is a direct channel in which products are in vibrationally excited states and in the rotationally ground state, and the other channel is a complex channel in which products are in rotationally excited states due to a long-lived [FHCl](-) complex. Rotational- and vibrational-state populations are reasonably explained by the two-channel model. In order to elucidate the selectivity of the reaction channels, the collision angle for each trajectory is analyzed. It is concluded from the trajectory calculations that collinear collisions lead to the direct channel, whereas both collisions at large impact parameters and side-attack collisions lead to the intermediate-complex channel.
  • M ABE, Y INAGAKI, LL SPRINGSTEEN, Y MATSUMI, M KAWASAKI, H TACHIKAWA
    JOURNAL OF PHYSICAL CHEMISTRY 98 48 12641 - 12645 1994年12月 [査読有り][通常論文]
     
    Rotational distributions of CO molecules excited by collisions with O(D-1) atoms (average relative translational energy 8 kcal/mol) were measured by probing the product CO(v = 0-3) with vacuum ultraviolet laser-induced fluorescence. The inelastic collisions are of two types. The adiabatic collisions involve motion on the first excited singlet surface of the CO2 system, whereas the nonadiabatic collisions begin on this singlet surface but end on the lowest triplet surface before dissociating to O(P-3) and CO. The measured rotational distributions for CO(v = 2 and 3) which can only come from the nonadiabatic collisions agree with the results of a trajectory calculation performed on the ab initio lowest tripler potential energy surface of CO2. However, the rotational distributions measured for CO(v = 0 and 1) show a significant difference from the trajectory calculation. The reason is that excitation of the v = 0 and 1 levels can be accomplished by either adiabatic (singlet surface) or nonadiabatic (triplet surface) collisions. Vibrational distributions of CO(v 1-6) excited by collision with thermal O(D-1) atoms were also measured and compared with the trajectory calculation.
  • H TACHIKAWA, N OHTA
    CHEMICAL PHYSICS LETTERS 224 5-6 465 - 469 1994年07月 [査読有り][通常論文]
     
    The rate constants of the dissociation of acetaldehyde following excitation into S1, CH3CHO-->CH3+HCO, are calculated with the Rice-Ramsperger-Kassel-Marcus (RRKM) theory including the tunneling effect and with the RRK theory for the following two processes: one proceeds on the potential energy surface (PES) of T1 following intersystem crossing with the tunneling mechanism (channel I), and another proceeds on PES of S0 following internal conversion (channel II). Based on the calculation, it is proposed that channel II is a significant reaction pathway on excitation at around 320 nm, whereas channel I is dominant at shorter excitation wavelengths.
  • H TACHIKAWA, S TOMODA
    CHEMICAL PHYSICS 182 2-3 185 - 194 1994年05月 [査読有り][通常論文]
     
    Ab initio MR-SD-CI and classical trajectory calculations have been performed to elucidate the vibrational mode specificity of the title reaction, whose reactive cross section is enhanced by vibrational excitation of the nu2 umbrella-bending mode of NH3+. Potential energy surfaces (PESs) of the reaction have been obtained for vibrationally ground and excited states (vibrational quantum numbers, upsilon = 0 and 2, respectively) by assuming a hydrogen-bonded structure with fixed bending angles. The MO calculations show that a hydrogen transfer is composed of two elementary steps: (1) an electron transfer from NH3 to NH3+ at the avoided crossing region on the entrance PES, and (2) a proton transfer in the (NH3 . NH3) + intermediate complex region. The PESs show that the avoided crossing point shifts to larger intermolecular separation due to vibrational excitation. Using the ab initio fitted PESs, the classical trajectory calculations elucidate the reaction dynamics. The maximum value of the impact parameter (b(max)) for the reaction is increased by the vibrational excitation. Based on these theoretical results, a simple reaction model has been proposed, in which the electron capturing volume of NH3+ increases with increasing vibrational quantum number upsilon.
  • TACHIKAWA H, TAKAMURA H, YOSHIDA H
    J. Phys. Chem. 98 20 5298 - 5302 1994年05月 [査読有り][通常論文]
     
    The gas-phase proton-transfer reaction O- + HF --> OH(v = 0,1) + F- has been studied with the ab initio MO method and quasiclassical trajectory calculations. A strongly bound intermediate complex [OHF](-) is found on the ground-state potential energy surface (PES) obtained by the ab initio MO method. The intermediate complex is most stable at the collinear form. Three-dimensional quasiclassical trajectory calculations are performed with ab initio fitted PESs. The results show that the enhanced collision energy from 1.198 to 4.10 kcal/mol increases the product OH(v = 1) fractional population, P(v = 1) = {OH(v = 1)l[OM(v = 0) + OH(v 1)]}. The theoretical result suggests that this increase is due to the energy transfer from the translational mode to the vibrational mode of O-H in the deeper intermediate complex region. The trajectory calculations show that P(v = 1) at a collision energy of 5.31 kcal/mol is slightly smaller than that of 4.10 kcal/mol. These results are in reasonable agreement with experimental features derived by Leone and co-workers [J. Chem. Phys. 1992, 96, 298]. On the basis of the theoretical calculations, we propose a reaction model composed of two reaction channels: one is an intermediate complex channel model in which the reaction proceeds via a long-lived intermediate complex, [OHF](-), and the other is a direct channel model in which the reaction proceeds directly without the long-lived complex. The direct channel gives the vibrationally excited OH(v = 1, J = 0) radical, whereas the complex channel leads to the vibrationally ground and rotationally excited OH(v = 0, J = J') radical.
  • N ICHINOSE, K MIZUNO, Y OTSUJI, H TACHIKAWA
    TETRAHEDRON LETTERS 35 4 587 - 590 1994年01月 [査読有り][通常論文]
     
    Electronic interaction between C alpha-C beta sigma bonds of the alkyl groups and pi-orbitals on the 4-acetylphenyl ring in the lowest triplet state of 4-acetylphenylpropane and 1,2-bis(4-acetylphenyl)ethane was studied as a function of C alpha-C beta bond length by means of semiempirical MNDO MO calculations. The transition and final states of the title reaction were energetically estimated from potential curves of the lowest and sigma,sigma* triplet states to determine energy barriers and heats of reaction. The reactivity features of the photoreaction were discussed on the basis of these results.
  • H TACHIKAWA, S LUNELL, C TORNKVIST, A LUND
    JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM 110 1 25 - 33 1994年01月 [査読有り][通常論文]
     
    A vibrational coupling (VC) model previously introduced by us (H. Tachikawa, S. Lunell, C. Tornkvist and A. Lund, Int. J. Quantum Chem., 43 (1992) 449) to estimate reaction rates including solvent effects has been applied to a reaction in the crystalline phase, namely the intramolecular hydrogen transfer reaction CH3O --> CH2OH in the methanol polycrystalline phase. The calculations were carried out at the ab initio HF and CCD-ST4 (double substituted coupled cluster theory) levels with 3-21G and D95V* * basis sets. The VC between the reaction system and the surrounding four methanol molecules was considered in the present calculation. The VC effect slightly increased the reaction rate in all energy regions. The reaction mechanism in the methanol polycrystalline phase is discussed.
  • H TACHIKAWA, A OHTAKE, H YOSHIDA
    JOURNAL OF PHYSICAL CHEMISTRY 97 46 11944 - 11949 1993年11月 [査読有り][通常論文]
     
    Potential energy surfaces (PESs) of the charge-transfer reaction N+ + CO --> N + CO+ have been calculated by ab-initio MO methods in order to shed light on the detailed reaction mechanism. This reaction is a mode-specific one in which the vibrational modes of the product CO+ cation are populated in a non-Boltzmann distribution. The ab-initio MO calculation including electron correlation gives a strongly bound [NCO+] complex (1(3) Sigma(-)) on the ground-state PES and a weakly bound [NCO+]* complex (2(3)A '') on the first excited-state PES. On the basis of the ab-initio MO calculations, we propose a reaction model composed of dual reaction channels in the charge-transfer process: one is an intermediate channel model in which the reaction proceeds via an intermediate complex (the ground-state NCO+ complex), and the other is a direct channel model in which the reaction proceeds directly without the ground-state intermediate. The mechanism of the charge transfer is discussed based on the PES characteristics. Furthermore, using LEPS (London-Eyring-Polanyi-Sato)-PESs fitted to the ab-initio PESs, classical trajectory calculations were performed. We find that the intermediate channel gives vibrationally excited CO+ cations, whereas the CO+ cation formed via the direct channel is in the vibrational ground state.
  • Hiroto Tachikawa
    Chemical Physics Letters 212 1-2 27 - 31 1993年09月03日 [査読有り][通常論文]
     
    The reaction mechanism of the radical isomerizations of CH3O/CH2OH in frozen methanol has been investigated by the ab initio molecular orbital method and RRKM theory. We consider two reaction channels as the conversion pathway one is an intramolecular hydrogen rearrangement in CH3O (channel I) and the other a hydrogen abstraction from a matrix methanol molecule by CH3O (channel II). Activation energies for channels I and II are 34.8 and 14.7 kcal/mol at the MP2/6-31G* level, respectively. The RRKM calculations show that the reaction rate for channel II is significantly faster than that for channel I at low energy, whereas channel I is the dominant pathway at energies above 1.7 eV. The quantum-mechanical tunnel effect plays an important role on the rate of this isomerization reaction. Solvation effects on the reaction rate are also discussed, using a continuum model. © 1993.
  • H TACHIKAWA, N HOKARI, H YOSHIDA
    JOURNAL OF PHYSICAL CHEMISTRY 97 39 10035 - 10041 1993年09月 [査読有り][通常論文]
     
    The H atom abstraction from methanol by methyl radical has been studied theoretically based on ab-initio MO calculations of the reaction system at the HF/3-2lG and MP4SDQ/6-31G**//MP2/6-31G levels. The rate constant was estimated for two reaction channels, CH3OH + CH3 --> CH2OH + CH4 and CH3OH + CH3 --> CH3O + CH4, through the intrinsic reaction coordinate by the RRKM theory including the tunneling effect and through the short-cut paths on the two-dimensional potential energy surface. The Arrhenius plot of the rate constant for both the reaction channels starts to deviate from a straight line at about 100 K and approaches a limiting value, showing the importance of the quantum tunneling effect at low temperature. The H abstraction from the hydroxyl group is theoretically predicted to dominate over that from the methyl group at low temperature, in contradiction with previous results of ESR experiments on the methyl radical in solid methanol. This contradiction is possibly explained by taking into account the hydrogen bonding in condensed phases which effectively blocks the reaction site for the H abstraction from the hydroxyl group.
  • H TACHIKAWA, H MURAI, H YOSHIDA
    JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 89 14 2369 - 2373 1993年07月 [査読有り][通常論文]
     
    The geometric structure and electronic state of ion pairs formed by an electron transfer from an alkali metal atom to the C=O group of a carbonyl compound, have been determined using ab initio molecular orbital (MO) and multireference single and double excitation configuration interaction (MRSDCI) methods. As model systems of the ion pair, acetone-Na (AT-Na) and formaldehyde-Na (FA-Na) systems were chosen. The geometry optimizations of the FA-Na ion pair gave two structures as the stable form. One is a linear form with a C-0-Na angle of 168.7-degrees and the other is the pi-form with an angle of 87.6-degrees. The total energies of both ion pairs are similar, although the energy calculation shows that the pi form is slightly more stable than the linear form. On the other hand, the geometry optimization of the AT-Na ion pair gave only a linear form for the stable structure. The MRSDCI wavefunctions of the ion pairs indicate that the interaction between the alkali metal and the carbonyl group is composed of an attractive Coulomb force [C=0-...Na+] at the ground state, whereas the nature of the bonding is determined by the weakly attractive van der Waals force [C=0...Na] at the first excited state. From an analysis of the excited-state wavefunctions, the first absorption band of the ion pairs is assigned to the charge-transfer (CT) transition expressed by pi(C=O)* --> Na(3s). The solvent effects on the spin density of the carbonyl oxygen in a 2-methyltetrahydrofuran (MTHF) matrix were also discussed on the basis of the fractional charge model.
  • Hiroto Tachikawa, Anders Lund, Masaaki Ogasawara
    Canadian Journal of Chemistry 71 1 118 - 124 1993年01月01日 [査読有り][通常論文]
     
    Model calculations were made on the hydrated electron by using the ab initio MO method combined with the MR-SD-Cl method and the coupled cluster theory. The models used in the calculations were water clusters denoted by [e(H2O)n(H2O)m], where n = 2,3,4, and 6 for the first solvation shell and m = 0–28 for the second and third solvation shells. In these model calculations, the interactions between the excess electron and the water molecules in the first solvation shell are explicitly calculated by ab initio MO methods and the water molecules in the second and third solvation shells were represented by the fractional charges obtained at the MP2/D95V** level. The stabilization energies and the solvation radius r(e–O), in terms of the distance between the center of the cavity and an oxygen atom of the surrounding water molecules, increased monotonically with the number of water molecules in the first solvation shell. On the other hand, the first excitation energy was not dependent on the number of water molecules in solvation shells, but constant, with the value of ca. 2.0 eV. On the basis of the present calculations, we suggest that (1) the energetic stability of excess electrons depends on both short-range interaction and long-range interaction, (2) the first excitation energy is critically affected by only the short-range interactions, and the excitation is theoretically attributed to the1s→2p transition of the excess electron.
  • 土田猛, 田地川浩人
    表面科学 14 5 272 - 277 1993年 [査読有り][通常論文]
  • H KONNO, H TACHIKAWA, A FURUSAKI, R FURUICHI
    ANALYTICAL SCIENCES 8 5 641 - 646 1992年10月 [査読有り][通常論文]
     
    Lanthanum(III) chromium(V) tetraoxide, LaCrO4, was synthesized by a thermal decomposition method and characterized by X-ray photoelectron spectroscopy and ab initio molecular orbital calculations. The chromium (V) state in LaCrO4 is stable in both air and vacuum. The electron binding energies, E(B), and Auger parameters, alpha, of Cr(V) and La(III) indicated that the covalency of the Cr-O bonds in CrO4 tetrahedra is higher than that in CrO6 octahedra of LaCrO3, and that La(III) in LaCrO4 is more ionic than in LaCrO3. The results of ab initio molecular orbital calculations agreed with the measured characteristics, that is, the electrons are flowing from oxygen to Cr(V) and the covalency plays a significant part in the Cr-O bonds. This behavior of the Cr-O bond was considered to contribute to stabilizing CrO43-tetrahedra.
  • H TACHIKAWA, S LUNELL, C TORNKVIST, A LUND
    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 43 4 449 - 461 1992年07月 [査読有り][通常論文]
     
    A vibrational coupling model to treat the solvation effects in chemical reaction rate calculations is proposed and applied to the intramolecular hydrogen transfer reaction CH3O. --> .CH2OH in the condensed phase. The effect of solvation is taken into account in two ways: (1) the solvent effect on the activation energy of the reaction is simulated by including 39 surrounding water molecules, represented by fractional charges at the assumed atomic positions, in the potential energy surface calculation; and (2) the vibrational couplings between the 10 nearest solvent molecules and the molecules constituting the reaction system are explicitly included in a vibrational frequency calculation. RRKM theory with Miller's tunneling correction included is employed to calculate the rate constants. The effect of solvation causes a significant change in the chemical reaction rate, mainly through a lowering of the activation energy. The vibrational coupling causes a slight increase of the rate constant in the tunneling region by perturbing the vibrational frequencies of the reactant and transition states, which appear in thc rate-constant expression, but has little effect at higher temperatures.
  • H TACHIKAWA, M SHIOTANI, K OHTA
    JOURNAL OF PHYSICAL CHEMISTRY 96 1 164 - 171 1992年01月 [査読有り][通常論文]
     
    Structure and formation mechanisms of dimer radical cations of methyl- and dimethylacetylene (MA and DMA) have been studied by means of ESR spectroscopy and ab initio MO calculations. Monomer radical cations were generated in halocarbon matrices by ionization radiation at low temperature. It was found that the methylacetylene radical cation, MA+, is stabilized as a complex cation with a chlorine atom of a matrix molecule immediately after irradiation at 77 or 4 K. When the sample was warmed at 105 K in CF2ClCFCl2, the matrix complex cation was converted into a dimer radical cation of methylacetylene, MA2+, characterized by a 9.0-G hyperfine (hf) splitting due to eight hydrogen atoms. Upon further annealing, the dimer cation apparently dissociated, since the propagyl radical, CH2C = CHBAR, could be detected. The dimethylacetylene radical cation was stabilized in the matrix as an isolated monomer cation, DMA+, after irradiation at low temperature. Similar to the MA system, subsequent annealing of DMA+ gave rise to a dimer cation of dimethylacetylene, DMA2+ (9.0 G, 12 H). Comparison of the experimental hf splittings with the results of ab initio MO calculations leads us to conclude that the structures of the both dimer cations, MA2+ and DMA2+, are cyclic, i.e., in the forms of the dimethyl- and tetra-methylcyclobutadiene radical cations, respectively. It is proposed that the formation occurs through a [3+4] cycloaddition reaction of the monomer cation with the parent molecule. The proposed electronic ground states of MA2+ and DMA2+ are 2A2 in C2-upsilon symmetry (two methyl groups in adjacent positions) and 2B2g in D2h symmetry, respectively. The formation mechanisms of these two dimer cations are discussed on the basis of ab initio MO calculations.
  • H TACHIKAWA, H YOSHIDA, M OGASAWARA
    RADIATION PHYSICS AND CHEMISTRY 37 1 107 - 110 1991年 [査読有り][通常論文]
     
    Ab initio molecular orbital (MO) calculations were carried out on the anion radical of methyl isobutyrate, a model of the poly(methylmethacrylate) (PMMA) anion. Calculations were also made on the cation radical for comparison. The results indicates that a strong absorption band at < 320 nm and a weak one at 440 nm were attributed to the pi-pi* and n-pi* transitions of the PMMA anion, respectively. It was found, from the geometry optimization, that the carbonyl group of the anion was bent and the carbonyl oxygen had deviated from the sp2 plane of the carbonyl carbon. Molecular orbital contour maps of singly occupied MO suggested that the excess electrons were mainly distributed on the carbonyl group of the polymer. The stability of the PMMA anion and cation is discussed in terms of the potential energy curves calculated as a function of the O-CH3 distance.
  • H TACHIKAWA, M OGASAWARA
    JOURNAL OF PHYSICAL CHEMISTRY 94 5 1746 - 1750 1990年03月 [査読有り][通常論文]
  • H TACHIKAWA, T ICHIKAWA, H YOSHIDA
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 112 3 977 - 982 1990年01月 [査読有り][通常論文]
  • H TACHIKAWA, T ICHIKAWA, H YOSHIDA
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 112 3 982 - 987 1990年01月 [査読有り][通常論文]
  • H TACHIKAWA, M OGASAWARA, M LINDGREN, A LUND
    JOURNAL OF PHYSICAL CHEMISTRY 92 7 1712 - 1715 1988年04月 [査読有り][通常論文]

MISC

  • Yoshizawa Saori, Abe Shigeaki, Mutoh Mami, Kusaka Teruo, Nakamura Mariko, Yoshida Yasuhiro, Iida Junichiro, Kawabata Hiroshi, Tachikawa Hiroto Jpn. J. Appl. Phys. 56 (1) 2016年11月08日 [査読無し][通常論文]
     
    Oligosilane-functionalized C<inf>60</inf>fullerenes [namely, C<inf>60</inf>–(SiH<inf>2</inf>)<inf>n</inf>–H, n = 1–4] have been investigated by the density functional theory (DFT) method to elucidate the structures and electronic states of oligosilane-radical added fullerene. The DFT calculation showed that oligosilane radicals bind to the carbon atom of C<inf>60</inf>in the on-top site, and a strong Si–C heterojunction is formed. The binding energies of oligosilane radicals to C<inf>60</inf>were calculated to be 24.6–28.2 kcal/mol at the CAM-B3LYP/6-311G(d,p) level. The electronic states of oligosilane-functionalized fullerenes C<inf>60</inf>–(SiH<inf>2</inf>)<inf>n</inf>–H are discussed on the basis of theoretical results.
  • Tachikawa Hiroto, Kawabata Hiroshi Jpn. J. Appl. Phys. 55 (6) 2016年04月26日 [査読無し][通常論文]
     
    Functionalized graphenes are known as a high-performance molecular device. In the present study, the structures and electronic states of the aryl radical functionalized graphene have been investigated by the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of graphene (GR). Also, the mechanism of aryl radical reaction with GR was investigated. The benzene, biphenyl, p-terphenyl, and p-quaterphenyl radicals [denoted by (Bz)<inf>n</inf>(n = 1–4), where n means numbers of benzene rings in aryl radical] were examined as aryl radicals. The DFT calculation of GR–(Bz)<inf>n</inf>(n = 1–4) showed that the aryl radical binds to the carbon atom of GR, and a C–C single bond was formed. The binding energies of aryl radicals to GR were calculated to be ca. 6.0 kcal mol<sup>−1</sup>at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists in the aryl radical addition: the barrier heights were calculated to be 10.0 kcal mol<sup>−1</sup>. The electronic states of GR–(Bz)<inf>n</inf>were examined on the basis of theoretical results.
  • Shigeaki Abe, Shimpei Kawano, Yu Toida, Mariko Nakamura, Satoshi Inoue, Hidehiko Sano, Yasuhiro Yoshida, Hiroshi Kawabata, Hiroto Tachikawa Japanese Journal of Applied Physics 55 (3) 2016年03月01日 [査読無し][通常論文]
     
    The structures and electronic states of alkyl-radical-functionalized C20 fullerenes (denoted by C20-R) have been investigated using density functional theory (DFT). The different alkyl radicals investigated were methyl, ethyl, propyl, and butyl radicals. The DFT calculation indicated that the alkyl radical binds to the carbon atom of C20 in the on-top site, thus forming a strong C-C single bond. The binDing energies of the alkyl radicals to C20 were calculated to be 83.9-86.6 kcal/mol at the CAM-B3LYP/6-311G(d,p) level. The electronic states of the C20-R complex are discussed on the basis of the theoretical results.
  • Tachikawa Hiroto Theoretical chemistry accounts 135 (3) 1 -9 2016年02月20日 [査読無し][通常論文]
     
    Ionizing radiation to DNA induces sometimes the DNA damage. In this report, the ionization dynamics of uracil dimer (U)(2) and its water complex (U)(2)-H2O have been investigated by means of direct ab initio molecular dynamics (AIMD) method in order to elucidate the effects of single water molecule on the reaction rate of proton transfer (PT) in DNA model base pair. The (U)(2) dimer is widely used as a simplified mimetic model of Watson-Crick base pair. The static ab initio calculation showed that two conformers exist as neutral complex of (U)(2)-H2O. The direct AIMD calculation of ionization process of (U)(2)-H2O showed that the rate of PT is affected even by a single water molecule, while it was dependent on the position of H2O around (U)(2). The interaction of water molecule with (U)(2) affected the potential energy curve for PT. Especially, the activation barrier along the PT coordinate was significantly changed by the interaction with one H2O molecule. The effects of one H2O molecule on the PT process were discussed on the basis of theoretical results.
  • Tachikawa Hiroto, Kawabata Hiroshi International journal of quantum chemistry 116 (2) 123 -129 2016年01月16日 [査読無し][通常論文]
     
    High energy irradiation to the hydrogen bonded system is important in relevance with the initial process of DNA and enzyme damages. In the present study, the effects of radiation to catalytic triad have been investigated by means of direct ab-initio molecular dynamics (AIMD) calculation. As a model of the catalytic triad, Ser-His-Glu residue, which is one of the important enzymes in the acylation reaction, was examined. The ionization and electron attachment processes in Ser-HisGlu were investigated as the radiation effects. The direct AIMD calculation showed that a proton of His is spontaneously transferred to carbonyl oxygen of Glu after the ionization. However, the whole structure of catalytic triad was essentially kept after the ionization. On the other hand, in the case of the electron capture in the model catalytic triad Ser-His-Glu, the dissociation of Glu residue from [Ser-His](2) was found as a product channel. The mechanism of ionization and electron capture process in the catalytic triad was discussed on the basis of theoretical results. (C) 2015 Wiley Periodicals, Inc.
  • Tetsuji Iyama, Hiroshi Kawabata, Takahiro Fukuzumi, Hiroto Tachikawa 2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS) 2016年 [査読有り][通常論文]
     
    Structures and electronic states of the aryl radical functionalized graphene have been investigated by means of density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of graphene (GR). Also, the reaction mechanism of aryl radical with GR was investigated. The benzene, biphenyl, pterphenyl, and p-quaterphenyl radicals (denoted by (Bz)n (n=1-4), where n means numbers of benzene rings in aryl radical) were examined as aryl radicals. The DFT calculation of GR-(Bz)n (n=1-4) showed that the aryl radical binds to the carbon atom of GR, and a C-C single bond was formed. The binding energies of aryl radicals to GR were calculated to be ca. 6.0 kcal mol-1 at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists in the aryl radical addition: the barrier heights were calculated to be 10.0 kcal/mol. The electronic states of GR-(Bz) n were discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata 2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS) 2016年 [査読有り][通常論文]
  • Tachikawa Hiroto, Kawabata Hiroshi Jpn. J. Appl. Phys. 55 (2) 2015年12月21日 [査読無し][通常論文]
     
    Functionalized fullerenes are known as a high-performance molecules. In this study, the alkyl-functionalized fullerenes (denoted by R–C<inf>60</inf>) have been investigated by means of the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of fullerene. Also, the reaction mechanism of alkyl radicals with C<inf>60</inf>was investigated. The methyl, ethyl, propyl, and butyl radicals (denoted by n = 1–4, where n means the number of carbon atoms in the alkyl radical) were examined as alkyl radicals. The DFT calculation showed that the alkyl radical binds to the carbon atom of C<inf>60</inf>at the on-top site, and a strong C–C single bond is formed. The binding energies of alkyl radicals to C<inf>60</inf>were distributed in the range of 31.8–35.1 kcal mol<sup>−1</sup>at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists before alkyl addition, the barrier heights were calculated to be 2.1–2.8 kcal mol<sup>−1</sup>. The electronic states of R–C<inf>60</inf>complexes were discussed on the basis of the theoretical results.
  • Tachikawa Hiroto, Iyama Tetsuji, Kawabata Hiroshi Japanese journal of applied physics : JJAP 52 (1) 01AH01 -1-4 2013年01月
  • 阿部薫明, 小峰梨果, 石川紘佑, 赤坂司, 亘理文夫, 田地川浩人 日本歯科理工学会誌 31 (2) 2012年
  • 五十嵐学, 田地川浩人, 石橋輝雄, 玉城英彦 日本化学会北海道支部研究発表会講演要旨集 2005 118 2005年01月21日 [査読無し][通常論文]
  • Masahiro Kawasaki, Akihiro Sugita, Christopher Ramos, Yutaka Matsumi, Hiroto Tachikawa The Journal of Physical Chemistry A 108 (39) 8119 -8124 2004年09月 [査読有り][通常論文]
     
    A deuterated water dimer, (D2O)(2), absorbs a photon at 205 nm releasing a fragment D atom. The negative angular anisotropy parameters are observed experimentally with photofragment imaging spectroscopy. In this dissociation, one of the translational energy distributions obtained for the fragment D atoms peaks at around 1 kcal mol(-1), which is much smaller than the maximum available energy, 16.2 kcal mol(-1). These results suggest an energy loss process of the fragment D atom, which is induced by a collision with the oxygen atom in the dimer before it leaves the parent molecule. A direct ab initio trajectory calculation for the internal collision process of the D atom in the dimer has been performed. The obtained energy loss is in good agreement with the present experimental results.
  • 五十嵐学, 田地川浩人, 西平順, 石橋輝雄 日本化学会北海道支部研究発表会講演要旨集 2004 125 2004年01月21日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 西平順, 石橋輝雄 分子構造総合討論会講演要旨集(CD−ROM) 2003 4PA047 2003年09月20日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 日本化学会北海道支部研究発表会講演要旨集 2003 99 2003年01月31日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 分子構造総合討論会講演要旨集 2002 709 2002年10月01日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 化学反応討論会講演要旨集 18th 120 2002年06月18日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 日本化学会北海道支部研究発表会講演要旨集 2002 124 2002年01月20日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 分子構造総合討論会講演要旨集 2001 479 2001年09月24日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 日本化学会北海道支部研究発表会講演要旨集 2001 116 2001年01月19日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 分子構造総合討論会講演要旨集 2000 771 2000年09月27日 [査読無し][通常論文]
  • 青木芳尚, 金野英隆, 田地川浩人, 稲垣道夫 日本化学会北海道支部研究発表会講演要旨集 1999 12 1999年02月02日 [査読無し][通常論文]
  • 山田義久, 五十嵐学, 田地川浩人 分子構造総合討論会講演要旨集 1998 156 1998年09月 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人 分子構造総合討論会講演要旨集 1998 154 1998年09月 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人 化学反応討論会講演要旨集 14th 32 1998年05月 [査読無し][通常論文]
  • H Tachikawa JOURNAL OF ORGANOMETALLIC CHEMISTRY 547 (2) 337 -341 1997年12月 [査読有り][通常論文]
     
    The electronic structures for the ground and low-lying excited states of Linear germane-silane (Ge/Si) copolymer radical anions have been determined by means of the semi-empirical PM3-CI method. The permethylgermane-silane radical anion [Me(SiMe2)(n)(GeMe2)(n)Me](-) (n = 3-7) was chosen as a model compound of Ge/Si copolymer radical anion. In all Ge/Si copolymers, an unpaired electron is only localized on the Ge-site, although a Si atom binding to Ge atom has a slight spin density. The spin orbital is sigma* type composed of 4p orbitals in Ge atoms. The CI calculation predicted that the radical anions have an absorption band in IR region. The excitation energy for IR band is slightly blue-shifted as a function of number of chain atoms and the oscillator strength is largely increased. The band structure for the radical anions is discussed on the basis of theoretical results. (C) 1997 Elsevier Science S.A.
  • 市川恒樹, 田地川浩人, 熊谷純, 熊田高之, 宮崎哲郎 ESR討論会講演要旨集 36th 17 -18 1997年10月 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 市川恒樹 フッ素化学討論会講演要旨集 21st 104-105 1997年10月 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 市川恒樹 分子構造総合討論会講演要旨集 1997 148 1997年10月 [査読無し][通常論文]
  • Electronic structures of linear polysilane radical cations at ground and low-lying excited states : A theoretical Study
    Hiroto Tachikawa 1997年 [査読有り][通常論文]
  • Formation and isomerization mechanisms of M+CO2-(M=Li, Na)ion-pair complexes. An Abinitio MO and RPKM study
    H. Tachikawa, Y. Takatori, A. Ohtake, J. Kumagai, H. Yoshida Theochem. 342 1-7 1995年10月20日 [査読有り][通常論文]
     
    Structures and electronic states of the M(+)CO(2)(-) (M = Li and Na) ion-pairs have been investigated by means of ab initio MO calculations. The potential energy surfaces (PESs) for the ion-pair formation reaction (M + CO2 --> M(+)CO(2)(-)) show that the ground state MCO(2) complex has a van der Waals (vdW) character (M . CO2) at the entrance region in the reaction and an ionic one (M(+)CO(2)(-)) at short M-C distances and that the activation barrier is found at the intermediate region between the vdW and ion-pair states. The wavefunctions of the ion-pair for the low-lying excited states are obtained by the multireference single and double excitation configuration interaction (MR-SD-CI) method. The first and second electronic excitations are characterized by charge-transfer transition from CO2- to Na+ and local excitation within the CO2- moiety in M(+)CO(2)(-) respectively. In order to elucidate the isomerization mechanism of the Li+CO2- ion-pair from C-s to C-2v structures, which was observed by Kafafi et al. (J. Am. Chem. Sec., 105 (1983) 3886), the Rice-Ramsperger-Kassel and Marcus (RRKM) theory is applied to calculate the microcanonical reaction rate along the reaction coordina

書籍等出版物

  • 有機エレクトロニクスの展開
    情報機構 2007年
  • 化学結合の量子論入門
    三共出版 1994年

所属学協会

  • 日本放射線化学会   日本化学会   アメリカ化学会   

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    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2018年04月 -2021年03月 
    代表者 : 田地川 浩人
     
    微視的溶媒和クラスターは、少数の溶媒分子によって取り囲まれた分子からできるクラスターであり、溶質の周りの溶媒を部分的に切り出したナノスケールの溶液といえる。最近、クラスターを任意に生成する実験により、反応ダイナミクスの解明が可能となってきた。これに対し、溶媒和クラスターに関する理論的なアプローチは極めて少ない。本研究課題では、ダイレクト・アブイニシオ分子動力学法を、微視的溶媒和クラスター内での反応ダイナミクスの理論解明に応用した。本年度は、以下の2テーマについて詳細な計算を行った。 (1) 微視的溶媒和された放射性セシウムがセメントに効率良く取り込まれるメカニズムを解明 東日本大震災による事故により、福島第一原発から大量の放射性セシウムが放出され、現在もなお、土壌やプラントを汚染している。最近の実験により、セメントの主成分であるケイ酸カルシウム水和物(C-S-H)が、セシウムを効率的に保持することが明らかになった。しかしながら、保持のメカニズムは、全くわかってなかった。本研究では、放射性セシウムとC-S-H表面との相互作用を理論的に研究し、C-S-Hが効率よく放射性セシウムを取り込むメカニズムを解明した。 (2) DNA2重らせんモデル分子への放射線照射効果の理論解明 DNAへ放射線照射すると、(a) 水素結合に沿ってプロトン移動(PT)、または(b)リング間結合を起こし、DNA損傷が生じることが知られている。しかしながら、メカニズムについては、ほんどわかっていない。本研究では、最も単純な2重水素結合系である水和ギ酸ダイマーをDNAモデル分子として、光によって誘起される反応ダイナミクスを研究した。その結果、イオン化では(a)、(b)の両方の競争反応が進行すること、および電子付加では、PTのみが起こることを明らかかにした。さらに、反応経路(a)、(b)の選択制の原因を解明した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 山田 一夫, 田地川 浩人, 渡邊 禎之
     
    コンクリートの耐久性には、その空隙水中のアルカリイオン(Na, K, Cs)濃度が影響するものがある。その濃度はコンクリートの結合材であるセメント水和物への収着で決定され、そのモデル化が耐久性の超長期予想に必須である。本研究では、収着実験結果について、個体NMR分析、及び分子動力学・量子化学計算によりアルカリイオンの原子レベルの基本的挙動を明らかにしたうえで、アルカリの移動を超長期にわたり予測できる多元素物質移動計算に必要な基盤情報を得た。
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 田地川 浩人
     
    微視的溶媒和クラスターは、少数の溶媒和分子によって取り囲まれた分子からなるクラスターであり、溶質の周りの溶媒を部分的に切り出したナノスケールの溶液といえる。本研究では、ダイレクト・アブイニシオ分子動力学法を用いて、微視的溶媒和クラスター内での反応ダイナミクスを理論的に研究した。特に、光照射後の反応ダイナミクスを実時間で追尾し、反応への微視的溶媒和の効果を理論的に予測した。特に水クラスター中のプロトン移動速度の決定、および 単一分子デバイスの電導性への微視的溶媒和の効果等について研究した。その結果、微視的溶媒和により反応速度のみならず、反応のメカニズムが大きな影響を受けることを明らかにした。
  • 日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2013年06月 -2018年03月 
    代表者 : 深澤 倫子, 田地川 浩人, 三浦 均, 野村 英子, 相川 祐理
     
    本課題では、古典分子動力学法、ダイレクト・アブイニシオ分子動力学法、第一原理法、数値シミュレーション等の理論的手法を用いて、星間分子雲から原始惑星系に至るプロセスで起こる氷および有機物の生成・進化の過程を解明することを目的として研究を実施した。成果として、アモルファス状態の氷やフォルステライトの表面構造や、氷表面上に吸着した水ダイマーやアンモニアダイマーの拡散機構等、ミクロな素過程が明らかになった。さらに、降着衝撃波による氷ダストの昇華過程や、塵表面反応を含めた化学反応計算や重水素濃縮過程のモデル化に成功した。これらの成果は随時、学術論文や学会等で報告しており、いずれも高く評価されている。
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2012年04月 -2015年03月 
    代表者 : 田地川 浩人
     
    微視的溶媒和クラスターは、少数の溶媒分子によって取り囲まれた分子(溶質)からできるクラスターであり、溶質の周りの溶媒を部分的に切り出した、いわばナノスケールの溶液といえる。本研究では、ダイレクト・アブイニシオ分子動力学法を用いて、微視的溶媒和クラスター内での反応ダイナミクスを理論的に研究した。特に、光照射後の反応ダイナミクスを実時間で追尾し、反応への微視的溶媒和の効果を理論的に予測した。具体的系として、水和DNA塩基対、および、水和チミンダイマー等を取上げ、光照射に伴う反応ダイナミックスを理論的に研究した。その結果、微視的溶媒和の効果により、反応が加速することを明らかにした。
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2009年 -2011年 
    代表者 : 田地川 浩人
     
    クラスター内に閉じ込められた分子の光による反応ダイナミクスについての情報は極めて限られている。本研究では、(1)溶媒和クラスター内での反応チャンネルを支配している因子の解明、および、(2)反応チャンネルを制御する方法の開発をめざし、ダイレクト・アブイニシオMD法により、いくつかの微視的クラスターのイオン化に伴う反応ダイナミックスを理論的に研究した。その結果、クラスターの温度により、イオン化の際の反応チャンネルを任意に制御できることを明らかにした。
  • ダイレクト・アブイニシオ・ダイナミクス法の開発と分子設計への応用
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2005年 -2006年 
    代表者 : 田地川 浩人
     
    本研究では、ポテンシャル面を解析関数にフイッティングする事無しに、各時間で全エネルギーおよび全原子核上のエネルギー勾配を計算しながら反応軌跡を時間発展する方法(ダイレクト・アブイニシオ・ダイナミックス法)の開発、およびその分子設計への応用を目的とし、以下の研究を遂行した。テーマとして「クラスターのイオン化ダイナミックス、および電子捕捉ダイナミックス」および「SN2反応へのクラスター場(溶媒分子)の効果」について研究し、その反応メカニズムの解明、および実験計画の指針となるモデルの構築を行った。具体的な研究成果を以下に示す。 1.クラスターの光イオン化(および電子付加)ダイナミックスの実時間追尾 水クラスターのイオン化過程および電子捕捉過程を、ダイレクト・アブイニシオ・ダイナミックス法により理論的に研究し、1)反応チャンネルを支配している因子の解明、および、2)これらの反応チャンネルを制御する方法の開発を解明した。特に、水のイオン化の初期過程では、イオン化された1つの水価カチオンのプロトンが隣接する水分子に引き抜かれて、水酸気基イオンになり、その後、周りの水分子の再配向が起こることを明らかにした。水クラスターの電子捕捉過程では、表面状態溶媒和から、内部へ徐々に捕捉されていく過程が存在することを明らかにした。 2.S_N2反応へのクラスタ場(溶媒分子)の効果 S_N2反応(OH^-+CH,Cl)への溶媒効果を理論的に研究した。この反応の生成チャンネルとして、3体解離(CH_3OH + Cl^-+H2O)、ハロゲンの水和(Cl^---H_2O + CH_3OH)、およびCH_3OHの水和の3つの反応チャンネルがあることを明らかにした。さらに、それらの反応チャンネルは、衝突前の水分子の位置により、支配されていることを明らかにした。また、それらのチャンネルの分岐比が衝突エネルギーにより、大きく変化することを理論的に予測した。
  • ダイレクト・アブイニシオ・ダイナミクス法の開発と反応設計への応用
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2003年 -2004年 
    代表者 : 田地川 浩人
     
    本研究では、ポテンシャル面を解析関数にフイッティングする事無しに、各時間で全エネルギーおよび全原子核上のエネルギー勾配を計算しながら、反応軌跡を時間発展する方法(ダイレクト・アブイニシオ・ダイナミックス法)の開発およびその反応系への応用を目的とし、以下の研究を遂行した。特に本年度は「クラスターのイオン化ダイナミックス、および電子捕捉ダイナミックス」および「S_N2反応へのクラスター場(溶媒分子)の効果」について研究し、その反応メカニズムの解明、および、今後の実験計画の指針となるモデルの構築を行った。具体的な研究成果を以下に示す。 ●クラスターの光イオン化(および電子付加)ダイナミックスの実時間追尾 水クラスターのイオン化過程および電子捕捉過程を、ダイレクト・アブイニシオ・ダイナミックス法により理論的に研究し、1)反応チャンネルを支配している因子の解明、および、2)これらの反応チャンネルを制御する方法の開発を解明した。特に、水のイオン化の初期過程では、イオン化された1つの水価カチオンのプロトンが隣接する水分子に引き抜かれて、水酸気基イオンになり、その後、周りの水分子の再配向が起こることを明らかにした。水クラスターの電子捕捉過程では、表面状態溶媒和から、内部へ徐々に捕捉されていく過程が存在することを明らかにした。 ●S_N2反応へのクラスター場(溶媒分子)の効果 S_N2反応(OH-+CH_3Cl)への溶媒効果を理論的に研究した。この反応の生成チャンネルとして、3体解離(CH_3OH+Cl^-+H_2O)、ハロゲンの水和(Cl^--H_2O+CH_3OH)、およびCH_3OHの水和の3つの反応チャンネルがあることを明らかにした。さらに、それらの反応チャンネルは、衝突前の水分子の位置により、支配されていることを明らかにした。また、それらのチャンネルの分岐比が衝突エネルギーにより、大きく変化することを理論的に予測した。
  • ダイレクトダイナミックス法によるダイアモンド、グラファイト中の化学種の拡散機構
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2002年 -2004年 
    代表者 : 清水 晃, 田地川 浩人
     
    ガラス質カーボン繊維およびアモルファスカーボンは、リチウム2次電池の陰極として極めて効率の良い材料の一つであり、その化学的修飾により、さらなる高機能化が可能な物質として期待されている。しかしながら、カーボンシート上でのリチウムの電子状態および拡散メカニズムが不明であるため、新規な機能を有するカーボン材料の開発は試行錯誤的要素が強い。本研究では、ダイレクト・ダイナミックス法により、ガラス質炭素のカーボンシート上のリチウムの電子状態を理論的に明らかにし、さらに量子動力学計算にもとずき、拡散のメカニズムを解明した。また、新規な性能を持つグラファイトを分子設計した。 ダイレクト・ダイナミックス計算は、水素終端した炭素数50個あるいは150個からなるクラスターモデルを用いて、半経験MO(AM1)レベルにて計算した。構造最適化により、リチウムイオン(Li^+)および原子(Li)はともにクラスターモデルの周辺部で安定化することを明らかにした。各原子の電荷の検討結果と合わせると、Li^+イオンは、カーボンシートの周辺のエッジ部分(side edge)とカーボンシートの周辺の角のエッジ部分(corner edge)の両方の炭素とイオン結合をするが、Li原子はside edgeの炭素とsp^3混成軌道により共有結合的に強く結合することを明らかにした。カーボンシート上でのリチウムイオンおよび原子の拡散メカニズムを明らかにするため、ダイレクト・ダイナミックス法により、拡散ダイナミックスを計算した。その結果、リチウムイオンと原子は、まったく異なる動的挙動をとることが明らかになった。Li^+は解離して拡散によりクラスターのバルクを横切り、その後、クラスターから脱出する。拡散経路は最高被占軌道(HOMO)の節に沿って起こる。一方、リチウム原子は、共有結合を保ったまま、side edgeの炭素の周囲を振動するのみであり、700K以下では脱出は起こらないことを明らかにした。また、カーボンシート上にアルミニウムをドープすることにより、拡散速度が、8-10倍に加速する減少を発見し、新規なカーボン材料を理論設計した。
  • 全自由度を考慮したアブイニシオ・ダイナミックス法の開発と反応系への応用
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2001年 -2002年 
    代表者 : 田地川 浩人
     
    本研究では、ポテンシャル面を解析関数にフイッティングする事無しに、各時間で全エネルギーおよび全原子核上のエネルギー勾配を計算しながら、反応軌跡を時間発展する方法(ダイレクト・アブイニシオ・ダイナミックス法)の開発およびその反応系への応用を目的とし、以下の研究を遂行した。特に本年度は「クラスターのイオン化ダイナミックス、および電子捕捉ダイナミックス」および「S_N2反応へのクラスター場(溶媒分子)の効果」について研究し、その反応メカニズムの解明、および、今後の実験計画の指針となるモデルの構築を行った。具体的な研究成果を以下に示す。 (1)クラスター内反応場での新規な反応の理論設計、および、それらの化学反応を実時間で追尾することが可能となった。 (2)半導体およびグラファイト中の原子および分子(たとえば半導体中の不純物やホスト格子に捕捉された分子)の拡散現象(拡散速度の理論計算)を純理論的に明らかにすることができた。 (3)ポリマー中での伝導電子およびホールの存在状態、およびポリマー鎖上での移動現象を実時間で追尾することが可能となった。 (4)分子設計に必要となる分子特性(吸収スペクトル、磁気的特性)の温度依存性および外部刺激に対する分子の緩和過程を理論的に予測した。
  • ダイレクト・アブイニシオ・ダイナミックス法によるイオン・分子反応の理論的研究
    日本学術振興会:科学研究費助成事業 奨励研究(A)
    研究期間 : 1998年 -1999年 
    代表者 : 田地川 浩人
     
    本研究では、イオン分子反応、特にプロトン移動反応における反応生成物の振動・回転量子数分布を支配している因子を、本研究で開発したダイレクト・ダイナミックス法により明らかにすることを目的とした。さらにこれまでに実験が行われていない反応系について、振動・回転状態分布を理論的に予測し、実験計画の指針となるモデルを構築することが本研究の目標である。昨年度は、2分子衝突反応系でのイオン・分子反応を研究し、その反応を支配している因子を明らかにした。本年度は、さらに、ダイナミックスの詳細を明らかにするため,これらの中性ダイマーおよびファンデルワールス錯体からのイオン化に伴うダイナミックスを同様な方法で取り扱い、量子状態分布の特異性についての原因を明らかにした。対象とした反応系は、水ダイマー、メタノールダイマー、エチレン-HF錯体およびベンゼン-HF錯体である。たとえば、ベンゼンHF錯体の場合、 Bz・・HF+hν・e→ (Bz・・HF)^+→Bz^+・・FH 錯合体生成 → Bz^+ + HF 解離チャンネル 2つの反応チャンネルが存在し、これらの分岐比が中性錯体の温度により大きく変わることを理論的に予測した。これらダイマーや錯体からの反応は、衝突配向を規定したダイナミックスを取り扱うことに相当し、全反応と比較することによりダイナミックスについての詳細を追うことができる。それらの2分子反応系と比較する事により、ダイナミックスについて詳細なメカニズムを明らかにした。以上、本研究で開発したダイレクト・アブイニシオ・ダイナミックス法により、多次元系の化学反応の詳細が議論できた。
  • 水素原子トンネル移動反応への媒質効果に関する理論的研究
    日本学術振興会:科学研究費助成事業 重点領域研究
    研究期間 : 1996年 -1996年 
    代表者 : 田地川 浩人
     
    トンネル効果が観測されている水素原子移動反応は、WilliamsらおよびMiyazakiらの実験で代表されるように低温固相(マトリックス、結晶中等)中で観測されている。その意味で、観測されている反応速度等の実測値は、媒質の効果を含むものである。しかしながら、従来のトンネル効果の理論的取り扱いは、この媒質効果を2次的あるいはそれ以下の要素として考えられており、直接には取り扱ってこなかった。本研究では、トンネル効果と媒質効果の両方を同時に取り扱うモデルを構築し、いくつかの実測されている系に適用し、トンネル効果を含む反応速度が媒質によりどのような影響を受けるかを明らかにするのを目的とする。 メトキシラジカルからメタノールラジカルへの分子内水素原子移動反応は、、メタノール結晶中で4Kから77Kへの昇温により反応が進行することが知られている。これに対し、マトリックス中では、結晶中に比べ反応速度が大きく、4Kですでに水素原子移動が終了した生成物(CH2OH)が観測される。本研究では、この反応へ及ぼす媒質の効果を理論的に明らかにするため、気相(真空)中、メタノール結晶中および凝縮相(水クラスター)中での、この反応モデル計算を行った。また、反応が4K〜77Kと低温で進行することからトンネル効果も重要となると考えられる。そこで、本研究では、トンネル効果および媒質効果の両方を取り入れるモデルを構築し、反応への応用を試みた。 反応系の振動モードは、回りの媒質により影響を受ける。気相中では、反応系中の振動モードは、互いに直交しているが、近くに溶媒分子がくると、その溶媒分子の振動モードを通して、反応分子中の振動モードどうしがカップルすると考えることが出来る。結果として、振動数がシフトする。このシフト量を反応座標に沿って見積もることにより、媒質の効果を含んだ反応速度定数の計算が可能となる。実際の計算では、遷移状態理論の範囲で、トンネル効果を含むRRKM理論を適用した。これにより、トンネル効果および媒質効果の両方を含む反応速度の見積もりが出来る。計算の結果、反応速度への媒質効果は、古典的障壁より低いエネルギー領域(トンネリング領域)で顕著になることが明らかになった。また、得られた反応速度は、77K以下の低温で、k(気相)
  • 気相プロトン移動反応における量子状態選択性に関する理論的研究
    日本学術振興会:科学研究費助成事業 奨励研究(A)
    研究期間 : 1996年 -1996年 
    代表者 : 田地川 浩人
     
    本研究は、化学反応における振動および回転量子状態の選択性の原因を、ab-initio分子軌道法、擬古典トラジェクトリー法および量子波束ダイナミックス法により理論的に明らかにすることを目的としている。さらに、これまでに実験が行われていない反応について、振動・回転分布を理論的に予測し、実験計画の指針となるモデルを構築することが本研究の最終目標である。「反応物の振動回転状態を指定したとき、生成物の振動回転はどのように分布するか」という問題は、化学反応動力学を理解する上で基本的かつ重要な問題である。そこで本研究では、1)イオン-分子系でのプロトン移動反応を中心に量子状態選択性に関する理論的研究を行った。研究対象として、アンモニアカチオンによる中性アンモニア分子からのプロトン引き抜き反応: ND_3(v, J)+NH_3-->NHD_3^++NH_2 を取り扱った。本研究では、この反応にポテンシャル面を電子相関を考慮したアブイニシオ法で求め、その面上でのダイナミクスを取り扱うことにより、反応の詳細なメカニズムを議論し、反応のモデルを提出した。[H, Tachikawa, Chem.Phys., 1996, 211, 305].特に、1) vlモードの励起により、反応断面積が増加する事、および、2)衝突エネルギーの増加により反応断面積が現象することを見いだした。さらに、本研究では、気相エネルギー移動反応への拡張も行った。研究対象は、オゾン層でのエネルギー移動反応で重要になる励起酸素原子から大気中の窒素分子へのエネルギー移動反応:O (1D)+N2->O (3P)+N2を取り扱った。その結果、励起酸素原子は、オゾンが分解した直後の励起酸素原子の状態ではエネルギー移動は起こさないが、数回の衝突の後、窒素分子へのエネルギー移動を起こす事を明らかにし、大気中での反応のモデルを提出した。[H, Tachikawa, et.al, J.Phys.Chem., 1997, 101 (in press)].
  • 化学反応における振動・回転量子状態選択性に関する理論的研究
    日本学術振興会:科学研究費助成事業 奨励研究(A)
    研究期間 : 1995年 -1995年 
    代表者 : 田地川 浩人
     
    本研究では、化学反応における生成物の振動および回転量子数分布を支配している因子を、分子軌道法および擬古典トラジェクトリー法により明らかにすることを目的としている。さらに、これまでに実験が行われていない反応について、振動回転状態分布を理論的に予測し、実験計画の指針となるモデルを構築することが本研究の目標である。本年度の研究対象として、遷移状態分光として最近注目をあびているイオン-分子反応(プロトン移動反応)を研究した。 A^-+H-B(v,J)→[AHB]^-→A-H(v′,J′)+B^- 反応I 具体的な反応系としては、2つの気相プロトン移動反応 O^-+HF→OHW(v,J)+F^- F^-+HCl→HF(v,J)+Cl^- を特に詳細に研究した。 この研究により、反応Iのタイプのプロトン移動反応のダイナミックスは、2つの反応チャンネル(中間体およびダイレクトチャンネル)の重ね合わせにより説明できることを明らかにした。この原因として、衝突直前の配向角(衝突角)が、その反応生成物の振動回転状態を支配していることを明らかにした。また、ごく最近、類似反応 O^-+HCl→OH(v,J)+Cl^- F^-+HF→HF(v,J)+F^- について同様な研究を行い、このモデルの妥当性を確認した。これまで、反応のkinematicsがダイナミックスを支配していると考えられてきたが、本研究により、この効果の他に、衝突角のファクターがダイナミックスへ大きく影響することが明らかになった。
  • 周波数掃引型超高速超高感度ESRスペクトロメーターの試作
    日本学術振興会:科学研究費助成事業 試験研究(B)
    研究期間 : 1994年 -1995年 
    代表者 : 市川 恒樹, 田地川 浩人
     
    本研究では、10^<-15>モル程度の固体中の常磁性種を,検出時間にして百マイクロ秒以内に測定する高速高感度ESRスペクトロメーターを試作することを目指した. 測定法としては,断熱高速通過条件下で常磁性種がスピン共鳴条件を通過する際に生じる過渡信号検出法を採用した。周波数掃引による断熱通過の場合には,掃引に用いる電圧制御マイクロ波発信器からの位相雑音によって信号強度が不規則に変動するため,断熱高速通過法としては磁場掃引法を採用した。この場合,磁場を繰り返し掃引しながらマイクロ波を断続的に印加することで断熱高速通過を達成した。このESR信号を数値解析したところ,この方法は横緩和時間が100マイクロ秒以上の常磁性種を検出するのに適していることが判明した。このような常磁性種の検出感度は通常のCWESRの場合の100倍以上に達する。この測定法は極低温固体中の有機ラジカルのような常磁性緩和時間の長いわずかな常磁性種を検出するには非常に適した方法であることがわかった。
  • 状態選択された分子の反応ダイナミックスに関する理論的研究
    日本学術振興会:科学研究費助成事業 奨励研究(A)
    研究期間 : 1993年 -1993年 
    代表者 : 田地川 浩人
     
    本研究は、1)振動および回転状態を選択された分子の反応性を支配している因子、および2)反応生成物の振動回転分布などから衝突過程のメカニズムをAb-initio分子軌道法および擬古典トラジェクトリー法により理論的に明らかにすることを目的としている。研究対象として、アンモニアカチオンによる中性アンモニア分子からの水素原子引き抜き反応:ND_3^+(v)+NH_3→NHD_3^++NH_2を取り扱った。 この反応の反応断面積は、ND_3^+のnu_2モード振動量子数vに大きく依存し、vの増加にともない反応断面積が著しく増加することが実験的に知られている。従って、この反応は、状態選択的化学反応の代表例であると考えられる。本研究では、この反応のポテンシャル面をMR-SD-CI法で求め、その面上でのトラジェクトリ-計算を行うことにより、反応の詳細なメカニズムを議論しさらに反応のモデルを提出した。[H.Tachikawa and S.Tomoda,Chem.Phys.,1994,99(in press)]このモデルでは、アンモニアカチオンのnu_2モードの増加は、中性アンモニア分子からの電子の有効捕捉体積の増加と考えており、これまでの実験事実を矛盾なく説明した。 本研究では、電荷移動反応における反応生成物の振動回転状態特異性についても拡張した。低エネルギー領域での電荷移動反応の生成物の振動状態分布は,フランクコンドン機構およびエネルギー共鳴機構により議論されているが,最近これらの機構では説明できないいくつかの反応が知られるようになってきている.その1つに,窒素カチオンから一酸化炭素への電荷移動反応:N^+(^3P)+CO(X^1SIGMA^+,v=0)→N(^4S)+CO^+(X^2SIGMA^+,v,J) がある.本研究では,理論的方法により,この反応のメカニズムを明らかにし,これまでにないモデルを提出した.[H.Tachikawa et al.J.Phys.Chem.1993,97,11944]
  • 力学的に制御される化学反応
    日本学術振興会:科学研究費助成事業 一般研究(B)
    研究期間 : 1992年 -1993年 
    代表者 : 市川 恒樹, 田地川 浩人, 小泉 均
     
    アルカンを含む低温マトリックス中に生じた水素原子はアルカンから水素を引き抜くが,その炭素位置は反応の活性化エネルギーだけでなく生成ラジカルの構造緩和の容易差によっても支配され,非晶質マトリックス中のn-アルカンでは分子端から2番目の2級炭素で優先的に水素引き抜きが生じる. アルケンを含む低温マトリックス中では,水素原子はアルケン二重結合を作っている2つの炭素の内の一方に付加する.マトリックスがメタノールの場合には,付加する炭素の位置は付加の活性化エネルギーによって決定される.しかしながら,水素の活性が低いアダマンタンマトリックス中では,反応位置は生成アルキルラジカルの構造緩和の容易さによっても支配され,分子端に近い炭素位置ほど付加が生じ易くなる.水素原子がメチルラジカルに変わると,アルケンアリル位からの水素引き抜きが優先するが,この場合には,水素が引き抜かれる炭素の位置は生成するアルキルラジカルの構造緩和の容易さによっても支配され,分子端に近い炭素ほど引き抜きが起き易い. これらの結果は反応を量子論的に考察することにより理解される.すなわち反応系と生成系との間の相互作用が弱い水素引き抜きやアダマンタン中での水素付加反応では,系は反応系と生成系の1量子状態との間の共鳴状態となるため,生成系への安定化速度は構造緩和速度に比例することとなる。これに対して,反応のポテンシャル障壁が低く,反応系と生成系の相互作用が強い,メタノールマトリックス中での水素原子付加反応では,反応系は多数の生成系と結合するため,生成系から反応系への転換は生ぜず,反応速度は相互作用の大きさのみで決定されるようになる.
  • 置換ポリアセチレンにおける過剰電子の局在化と非局在化
    日本学術振興会:科学研究費助成事業 一般研究(C)
    研究期間 : 1991年 -1991年 
    代表者 : 小笠原 正明, 田地川 浩人
     
    1.芳香族置換ポリアセチレンのラジカルアニオンの吸収スペクトルを2ーメチルテトラヒドロフラン(MTHF)溶媒中で測定した.ポリマ-のラジカルアニオンは,77Kまたは4Kの低温で凍らせたポリマ-溶液にガンマ線照射するか,あるいは室温または140Kで電子線パルスを照射することによってつくり出した.この実験によって以下のことが明らかになった. (1)MTHFに溶解したポリ(1ーフェニルー1ープロピン)(PPPr)には,2種類の電子捕捉サイト(サイトI,サイトII)がある. (2)低温で凍らせた状態では,溶媒のイオン化により生成した過剰電子はまずサイトIに捕捉されてラジカルアニオンとなり,390nmと560nmにλ_をもち800nmにョルダ-を有する吸収スペクトルを与える. (3)温度を上げると640nmにλ_を持つサイトIIに移る.このサイトに捕捉された電子はPPPrのモデル化合物であるβーメチルスチレンのラジカルアニオンによく似たスペクトルを与える.このことから,過剰電子は最終的に1モノマ-単位程度の狭いの領域に局在化していることがわかった. (4)サイトIとサイトIIのちがいは,モノマ-の結合モ-ドのちがいによる. (5)ポリ(フェニルエチレン)(PPA)では近赤外領域に2量体の生成を示すバンドが観測され,電子は2個のモノマ-単位に非局在化していることがわかった。 2.PPPrの2量体モデル化合物であるジ-βーメチルスチレンに電子を付加したものとしないものについてMNDOC法による分子軌道法計算を行った.その結果,過剰電子が付加するとしないとにかかわらず,分子の主鎖は90度もねじれていることがわかった。PPPrにおいて電子が狭い範囲に局在化するのは、かさ高いフェニル基とメチル基の反発的相互作用によって主鎖が著しくねじれるためと結論された.
  • 電子スピンエコー法による水素原子トンネリング反応への溶媒効果の研究
    日本学術振興会:科学研究費助成事業 奨励研究(A)
    研究期間 : 1990年 -1990年 
    代表者 : 田地川 浩人
  • 1) 分子動力学的理論によるナノ機能性分子設計 2) 生体内SN2反応の理論モデリング 3) 特殊反応場クラスター内における反応設計理論 4) 新規な機能をもつ有機・高分子の動力学的分子設計


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