Researcher Database

Naoki Watanabe
Institute of Low Temperature Science Frontier Ice and Snow Science
Professor

Researcher Profile and Settings

Affiliation

  • Institute of Low Temperature Science Frontier Ice and Snow Science

Job Title

  • Professor

Degree

  • (BLANK)

J-Global ID

Research Interests

  • 原子・分子   星間物質   低温表面反応   atoms & molecules   ice surface   Astrochemistry   

Research Areas

  • Natural sciences / Space and planetary science
  • Natural sciences / Semiconductors, optical and atomic physics

Education

  •        - 1992  Tokyo Metropolitan University  Graduate School of Science
  •        - 1992  Tokyo Metropolitan University  Graduate School, Division of Natural Science
  •        - 1987  Nihon University  College of Science and Technology
  •        - 1987  Nihon University  Faculty of Science and Engineering

Association Memberships

  • JAPAN GEOSCIENCE UNION   原子衝突学会   THE JAPANESE SOCIETY FOR PLANETARY SCIENCES   日本物理学会   

Research Activities

Published Papers

  • Hideyuki Nakano, Naoki Hirakawa, Yasuhiro Matsubara, Shigeru Yamashita, Takuo Okuchi, Kenta Asahina, Ryo Tanaka, Noriyuki Suzuki, Hiroshi Naraoka, Yoshinori Takano, Shogo Tachibana, Tetsyua Hama, Yasuhiro Oba, Yuki Kimura, Naoki Watanabe, Akira Kouchi
    Scientific Reports 10 7755  2020/12 [Refereed][Not invited]
  • Akira Kouchi, Kenji Furuya, Tetsuya Hama, Takeshi Chigai, Takashi Kozasa, Naoki Watanabe
    ASTROPHYSICAL JOURNAL LETTERS 891 (1) 2041-8205 2020/03 [Refereed][Not invited]
     
    The importance of the activation energy of surface diffusion (E-sd) of adsorbed molecules on amorphous solid water (ASW) has been widely discussed in terms of chemical reactions on ASW at low temperatures. However, in previous work, E-sd has not been measured directly but estimated from indirect experiments. It has been assumed in chemical network calculations that E-sd is between 0.3 and 0.8 of the desorption energies of a molecule. It remains important to obtain direct measurements of E-sd. We performed in situ observations of the deposition process of CO and CO2 on ASW using transmission electron microscopy (TEM) and deduced the E-sd of CO and CO2 on ASW to be 350 50 and 1500 100 K, respectively. The value of E-sd of CO is approximately 0.3 of the total adsorption energy of CO on ASW, i.e., much smaller than assumed in chemical network calculations, where the corresponding figure is 575 K, assuming approximately 0.5 of the desorption energy. We demonstrated that TEM is very useful not only for the observation of ices but also for the measurement of some physical properties that are relevant in astrochemistry and astrophysics. Using the E-sd of CO measured in the present study (350 K), we have updated the chemical network model of Furuya et al., confirming that CO2 could be efficiently formed by the reaction CO + OH -> CO2 + H in the initial stages of the evolution of molecular clouds.
  • Furuya Kenji, Aikawa Yuri, Hama Tetsuya, Watanabe Naoki
    ASTROPHYSICAL JOURNAL 882 (2) 0004-637X 2019/09/10 [Refereed][Not invited]
  • Nucleobase synthesis in interstellar ices
    Y. Oba, Y. Takano, H. Naraoka, N. Watanabe, A. Kouchi
    Nature Communications 10 4413  2019/09 [Refereed][Not invited]
  • Hama, Tetsuya, Seki, Kousuke, Ishibashi, Atsuki, Miyazaki, Ayane, Kouchi, Akira, Watanabe, Naoki, Shimoaka, Takafumi, Hasegawa, Takeshi
    PLANT AND CELL PHYSIOLOGY 60 (7) 1567 - 1580 0032-0781 2019/07 [Refereed][Not invited]
     
    The surface of most aerial plant organs is covered with the cuticle, a membrane consisting of a variety of organic compounds, including waxes, cutin (a polyester) and polysaccharides. The cuticle serves as the multifunctional interface between the plant and the environment, and plays a major role in protecting plants against various environmental stress factors. Characterization of the molecular arrangements in the intact cuticle is critical for the fundamental understanding of its physicochemical properties; however, this analysis remains technically challenging. Here, we describe the nondestructive characterization of the intact cuticle of Brassica oleracea L. leaves using polarization modulation-infrared (IR) reflection-absorption spectroscopy (PM-IRRAS). PM-IRRAS has a probing depth of less than several hundreds of nanometers, and reveals the crystalline structure of the wax covering the cuticle surface (epicuticular wax) and the nonhydrogen-bonding character of cutin. Combined analysis using attenuated total reflection- IR spectra suggested that hemicelluloses xylan and xyloglucan are present in the outer cuticle region close to the epicuticular wax, whereas pectins are dominant in the inner cuticle region (depth of <= 2 mu m). PM-IRRAS can also determine the average orientation of the cuticular molecules, as indicated by the positive and negative spectral peaks. This unique advantage reveals the orientational order in the intact cuticle; the hydrocarbon chains of the epicuticular wax and cutin and the backbones of hemicelluloses are oriented perpendicular to the leaf surface. PM-IRRAS is a versatile, informative and easy-to-use technique for studying plant cuticles because it is nondestructive and does not require sample pretreatment and background measurements.
  • Masashi Tsuge, Tetsuya Hama, Yuki Kimura, Akira Kouchi, Naoki Watanabe
    The Astrophysical Journal 878 (1) 23  2019/06 [Refereed][Not invited]
  • Physico-chemical behavior of hydrogen sulfide induced by reactions with H and D atoms on different types of ice surfaces at low temperature
    Y. Oba, T. Tomaru, A. Kouchi, N. Watanabe
    Astrophysical Journal 874 8pp  2019/04 [Refereed][Not invited]
  • Ultraviolet-photon exposure stimulates negative current conductivity in amorphous ice below 50 K
    N. Watanabe, W. M. C. Sameera, H. Hidaka, A. Miyazaki, A. Kouchi
    Chemical Physics Letters 737 136820  2019 [Refereed][Not invited]
  • Y. Kimura, M. Tsuge, V. Pirronello, A. Kouchi, N. Watanabe
    Astrophys. J. Lett. 858 (L23) 5pp  2018/05 [Refereed][Not invited]
  • Tetsuya Hama, Akira Kouchi, Naoki Watanabe
    Astrophysical Journal Letters 857 (2) 6pp  2041-8213 2018/04/20 [Refereed][Not invited]
     
    Water has two nuclear-spin isomers: ortho- and para-H2O. Some observations of interstellar space and cometary comae have reported the existence of gaseous H2O molecules with anomalous ortho-to-para ratios (OPRs) less than the statistical value of three. This has been often used to estimate the formation temperature of ice on dust, which is inferred to be below 50 K. The relation between the nuclear-spin dynamics of H2O in ice at low temperatures and the OPR of gaseous H2O desorbed from the ice has yet to be explored in a laboratory. Consequently, the true meaning of the observed OPRs remains debated. We measure the OPR of H2O photodesorbed from ice made from para-H2O monomers at 11 K, which was prepared by the sublimation of Ne from a para-H2O/Ne matrix. The photodesorbed H2O molecules from the ice have the statistical OPR value of three, demonstrating the immediate nuclear-spin-state mixing of H2O toward the statistical value of ice even at 11 K. The OPR of H2O thermally desorbed from the ice also shows the expected statistical value. Our results indicate that the OPR of H2O desorbed from interstellar ice should be the statistical value regardless of the formation process of the ice, which cannot be used to deduce the ice-formation temperature. This study highlights the importance of interstellar gas-phase processes in understanding anomalous abundance ratios of nuclear-spin isomers of molecules in space.
  • Y. Oba, T. Tomaru, T. Lamberts, A. Kouchi, N. Watanabe
    Nature Astronomy 2 (3) 228 - 232 2397-3366 2018/03/01 [Refereed][Not invited]
     
    In molecular clouds at temperatures as low as 10 K, all species except hydrogen and helium should be locked in the heterogeneous ice on dust grain surfaces. Nevertheless, astronomical observations have detected over 150 different species in the gas phase in these clouds. The mechanism by which molecules are released from the dust surface below thermal desorption temperatures to be detectable in the gas phase is crucial for understanding the chemical evolution in such cold clouds. Chemical desorption, caused by the excess energy of an exothermic reaction, was first proposed as a key molecular release mechanism almost 50 years ago 1 . Chemical desorption can, in principle, take place at any temperature, even below the thermal desorption temperature. Therefore, astrochemical network models commonly include this process 2,3 . Although there have been a few previous experimental efforts 4-6, no infrared measurement of the surface (which has a strong advantage to quantify chemical desorption) has been performed. Here, we report the first infrared in situ measurement of chemical desorption during the reactions H + H2S → HS + H2 (reaction 1) and HS + H → H2S (reaction 2), which are key to interstellar sulphur chemistry 2,3 . The present study clearly demonstrates that chemical desorption is a more efficient process for releasing H2S into the gas phase than was previously believed. The obtained effective cross-section for chemical desorption indicates that the chemical desorption rate exceeds the photodesorption rate in typical interstellar environments.
  • Tetsuya Hama, Akira Kouchi, Naoki Watanabe, Shinichi Enami, Takafumi Shimoaka, Takeshi Hasegawa
    Journal of Physical Chemistry B 121 (49) 11124 - 11131 1520-5207 2017/12/14 [Refereed][Not invited]
     
    The outermost surface of the leaves of land plants is covered with a lipid membrane called the cuticle that protects against various stress factors. Probing the molecular-level structure of the intact cuticle is highly desirable for understanding its multifunctional properties. We report the in situ characterization of the surface structure of Kalanchoe pinnata leaves using polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). Without sample pretreatment, PM-IRRAS measures the IR spectra of the leaf cuticle of a potted K. pinnata plant. The peak position of the CH2-related modes shows that the cuticular waxes on the leaf surface are mainly crystalline, and the alkyl chains are highly packed in an all-trans zigzag conformation. The surface selection rule of PM-IRRAS revealed the average orientation of the cuticular molecules, as indicated by the positive and negative signals of the IR peaks. This unique property of PM-IRRAS revealed that the alkyl chains of the waxes and the main chains of polysaccharides are oriented almost perpendicular to the leaf surface. The nondestructive, background-free, and environmental gas-free nature of PM-IRRAS allows the structure and chemistry of the leaf cuticle to be studied directly in its native environment.
  • Yasuhiro Oba, Yoshinori Takano, Hiroshi Naraoka, Akira Kouchi, Naoki Watanabe
    ASTROPHYSICAL JOURNAL 849 (2) 9pp  0004-637X 2017/11 [Refereed][Not invited]
     
    Hexamethylenetetramine (HMT) is a representative product after the photolysis of interstellar ice analogs containing methanol followed by warming-up to room temperature. Since interstellar methanol is often significantly enriched in deuterium (D), the HMT photoproduct is expected to inherit D atoms from deuterated methanol. However, D fractionation upon the formation of HMT is not well understood, especially when it is produced from partly deuterated methanol isotopologues such as CH2DOH and CH3OD. Here, we experimentally studied the composition of deuterated HMT (d(n)-HMT, where n is the number of D atoms) at the isotopologue level formed by the photolysis of ice mixtures containing deuterated methanol, CH2DOH or CH3OD, at 10 or 77 K. The analyses were performed using a state-of-the-art high-resolution mass spectrometer coupled with a compoundspecific separation technique. The formation of dn-HMT (n = 0-8) was confirmed under all experimental conditions. In addition, methyl-and hydroxyl-substituted HMT and their deuterated isotopologues were also obtained in the products. The deuterium enrichment was outstanding when CH2DOH was used rather than CH3OD, and when photolysis was performed at 77 K rather than 10 K. We found that the deuteration level of the formed HMT far exceeded that of the reactants under the present experimental conditions. These results obtained during stable isotope probing of deuterium strongly suggest that HMT can play a role as an organic pool of interstellar D atoms. These may be distributed into other chemical species through molecular evolution in space.
  • Shogo Tachibana, Akira Kouchi, Tetsuya Hama, Yasuhiro Oba, Laurette Piani, Iyo Sugawara, Yukiko Endo, Hiroshi Hidaka, Yuki Kimura, Ken-Ichiro Murata, Hisayoshi Yurimoto, Naoki Watanabe
    Science advances 3 (9) eaao2538  2017/09 [Refereed][Not invited]
     
    Interstellar ice is believed to be a cradle of complex organic compounds, commonly found within icy comets and interstellar clouds, in association with ultraviolet (UV) irradiation and subsequent warming. We found that UV-irradiated amorphous ices composed of H2O, CH3OH, and NH3 and of pure H2O behave like liquids over the temperature ranges of 65 to 150 kelvin and 50 to 140 kelvin, respectively. This low-viscosity liquid-like ice may enhance the formation of organic compounds including prebiotic molecules and the accretion of icy dust to form icy planetesimals under certain interstellar conditions.
  • Tetsuya Hama, Shinnosuke Ishizuka, Tomoya Yamazaki, Yuki Kimura, Akira Kouchi, Naoki Watanabe, Toshiki Sugimoto, Valerio Pirronello
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 19 (27) 17677 - 17684 1463-9076 2017/07 [Refereed][Not invited]
     
    Crystalline ice formation requires water molecules to be sufficiently mobile to find and settle on the thermodynamically most stable site. Upon cooling, however, diffusion and rearrangement become increasingly kinetically difficult. Water ice grown by the condensation of water vapor in laboratory is thus generally assumed to be in a metastable amorphous form below 100 K. Here, we demonstrate the possibility of crystalline ice formation at extremely low temperature using a water/neon matrix (1/1000, 30000 monolayers) prepared at 6 K, which is subsequently warmed to 11-12 K. In situ infrared spectroscopy revealed the assembly of the dispersed water molecules, forming crystalline ice I during the sublimation of the neon matrix for 40-250 seconds. This finding indicates that the high mobility of the water molecules during matrix sublimation can overcome the kinetic barrier to form crystals even at extremely low temperature.
  • Rafael Escribano, Emilio Artacho, Akira Kouchi, Tetusya Hama, Yuki Kimura, Hiroshi Hidaka, Naoki Watanabe
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 19 (10) 7280 - 7287 1463-9076 2017/03 [Refereed][Not invited]
     
    Models for the inclusion of water molecules in carbon monoxide matrices are developed using density functional theory applied to amorphous solid systems. The models cover a large range of systems for smaller or larger CO matrices with different water content, consisting of either individual H2O molecules or small clusters linked by H-bonds. The vibrational spectra of the samples are predicted at the minimum of their potential energy surface. The spectra allow instances where the water molecules remain isolated or form aggregates to be discerned, and they also provide an indication of the strength of the H-bonding, when present. The calculations support recent experimental observations that linked IR bands at 3707 cm(-1) and 3617 cm(-1) to the presence of unbound water molecules in water-poor CO/H2O mixed ices. Assignment of some observed bands to water dimers or trimers is suggested as well. The residual static pressure in fixed-volume simulation cells is also calculated.
  • Tetsuya Hama, Akira Kouchi, Naoki Watanabe
    XXX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2017) 875 1742-6588 2017 [Refereed][Not invited]
     
    The ortho-to-para ratio of water photodesorbed from ice at 10 K shows a statistical value of 3, and does not reflect the formation temperature of the ice.
  • Shinnosuke Ishizuka, Yuki Kimura, Tomoya Yamazaki, Tetsuya Hama, Naoki Watanabe, Akira Kouchi
    CHEMISTRY OF MATERIALS 28 (23) 8732 - 8741 0897-4756 2016/12 [Refereed][Not invited]
     
    Multiple pathways in crystal nucleation are now known to be more common than previously predicted; it is, therefore, crucial to understand the early stages of crystallization. Even in relatively simple vapor-phase homogeneous nucleation, the process has significant potential diversity. Here, we experimentally show crystalline Al2O3 nanoparticles forming via precisely two steps in the nucleation process from supersaturated vapor with a moderate cooling rate. In situ FT-IR measurement of nucleation allowed us to observe the formation of Al2O3 nanoparticles. Liquid-like particles first nucleated from the vapor before crystallizing. The crystalline phase was preserved by quenching without further transformation into the most stable alpha-Al2O3 polymorph. The precipitated phase changed from delta-Al2O3 for pure Al2O3 to gamma-Al2O3 or theta-Al2O3 by adding Sb or Cr, respectively. We demonstrate that a two-step process occurs in homogeneous nucleation of refractory materials from supersaturated vapor, which may facilitate polymorphic control in industry formation in space. and improve understanding of cosmic dust
  • Yasuhiro Oba, Naoki Watanabe, Akira Kouchi
    CHEMICAL PHYSICS LETTERS 662 14 - 18 0009-2614 2016/10 [Refereed][Not invited]
     
    We report an experimental study on the catalytic effect of solid water on the reactivity of hydrogen abstraction (H-abstraction) from dimethyl ether (DME) in the low-temperature solid DME-H2O complex. When DME reacted with deuterium atoms on a surface at 15-25 K, it was efficiently deuterated via successive tunneling H-abstraction and deuterium (D)-addition reactions. The 'effective rate constant for DME-H2O + D was found to be about 20 times smaller than that of pure DME + D. This provides the first evidence that the presence of solid water has a negative catalytic effect on tunneling H-abstraction reactions. (C) 2016 Elsevier B.V. All rights reserved.
  • Yasuhiro Oba, Kazuya Osaka, Takeshi Chigai, Akira Kouchi, Naoki Watanabe
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 462 (1) 689 - 695 0035-8711 2016/10 [Refereed][Not invited]
     
    Ethanol (CH3CH2OH) is one of the most abundant complex organic molecules in star-forming regions. Despite its detection in the gas phase only, ethanol is believed to be formed by low temperature grain-surface reactions. Methanol, the simplest alcohol, has been a target for observational, experimental, and theoretical studies in view of its deuterium enrichment in the interstellar medium; however, the deuterium chemistry of ethanol has not yet been an area of focus. Recently, deuterated dimethyl ether, a structural isomer of ethanol, was found in star forming regions, indicating that deuterated ethanol can also be present in those environments. In this study, we performed laboratory experiments on the deuterium fractionation of solid ethanol at low temperatures through a reaction with deuterium (D) atoms at 10 K. Hydrogen (II)-D substitution, which increases the deuteration level, was found to occur on the ethyl group but not on the hydroxyl group. In addition, when deuterated ethanol (e.g. CD3CD2OD) solid was exposed to H atoms at 10 K, D-H substitution that reduced the deuteration level occurred on the ethyl group. Based on the results, it is likely that deuterated ethanol is present even under H-atom-dominant conditions in the interstellar medium.
  • Yasuhiro Oba, Yoshinori Takano, Naoki Watanabe, Akira Kouchi
    ASTROPHYSICAL JOURNAL LETTERS 827 (1) L18 (7pp)  2041-8205 2016/08 [Refereed][Not invited]
     
    Deuterium (D) atoms in interstellar deuterated methanol might be distributed into complex organic molecules through molecular evolution by photochemical reactions in interstellar grains. In this study, we use a state-of-the-art high-resolution mass spectrometer coupled with a high-performance liquid chromatography system to quantitatively analyze amino acids and their deuterated isotopologues formed by the photolysis of interstellar ice analogs containing singly deuterated methanol CH2DOH at 10 K. Five amino acids (glycine, alpha-alanine, beta-alanine, sarcosine, and serine) and their deuterated isotopologues whose D atoms are bound to carbon atoms are detected in organic residues formed by photolysis followed by warming up to room temperature. The abundances of singly deuterated amino acids are in the range of 0.3-1.1 relative to each nondeuterated counterpart, and the relative abundances of doubly and triply deuterated species decrease with an increasing number of D atoms in a molecule. The abundances of amino acids increase by a factor of more than five upon the hydrolysis of the organic residues, leading to decreases in the relative abundances of deuterated species for alpha-alanine and beta-alanine. On the other hand, the relative abundances of the deuterated isotopologues of the other three amino acids did not decrease upon hydrolysis, indicating different formation mechanisms of these two groups upon hydrolysis. The present study facilitates both qualitative and quantitative evaluations of D fractionation during molecular evolution in the interstellar medium.
  • A. Kouchi, T. Hama, Y. Kimura, H. Hidaka, R. Escribano, N. Watanabe
    CHEMICAL PHYSICS LETTERS 658 287 - 292 0009-2614 2016/08 [Refereed][Not invited]
     
    A novel method for the formation of amorphous ice involving matrix sublimation has been developed. A CO-rich CO:H2O mixed ice was deposited at 8-10 K under ultra-high vacuum condition, which was then allowed to warm. After the sublimation of matrix CO at 35 K, amorphous ice remained. The amorphous ice formed exhibits a highly porous microscale texture; however, it also rather exhibits a density similar to that of high-density amorphous ice formed under high pressure. Furthermore, unlike conventional vapor-deposited amorphous ice, the amorphous ice is stable up to 140 K, where it transforms directly to cubic ice Ic. (C) 2016 Elsevier B.V. All rights reserved.
  • Yoichi Nakai, Hiroshi Hidaka, Naoki Watanabe, Takao M. Kojima
    JOURNAL OF CHEMICAL PHYSICS 144 (22) 224306(11pp)  0021-9606 2016/06 [Refereed][Not invited]
     
    We measured equilibrium constants for H3O+(H2O)(n-1) + H2O <-> H3O+(H2O)(n) (n = 4-9) reactions taking place in an ion drift tube with various applied electric fields at gas temperatures of 238-330 K. The zero-field reaction equilibrium constants were determined by extrapolation of those obtained at non-zero electric fields. From the zero-field reaction equilibrium constants, the standard enthalpy and entropy changes, Delta H-n,n-1(0) and Delta S-n, n-1(0), of stepwise association for n = 4-8 were derived and were in reasonable agreement with those measured in previous studies. We also examined the electric field dependence of the reaction equilibrium constants at non-zero electric fields for n = 4-8. An effective temperature for the reaction equilibrium constants at non-zero electric field was empirically obtained using a parameter describing the electric field dependence of the reaction equilibrium constants. Furthermore, the size dependence of the parameter was thought to reflect the evolution of the hydrogen-bond structure of H3O+(H2O)(n) with the cluster size. The reflection of structural information in the electric field dependence of the reaction equilibria is particularly noteworthy. Published by AIP Publishing.
  • Hirokazu Ueta, Naoki Watanabe, Tetsuya Hama, Akira Kouchi
    PHYSICAL REVIEW LETTERS 116 (25) 253201(5pp)  0031-9007 2016/06 [Refereed][Not invited]
     
    The surface temperature dependence of the ortho-to-para conversion of H-2 on amorphous solid water is first reported. A combination of photostimulated desorption and resonance-enhanced multiphoton ionization techniques allowed us to sensitively probe the conversion on the surface of amorphous solid water at temperatures of 9.2-16 K. Within a narrow temperature window of 8 K, the conversion time steeply varied from similar to 4.1 x 10(3) to similar to 6.4 x 10(2) s. The observed temperature dependence is discussed in the context of previously suggested models and the energy dissipation process. The two-phonon process most likely dominates the conversion rate at low temperatures.
  • Hydrogenation /and Deuteration of C2H2 and C2H4 on Cold Grains: Clue to the Formation Mechanism of C2H6 with Astronomical Interest
    H. Kobayashi, H. Hidaka, T. Lamberts, T. Hama, H. Kawakita, J. Kästner, N. Watanabe
    The Astrophysical Journal 837 155  2016 [Refereed][Not invited]
  • Tetsuya Hama, Akira Kouchi, Naoki Watanabe
    SCIENCE 351 (6268) 65 - 67 0036-8075 2016/01 [Refereed][Not invited]
     
    The anomalously low ortho-to-para ratios (OPRs) exhibited by gaseous water in space have been used to determine the formation temperature (<50 kelvin) of ice on cold interstellar dust. This approach assumes that the OPR of water desorbed from ice is related to the ice formation temperature on the dust. However, we report that water desorbed from ice at 10 kelvin shows a statistical high-temperatureOPRof 3, even when the ice is produced in situ by hydrogenation of O-2, a known formation process of interstellar water. This invalidates the assumed relation between OPR and temperature. The necessary reinterpretation of the low OPRs will help elucidate the chemical history of interstellar water from molecular clouds and processes in the early solar system, including comet formation.
  • K. Kuwahata, T. Hama, A. Kouchi, N. Watanabe
    PHYSICAL REVIEW LETTERS 115 (13) 133201  0031-9007 2015/09 [Refereed][Not invited]
     
    Reported here is the first observation of the tunneling surface diffusion of a hydrogen (H) atom on water ice. Photostimulated desorption and resonance-enhanced multiphoton ionization methods were used to determine the diffusion rates at 10 Kon amorphous solid water and polycrystalline ice. H-atom diffusion on polycrystalline ice was 2 orders of magnitude faster than that of deuterium atoms, indicating the occurrence of tunneling diffusion. Whether diffusion is by tunneling or thermal hopping also depends on the diffusion length of the atoms and the morphology of the surface. Our findings contribute to a better understanding of elementary physicochemical processes of hydrogen on cosmic ice dust.
  • 羽馬哲也, 香内晃, 渡部直樹
    日本物理学会誌 70 (8) 608 - 613 2015/08 [Refereed][Not invited]
  • Yasuhiro Oba, Naoki Watanabe, Yoshihiro Osamura, Akira Kouchi
    CHEMICAL PHYSICS LETTERS 634 53 - 59 0009-2614 2015/08 [Refereed][Not invited]
     
    We report experimental evidence that chiral glycine (NH2CHDCOOH) is formed by the surface reaction of normal glycine (NH2CH2COOH) solid with deuterium (D) atom at 12K under the simulative conditions of interstellar molecular clouds. Chiral glycine formation is most likely initiated by the tunneling abstraction reaction of H atom by D atom followed by the addition of D atom to the glycine radical (NH2CHCOOH). Given that chiral glycine can form in such a primordial low-temperature environment, it might source molecular chirality as molecular clouds evolve into planetary systems. (C) 2015 Elsevier B.V. All rights reserved.
  • Tetsuya Hama, Hirokazu Ueta, Akira Kouchi, Naoki Watanabe
    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 112 (24) 7438 - 7443 0027-8424 2015/06 [Refereed][Not invited]
     
    Classical transition-state theory is fundamental to describing chemical kinetics; however, quantum tunneling is also important in explaining the unexpectedly large reaction efficiencies observed in many chemical systems. Tunneling is often indicated by anomalously large kinetic isotope effects (KIEs), because a particle's ability to tunnel decreases significantly with its increasing mass. Here we experimentally demonstrate that cold hydrogen (H) and deuterium (D) atoms can add to solid benzene by tunneling; however, the observed H/D KIE was very small (1-1.5) despite the large intrinsic H/D KIE of tunneling (greater than or similar to 100). This strong reduction is due to the chemical kinetics being controlled not by tunneling but by the surface diffusion of the H/D atoms, a process not greatly affected by the isotope type. Because tunneling need not be accompanied by a large KIE in surface and interfacial chemical systems, it might be overlooked in other systems such as aerosols or enzymes. Our results suggest that surface tunneling reactions on interstellar dust may contribute to the deuteration of interstellar aromatic and aliphatic hydrocarbons, which could represent a major source of the deuterium enrichment observed in carbonaceous meteorites and interplanetary dust particles. These findings could improve our understanding of interstellar physicochemical processes, including those during the formation of the solar system.
  • Tetsuya Hama, Hirokazu Ueta, Akira Kouchi, Naoki Watanabe, Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 5 (21) 3843 - 3848 1948-7185 2014/11 [Refereed][Not invited]
     
    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.
  • Yasuhiro Oba, Kazuya Osaka, Naoki Watanabe, Takeshi Chigai, Akira Kouchi
    FARADAY DISCUSSIONS 168 185 - 204 1359-6640 2014/08 [Refereed][Not invited]
     
    We performed laboratory experiments on the formation of water and its isotopologues by surface reactions of hydrogen peroxide (H2O2) with hydrogen (H) atoms and their deuterated counterparts (D2O2, D) at 10-30 K. High-purity H2O2 (>95%) was prepared in situ by the codeposition of molecular oxygen and H atoms at relatively high temperatures (45-50 K). We determined that the high-purity H2O2 solid reacts with both H and deuterium (D) atoms at 10-30 K despite the large activation barriers (similar to 2000 K). Moreover, the reaction rate for H atoms is approximately 45 times faster than that for D atoms at 15 K. Thus, the observed large isotope effect indicates that these reactions occurred through quantum tunneling. We propose that the observed HDO/H2O ratio in molecular clouds might be a good tool for the estimation of the atomic D/H ratio in those environments.
  • Yasuhiro Oba, Takeshi Chigai, Yoshihiro Osamura, Naoki Watanabe, Akira Kouchi
    METEORITICS & PLANETARY SCIENCE 49 (1) 117 - 132 1086-9379 2014/01 [Refereed][Not invited]
     
    We experimentally studied hydrogen (H)-deuterium (D) substitution reactions of solid methylamine (CH3NH2) under astrophysically relevant conditions. We also calculated the potential energy surface for the H-D substitution reactions of methylamine isotopologues using quantum chemical methods. Despite the relatively large energy barrier of more than 18kJmol(-1), CH3NH2 reacted with D atoms to yield deuterated methylamines at 10K, suggesting that the H-D substitution reaction proceeds through quantum tunneling. Deuterated methylamines reacted with H atoms as well. On the basis of present results, we propose that methylamine has potential for D enrichment through atomic surface reactions on interstellar grains at very low temperatures in molecular clouds. D enrichment would occur in particular in the methyl group of methylamine.
  • Yasuhiro Oba, Takeshi Chigai, Yoshihiro Osamura, Naoki Watanabe, Akira Kouchi
    METEORITICS & PLANETARY SCIENCE 49 (1) 117 - 132 1086-9379 2014/01 [Refereed][Not invited]
     
    We experimentally studied hydrogen (H)-deuterium (D) substitution reactions of solid methylamine (CH3NH2) under astrophysically relevant conditions. We also calculated the potential energy surface for the H-D substitution reactions of methylamine isotopologues using quantum chemical methods. Despite the relatively large energy barrier of more than 18kJmol(-1), CH3NH2 reacted with D atoms to yield deuterated methylamines at 10K, suggesting that the H-D substitution reaction proceeds through quantum tunneling. Deuterated methylamines reacted with H atoms as well. On the basis of present results, we propose that methylamine has potential for D enrichment through atomic surface reactions on interstellar grains at very low temperatures in molecular clouds. D enrichment would occur in particular in the methyl group of methylamine.
  • Tetsuya Hama, Naoki Watanabe
    CHEMICAL REVIEWS 113 (12) 8783 - 8839 0009-2665 2013/12 [Refereed][Not invited]
  • N. Watanabe, T. Hama, A. Kouchi
    AIP Conference Proceedings 1543 308 - 316 2013 [Refereed][Invited]
  • Naoki Watanabe, Tetsuya Hama, Akira Kouchi
    FIRST INTERNATIONAL CONFERENCE ON CHEMICAL EVOLUTION OF STAR FORMING REGION AND ORIGIN OF LIFE (ASTROCHEM2012) 1543 308 - 316 0094-243X 2013 [Refereed][Invited]
     
    To clarify the meaning of the nuclear spin temperatures of H-2 and H2O molecules associated with various astronomical targets, it is important to understand the mechanisms that could alter these temperatures; i.e., the molecules' ortho/para nuclear-spin ratio (OPR). We have performed a series of experiments to investigate how the OPRs of H-2 and H2O behave on the surface of amorphous solid water (ASW), which is analogous to cosmic ice dust. The OPR of H-2 initially shows a high temperature limit of 3 upon its formation through H-H recombination at similar to 10 K and gradually decreases toward lower temperatures on the surface. The spin temperatures of H2O molecules that are thermally desorbed from various types of ASW at similar to 10 K always return the high-temperature limit.
  • H. Hidaka, M. Watanabe, A. Kouchi, N. Watanabe
    FIRST INTERNATIONAL CONFERENCE ON CHEMICAL EVOLUTION OF STAR FORMING REGION AND ORIGIN OF LIFE (ASTROCHEM2012) 1543 318 - 325 0094-243X 2013 [Refereed][Not invited]
     
    The elucidation of formation pathways and mechanisms of deuterated species that have been detected by astronomical observations is important in studying chemical evolution in space. Formaldehyde and methanol are well-known molecules not only as reaction products on grain surfaces, but also as highly deuterated molecules. We have conducted experimental studies to clarify the formation mechanisms of deuterated formaldehyde and methanol on low temperature solid surfaces. In this paper, we summarize our experimental findings of the exposure of solid H2CO and D2CO on amorphous solid water to D and H atoms at 10-20 K, respectively. The isotope exchange reactions were observed in both reaction systems of D + H2CO and H + D2CO. In contrast, the addition reactions were only observed in the H + D2CO system because D addition to H2CO is much slower than isotope exchange. This isotope dependence on the reaction pathways can be explained by the quantum tunneling effect.
  • Tetsuya Hama, Kazuaki Kuwahata, Naoki Watanabe, Akira Kouchi, Yuki Kimura, Takeshi Chigai, Valerio Pirronello
    ASTROPHYSICAL JOURNAL 757 (2) 185 - (12pp) 0004-637X 2012/10 [Refereed][Not invited]
     
    To understand elementary processes leading to H-2 formation, and the hydrogenation and deuteration reactions of adsorbed species on dust grains in dense clouds, we experimentally investigated the diffusion of atomic hydrogen and deuterium on amorphous solidwater (ASW) at temperatures of 8-15 K. The present study extended our previous study for selective detections of H and D atoms, and of H-2 (J = 0 and 1) and D-2 (J = 0 and 1) molecules adsorbed on ASW using both photo-stimulated desorption and resonance-enhanced multiphoton ionization, to investigate potential sites on ASW for diffusion, recombination dynamics, and the diffusion mechanism of H and D atoms. Our results demonstrate that the ASW surface contains various potential sites that can be categorized into at least three groups: very shallow, middle-, and deep-potential sites, with diffusion activation energies of <= 18, 22 (23 meV for D atoms), and >= 30 meV, respectively. The present study pictured the outline of H-2 formation on cosmic ice dust at low temperatures: H atoms landing on the dust will diffuse rapidly at the abundant shallow and middle sites on ASW, and finally become trapped at deep sites. The H atoms that arrive next recombine with such trapped H atoms to yield H-2 molecules. The small isotopic difference between the diffusion of H and D atoms on ASW indicates that the diffusion mechanism can be explained by thermal hopping, at least at middle-potential sites.
  • Tetsuya Hama, Kazuaki Kuwahata, Naoki Watanabe, Akira Kouchi, Yuki Kimura, Takeshi Chigai, Valerio Pirronello
    ASTROPHYSICAL JOURNAL 757 (2) 185 - (12pp) 0004-637X 2012/10 [Refereed][Not invited]
     
    To understand elementary processes leading to H-2 formation, and the hydrogenation and deuteration reactions of adsorbed species on dust grains in dense clouds, we experimentally investigated the diffusion of atomic hydrogen and deuterium on amorphous solidwater (ASW) at temperatures of 8-15 K. The present study extended our previous study for selective detections of H and D atoms, and of H-2 (J = 0 and 1) and D-2 (J = 0 and 1) molecules adsorbed on ASW using both photo-stimulated desorption and resonance-enhanced multiphoton ionization, to investigate potential sites on ASW for diffusion, recombination dynamics, and the diffusion mechanism of H and D atoms. Our results demonstrate that the ASW surface contains various potential sites that can be categorized into at least three groups: very shallow, middle-, and deep-potential sites, with diffusion activation energies of <= 18, 22 (23 meV for D atoms), and >= 30 meV, respectively. The present study pictured the outline of H-2 formation on cosmic ice dust at low temperatures: H atoms landing on the dust will diffuse rapidly at the abundant shallow and middle sites on ASW, and finally become trapped at deep sites. The H atoms that arrive next recombine with such trapped H atoms to yield H-2 molecules. The small isotopic difference between the diffusion of H and D atoms on ASW indicates that the diffusion mechanism can be explained by thermal hopping, at least at middle-potential sites.
  • Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    ASTROPHYSICAL JOURNAL 749 (1) 67 - (12pp) 0004-637X 2012/04 [Refereed][Not invited]
     
    The present study experimentally demonstrated that solid H2O is formed through the surface reaction OH + H-2 at 10 K. This is the first experimental evidence of solid H2O formation using hydrogen in its molecular form at temperatures as low as 10 K. We further found that H2O formation through the reaction OH + H-2 is about one order of magnitude more effective than HDO formation through the reaction OH + D-2. This significant isotope effect results from differences in the effective mass of each reaction, indicating that the reactions proceed through quantum tunneling.
  • Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    ASTROPHYSICAL JOURNAL 749 (1) 67 - (12pp) 0004-637X 2012/04 [Refereed][Not invited]
     
    The present study experimentally demonstrated that solid H2O is formed through the surface reaction OH + H-2 at 10 K. This is the first experimental evidence of solid H2O formation using hydrogen in its molecular form at temperatures as low as 10 K. We further found that H2O formation through the reaction OH + H-2 is about one order of magnitude more effective than HDO formation through the reaction OH + D-2. This significant isotope effect results from differences in the effective mass of each reaction, indicating that the reactions proceed through quantum tunneling.
  • 渡部 直樹, 香内 晃, 羽馬 哲也, 日高 宏, 大場 康弘, 千貝 健
    表面科学 33 662 - 668 2012 [Refereed][Not invited]
  • Yasuhiro Oba, Naoki Watanabe, Akira Kouchi, Tetsuya Hama, Valerio Pirronello
    Physical Chemistry Chemical Physics 13 (35) 15792 - 15797 1463-9076 2011/09/21 [Refereed][Not invited]
     
    We investigated the OH-related formation routes of two astrophysically important molecules, H2O and CO2, under relatively warm astrophysical conditions. OH radicals, together with other neutral species such as H, O, H2, and O2, were produced in H2O microwave-discharge plasma and cooled to 100 K before being deposited on an Al substrate at 40-60 K. H2O formed at 40 and 50 K, but not at 60 K. Taking the experimental conditions into account, a possible route of H 2O formation is via reactions involving OH + OH, which yield H 2O2 as the main reaction product. The present study is the first to show experimentally that surface reactions of two OH radicals can yield H2O at low temperatures. The products' branching ratio was 0.2 and 0.8 for H2O and H2O2, respectively. When CO was co-deposited with neutral species that formed in the H2O plasma, CO2 was formed at 40-60 K. H2CO3 formed at 40 and 50 K. The present results may suggest that chemical reactions related to OH radicals are effective at yielding various molecules in relatively warm astrophysical environments, such as protostars. © 2011 the Owner Societies.
  • T. Hama, N. Watanabe, A. Kouchi, M. Yokoyama
    ASTROPHYSICAL JOURNAL LETTERS 738 (1) L15 - (5pp) 2041-8205 2011/09 [Refereed][Not invited]
     
    The nuclear-spin temperature of molecules observed in interstellar space or cometary coma is an important key to understanding physical and chemical histories of the molecules. The present Letter reports measurements of nuclear-spin states and rotational temperatures of thermally desorbed H2O molecules from amorphous solid water (ASW) by combining temperature-programmed desorption and resonance-enhanced multiphoton ionization (REMPI). REMPI spectra of desorbed H2O molecules were measured at similar to 150 K from vapor-deposited ASW at 8 K. The nuclear-spin temperature of desorbed H2O molecules exhibits almost an upper limit to the ortho-to-para ratio of close to 3. No discernible change was observed in the H2O REMPI spectrum, neither after leaving the deposited ASW for 9 days in a vacuum chamber at 8 K, nor in the presence of O-2 molecules, nor upon exposure of ASW to vacuum-ultraviolet (VUV) photons. Desorbed H2O molecules were also investigated from ASW produced by VUV irradiation of a CH4/O-2 mixture at 8 K. The resulting H2O spectrum showed a high nuclear-spin temperature. These results suggest that the nuclear-spin temperatures of gaseous H2O molecules thermally desorbed from ice do not necessarily reflect the surface temperature at which H2O molecules condensed or formed under some laboratory conditions. We discuss the possibility of nuclear-spin conversion of H2O in water ice. The present study advocates the importance of further studies to give an interpretation of nuclear-spin temperatures of molecules observed in interstellar space or cometary coma.
  • T. Hama, N. Watanabe, A. Kouchi, M. Yokoyama
    ASTROPHYSICAL JOURNAL LETTERS 738 (1) L15 - (5pp) 2041-8205 2011/09 [Refereed][Not invited]
     
    The nuclear-spin temperature of molecules observed in interstellar space or cometary coma is an important key to understanding physical and chemical histories of the molecules. The present Letter reports measurements of nuclear-spin states and rotational temperatures of thermally desorbed H2O molecules from amorphous solid water (ASW) by combining temperature-programmed desorption and resonance-enhanced multiphoton ionization (REMPI). REMPI spectra of desorbed H2O molecules were measured at similar to 150 K from vapor-deposited ASW at 8 K. The nuclear-spin temperature of desorbed H2O molecules exhibits almost an upper limit to the ortho-to-para ratio of close to 3. No discernible change was observed in the H2O REMPI spectrum, neither after leaving the deposited ASW for 9 days in a vacuum chamber at 8 K, nor in the presence of O-2 molecules, nor upon exposure of ASW to vacuum-ultraviolet (VUV) photons. Desorbed H2O molecules were also investigated from ASW produced by VUV irradiation of a CH4/O-2 mixture at 8 K. The resulting H2O spectrum showed a high nuclear-spin temperature. These results suggest that the nuclear-spin temperatures of gaseous H2O molecules thermally desorbed from ice do not necessarily reflect the surface temperature at which H2O molecules condensed or formed under some laboratory conditions. We discuss the possibility of nuclear-spin conversion of H2O in water ice. The present study advocates the importance of further studies to give an interpretation of nuclear-spin temperatures of molecules observed in interstellar space or cometary coma.
  • Tetsuya Hama, Masaaki Yokoyama, Akihiro Yabushita, Masahiro Kawasaki, Naoki Watanabe
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 269 (9) 1011 - 1015 0168-583X 2011/05 [Refereed][Not invited]
     
    Water ice is the major solid component in a variety of astrophysical environments, e.g., cold and dense molecular clouds. Photodesorption plays a dominant role in consuming ice in such cold regions. In this study, photodesorption of vibrationally ground-state H(2)O(v = 0) from amorphous solid water has been investigated at 157 nm. Using a resonance-enhanced multiphoton ionization technique, the translational and rotational energy distributions of photodesorbed H(2)O(v = 0) were measured, i.e., Boltzmann distributions at 1800 and 300 K, respectively. These energies are in good accordance with those predicted by classical molecular calculations for water photodesorption due to a kick-out mechanism following absorption of a single photon; hot H atom released by photodissociation of H(2)O in ice transfers enough momentum to another H(2)O molecule to kick it off the surface. Desorption of D(2)O(v = 0) following 193 nm photoirradiation of a D(2)O/H(2)S mixed ice was investigated to provide further direct evidence for the operation of a kick-out mechanism. The other desorption mechanisms were also discussed in the context of possible photodesorption of vibrationally excited H(2)O. (c) 2010 Elsevier B.V. All rights reserved.
  • Tetsuya Hama, Masaaki Yokoyama, Akihiro Yabushita, Masahiro Kawasaki, Naoki Watanabe
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 269 (9) 1011 - 1015 0168-583X 2011/05 [Refereed][Not invited]
     
    Water ice is the major solid component in a variety of astrophysical environments, e.g., cold and dense molecular clouds. Photodesorption plays a dominant role in consuming ice in such cold regions. In this study, photodesorption of vibrationally ground-state H(2)O(v = 0) from amorphous solid water has been investigated at 157 nm. Using a resonance-enhanced multiphoton ionization technique, the translational and rotational energy distributions of photodesorbed H(2)O(v = 0) were measured, i.e., Boltzmann distributions at 1800 and 300 K, respectively. These energies are in good accordance with those predicted by classical molecular calculations for water photodesorption due to a kick-out mechanism following absorption of a single photon; hot H atom released by photodissociation of H(2)O in ice transfers enough momentum to another H(2)O molecule to kick it off the surface. Desorption of D(2)O(v = 0) following 193 nm photoirradiation of a D(2)O/H(2)S mixed ice was investigated to provide further direct evidence for the operation of a kick-out mechanism. The other desorption mechanisms were also discussed in the context of possible photodesorption of vibrationally excited H(2)O. (c) 2010 Elsevier B.V. All rights reserved.
  • 大場 康弘, 渡部 直樹, 香内 晃, 羽馬 哲也, ピロネロ バレリオ
    地球化学 45 213 - 226 2011 [Refereed][Not invited]
  • Takashi Kinugawa, Akihiro Yabushita, Masahiro Kawasaki, Tetsuya Hama, Naoki Watanabe
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 (35) 15785 - 15791 1463-9076 2011 [Refereed][Not invited]
     
    Photodissociation of amorphous ice films of carbon dioxide and water co-adsorbed at 90 K was carried out at 157 nm using oxygen-16 and -18 isotopomers with a time-of-flight photofragment mass spectrometer. O(P-3(J)) atoms, OH (v = 0) radicals, and CO (v = 0,1) molecules were detected as photofragments. CO is produced directly from the photodissociation of CO2. Two different adsorption states of CO2, i.e., physisorbed CO2 on the surface of amorphous solid water and trapped CO2 in the pores of the film, are clearly distinguished by the translational and internal energy distributions of the CO molecules. The O atom and OH radical are produced from the photodissociation of H2O. Since the absorption cross section of CO2 is smaller than that of H2O at 157 nm, the CO2 surface abundance is relatively increased after prolonged photoirradiation of the mixed ice film, resulting in the formation of a heterogeneously layered structure in the mixed ice at low temperatures. Astrophysical implications are discussed.
  • Hiroshi Hidaka, Motohiro Watanabe, Akira Kouchi, Naoki Watanabe
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 (35) 15798 - 15802 1463-9076 2011 [Refereed][Not invited]
     
    A Fourier transform infrared absorption spectroscopy (FTIR) study showed that NH3 was formed by the successive reaction of hydrogen atoms with nitrogen atoms in an N-2 matrix at 10 K. Reactions appeared to proceed via the Langmuir-Hinshelwood mechanism because NH3 formation was not observed at 20 K. At this temperature, H atoms did not adsorb significantly onto the N-2 matrix; i.e., the surface residence times were short. Furthermore, NH3 yields via the successive hydrogenation of N atoms were significant, even after H atom deposition onto the N-2 matrix containing trapped N atoms onto which had been deposited a superficial pure solid N-2 adlayer. This result clearly indicates that H atoms diffuse in pure solid N-2 matrices at 10 K.
  • Laboratory investigations of physico-chemical processes occurring in icy mantles on interstellar dust grains
    V. Pirronello, M. Accolla, T. Hama, H. Hidaka, A. Kouchi, G. Manico, Y. Oba, N. Watanabe
    Physics and Chemistry of ice 2010 361 - 368 2011 [Refereed][Not invited]
  • Hiroshi Hidaka, Motohiro Watanabe, Akira Kouchi, Naoki Watanabe
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 (35) 15798 - 15802 1463-9076 2011 [Refereed][Not invited]
     
    A Fourier transform infrared absorption spectroscopy (FTIR) study showed that NH3 was formed by the successive reaction of hydrogen atoms with nitrogen atoms in an N-2 matrix at 10 K. Reactions appeared to proceed via the Langmuir-Hinshelwood mechanism because NH3 formation was not observed at 20 K. At this temperature, H atoms did not adsorb significantly onto the N-2 matrix; i.e., the surface residence times were short. Furthermore, NH3 yields via the successive hydrogenation of N atoms were significant, even after H atom deposition onto the N-2 matrix containing trapped N atoms onto which had been deposited a superficial pure solid N-2 adlayer. This result clearly indicates that H atoms diffuse in pure solid N-2 matrices at 10 K.
  • Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    Phys. Chem. Chem. Phys. 13 (35) 15792 - 15797 1463-9076 2011 [Refereed][Not invited]
  • Takashi Kinugawa, Akihiro Yabushita, Masahiro Kawasaki, Tetsuya Hama, Naoki Watanabe
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 (35) 15785 - 15791 1463-9076 2011 [Refereed][Not invited]
     
    Photodissociation of amorphous ice films of carbon dioxide and water co-adsorbed at 90 K was carried out at 157 nm using oxygen-16 and -18 isotopomers with a time-of-flight photofragment mass spectrometer. O(P-3(J)) atoms, OH (v = 0) radicals, and CO (v = 0,1) molecules were detected as photofragments. CO is produced directly from the photodissociation of CO2. Two different adsorption states of CO2, i.e., physisorbed CO2 on the surface of amorphous solid water and trapped CO2 in the pores of the film, are clearly distinguished by the translational and internal energy distributions of the CO molecules. The O atom and OH radical are produced from the photodissociation of H2O. Since the absorption cross section of CO2 is smaller than that of H2O at 157 nm, the CO2 surface abundance is relatively increased after prolonged photoirradiation of the mixed ice film, resulting in the formation of a heterogeneously layered structure in the mixed ice at low temperatures. Astrophysical implications are discussed.
  • Yasuhiro Oba, Naoki Watanabe, Akira Kouchi, Tetsuya Hama, Valerio Pirronello
    ASTROPHYSICAL JOURNAL 722 (2) 1598 - 1606 0004-637X 2010/10 [Refereed][Not invited]
     
    We present the experimental results of carbonic acid (H2CO3) formation through surface reactions of CO molecules with non-energetic hydroxyl (OH) radicals at 10-40 K. The formation of H2CO3 was clearly identified both in the IR spectra and in the thermally programmed desorption mass spectra. The H2CO3 yield was rather high, amounting to approximately 40%-70% relative to that of CO2 formed by the reaction of CO with OH. The structure of H2CO3 formed by reactions of CO with OH may differ from that formed by energetic processes such as UV irradiation, ion irradiation, and electron irradiation of H2O/CO2 binary ices. In this paper, we envisage some of the possible roles H2CO3 may have in the interstellar medium, such as enriching grain mantles of new molecules via acid-base reactions with basic species and contributing to the formation of the unidentified band at 6.8 mu m; we suggest possible reasons for its non-detection yet and discuss the restoration of carbonic acid molecules in the gas phase.
  • Yasuhiro Oba, Naoki Watanabe, Akira Kouchi, Tetsuya Hama, Valerio Pirronello
    ASTROPHYSICAL JOURNAL 722 (2) 1598 - 1606 0004-637X 2010/10 [Refereed][Not invited]
     
    We present the experimental results of carbonic acid (H2CO3) formation through surface reactions of CO molecules with non-energetic hydroxyl (OH) radicals at 10-40 K. The formation of H2CO3 was clearly identified both in the IR spectra and in the thermally programmed desorption mass spectra. The H2CO3 yield was rather high, amounting to approximately 40%-70% relative to that of CO2 formed by the reaction of CO with OH. The structure of H2CO3 formed by reactions of CO with OH may differ from that formed by energetic processes such as UV irradiation, ion irradiation, and electron irradiation of H2O/CO2 binary ices. In this paper, we envisage some of the possible roles H2CO3 may have in the interstellar medium, such as enriching grain mantles of new molecules via acid-base reactions with basic species and contributing to the formation of the unidentified band at 6.8 mu m; we suggest possible reasons for its non-detection yet and discuss the restoration of carbonic acid molecules in the gas phase.
  • Naoki Watanabe, Yuki Kimura, Akira Kouchi, Takeshi Chigai, Tetsuya Hama, Valerio Pirronello
    ASTROPHYSICAL JOURNAL LETTERS 714 (2) L233 - L237 2041-8205 2010/05 [Refereed][Not invited]
     
    Physicochemical processes (H-atom sticking, diffusion, recombination, and the nuclear spin temperature of nascent H-2 molecules) important in the formation of molecular hydrogen have been experimentally investigated on amorphous solid water (ASW). A new type of experiment is performed to shed light on a longstanding dispute. The diffusion rate of H atom is directly measured at 8 K and is found to consist of a fast and a slow component due to the presence of at least two types of potential sites with the energy depths of similar to 20 and >50 meV, respectively. The fast diffusion at the shallow sites enables efficient H-2 formation on interstellar ice dust even at 8 K, while H atoms trapped in the deeper sites hardly migrate. The spin temperature of nascent H-2 formed by recombination on ASW has been obtained for the first time and is higher than approximately 200 K. After formation, H-2 molecules are trapped and their spin temperature decreases due to the conversion of spin states on ASW.
  • Eui-Seong Moon, Heon Kang, Yasuhiro Oba, Naoki Watanabe, Akira Kouchi
    ASTROPHYSICAL JOURNAL 713 (2) 906 - 911 0004-637X 2010/04 [Refereed][Not invited]
     
    We present direct evidence for ammonium ion (NH4+) formation through ultraviolet (UV) photolysis of NH3-H2O mixture ice that does not contain acids. NH4+ forms by the reaction of NH3 with protonic defects (H3O+) in the UV-photolyzed ice. Our observations may explain the deficient counter-anions in interstellar ice relative to the abundance of NH4+. Also, H3O+ may play an important role in the acid-base chemistry of interstellar ice in UV-irradiating environments. IR absorption results suggest that NH4+ is a potential contributor to the interstellar 6.85 mu m band but is not a dominant component.
  • Tetsuya Hama, Masaaki Yokoyama, Akihiro Yabushita, Masahiro Kawasaki, Stefan Andersson, Colin M. Western, Michael N. R. Ashfold, Richard N. Dixon, Naoki Watanabe
    JOURNAL OF CHEMICAL PHYSICS 132 (16) 164508  0021-9606 2010/04 [Refereed][Not invited]
     
    Following 157 nm photoexcitation of amorphous solid water and polycrystalline water ice, photodesorbed water molecules (H(2)O and D(2)O), in the ground vibrational state, have been observed using resonance-enhanced multiphoton ionization detection methods. Time-of-flight and rotationally resolved spectra of the photodesorbed water molecules were measured, and the kinetic and internal energy distributions were obtained. The measured energy distributions are in good accord with those predicted by classical molecular dynamics calculations for the kick-out mechanism of a water molecule from the ice surface by a hot hydrogen (deuterium) atom formed by photodissociation of a neighboring water molecule. Desorption of D(2)O following 193 nm photoirradiation of a D(2)O/H(2)S mixed ice was also investigated to provide further direct evidence for the operation of a kick-out mechanism. (C) 2010 American Institute of Physics. [doi:10.1063/1.3386577]
  • Yasuhiro Oba, Naoki Watanabe, Akira Kouchi, Tetsuya Hama, Valerio Pirronello
    ASTROPHYSICAL JOURNAL LETTERS 712 (2) L174 - L178 2041-8205 2010/04 [Refereed][Not invited]
     
    Surface reactions between carbon monoxide and non-energetic hydroxyl radicals were carried out at 10 K and 20 K in order to investigate possible reaction pathways to yield carbon dioxide in dense molecular clouds. Hydroxyl radicals, produced by dissociating water molecules in microwave-induced plasma, were cooled down to 100 K prior to the introduction of CO. The abundances of species were monitored in situ using a Fourier transform infrared spectrometer. Formation of CO2 was clearly observed, even at 10 K, suggesting that reactions of CO with OH proceed with little or no activation barrier. The present results indicate that CO2 formation, due to reactions between CO and OH, occurs in tandem with H2O formation, and this may lead to the formation of CO2 ice in polar environments, as typically observed in molecular clouds.
  • Tetsuya Hama, Masaaki Yokoyama, Akihiro Yabushita, Masahiro Kawasaki, Stefan Andersson, Colin M. Western, Michael N. R. Ashfold, Richard N. Dixon, Naoki Watanabe
    JOURNAL OF CHEMICAL PHYSICS 132 (16) 164508  0021-9606 2010/04 [Refereed][Not invited]
     
    Following 157 nm photoexcitation of amorphous solid water and polycrystalline water ice, photodesorbed water molecules (H(2)O and D(2)O), in the ground vibrational state, have been observed using resonance-enhanced multiphoton ionization detection methods. Time-of-flight and rotationally resolved spectra of the photodesorbed water molecules were measured, and the kinetic and internal energy distributions were obtained. The measured energy distributions are in good accord with those predicted by classical molecular dynamics calculations for the kick-out mechanism of a water molecule from the ice surface by a hot hydrogen (deuterium) atom formed by photodissociation of a neighboring water molecule. Desorption of D(2)O following 193 nm photoirradiation of a D(2)O/H(2)S mixed ice was also investigated to provide further direct evidence for the operation of a kick-out mechanism. (C) 2010 American Institute of Physics. [doi:10.1063/1.3386577]
  • Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    Astrophys. J. Lett. 712 (2,Pt.2) L174 - L178 0004-637X 2010 [Refereed][Not invited]
  • N. Watanabe, Y. Kimura, A. Kouchi, T. Chigai, T. Hama, V. Pirronello
    Astrophys. J. Lett. 714 (2,Pt.2) L233 - L237 0004-637X 2010 [Refereed][Not invited]
  • N. Watanabe, Y. Kimura, A. Kouchi, T. Chigai, T. Hama, V. Pirronello
    Astrophys. J. Lett. 714 (2,Pt.2) L233 - L237 0004-637X 2010 [Refereed][Not invited]
  • E-S. Moon, H. Kang, Y. Oba, N. Watanabe, A. Kouchi
    Astrophys. J. 713 (2,Pt.1) 906 - 911 0004-637X 2010 [Refereed][Not invited]
  • Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    Astrophys. J. Lett. 712 (2,Pt.2) L174 - L178 0004-637X 2010 [Refereed][Not invited]
  • Hiroshi Hidaka, Motohiro Watanabe, Akira Kouchi, Naoki Watanabe
    Journal of Physics: Conference Series 194 (13) 132024  1742-6596 2009/12/24 [Refereed][Not invited]
     
    Reaction routes when H2CO and D2CO were exposed to the D and H atoms on amorphous solid water (ASW) at 10-20 K, respectively, were studied experimentally by IR spectroscopy. For D + H2CO on ASW, H2CO was converted to HDCO and D2CO by the H-D substitution reactions. Although CD3OD was slightly observed, doubly- and triply-deuterated methanol, CH2DOD and CHD2OD, were not observed. This implies that the D additions to H2CO (formation of deuterated methanol) is a minor reaction route. On the other hand, for H + D2CO, H addition reactions to form CHD2OH proceed significantly as much as conversions to HDCO and H2CO, which evolve to CH2DOH and CH3OH by the further H additions, respectively. Therefore, in this reaction system, two kind of reaction routes for D2CO HDCO H2CO CH3OH and D2CO CHD2OH are competitive.
  • Hiroshi Hidaka, Motohiro Watanabe, Akira Kouchi, Naoki Watanabe
    Journal of Physics: Conference Series 194 (13) 132024  1742-6596 2009/12/24 [Refereed][Not invited]
     
    Reaction routes when H2CO and D2CO were exposed to the D and H atoms on amorphous solid water (ASW) at 10-20 K, respectively, were studied experimentally by IR spectroscopy. For D + H2CO on ASW, H2CO was converted to HDCO and D2CO by the H-D substitution reactions. Although CD3OD was slightly observed, doubly- and triply-deuterated methanol, CH2DOD and CHD2OD, were not observed. This implies that the D additions to H2CO (formation of deuterated methanol) is a minor reaction route. On the other hand, for H + D2CO, H addition reactions to form CHD2OH proceed significantly as much as conversions to HDCO and H2CO, which evolve to CH2DOH and CH3OH by the further H additions, respectively. Therefore, in this reaction system, two kind of reaction routes for D2CO HDCO H2CO CH3OH and D2CO CHD2OH are competitive.
  • H. Hidaka, M. Watanabe, A. Kouchi, N. Watanabe
    ASTROPHYSICAL JOURNAL 702 (1) 291 - 300 0004-637X 2009/09 [Refereed][Not invited]
     
    Grain surface reaction has been expected to be a key process for deuterium enrichment in interstellar molecules. We focus on formaldehyde, which is predicted to be formed on cold grain surface in astrophysical models and is known to be deuterium-enriched in a molecular cloud. Reaction routes and effective reaction rate constants are experimentally investigated when H2CO and D2CO are exposed to D and H atoms on amorphous solid water (ASW) at 10-20 K, respectively. For D + H2CO on ASW, H2CO was converted to HDCO and D2CO by the H-D substitution reactions. Although CD3OD was slightly observed, doubly and triply deuterated methanol, CH2DOD and CHD2OD, were not observed. This implies that D addition to H2CO (formation of deuterated methanol) is a minor reaction route. On the other hand, for H + D2CO, H addition reactions to form CHD2OH proceed at a significant rate. Simultaneously, a competitive reaction, the substitution reaction by H atoms and subsequent H addition (D2CO -> HDCO -> H2CO -> CH3OH) also proceed at a significant rate. However, no H addition to HDCO was observed. The effective surface reaction routes when CO is exposed to H and D atoms are summarized using the present experimental results and the previous results of our group.
  • Tetsuya Hama, Akihiro Yabushita, Masaaki Yokoyama, Masahiro Kawasaki, Naoki Watanabe
    JOURNAL OF CHEMICAL PHYSICS 131 (11) 114510  0021-9606 2009/09 [Refereed][Not invited]
     
    Vacuum ultraviolet photolysis of water ice in the first absorption band was studied at 157 nm. Translational and internal energy distributions of the desorbed species, O(D-1) and OH(nu= 0,1), were directly measured with resonance-enhanced multiphoton ionization method. Two different mechanisms are discussed for desorption of electronically excited O(D-1) atoms from the ice surface. One is unimolecular dissociation of H2O to H-2+O(D-1) as a primary photoprocess. The other is the surface recombination reaction of hot OH radicals that are produced from photodissociation of hydrogen peroxide as a secondary photoprocess. H2O2 is one of the major photoproducts in the vacuum ultraviolet photolysis of water ice. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3194798]
  • Tetsuya Hama, Akihiro Yabushita, Masaaki Yokoyama, Masahiro Kawasaki, Naoki Watanabe
    JOURNAL OF CHEMICAL PHYSICS 131 (11) 114511  0021-9606 2009/09 [Refereed][Not invited]
     
    Desorption of ground state O(P-3(J= 2,1,0)) atoms following the vacuum ultraviolet photolysis of water ice in the first absorption band was directly measured with resonance-enhanced multiphoton ionization (REMPI) method. Based on their translational energy distributions and evolution behavior, two different formation mechanisms are proposed: One is exothermic recombination reaction of OH radicals, OH+OH -> H2O+O(P-3(J)) and the other is the photodissociation of OH radicals on the surface of amorphous solid water. The translational and internal energy distributions of OH radicals as well as the evolution behavior were also measured by REMPI to elucidate the roles of H2O2 and OH in the O(P-3(J)) formation mechanisms. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3194797]
  • Tetsuya Hama, Akihiro Yabushita, Masaaki Yokoyama, Masahiro Kawasaki, Naoki Watanabe
    JOURNAL OF CHEMICAL PHYSICS 131 (11) 114510  0021-9606 2009/09 [Refereed][Not invited]
     
    Vacuum ultraviolet photolysis of water ice in the first absorption band was studied at 157 nm. Translational and internal energy distributions of the desorbed species, O(D-1) and OH(nu= 0,1), were directly measured with resonance-enhanced multiphoton ionization method. Two different mechanisms are discussed for desorption of electronically excited O(D-1) atoms from the ice surface. One is unimolecular dissociation of H2O to H-2+O(D-1) as a primary photoprocess. The other is the surface recombination reaction of hot OH radicals that are produced from photodissociation of hydrogen peroxide as a secondary photoprocess. H2O2 is one of the major photoproducts in the vacuum ultraviolet photolysis of water ice. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3194798]
  • H. Hidaka, M. Watanabe, A. Kouchi, N. Watanabe
    ASTROPHYSICAL JOURNAL 702 (1) 291 - 300 0004-637X 2009/09 [Refereed][Not invited]
     
    Grain surface reaction has been expected to be a key process for deuterium enrichment in interstellar molecules. We focus on formaldehyde, which is predicted to be formed on cold grain surface in astrophysical models and is known to be deuterium-enriched in a molecular cloud. Reaction routes and effective reaction rate constants are experimentally investigated when H2CO and D2CO are exposed to D and H atoms on amorphous solid water (ASW) at 10-20 K, respectively. For D + H2CO on ASW, H2CO was converted to HDCO and D2CO by the H-D substitution reactions. Although CD3OD was slightly observed, doubly and triply deuterated methanol, CH2DOD and CHD2OD, were not observed. This implies that D addition to H2CO (formation of deuterated methanol) is a minor reaction route. On the other hand, for H + D2CO, H addition reactions to form CHD2OH proceed at a significant rate. Simultaneously, a competitive reaction, the substitution reaction by H atoms and subsequent H addition (D2CO -> HDCO -> H2CO -> CH3OH) also proceed at a significant rate. However, no H addition to HDCO was observed. The effective surface reaction routes when CO is exposed to H and D atoms are summarized using the present experimental results and the previous results of our group.
  • Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
    ASTROPHYSICAL JOURNAL 701 (1) 464 - 470 0004-637X 2009/08 [Refereed][Not invited]
     
    Formation of H2O molecules through the codeposition of oxygen molecules and hydrogen atoms is examined in situ using IR spectroscopy at 10-40 K under various O-2 and H fluxes. It is found that H2O and H2O2 are continuously formed by reaction, even at 40 K. The H2O ice formed is amorphous, but has a compact (not microporous) structure compared to vapor-deposited amorphous H2O ice, because dangling OH bonds are not observed in the IR spectrum. This is consistent with astronomical observations in molecular clouds and theoretical predictions, which suggest that hydrogenation of O-2 is one of the potential routes for reproducing these IR spectral characteristics. The composition of the ice formed by codeposition varies with the O-2/H ratio and temperature. Although no data are available at present for the H2O/H2O2 ratio of ice in molecular clouds, this study suggests that hydrogenation of O-2 has a potential to yield a H2O/H2O2 ratio of 5 or more in molecular clouds.
  • Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
    ASTROPHYSICAL JOURNAL 701 (1) 464 - 470 0004-637X 2009/08 [Refereed][Not invited]
     
    Formation of H2O molecules through the codeposition of oxygen molecules and hydrogen atoms is examined in situ using IR spectroscopy at 10-40 K under various O-2 and H fluxes. It is found that H2O and H2O2 are continuously formed by reaction, even at 40 K. The H2O ice formed is amorphous, but has a compact (not microporous) structure compared to vapor-deposited amorphous H2O ice, because dangling OH bonds are not observed in the IR spectrum. This is consistent with astronomical observations in molecular clouds and theoretical predictions, which suggest that hydrogenation of O-2 is one of the potential routes for reproducing these IR spectral characteristics. The composition of the ice formed by codeposition varies with the O-2/H ratio and temperature. Although no data are available at present for the H2O/H2O2 ratio of ice in molecular clouds, this study suggests that hydrogenation of O-2 has a potential to yield a H2O/H2O2 ratio of 5 or more in molecular clouds.
  • Akihiro Yabushita, Tetsuya Hama, Masaaki Yokoyama, Masahiro Kawasaki, Stefan Andersson, Richard N. Dixon, Michael N. R. Ashfold, Naoki Watanabe
    ASTROPHYSICAL JOURNAL LETTERS 699 (2) L80 - L83 2009/07 [Refereed][Not invited]
     
    For interstellar grains coated with water ice, the most important desorption mechanism at the edge of molecular clouds is photodesorption of water. To reveal details of the photodesorption mechanism, we have measured the translational and rotational energies of H(2)O (v = 0) molecules photodesorbed from amorphous solid water and polycrystalline ice following excitation within the first absorption band using a 157 nm laser. The measured translational and rotational temperatures are 1800 K and 300 K, respectively. These energies are in good accord with those predicted by classical molecular dynamics calculations for the "kick-out" of an H(2)O molecule in the ice by an energetic H atom. The statistical ortho: para ratio of g(OPR) = 3 is appropriate for the Boltzmann rotational distribution of the H(2)O molecules.
  • Akihiro Yabushita, Tetsuya Hama, Masaaki Yokoyama, Masahiro Kawasaki, Stefan Andersson, Richard N. Dixon, Michael N. R. Ashfold, Naoki Watanabe
    ASTROPHYSICAL JOURNAL LETTERS 699 (2) L80 - L83 2009/07 [Refereed][Not invited]
     
    For interstellar grains coated with water ice, the most important desorption mechanism at the edge of molecular clouds is photodesorption of water. To reveal details of the photodesorption mechanism, we have measured the translational and rotational energies of H(2)O (v = 0) molecules photodesorbed from amorphous solid water and polycrystalline ice following excitation within the first absorption band using a 157 nm laser. The measured translational and rotational temperatures are 1800 K and 300 K, respectively. These energies are in good accord with those predicted by classical molecular dynamics calculations for the "kick-out" of an H(2)O molecule in the ice by an energetic H atom. The statistical ortho: para ratio of g(OPR) = 3 is appropriate for the Boltzmann rotational distribution of the H(2)O molecules.
  • 宇宙における水分子生成過程の解明に至まで
    香内晃, 渡部直樹
    雪氷 71 395  2009 [Refereed][Not invited]
  • 大場康弘, 宮内直弥, 千貝健, 日高宏, 渡部直樹, 香内 晃
    地球化学 43 117 - 131 2009 [Refereed][Not invited]
  • Tetsuo Koizumi, Takao M. Kojima, Mutsumi Sano, Naoki Watanabe
    14TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF HIGHLY CHARGED IONS (HCI 2008) 163 (1) 12099  1742-6588 2009 [Refereed][Not invited]
     
    Using an ion-photon merged-beam apparatus, photoion yield spectra of Cs2+ and Cs3+ from the 4d photoionization of Cs+ have been measured as a function of photon energy in the range 80-140 eV. Above 90 eV, the 4d giant resonance peak is observed clearly for Cs3+ spectrum. Below 90 eV, some prominent discrete peaks are observed for both Cs2+ and Cs3+. These discrete peaks can be attributed to the 4d-np and 4d-nf transitions.
  • T. Hama, A. Yabushita, M. Yokoyama, M. Kawasaki, N. Watanabe
    J. Chem. Phys. 131 (11) 114511  0021-9606 2009 [Refereed][Not invited]
  • N. Watanabe, A. Kouchi, H. Hidaka, Y. Oba, N. Miyauchi
    Journal of Physics: Conference Series 194 (1) 12044 - (5pages) 1742-6596 2009 [Refereed][Not invited]
     
    Reactions of atomic hydrogen with CO and O2 on amorphous solid water (ASW), relevant to chemical evolution on cosmic ice dust, were experimentally investigated at around 10 K. Successive addition of hydrogen atoms to CO and O2 produces H2CO, CH3OH, and H2O2, H2O, respectively. At such low temperatures, some of hydrogen additions such as H + CO HCO proceed via tunneling reactions rather than thermally-activated reactions. Effective reaction rates and isotope effect of the tunneling reactions to produce HCO and H2O were measured. The surface of ASW was found to enhance the effective rate of hydrogen addition to CO at relatively higher temperatures, namely around 20 K. © 2009 IOP Publishing Ltd.
  • A. Kouchi, Y. Oba, N. Miyauchi, H. Hidaka, N. Watanabe
    Cryobiology Elsevier {BV} 59 (3) 370  2009 [Refereed][Not invited]
  • N. Watanabe, A. Kouchi, H. Hidaka, Y. Oba, N. Miyauchi
    J. Phys. Conf. Ser. 194 (1) 012044 - (5pages) 2009 [Refereed][Not invited]
  • Tetsuo Koizumi, Takao M. Kojima, Mutsumi Sano, Naoki Watanabe
    14TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF HIGHLY CHARGED IONS (HCI 2008) 163 (1) 012099  1742-6588 2009 [Refereed][Not invited]
     
    Using an ion-photon merged-beam apparatus, photoion yield spectra of Cs2+ and Cs3+ from the 4d photoionization of Cs+ have been measured as a function of photon energy in the range 80-140 eV. Above 90 eV, the 4d giant resonance peak is observed clearly for Cs3+ spectrum. Below 90 eV, some prominent discrete peaks are observed for both Cs2+ and Cs3+. These discrete peaks can be attributed to the 4d-np and 4d-nf transitions.
  • Naoki Watanabe, Akira Kouchi
    PROGRESS IN SURFACE SCIENCE 83 (10-12) 439 - 489 0079-6816 2008/12 [Refereed][Not invited]
     
    Chemical reactions on the surface of cosmic ice dust play an important role in chemical evolution in space. Arnong the many kinds of molecules observed, the abundances of some major species such as hydrogen molecules cannot be explained by gas-phase synthesis; therefore, surface reactions oil cosmic dust are considered for the synthesis of such molecules. Experimental research on surface reactions relevant to cosmic ice dust has been conducted since the late 1980s. Early experiments were rather qualitative, and so the details of reactions were not clear. In the last decade, many scientists from various fields including surface science have been motivated to extend the knowledge in this area of research, and have performed sophisticated experiments regarding surface reactions on cosmic ice dust. The aim of this article is to review the recent progress in surface astrochemistry. In particular, focus is made on experiments concerning the synthesis of abundant molecules such as H-2, H2O, CO2, H2CO and CH3OH oil ice surfaces at very low temperatures. (C) 2008 Elsevier Ltd. All rights reserved.
  • Naoki Watanabe, Akira Kouchi
    Progress in Surface Science 83 (10-12) 439 - 489 0079-6816 2008/12 [Refereed][Not invited]
     
    Chemical reactions on the surface of cosmic ice dust play an important role in chemical evolution in space. Among the many kinds of molecules observed, the abundances of some major species such as hydrogen molecules cannot be explained by gas-phase synthesis therefore, surface reactions on cosmic dust are considered for the synthesis of such molecules. Experimental research on surface reactions relevant to cosmic ice dust has been conducted since the late 1980s. Early experiments were rather qualitative, and so the details of reactions were not clear. In the last decade, many scientists from various fields including surface science have been motivated to extend the knowledge in this area of research, and have performed sophisticated experiments regarding surface reactions on cosmic ice dust. The aim of this article is to review the recent progress in surface astrochemistry. In particular, focus is made on experiments concerning the synthesis of abundant molecules such as H2, H2O, CO2, H2CO and CH3OH on ice surfaces at very low temperatures. © 2008 Elsevier Ltd. All rights reserved.
  • 大場 康弘, 宮内 直弥, 千貝 健, 日高 宏, 渡部 直樹, 香内 晃
    日本惑星科学会秋期講演会予稿集 日本惑星科学会 2008 (0) 2008/11 [Not refereed][Not invited]
  • Akihiro Yabushita, Tetsuya Hama, Daisuke Iida, Noboru Kawanaka, Masahiro Kawasaki, Naoki Watanabe, Michael N. R. Ashfold, Hans-Peter Loock
    JOURNAL OF CHEMICAL PHYSICS 129 (4) 044501  0021-9606 2008/07 [Refereed][Not invited]
     
    The production of H(2) in highly excited vibrational and rotational states (v=0-5, J=0-17) from the 157 nm photodissociation of amorphous solid water ice films at 100 K was observed directly using resonance-enhanced multiphoton ionization. Weaker signals from H(2)(v=2,3 and 4) were obtained from 157 nm photolysis of polycrystalline ice, but H(2)(v=0 and 1) populations in this case were below the detection limit. The H(2) products show two distinct formation mechanisms. Endothermic abstraction of a hydrogen atom from H(2)O by a photolytically produced H atom yields vibrationally cold H(2) products, whereas exothermic recombination of two H-atom photoproducts yields H(2) molecules with a highly excited vibrational distribution and non-Boltzmann rotational population distributions as has been predicted previously by both quantum-mechanical and molecular dynamics calculations. (C) 2008 American Institute of Physics.
  • Akihiro Yabushita, Tetsuya Hama, Daisuke Iida, Noboru Kawanaka, Masahiro Kawasaki, Naoki Watanabe, Michael N. R. Ashfold, Hans-Peter Loock
    JOURNAL OF CHEMICAL PHYSICS 129 (4) 044501  0021-9606 2008/07 [Refereed][Not invited]
     
    The production of H(2) in highly excited vibrational and rotational states (v=0-5, J=0-17) from the 157 nm photodissociation of amorphous solid water ice films at 100 K was observed directly using resonance-enhanced multiphoton ionization. Weaker signals from H(2)(v=2,3 and 4) were obtained from 157 nm photolysis of polycrystalline ice, but H(2)(v=0 and 1) populations in this case were below the detection limit. The H(2) products show two distinct formation mechanisms. Endothermic abstraction of a hydrogen atom from H(2)O by a photolytically produced H atom yields vibrationally cold H(2) products, whereas exothermic recombination of two H-atom photoproducts yields H(2) molecules with a highly excited vibrational distribution and non-Boltzmann rotational population distributions as has been predicted previously by both quantum-mechanical and molecular dynamics calculations. (C) 2008 American Institute of Physics.
  • H. Hidaka, N. Miyauchi, A. Kouchi, N. Watanabe
    CHEMICAL PHYSICS LETTERS 456 (1-3) 36 - 40 0009-2614 2008/04 [Refereed][Not invited]
     
    Experiments on the hydrogenation of CO on crystalline and amorphous ice at 15 K were carried out to investigate the structural effects of the ice surface. The effective rate of H atom addition to CO on the amorphous ice was found to be larger than that on the crystalline ice, while CO depletion on crystalline ice became larger after long exposure. We demonstrated that the CO-coverage on the ice surfaces dominates the effective reaction rate rather than the surface structure. The larger depletion of CO on crystalline ice, as compared to amorphous ice, suggests easier desorption of CO and/or products by the heat of the reaction. (C) 2008 Elsevier B.V. All rights reserved.
  • N. Miyauchi, H. Hidaka, T. Chigai, A. Nagaoka, N. Watanabe, A. Kouchi
    CHEMICAL PHYSICS LETTERS 456 (1-3) 27 - 30 0009-2614 2008/04 [Refereed][Not invited]
     
    The reactions of cold H atoms with solid O-2 molecules were investigated at 10 K. The formation of H2O2 and H2O has been confirmed by in situ infrared spectroscopy. We found that the reaction proceeds very efficiently and obtained the effective reaction rates. This is the first clear experimental evidence of the formation of water molecules under conditions mimicking those found in cold interstellar molecular clouds. Based on the experimental results, we discuss the reaction mechanism and astrophysical implications. (C) 2008 Elsevier B.V. All rights reserved.
  • N. Miyauchi, H. Hidaka, T. Chigai, A. Nagaoka, N. Watanabe, A. Kouchi
    CHEMICAL PHYSICS LETTERS 456 (1-3) 27 - 30 0009-2614 2008/04 [Refereed][Not invited]
     
    The reactions of cold H atoms with solid O-2 molecules were investigated at 10 K. The formation of H2O2 and H2O has been confirmed by in situ infrared spectroscopy. We found that the reaction proceeds very efficiently and obtained the effective reaction rates. This is the first clear experimental evidence of the formation of water molecules under conditions mimicking those found in cold interstellar molecular clouds. Based on the experimental results, we discuss the reaction mechanism and astrophysical implications. (C) 2008 Elsevier B.V. All rights reserved.
  • H. Hidaka, N. Miyauchi, A. Kouchi, N. Watanabe
    CHEMICAL PHYSICS LETTERS 456 (1-3) 36 - 40 0009-2614 2008/04 [Refereed][Not invited]
     
    Experiments on the hydrogenation of CO on crystalline and amorphous ice at 15 K were carried out to investigate the structural effects of the ice surface. The effective rate of H atom addition to CO on the amorphous ice was found to be larger than that on the crystalline ice, while CO depletion on crystalline ice became larger after long exposure. We demonstrated that the CO-coverage on the ice surfaces dominates the effective reaction rate rather than the surface structure. The larger depletion of CO on crystalline ice, as compared to amorphous ice, suggests easier desorption of CO and/or products by the heat of the reaction. (C) 2008 Elsevier B.V. All rights reserved.
  • 分子雲で生じる低温表面反応:表面実験で探る分子進化
    日高宏, 渡部直樹, 香内晃
    低温科学 66 13  2008 [Refereed][Not invited]
  • A. Yabushita, T. Hama, D. Iida, N. Kawanaka, M. Kawasaki, N. Watanabe, M. N, R. Ashfold, H-P. Loock
    Astrophys. J. Lett. 682 (1) L69 - L72 2008 [Refereed][Not invited]
  • A. Yabushita, T. Hama, D. Iida, N. Kawanaka, M. Kawasaki, N. Watanabe, M. N, R. Ashfold, H-P. Loock
    Astrophys. J. Lett. 682 (1) L69 - L72 2008 [Refereed][Not invited]
  • N. Watanabe, O. Mouri, A. Nagaoka, T. Chigai, A. Kouchi, V. Pirronello
    ASTROPHYSICAL JOURNAL 668 (2) 1001 - 1011 0004-637X 2007/10 [Refereed][Not invited]
     
    Hydrogenation and photolysis of H2O-CO binary ice mixtures at 10-50 K have been revisited in order to quantitatively evaluate their relative importance in the chemical evolution of interstellar dust icy mantles. The dominant product of photolysis was CO2, with lower yields of formaldehyde, methanol, and formic acid, while only formaldehyde and methanol were obtained by hydrogenation reactions. Hydrogenation has higher formation efficiencies and yields of formaldehyde and methanol than photolysis. However, the contribution of photolysis should not be negligible for the formation of these molecules in molecular clouds. The simultaneous irradiation of binary ice mixtures with hydrogen atoms and UV photons resulted in relative abundances of CO2, formaldehyde, methanol, and formic acid that are consistent with the observed abundances. Our results show that the composition and structure of ice are crucial in the chemical evolution of ice mantles, as much as the temperature and the type of irradiation.
  • N. Watanabe, O. Mouri, A. Nagaoka, T. Chigai, A. Kouchi, V. Pirronello
    ASTROPHYSICAL JOURNAL 668 (2) 1001 - 1011 0004-637X 2007/10 [Refereed][Not invited]
     
    Hydrogenation and photolysis of H2O-CO binary ice mixtures at 10-50 K have been revisited in order to quantitatively evaluate their relative importance in the chemical evolution of interstellar dust icy mantles. The dominant product of photolysis was CO2, with lower yields of formaldehyde, methanol, and formic acid, while only formaldehyde and methanol were obtained by hydrogenation reactions. Hydrogenation has higher formation efficiencies and yields of formaldehyde and methanol than photolysis. However, the contribution of photolysis should not be negligible for the formation of these molecules in molecular clouds. The simultaneous irradiation of binary ice mixtures with hydrogen atoms and UV photons resulted in relative abundances of CO2, formaldehyde, methanol, and formic acid that are consistent with the observed abundances. Our results show that the composition and structure of ice are crucial in the chemical evolution of ice mantles, as much as the temperature and the type of irradiation.
  • H. Hidaka, A. Kouchi, N. Watanabe
    JOURNAL OF CHEMICAL PHYSICS 126 (20) 204707  0021-9606 2007/05 [Refereed][Not invited]
     
    An experiment on the addition reaction of a D atom (deuteration) to CO on a cold ice surface is performed by deuterium atom exposure of three types of samples (pure solid CO, CO-capped H2O ice, and CO-H2O mixed ice) at 10-20 K. The variation of IR absorption spectra for the samples was measured by a Fourier transform infrared spectrometer during exposure to deuterium atoms. Reactions on pure solid CO were observed only at 10 K, while reactions on CO-capped H2O ice and CO-H2O mixed ice were observed to proceed even at 20 K. This indicates that the coexistence of H2O at the surface raises the reactive temperature. In addition, the experiment on H atom exposure was also carried out at 15 K to compare the reaction rate constant between the H and D atoms. The ratio of reaction rate constant k(D)/k(H) obtained is about 0.08 at 15 K. The authors provide information on the potential energy for the H+CO reaction at the surface by using the ratio k(D)/k(H) and by a model calculation of the potential tunneling with the asymmetric Eckart potential. (C) 2007 American Institute of Physics.
  • Akihiro Nagaoka, Naoki Watanabe, Akira Kouchi
    JOURNAL OF PHYSICAL CHEMISTRY A 111 (16) 3016 - 3028 1089-5639 2007/04 [Refereed][Not invited]
     
    The surface reactions of CH3OH, CH2DOH, and CHD2OH with cold D atoms at 10 K were investigated using an atomic beam source and FTIR. Methyl-deuterated isotopologues CH2DOH, CHD2OH, and CD3OH were produced by exposure of amorphous solid CH3OH to D atoms at 10 K, and the pseudo-first-order rates for the reactions CH3OH + D -> CH2OH + HD, CH2DOH + D -> CHDOH + HD, and CHD2OH + D -> CD2OH + HD were estimated. The ratios of the reaction rates of the second and third reactions to the first reaction were 0.69 +/- 0.11 and 0.52 +/- 0.14, respectively. The difference in reaction rates is thought to be due to a secondary kinetic isotope effect on the H-abstraction reaction from the methyl side by D atoms.
  • Akihiro Nagaoka, Naoki Watanabe, Akira Kouchi
    JOURNAL OF PHYSICAL CHEMISTRY A 111 (16) 3016 - 3028 1089-5639 2007/04 [Refereed][Not invited]
     
    The surface reactions of CH3OH, CH2DOH, and CHD2OH with cold D atoms at 10 K were investigated using an atomic beam source and FTIR. Methyl-deuterated isotopologues CH2DOH, CHD2OH, and CD3OH were produced by exposure of amorphous solid CH3OH to D atoms at 10 K, and the pseudo-first-order rates for the reactions CH3OH + D -> CH2OH + HD, CH2DOH + D -> CHDOH + HD, and CHD2OH + D -> CD2OH + HD were estimated. The ratios of the reaction rates of the second and third reactions to the first reaction were 0.69 +/- 0.11 and 0.52 +/- 0.14, respectively. The difference in reaction rates is thought to be due to a secondary kinetic isotope effect on the H-abstraction reaction from the methyl side by D atoms.
  • 渡部直樹, 香内 晃, 毛利織絵, 長岡明宏, 日高 宏
    J. Vac. Soc. Jpn. 50 (4) 282 - 290 0559-8516 2007 [Refereed][Not invited]
  • H. Hidaka, A. Kouchi, N. Watanabe
    J. Chem. Phys. 126 (20) 204707  0021-9606 2007 [Refereed][Not invited]
  • N. Watanabe, A. Nagaoka, H. Hidaka, T. Shiraki, T. Chigai, A. Kouchi
    PLANETARY AND SPACE SCIENCE 54 (11) 1107 - 1114 0032-0633 2006/09 [Refereed][Not invited]
     
    Experiments on the hydrogenation of CO on pure CO and CO-H2O mixed ice have been performed at temperatures between 8 and 20 K. We obtained temperature and compositional dependence of the effective reaction rate constants. Results indicate that hydrogenation proceeds efficiently on pure solid CO and CO-H2O mixed ice at temperatures below 10 and 20 K, respectively. Rate constants for pure CO decreased significantly at 12 K compared to those obtained with CO-H2O mixed ice. Hydrogenation of CO at temperatures greater than 12 K were catalyzed by the H2O adjacent to the CO. The importance of the experimental results for some relevant astrophysical environments has also been outlined. (c) 2006 Elsevier Ltd. All rights reserved.
  • 星間塵表面での低温水素原子反応による分子進化
    渡部直樹, 長岡明宏, 日高宏, 香内晃
    固体物理11 41 755 - 764 2006 [Refereed][Not invited]
  • Formation and Deuterium Fractionation of Organic Molecules on Grain Surfaces
    N.Watanabe
    Astrochemistry: Recent Successes and Current Challenges, Cambridge University Press 415 - 426 2006 [Refereed][Not invited]
  • Deuterium fractionation in the reactions of D+H2CO and H+D2CO at 15 K
    Hiroshi Hidaka, Naoki Watanabe, Akira Kouchi
    ASTROCHEMISTRY: FROM LABORATORY STUDIES TO ASTRONOMICAL OBSERVATIONS 855 107 - + 0094-243X 2006 [Refereed][Not invited]
     
    The reaction of cold H and D atoms with solid formaldehyde (D2CO and H2CO) deposited on amorphous H2O ice at 15 K was studied experimentally by in-situ FTIR spectroscopy. New routes of formation of deuterated formaldehyde (HDCO and D2CO) were identified. In the reaction of D atoms with H2CO, H-D substitution was observed, H2CO -> HDCO -> D2CO, and for the reaction of H atoms with D2CO, the analogous D-H substitution was observed, D2CO -> HDCO -> H2CO. In the reaction of D atoms with H2CO, the rate of H-D substitution was greater than that of formation of deuterated methanol-d(2-4) by addition of 2D atoms to formaldehyde-d(0-2). However, in the reaction of H atoms with D2CO, the rate of D-H substitution was comparable to that of addition of 2H atoms to D2CO.
  • Efficient formation of deuterated methanol by H-D substitution on interstellar grain surfaces
    Akihiro Nagaoka, Naoki Watanabe, Akira Kouchi
    ASTROCHEMISTRY: FROM LABORATORY STUDIES TO ASTRONOMICAL OBSERVATIONS 855 69 - + 0094-243X 2006 [Refereed][Not invited]
     
    We performed an experiment in which pure solid CO was simultaneously exposed to cold H and D atoms at 10 K, and observed efficient formation of H2CO, CH3OH and deuterated isotopologues HDCO, D2CO, CH2DOH, CHD2OH, and CD3OH. The D/H ratios obtained for formaldehyde and methanol are in good agreement with previously reported observations. We found that the H-D substitution reaction in methanol is a key process in the formation of deuterated methanol, especially multi-deuterated isotopologues CHD2OH and CD3OH.
  • Relative Reaction Rates of hydrogenation and deuteration of solid CO at very low temperatures
    N. Watanabe, H. Hidaka, A. Kouchi
    Eds. R. I. Kaiser, P. Bernath, Y. Osamura, S. Petrie, & A. M. Mebel, Astrochemistry from laboratory Studies to Astronomical Observations, AIP, New York 122 - 127 2006 [Refereed][Not invited]
  • 星間塵表面での低温水素原子反応による分子進化
    渡部直樹, 長岡明宏, 日高宏, 香内晃
    固体物理 特集号 <新しい水素の科学> 41 (1) 59 - 68 2006 [Refereed][Not invited]
  • TM Kojima, FF Chen, M Kitajima, T Koizumi, Y Nakai, H Yamaoka, N Watanabe
    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 144 71 - 74 0368-2048 2005/06 [Refereed][Not invited]
     
    The relative photoion yield in the 4d photoionization of Eu+ has been measured with an energy resolution of E/Delta E similar or equal to 820. The obtained spectrum shows that the 4d 'giant resonance' of Eu+ is not a single peak but consists of many resonances. The result is compared with a recent theoretical calculation and our previous result which has been measured with lower resolution. The calculation well reproduces the experimental result in the region of E >= 140 eV, while some peaks are not corresponding in lower energy region. (c) 2004 Elsevier B.V. All rights reserved.
  • TM Kojima, FF Chen, M Kitajima, T Koizumi, Y Nakai, H Yamaoka, N Watanabe
    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 144 71 - 74 0368-2048 2005/06 [Refereed][Not invited]
     
    The relative photoion yield in the 4d photoionization of Eu+ has been measured with an energy resolution of E/Delta E similar or equal to 820. The obtained spectrum shows that the 4d 'giant resonance' of Eu+ is not a single peak but consists of many resonances. The result is compared with a recent theoretical calculation and our previous result which has been measured with lower resolution. The calculation well reproduces the experimental result in the region of E >= 140 eV, while some peaks are not corresponding in lower energy region. (c) 2004 Elsevier B.V. All rights reserved.
  • 渡部 直樹, 香内 晃
    日本物理学会誌 60 (1) 39 - 44 0029-0181 2005 [Refereed][Not invited]
  • 星間塵表面反応による星間分子の重水素濃集メカニズム
    渡部直樹, 長岡明宏, 日高宏, 香内晃
    日本惑星科学会誌 14 175 - 182 2005 [Refereed][Not invited]
  • A. Nagaoka, N. Watanabe, A. Kouchi
    Astrophys. J. Lett. 624 (1) L29 - L32 2005 [Refereed][Not invited]
  • A. Nagaoka, N. Watanabe, A. Kouchi
    Astrophys. J. Lett. 624 (1) L29 - L32 2005 [Refereed][Not invited]
  • H Hidaka, N Watanabe, T Shiraki, A Nagaoka, A Kouchi
    ASTROPHYSICAL JOURNAL 614 (2) 1124 - 1131 0004-637X 2004/10 [Refereed][Not invited]
     
    The conversion of formaldehyde (H2CO) to methanol (CH3OH) by successive hydrogenation on H2O ice was measured at 10, 15, and 20 K using atomic hydrogen beams of 30 and 300 K. The conversion rates and CH3OH yields under the 30 K beam are very similar to those under the 300 K beam at all ice temperatures, demonstrating that the reaction is independent of beam temperature. The dependence of the conversion rates on ice temperature is consistent with that for previous experiments on CO hydrogenation. The conversion rate for H2CO --> CH3OH at 15 K was found to be about half that for CO --> H2CO. The dependence of the reactions on the initial thickness of H2CO was also measured. More than 80% of H2CO was converted to CH3OH for H2CO layers of less than 1 monolayer in average thickness. Irradiation of CH3OH with H atoms did not produce H2CO, demonstrating that the reverse process, CH3OH --> H2CO (H abstraction), is minor compared to the forward process.
  • H Hidaka, N Watanabe, T Shiraki, A Nagaoka, A Kouchi
    ASTROPHYSICAL JOURNAL 614 (2) 1124 - 1131 0004-637X 2004/10 [Refereed][Not invited]
     
    The conversion of formaldehyde (H2CO) to methanol (CH3OH) by successive hydrogenation on H2O ice was measured at 10, 15, and 20 K using atomic hydrogen beams of 30 and 300 K. The conversion rates and CH3OH yields under the 30 K beam are very similar to those under the 300 K beam at all ice temperatures, demonstrating that the reaction is independent of beam temperature. The dependence of the conversion rates on ice temperature is consistent with that for previous experiments on CO hydrogenation. The conversion rate for H2CO --> CH3OH at 15 K was found to be about half that for CO --> H2CO. The dependence of the reactions on the initial thickness of H2CO was also measured. More than 80% of H2CO was converted to CH3OH for H2CO layers of less than 1 monolayer in average thickness. Irradiation of CH3OH with H atoms did not produce H2CO, demonstrating that the reverse process, CH3OH --> H2CO (H abstraction), is minor compared to the forward process.
  • 星間塵表面反応による有機分子生成および重水素濃集機構
    渡部直樹, 香内晃, 白木隆裕, 長岡明宏, 日高宏
    日本惑星科学会誌 13 226 - 232 2004 [Refereed][Not invited]
  • 星間塵上でのホルムアルデヒド,メタノールの生成機構-実験室からのアプローチ-
    渡部 直樹, 白木隆裕, 香内 晃
    天文月報 97 101 - 106 2004 [Refereed][Not invited]
  • Influence of ice composition on the formation on interstellar formaldehyde and methanol on dust grains
    A. Nagaoka, N. Watanabe, T. Shiraki, H. Hidaka, A. Kouchi
    Proceedings of the 37th isas luna and planetary symposium 4 91 - 94 2004 [Refereed][Not invited]
  • N. Watanabe, A. Nagaoka, T. Shiraki, A. Kouchi
    Astrophys. J. 616 (1) 638 - 643 2004 [Refereed][Not invited]
  • N. Watanabe, A. Nagaoka, T. Shiraki, A. Kouchi
    Astrophys. J. 616 (1) 638 - 643 2004 [Refereed][Not invited]
  • N Watanabe, T Shiraki, A Kouchi
    ASTROPHYSICAL JOURNAL 588 (2) L121 - L124 0004-637X 2003/05 [Refereed][Not invited]
     
    The formation of formaldehyde (H(2)CO) and methanol (CH(3) OH) by the successive addition of hydrogen atoms to CO molecules in H(2)O-CO mixed ice was measured at 10, 15, and 20 K. The maximum yield of CH(3)OH was obtained at 15 K, with the next highest yield at 10 K. At 20 K, the reactions proceeded very slowly, and the resulting yield of CH(3)OH was significantly smaller than at 10 and 15 K and was considered to be due to a fall in the sticking probability of hydrogen at this temperature. The observed temperature dependence indicates that the abundances of H(2)CO and CH(3)OH in a molecular cloud are strongly dependent on the temperature of dust as well as the flux of atomic hydrogen. The diffusion of hydrogen atoms in ice is also discussed based on measurements of the dependence of CO hydrogenation on ice thickness in the range of less than 30 monolayers.
  • N Watanabe, T Shiraki, A Kouchi
    ASTROPHYSICAL JOURNAL 588 (2) L121 - L124 0004-637X 2003/05 [Refereed][Not invited]
     
    The formation of formaldehyde (H(2)CO) and methanol (CH(3) OH) by the successive addition of hydrogen atoms to CO molecules in H(2)O-CO mixed ice was measured at 10, 15, and 20 K. The maximum yield of CH(3)OH was obtained at 15 K, with the next highest yield at 10 K. At 20 K, the reactions proceeded very slowly, and the resulting yield of CH(3)OH was significantly smaller than at 10 and 15 K and was considered to be due to a fall in the sticking probability of hydrogen at this temperature. The observed temperature dependence indicates that the abundances of H(2)CO and CH(3)OH in a molecular cloud are strongly dependent on the temperature of dust as well as the flux of atomic hydrogen. The diffusion of hydrogen atoms in ice is also discussed based on measurements of the dependence of CO hydrogenation on ice thickness in the range of less than 30 monolayers.
  • JSA Perry, JM Gingell, KA Newson, J To, N Watanabe, SD Price
    MEASUREMENT SCIENCE AND TECHNOLOGY 13 (9) 1414 - 1424 0957-0233 2002/09 [Refereed][Not invited]
     
    An experiment has been constructed to determine the rovibrational states populated in the formation of H-2 on the surface of cosmic dust under conditions approaching those of the interstellar medium (ISM). During the experiment, a beam of atomic hydrogen of controlled temperature is incident upon a target which is an analogue of cosmic dust. Molecular hydrogen desorbing from the target's surface is ionized using (2 + 1) resonance enhanced multiphoton ionization and detected using time-of-flight mass spectrometry. The experiment allows the rovibrational populations of the H-2 molecules desorbing from the cosmic dust targets to be determined providing information on the energy budget of the H-2 formation process in the ISM. Preliminary results from the experiment, to prove its viability, show that H-2 molecules formed on an highly oriented pyrolytic graphite surface have a measurable population of excited vibrational and rotational states.
  • JSA Perry, JM Gingell, KA Newson, J To, N Watanabe, SD Price
    MEASUREMENT SCIENCE AND TECHNOLOGY 13 (9) 1414 - 1424 0957-0233 2002/09 [Refereed][Not invited]
     
    An experiment has been constructed to determine the rovibrational states populated in the formation of H-2 on the surface of cosmic dust under conditions approaching those of the interstellar medium (ISM). During the experiment, a beam of atomic hydrogen of controlled temperature is incident upon a target which is an analogue of cosmic dust. Molecular hydrogen desorbing from the target's surface is ionized using (2 + 1) resonance enhanced multiphoton ionization and detected using time-of-flight mass spectrometry. The experiment allows the rovibrational populations of the H-2 molecules desorbing from the cosmic dust targets to be determined providing information on the energy budget of the H-2 formation process in the ISM. Preliminary results from the experiment, to prove its viability, show that H-2 molecules formed on an highly oriented pyrolytic graphite surface have a measurable population of excited vibrational and rotational states.
  • N Watanabe, A Kouchi
    ASTROPHYSICAL JOURNAL 571 (2) L173 - L176 0004-637X 2002/06 [Refereed][Not invited]
     
    Formaldehyde and methanol were produced efficiently by the hydrogenation of CO in H(2)O-CO ice at 10 K in an atomic hydrogen beam experiment. The relative yields to the initial CO were of the order of 10%, 3 orders of magnitude larger than those reported previously. This reveals for the first time experimentally that successive hydrogenation of CO is most likely to produce formaldehyde and methanol on the surface of icy grains in molecular clouds as suggested by theoretical models.
  • Naoki Watanabe, Akira Kouchi
    Astrophysical Journal 571 (2) L173 - L176 1538-4357 2002/06/01 [Refereed][Not invited]
     
    Formaldehyde and methanol were produced efficiently by the hydrogenation of CO in H2O-CO ice at 10 K in an atomic hydrogen beam experiment. The relative yields to the initial CO were of the order of 10%, 3 orders of magnitude larger than those reported previously. This reveals for the first time experimentally that successive hydrogenation of CO is most likely to produce formaldehyde and methanol on the surface of icy grains in molecular clouds as suggested by theoretical models.
  • Molecular ion mobility in helium gas at very low temperature
    H. Hidaka, S. Matoba, S. Jinno, H. Tanuma, N. Kobayashi
    Atomic collision research in japan -Progress report- 28 18 - 19 2002 [Refereed][Not invited]
  • N. Watanabe, A. Kouchi
    Astrophys. J. 567 (1) 651 - 655 2002 [Refereed][Not invited]
  • A. Kouchi, T. Kudo, H. Nakano, M. Arakawa, N. Watanabe, S. Sirono, M. Higa, N. Maeno
    Astrophys. J. Lett. 566 (2) L121 - L124 2002 [Refereed][Not invited]
  • A. Kouchi, T. Kudo, H. Nakano, M. Arakawa, N. Watanabe, S. Sirono, M. Higa, N. Maeno
    Astrophys. J. Lett. 566 (2) L121 - L124 2002 [Refereed][Not invited]
  • Naoki Watanabe, Akira Kouchi
    Astrophys. J. 567 (1) 651 - 655 2002 [Refereed][Not invited]
  • Y Itoh, A Ito, M Kitajima, T Koizumi, TM Kojima, H Sakai, M Sano, N Watanabe
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 34 (17) 3493 - 3499 0953-4075 2001/09 [Refereed][Not invited]
     
    Using the photon-ion merged-beam technique, we have measured the absolute photoionization cross sections for Xe2+ and Xe3+ formation from Xe+ at selected energies between 80 and 140 eV, and utilized the absolute data to normalize our previously reported relative cross sections. The structure and energy dependence of the cross sections for Xe+ deviate from those of neutral Xe; however, the maximum total cross section for Xe+ is, within the experimental error, the same as for Xe.
  • Y Itoh, A Ito, M Kitajima, T Koizumi, TM Kojima, H Sakai, M Sano, N Watanabe
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 34 (17) 3493 - 3499 0953-4075 2001/09 [Refereed][Not invited]
     
    Using the photon-ion merged-beam technique, we have measured the absolute photoionization cross sections for Xe2+ and Xe3+ formation from Xe+ at selected energies between 80 and 140 eV, and utilized the absolute data to normalize our previously reported relative cross sections. The structure and energy dependence of the cross sections for Xe+ deviate from those of neutral Xe; however, the maximum total cross section for Xe+ is, within the experimental error, the same as for Xe.
  • Formation of CO2 molecules from CO doped D2O amorphous ice by uv irradiation at 12K
    Naoki Watanabe, Akira Kouchi
    Prog. Rep. Atom. Coll. Res. Jpn. 27 62 - 63 2001 [Refereed][Not invited]
  • N Watanabe, T Horii, A Kouchi
    ASTROPHYSICAL JOURNAL 541 (2) 772 - 778 0004-637X 2000/10 [Refereed][Not invited]
     
    We have carried out experiments on the formation of D-2 molecules from amorphous D2O ice (thickness: 40, 120 Angstrom) by UV irradiation (lambda: 126, 172 Ka) at 12 K. Our results show that most of the D-2 products remain in and on the amorphous ice at 12 K; directly photodesorbed D-2 was little observed at 12 K. The amount of D2O destruction and D-2 yields after a dose of 10(18) photons cm(-2) at 12 K were about 10%-20% and 1%-2% of the initial number of D2O molecules, respectively. The formation reaction of D-2 was found to be a single-photon process via the first excited state of D2O. The reconstruction of D2O at 12 K (reverse reaction) was not observed within our experimental timescale (5 hr). We estimated the cross sections for the D2O destruction and the D-2 formation reactions by the photon impact at 12 K for the first time.
  • N. Watanabe, T. Horii, A. Kouchi
    Astrophys. J. 541 772 - 779 2000 [Refereed][Not invited]
  • A. A. Pavlychev, N. G. Fominykh, N. Watanabe, K. Soejima, E. Shigemasa, A. Yagishita
    Physical Review Letters 81 (17) 3623 - 3626 1079-7114 1998/10/26 [Refereed][Not invited]
     
    An essential correlation between intramolecular interference of photoelectron waves and core-hole molecular relaxation is revealed by analyzing the partial wave composition of the calculated angular distribution of photoelectrons in the N and O 1s−1σu* shape resonances of aligned N2 and CO2. The dominance of coherent (N2) and incoherent (CO2) interference is revealed. pf and spd hybridization controls the main direction of photoelectron emission from the N and O K shell, respectively. © 1998 The American Physical Society.
  • A. A. Pavlychev, N. G. Fominykh, N. Watanabe, K. Soejima, E. Shigemasa, A. Yagishita
    Physical Review Letters 81 (17) 3623 - 3626 1079-7114 1998/10/26 [Refereed][Not invited]
     
    An essential correlation between intramolecular interference of photoelectron waves and core-hole molecular relaxation is revealed by analyzing the partial wave composition of the calculated angular distribution of photoelectrons in the N and O 1s−1σu* shape resonances of aligned N2 and CO2. The dominance of coherent (N2) and incoherent (CO2) interference is revealed. pf and spd hybridization controls the main direction of photoelectron emission from the N and O K shell, respectively. © 1998 The American Physical Society.
  • N Watanabe, Y Awaya, A Fujino, Y Itoh, M Kitajima, TM Kojima, M Oura, R Okuma, M Sano, T Sekioka, T Koizumi
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 31 (18) 4137 - 4141 0953-4075 1998/09 [Refereed][Not invited]
     
    Photoion yields from doubly charged Xe ions were measured in the 4d-threshold energy region. The experiment was performed by a photon-ion merged-beam technique with synchrotron radiation as a light source. The measured spectrum mainly consists of strong 4d --> 5p transition lines at around 57 eV, a very broad peak at around 100 eV, and the preceding strong discrete peaks lying between 79 and 90 eV. The peak position of the broad peak changes very little from that in Xe+ photoion-yield spectra of Sane et al. The enhancement of discrete peaks in the Xe2+ spectrum implies a further collapse of nf-wavefunctions than that of Xe+.
  • N Watanabe, Y Awaya, A Fujino, Y Itoh, M Kitajima, TM Kojima, M Oura, R Okuma, M Sano, T Sekioka, T Koizumi
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 31 (18) 4137 - 4141 0953-4075 1998/09 [Refereed][Not invited]
     
    Photoion yields from doubly charged Xe ions were measured in the 4d-threshold energy region. The experiment was performed by a photon-ion merged-beam technique with synchrotron radiation as a light source. The measured spectrum mainly consists of strong 4d --> 5p transition lines at around 57 eV, a very broad peak at around 100 eV, and the preceding strong discrete peaks lying between 79 and 90 eV. The peak position of the broad peak changes very little from that in Xe+ photoion-yield spectra of Sane et al. The enhancement of discrete peaks in the Xe2+ spectrum implies a further collapse of nf-wavefunctions than that of Xe+.
  • TM Kojima, M Oura, Y Itoh, T Koizumi, M Sano, T Sekioka, N Watanabe, H Yamaoka, Y Awaya
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 31 (7) 1463 - 1468 0953-4075 1998/04 [Refereed][Not invited]
     
    Using an ion-photon merged-beam apparatus, photoion yield spectra of Eu2+ and Eu3+ from the 4d photoionization of Eu+ were measured as a function of photon energy in the range 110-160 eV. The measured spectra look very similar to those from a neutral Eu target. Both Eu2+ and Eu3+ yield spectra, a broad 'giant resonance' appears at 140 eV with some preceding small peaks at 131.5, 132.8 and 134.7 eV. The summit of the 'giant resonance' in the Eu2+ spectrum is split into two peaks. This is not observed in neutral Eu photoionization.
  • TM Kojima, M Oura, Y Itoh, T Koizumi, M Sano, T Sekioka, N Watanabe, H Yamaoka, Y Awaya
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 31 (7) 1463 - 1468 0953-4075 1998/04 [Refereed][Not invited]
     
    Using an ion-photon merged-beam apparatus, photoion yield spectra of Eu2+ and Eu3+ from the 4d photoionization of Eu+ were measured as a function of photon energy in the range 110-160 eV. The measured spectra look very similar to those from a neutral Eu target. Both Eu2+ and Eu3+ yield spectra, a broad 'giant resonance' appears at 140 eV with some preceding small peaks at 131.5, 132.8 and 134.7 eV. The summit of the 'giant resonance' in the Eu2+ spectrum is split into two peaks. This is not observed in neutral Eu photoionization.
  • E. Shigemasa, J. Adachi, K. Soejima, N. Watanabe, A. Yagishita, N.A. Cherepkov
    Physical Review Letters 80 (8) 1622 - 1625 0031-9007 1998 [Refereed][Not invited]
  • E. Shigemasa, J. Adachi, K. Soejima, N. Watanabe, A. Yagishita, N.A. Cherepkov
    Physical Review Letters 80 (8) 1622 - 1625 0031-9007 1998 [Refereed][Not invited]
  • N Watanabe, J Adachi, K Soejima, E Shigemasa, A Yagishita, NG Fominykh, AA Pavlychev
    PHYSICAL REVIEW LETTERS 78 (26) 4910 - 4913 0031-9007 1997/06 [Refereed][Not invited]
     
    Angular distributions of 1s sigma(g,u), photoelectrons from CO2 molecules, oriented parallel to the electric vector of incident light, have been measured. The angular distribution patters at sigma(g)* and sigma(u)* shape resonances are significantly different. From those expected in the virtual molecular orbitals concept. The analyses of the patterns have made it clear that the mixing of outgoing photoelectron partial waves and the interference between them are responsible for the observed patterns, unlike N-2 photoionization. Calculations based on a quasiatomic model bare reproduced the observed patterns fairly well.
  • N Watanabe, J Adachi, K Soejima, E Shigemasa, A Yagishita, NG Fominykh, AA Pavlychev
    PHYSICAL REVIEW LETTERS 78 (26) 4910 - 4913 0031-9007 1997/06 [Refereed][Not invited]
     
    Angular distributions of 1s sigma(g,u), photoelectrons from CO2 molecules, oriented parallel to the electric vector of incident light, have been measured. The angular distribution patters at sigma(g)* and sigma(u)* shape resonances are significantly different. From those expected in the virtual molecular orbitals concept. The analyses of the patterns have made it clear that the mixing of outgoing photoelectron partial waves and the interference between them are responsible for the observed patterns, unlike N-2 photoionization. Calculations based on a quasiatomic model bare reproduced the observed patterns fairly well.
  • T Kambara, A Igarashi, N Watanabe, Y Nakai, TM Kojima, Y Awaya
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 30 (5) 1251 - 1260 0953-4075 1997/03 [Refereed][Not invited]
     
    Using high resolution recoil-ion momentum spectroscopy we have measured differential cross sections of single-electron capture from He atoms by multiply charged boron ions, bare B5+ and hydrogen-like B4+, at 0.5-1.0 MeV/u. From the measurements of the longitudinal momentum distribution of the recoil ions, the final states of the captured electron in B4+(nl) and B3+(1snl) ions were analysed and the n = 1 ground states were clearly separated from the other excited states. Capture to the excited states gives the dominant contribution to the capture cross section. However, the fraction of captures to the ground state increases with the collision energy. Theoretical calculations based on the eikonal approximation well reproduces the experimental transverse recoil-ion momentum distribution of capture to both the ground and excited states.
  • T Kambara, A Igarashi, N Watanabe, Y Nakai, TM Kojima, Y Awaya
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 30 (5) 1251 - 1260 0953-4075 1997/03 [Refereed][Not invited]
     
    Using high resolution recoil-ion momentum spectroscopy we have measured differential cross sections of single-electron capture from He atoms by multiply charged boron ions, bare B5+ and hydrogen-like B4+, at 0.5-1.0 MeV/u. From the measurements of the longitudinal momentum distribution of the recoil ions, the final states of the captured electron in B4+(nl) and B3+(1snl) ions were analysed and the n = 1 ground states were clearly separated from the other excited states. Capture to the excited states gives the dominant contribution to the capture cross section. However, the fraction of captures to the ground state increases with the collision energy. Theoretical calculations based on the eikonal approximation well reproduces the experimental transverse recoil-ion momentum distribution of capture to both the ground and excited states.
  • 暗黒星雲における物質進化
    香内晃, 渡部, 直樹
    宇宙空間原子分子過程研究会 47 - 50 1997 [Refereed][Not invited]
  • S.D. Kravis, N. Watanabe, Y. Awaya, M. Kimura, T. Kojima, K. Okuno, M. Oura
    Physica Scripta T71 121 - 126 0031-8949 1997 [Refereed][Not invited]
  • T Koizumi, Y Awaya, A Fujino, Y Itoh, M Kitajima, TM Kojima, M Oura, R Okuma, M Sano, T Seikioka, N Watanabe, F Koike
    PHYSICA SCRIPTA T73 (T73) 131 - 132 0031-8949 1997 [Refereed][Not invited]
     
    Using a photon-ion merged-beam technique, we studied the photoionization of multiply charged Xeq+ (q = 1-3) ions in the 4d excitation region (50-140eV). Relative yield spectra of photoions created by single (q-->q+1) and double (q-->q+2) photoionization were measured as a function of photon energy. A broad ''4d giant resonance'' peak with some preceding discrete peaks appears in each total ion spectrum. The intensities of discrete peaks observed at around 4d ionization threshold strongly depend on the target charge state. Those for Xe3+ target are very strong, whereas those for Xe+ are weak. Peaks due to 4d-->5p transition, which cannot occur in the neutral Xe case, has also been observed for each ion-target. The experimental spectrum for Xe+ has been analyzed by a multiconfiguration Dirac-Fock calculation This calculation shows that results observed may be explained in terms of the correlation of valence and excited orbitals, and the effect of 4f-orbital collapse, of which the degree varies strongly with the change of the effective nuclear charge.
  • S.D. Kravis, N. Watanabe, Y. Awaya, M. Kimura, T. Kojima, K. Okuno, M. Oura
    Physica Scripta T71 121 - 126 0031-8949 1997 [Refereed][Not invited]
  • M. Sano, Y. Itoh, T. Koizumi, T. M. Kojima, S. D. Kravis, M. Oura, T. Sekioka, N. Watanabe, Y. Awaya, F. Koike
    Journal of Physics B: Atomic, Molecular and Optical Physics 29 (22) 5305 - 5313 0953-4075 1996/11/28 [Refereed][Not invited]
     
    Using a photon-ion merged-beam technique, we measured the relative yield spectra of Xe2+ and Xe3+ ions created by photoionization of Xe+ ions as a function of the photon energy in the 4d ionization region. The Xe3+ ion production, i.e. the double-electron ionization process is found to be dominant throughout the energy range investigated. A broad structure of 4d excitation ionization around 100 eV photon energy was observed in the Xe3+ yield spectrum. A spectral shoulder was observed for Xe3+ at around 85 eV, which was absent in the photoionization of neutral Xe. Some discrete lines were observed for both the Xe2+- and Xe3+-yield spectra below 75 eV. The experimental spectra were analysed by a multiconfiguration Dirac-Fock calculation. The largest structure at around 100 eV is attributable to 4d105s25p5 → 4d94f5s25p4np (n = 6, 7) two-electron transitions. The discrete lines were found to be due to 4d → np, nf transitions. A serious 4f-orbital collapse is suspected in the 4fnp two-electron excited states, whereas the collapse is moderate in the singly excited 4f-orbitals.
  • M. Sano, Y. Itoh, T. Koizumi, T. M. Kojima, S. D. Kravis, M. Oura, T. Sekioka, N. Watanabe, Y. Awaya, F. Koike
    Journal of Physics B: Atomic, Molecular and Optical Physics 29 (22) 5305 - 5313 0953-4075 1996/11/28 [Refereed][Not invited]
     
    Using a photon-ion merged-beam technique, we measured the relative yield spectra of Xe2+ and Xe3+ ions created by photoionization of Xe+ ions as a function of the photon energy in the 4d ionization region. The Xe3+ ion production, i.e. the double-electron ionization process is found to be dominant throughout the energy range investigated. A broad structure of 4d excitation ionization around 100 eV photon energy was observed in the Xe3+ yield spectrum. A spectral shoulder was observed for Xe3+ at around 85 eV, which was absent in the photoionization of neutral Xe. Some discrete lines were observed for both the Xe2+- and Xe3+-yield spectra below 75 eV. The experimental spectra were analysed by a multiconfiguration Dirac-Fock calculation. The largest structure at around 100 eV is attributable to 4d105s25p5 → 4d94f5s25p4np (n = 6, 7) two-electron transitions. The discrete lines were found to be due to 4d → np, nf transitions. A serious 4f-orbital collapse is suspected in the 4fnp two-electron excited states, whereas the collapse is moderate in the singly excited 4f-orbitals.
  • SD Kravis, M Abdallah, CL Cocke, CD Lin, M Stockli, B Walch, YD Wang, RE Olson, VD Rodriguez, W Wu, M Pieksma, N Watanabe
    PHYSICAL REVIEW A 54 (2) 1394 - 1403 1050-2947 1996/08 [Refereed][Not invited]
     
    A technique for electron spectroscopy which yields full two-dimensional momentum distributions for continuum electrons has been used to study ejected electrons from single ionization of lie by C6+ and proton projectiles at low velocities. Projectile velocities of 1.63, 1.38, and 1.16 a.u, for C6+ and 2.39, 1.71, 1.15, .85, and 0.63 a.u. for protons were used. All spectra show much broader distributions along the beam than transverse to the beam. For the case of proton bombardment, the spectra are strongly influenced by both target and projectile potentials, maximizing near the velocity of the saddle in the potential between the two, receding ion cores for the lowest projectile velocities. For C6+ projectiles, the spectra appear to be dominated by the projectile potential and the center of the distribution is strongly shifted toward the projectile velocity. Theoretical results from the continuum-distorted-wave-eikonal-initial state and classical-trajectory-Monte Carlo methods are in rather good agreement with the proton data but do not agree well with the C6+ data.
  • T Koizumi, Y Awaya, M Gonno, Y Itoh, M Kimura, TM Kojima, S Kravis, M Oura, M Sano, T Sekioka, N Watanabe, H Yamaoka, F Koike
    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 79 289 - 292 0368-2048 1996/05 [Refereed][Not invited]
     
    Using a photon-ion merged-beam apparatus, the relative photoion-yield spectra for doubly- and triply-charged ions from Xe+, Ba+ and Eu+ ions were measured in the 4d ionization region. The giant resonance peak appears for all target ions. The peak of Xe+ is broad and that of Eu+ is relatively narrow, similar to those observed in the neutral atoms. The spectrum of Xe3+ shows some structures around 87 and 93 eV. The summit of the giant resonance peak of Eu2+ is obviously split into two. These structures observed in the Xe3+ and Eu2+ spectra are not observed in the photoion spectra of the neutral targets. Some small peaks are observed in the Xe+ spectrum between 70 and 76 eV. A multi-configuration Dirac-Fock calculation reveals that these peaks are attributed to 4d-np and 4d-nf transitions. It was also found that the broad peak centered at 100 eV corresponds to shake-up resonance (4d(10)5s(2)5p(5)-->4d(9)4f5s(2)5p(4)np [n=6,7]) processes. Some prominent peaks that do not appear in the neutral Ba spectrum are observed clearly in the Ba+ one. These peaks are most probably due to the 4d-nf transition followed by Auger processes.
  • Y Negishi, N Watanabe, H Shiromaru, Y Achiba, N Kobayashi
    SURFACE REVIEW AND LETTERS 3 (1) 661 - 665 0218-625X 1996/02 [Refereed][Not invited]
     
    Ion-molecule reactions of silicon-carbon binary cluster ions SinCm+ (n = 1-2, m = 1-2) with O-2 molecules were studied by using an rf ion trap. The rate constants and branching ratios were determined for these cluster ions. For SiC2+, the rate constants for two isomers were obtained.
  • Molecular shape resonances studied by Angle-resolved PEPICO
    E. Shigemasa, J. Adachi, N. Watanabe, K. Soejima, A. Yagishita
    Eds. A. Yagishita and T. Sasaki: Atomic and Molecular Photoionization, Universal Academy Press, INC. 69 - 78 1996 [Refereed][Not invited]
  • Y. Negishi, N. Watanabe, H. Shiromaru, Y. Achiba, N. Kobayashi
    Surface Review and Letters 3 (1) 661 - 665 0218-625X 1996 [Refereed][Not invited]
     
    Ion-molecule reactions of silicon-carbon binary cluster ions SinC+m (n = 1-2, m = 1-2) with O2 molecules were studied by using an rf ion trap. The rate constants and branching ratios were determined for these cluster ions. For SiC+2, the rate constants for two isomers were obtained.
  • Y NEGISHI, A KIMURA, N KOBAYASHI, H SHIROMARU, Y ACHIBA, N WATANABE
    JOURNAL OF CHEMICAL PHYSICS 103 (23) 9963 - 9967 0021-9606 1995/12 [Refereed][Not invited]
     
    Ion-molecule reactions of silicon-carbon binary cluster ions SiCn+ (n=1-6) and SiCn- (n=2-4) with O-2 molecules were studied by using an rf ion trap. For all selected positive and negative parent ions, only SiCnO+ or SiCnO- were produced, respectively. The rate constants for the oxidation of these clusters were determined for the first time. The size dependence of the reactivities are discussed, and the presence of the ring form positive ions for n=3 and 5 are suggested. (C) 1995 American Institute of Physics.
  • Y NEGISHI, A KIMURA, N KOBAYASHI, H SHIROMARU, Y ACHIBA, N WATANABE
    JOURNAL OF CHEMICAL PHYSICS 103 (23) 9963 - 9967 0021-9606 1995/12 [Refereed][Not invited]
     
    Ion-molecule reactions of silicon-carbon binary cluster ions SiCn+ (n=1-6) and SiCn- (n=2-4) with O-2 molecules were studied by using an rf ion trap. For all selected positive and negative parent ions, only SiCnO+ or SiCnO- were produced, respectively. The rate constants for the oxidation of these clusters were determined for the first time. The size dependence of the reactivities are discussed, and the presence of the ring form positive ions for n=3 and 5 are suggested. (C) 1995 American Institute of Physics.
  • N WATANABE, H SHIROMARU, Y NEGISHI, Y ACHIBA, N KOBAYASHI, Y KANEKO
    CHEMICAL PHYSICS LETTERS 207 (4-6) 493 - 497 0009-2614 1993/05 [Refereed][Not invited]
     
    The reactions of C(n)Sc+ (n = 2-6) with O2 have been studied by using an rf ion trap. C(n)Sc+ was produced by the laser ablation of a mixed sample of graphite and scandium. Observed reaction product ions were ScO+ for all C(n)Sc+, and ScO2+ only for C(n)Sc+ with odd n. In the case of C6Sc+, the loss of 2C neutrals, leading to C4Sc+ production, was also observed. The estimated rate constants of C(n)SC+ + O2 reactions were found to alternate in magnitude with the cluster size; C(n)Sc+ clusters with even n have rate constants much lower than those with odd n.
  • N WATANABE, H SHIROMARU, Y NEGISHI, Y ACHIBA, N KOBAYASHI, Y KANEKO
    CHEMICAL PHYSICS LETTERS 207 (4-6) 493 - 497 0009-2614 1993/05 [Refereed][Not invited]
     
    The reactions of C(n)Sc+ (n = 2-6) with O2 have been studied by using an rf ion trap. C(n)Sc+ was produced by the laser ablation of a mixed sample of graphite and scandium. Observed reaction product ions were ScO+ for all C(n)Sc+, and ScO2+ only for C(n)Sc+ with odd n. In the case of C6Sc+, the loss of 2C neutrals, leading to C4Sc+ production, was also observed. The estimated rate constants of C(n)SC+ + O2 reactions were found to alternate in magnitude with the cluster size; C(n)Sc+ clusters with even n have rate constants much lower than those with odd n.
  • N. Watanabe, H. Shiromaru, Y. Negishi, Y.Achiba, N. Kobayashi, Y. Kaneko
    Z. Phys. D 26 (1) 252 - 254 1993 [Refereed][Not invited]
  • N. Watanabe, H. Shiromaru, Y. Negishi, Y.Achiba, N. Kobayashi, Y. Kaneko
    Z. Phys. D 26 (1) 252 - 254 1993 [Refereed][Not invited]
  • N WATANABE, H SHIROMARU, N KURIHARA, Y ACHIBA, N KOBAYASHI, Y KANEKO, J YODA
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 69 (2-3) 385 - 388 0168-583X 1992/06 [Refereed][Not invited]
     
    Positive and negative carbon cluster ions produced by laser ablation have been simultaneously stored in an RF ion trap. The size distributions of the stored cluster ions, which were measured by means of ion dumping followed by time-of-flight mass analysis, are consistent with that reported previously.
  • N WATANABE, H SHIROMARU, N KURIHARA, Y ACHIBA, N KOBAYASHI, Y KANEKO, J YODA
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 69 (2-3) 385 - 388 0168-583X 1992/06 [Refereed][Not invited]
     
    Positive and negative carbon cluster ions produced by laser ablation have been simultaneously stored in an RF ion trap. The size distributions of the stored cluster ions, which were measured by means of ion dumping followed by time-of-flight mass analysis, are consistent with that reported previously.

Conference Activities & Talks

  • 星間塵表面の化学:重水素濃集に果たす役割  [Invited]
    渡部 直樹
    日本地球化学会年会  2018/09
  • Measurements of activation energies for diffusion of hydrogen atom on pure CO solid  [Invited]
    N. Watanabe
    European Conference On Surface Science (ECOSS34)  2018/08
  • Infrared Measurements of Efficient Chemical Desorption of Hydrogen Sulfide from Amorphous Solid Water  [Invited]
    N. Watanabe
    COSPAR 2018, The Evolving Chemical Universe: from proto-stars to the Origin of Life  2018/07
  • Surface Chemistry of the ISM: Experimental Approach to grain surface processes  [Invited]
    N. Watanabe
    The Olympian Symposium 2018 Gas and stars from milli- to mega- parsecs  2018/05
  • H 2ortho-para conversion on amorphous solid water  [Invited]
    N. Watanabe
    International Conference on Photonic Electronic and Atomic Collisions(ICPEAC2017)  2017/07
  • 低温氷表面における水素の化学物理過程:宇宙の分子進化の鍵  [Not invited]
    渡部 直樹
    日本真空学会関西支部&日本表面科学会関西支部合同セミナー2017水素の挙動と物質科学 -最近の展開-  2017/07
  • Ortho-to-para nuclear spin conversion of H2 on ice: a key to chemical evolution in space  [Not invited]
    Naoki Watanabe
    XXXVI BIENNAIAL MEETING OF THE SPANISh ROYAL SOCIETY OF CHEMISTRY  2017/06
  • Physicochemical processes on Ice Dust towards Deuterium Enrichment  [Not invited]
    N. Watanabe
    International Symposium on Molecular Spectroscopy  2017/06
  • Physicohemical Processes on ice dust towards deuterium enrichment  [Not invited]
    N.Watanabe
    International Symposium on Molecular Spectroscopy 72ND MEETING  2017/06
  • Ortho-to-para ratios of hydrogen molecules desorbed from ice at around 10 K: What happens on cosmic ice dust?  [Invited]
    N. Watanabe, H. Ueta, T. Hama, A. Kouchi
    The 253thAmerican Chemical Society National Meeting  2017/04
  • Strong temperature dependence of ortho-to-para conversion of H2 on amorphous solid water at around 10 K  [Not invited]
    N. Watanabe
    EUROPEAN CONFERNCE ON LABORATORY ASTROPHYSICS (ECLA2016) GAS ON THE ROCKS  2016/11  Madrid, Spain
  • Experimental approach to hydrogen chemistry on grain surfaces: molecular formation  [Invited]
    N. Watanabe
    Center for Astrochemical Studies Seminar  2016/10  Max-Planck-Institut für extraterrestrische Physik, Germany
  • Experimental approach to ortho-to-para ratio of hydrogen and water molecules desorbed from ice at around 10 K  [Invited]
    Naoki Watanabe
    Workshop on Astrochemistry in Star and Planet Formation  2016/02  Riken, Saitama, Japan
  • Deuterium chemistry and nuclear spin conversion on grain surfaces: implication to deuterium enrichment  [Invited]
    N. Watanabe
    From clouds to protoplanetary disk: the astrochemical link  2015/10  Hans Harnack Haus, Berlin, Germany
  • Grain Surface Chemistry: What Happens Without Photons and Ions  [Invited]
    N. Watanabe
    A symposium to honor Lou Allamandola’s Contributions to the Molecular Universe  2015/09  Annapolis, MD, USA
  • Experimental Approach to Chemistry of Cosmic Dust  [Invited]
    N. Watanabe
    COST Action Our Astrochemical History CM1401  2015/05  The Czech Republic
  • Experimental approach to nonenergetic physicochemical processes on icy grains  [Invited]
    Naoki Watanabe
    Icy Grain Chemistry for Formation of Complex Organic Molecules: From Molecular Clouds to Protoplanetary Disks, Comets and Meteorites  2015/03  Tokyo Institute of Technology, Japan
  • Diffusion of hydrogen atom on amorphous solid water: Thermal or tunneling?  [Not invited]
    N. Watanabe
    247th ACS Chemistry & Materials for Energy  2014/03  Dallas, USA
  • Physics and chemistry of hydrogen on cosmic dust: diffusion, spin temperatures, and water formation  [Invited]
    N. Watanabe, T. Hama, H. Hidaka, Y. Kimura, A. Kouchi, Y. Oba, V. Pirronello
    First Workshop on Experimental Laboratory Astrophysics  2013/02  Kauai, Hawaii
  • Physicochemical Processes of Hydrogen on Ice: A Key for Chemical Evolution in Space  [Invited]
    N. Watanabe
    2nd International Symposium on Hierarchy and Holism  2013/02  Tokyo, Japan
  • Surface diffusion mechanism of atomic hydrogen and the ortho/para ratio of nascent H2 molecule on amorphous solid water at around 10 K  [Invited]
    N. Watanabe
    International Lorentz Center Workshop: Dynamical Phenomena at Surfaces: The Role of Complexity  2012/11  Leiden, The Netherlands
  • Surface diffusion mechanism of atomic hydrogen and the ortho/para ratio of nascent H2 molecule on amorphous solid water at around 10 K  [Invited]
    N. Watanabe
    International Lorentz Center Workshop: Dynamical Phenomena at Surfaces: The Role of Complexity  2012/11  Leiden, The Netherlands
  • Grain surface processes at very low temperatures: hydrogen diffusion and tunneling reactions  [Invited]
    N. Watanabe
    Gordon Research Conference, Radiation Driven Processes in Physics, Chemistry, Biology, and Industry  2012/07  New Hampshire, USA
  • Spin temperatures of hydrogen and water molecules on amorphous solid water  [Invited]
    N.Watanabe
    ASTROCHEM 2012  2012/07  Kolkata, India
  • Hydrogen processes on dust grains: H atom diffusion and water formation  [Invited]
    N.Watanabe
    30th COSPAR Scientific Assembly  2012/07  Mysore, India
  • Hydrogen processes on dust grains: H atom diffusion and water formation  [Invited]
    N.Watanabe
    30th COSPAR Scientific Assembly  2012/07  Mysore, India
  • Spin temperatures of hydrogen and water molecules on amorphous solid water  [Invited]
    N.Watanabe
    ASTROCHEM 2012  2012/07  Kolkata, India
  • Grain surface processes at very low temperatures: hydrogen diffusion and tunneling reactions  [Invited]
    N. Watanabe
    Gordon Research Conference, Radiation Driven Processes in Physics, Chemistry, Biology, and Industry  2012/07  New Hampshire, USA
  • Hydrogen chemistry on cold grain surfaces  [Invited]
    N.Watanabe
    XVIIIth Symposium on Atomic, Cluster, and Surface Physics  2012/01  Alpe d'Huez, France
  • Hydrogen chemistry on cold grain surfaces  [Invited]
    N.Watanabe
    XVIIIth Symposium on Atomic, Cluster, and Surface Physics  2012/01  Alpe d'Huez, France
  • Hydrogen tunneling reaction and its isotope effect at a low temperature ice surface: Origin of deuterium enrichments in interstellar formaldehyde and methanol  [Invited]
    N. Watanabe, H. Hidaka, A. Kouchi, N. Watanabe, H. Hidaka, A. Kouchi
    International Conference on the Research of Chemistry and Physics of Matrix Isolated Species(MATRIX2011)  2011/07  Vancouver, Canada
  • Hydrogen tunneling reaction and its isotope effect at a low temperature ice surface: Origin of deuterium enrichments in interstellar formaldehyde and methanol  [Invited]
    N. Watanabe, H. Hidaka, A. Kouchi, N. Watanabe, H. Hidaka, A. Kouchi
    International Conference on the Research of Chemistry and Physics of Matrix Isolated Species(MATRIX2011)  2011/07  Vancouver, Canada
  • Ice surface chemistry of hydrogen atom in space  [Invited]
    N. Watanabe, H. Hidaka, T. Hama, A. Kouchi, T. Chigai, Y. Kimura
    27th European Conference on Surface Science, ECOSS 27  2010/08  Groningen, the Netherlands
  • Ice surface chemistry of hydrogen atom in space  [Invited]
    N. Watanabe, H. Hidaka, T. Hama, A. Kouchi, T. Chigai, Y. Kimura
    27th European Conference on Surface Science, ECOSS 27  2010/08  Groningen, the Netherlands
  • Surface processes of atomic hydrogen at very low temperatures relevant to astrochemistry  [Invited]
    N. Watanabe
    24th International Conference on Atomic Collisions in Solids ICACS- 24  2010/07  Krak?w, Poland
  • Surface processes of atomic hydrogen at very low temperatures relevant to astrochemistry  [Invited]
    N. Watanabe
    24th International Conference on Atomic Collisions in Solids ICACS- 24  2010/07  Kraków, Poland
  • Chemistry of atomic hydrogen on interstellar ice grains at very low temperatures  [Invited]
    N. Watanabe, H. Hidaka, A. Kouchi, T. Hama, Y. Kimura
    Western Pacific Geophysics Meeting  2010/06  Taipei, Taiwan
  • Chemistry of atomic hydrogen on interstellar ice grains at very low temperatures  [Invited]
    N. Watanabe, H. Hidaka, A. Kouchi, T. Hama, Y. Kimura
    Western Pacific Geophysics Meeting  2010/06  Taipei, Taiwan
  • Physicochemical processes of atomic hydrogen on amorphous solid water at very low temperatures  [Invited]
    N. Watanabe, A. Kouchi, H. Hidaka, Y. Kimura, T. Hama
    239th American Chemical Society National Meeting & Exposition  2010/03  San Francisco, USA
  • Physicochemical processes of atomic hydrogen on amorphous solid water at very low temperatures  [Invited]
    N. Watanabe, A. Kouchi, H. Hidaka, Y. Kimura, T. Hama
    239th American Chemical Society National Meeting & Exposition  2010/03  San Francisco, USA
  • Ice surface reactions: its role in chemical evolution in space  [Invited]
    N.Watanabe
    ILTS International Symposium "Frontier of Low Temperature Science", Sapporo  2009/11  Sapporo
  • Ice surface reactions: its role in chemical evolution in space  [Invited]
    N.Watanabe
    ILTS International Symposium "Frontier of Low Temperature Science", Sapporo  2009/11  Sapporo
  • Tunneling reactions of atomic hydrogen and molecules on amorphous solid water at very low temperatures  [Invited]
    N. Watanabe
    Horiba-ISSP International Symposium on “Hydrogen and water in condensed matter physics”  2009/10  Chiba
  • Tunneling reactions of atomic hydrogen and molecules on amorphous solid water at very low temperatures  [Invited]
    N. Watanabe
    Horiba-ISSP International Symposium on “Hydrogen and water in condensed matter physics”  2009/10  Chiba
  • Nonenergetic reactions between hydrogen and molecules On Interstellar Grain Surfaces  [Invited]
    N. Watanabe
    XXVI International Conference on Photonic, Electronic, and Atomic Collisions  2009/07  Michigan, USA
  • Reactions of hydrogen atoms and molecules on amorphous solid water at very low temperatures  [Invited]
    N. Watanabe
    Gordon Research Conferences, Physics & Chemistry of Matrix-Isolated Species  2009/07  Oxford, UK
  • Reactions of hydrogen atoms and molecules on amorphous solid water at very low temperatures  [Invited]
    N. Watanabe
    Gordon Research Conferences, Physics & Chemistry of Matrix-Isolated Species  2009/07  Oxford, UK
  • Nonenergetic reactions between hydrogen and molecules On Interstellar Grain Surfaces  [Invited]
    N. Watanabe
    XXVI International Conference on Photonic, Electronic, and Atomic Collisions  2009/07  Michigan, USA
  • Experimental approach to grain surface reactions of hydrogen and deuterium atoms  [Invited]
    N.Watanabe
    International Lorentz Center Workshop: Interstellar Surfaces: From Laboratory to Models  2008/10  Leiden, Holland
  • Experimental approach to grain surface reactions of hydrogen and deuterium atoms  [Invited]
    N.Watanabe
    International Lorentz Center Workshop: Interstellar Surfaces: From Laboratory to Models  2008/10  Leiden, Holland
  • Grain surface chemistry: fractionation routes  [Invited]
    N. Watanabe
    The Molecular Univers: an International Meeting on Physics and Chemistry of the Intersteller Medium  2008/05  Arcachon, France
  • Grain surface chemistry: fractionation routes  [Invited]
    N. Watanabe
    The Molecular Univers: an International Meeting on Physics and Chemistry of the Intersteller Medium  2008/05  Arcachon, France
  • Simultaneous irradiation experiments of H2O-CO binary ice with UV photons and cold H atoms  [Invited]
    N. Watanabe, A. Nagaoka, O. MouriI, A. Kouchi, V. Pirronello
    Asia-Oceania Geosciences Society Annual Meeting  2007/08  Bangkok, Thailand
  • Simultaneous irradiation experiments of H2O-CO binary ice with UV photons and cold H atoms  [Invited]
    N. Watanabe, A. Nagaoka, O. MouriI, A. Kouchi, V. Pirronello
    Asia-Oceania Geosciences Society Annual Meeting  2007/08  Bangkok, Thailand
  • Laboratory study of chemical processes on interstellar ice grains  [Invited]
    N. Watanabe, A. Nagaoka, H. Hidaka, A. Kouchi
    XXIV International Union of Feodesy and Geophysics (IUGG) General Assembly  2007/07  Perguia, Italy
  • Laboratory study of chemical processes on interstellar ice grains  [Invited]
    N. Watanabe, A. Nagaoka, H. Hidaka, A. Kouchi
    XXIV International Union of Feodesy and Geophysics (IUGG) General Assembly  2007/07  Perguia, Italy
  • Reactions of hydrogen and deuterium atoms with CO, formaldehyde, and methanol on ice grains  [Invited]
    N.Watanabe
    International Astrophysics and Astrochemistry Meeting: Molecules in Space & Laboratory  2007/05  Paris, France
  • Reactions of hydrogen and deuterium atoms with CO, formaldehyde, and methanol on ice grains  [Invited]
    N.Watanabe
    International Astrophysics and Astrochemistry Meeting: Molecules in Space & Laboratory  2007/05  Paris, France
  • Formation of simple organic molecules by Hydrogenation on grain surfaces  [Invited]
    N. Watanabe
    International Astronomical Union Symposium: Astrochemistry,  2005/08  California,USA
  • Formation of simple organic molecules by Hydrogenation on grain surfaces  [Invited]
    N. Watanabe
    International Astronomical Union Symposium: Astrochemistry,  2005/08  California,USA
  • Formation of deuterated methanol by surface reactions at 10 K  [Invited]
    N. Watanabe, A. Nagaoka, A. Kouchi
    Asia-Oceania Geosciences Society Annual Meeting  2005/06  Singapore
  • Formation of deuterated methanol by surface reactions at 10 K  [Invited]
    N. Watanabe, A. Nagaoka, A. Kouchi
    Asia-Oceania Geosciences Society Annual Meeting  2005/06  Singapore
  • Evolution of CO molecule on dusts in dense core: formation of H2CO and CH3OH  [Invited]
    N. Watanabe
    The 4th International Symposium on New Trends of Physics, Recent Advances in Astrophysics and Planetary Science -from the early universe to the Solar system-  2005/03  Sapporo
  • Evolution of CO molecule on dusts in dense core: formation of H2CO and CH3OH  [Invited]
    N. Watanabe
    The 4th International Symposium on New Trends of Physics, Recent Advances in Astrophysics and Planetary Science -from the early universe to the Solar system-  2005/03  Sapporo

MISC

  • Inversion of surface voltage on H2O films affecting sublimation of CO underlayer
    Atsuki Ishibashi, Yasuhiro Oba, Tetsuya Hama, Akira Kouchi, Naoki Watanabe  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  258-  2019/08  [Not refereed][Not invited]
  • Activation energy of OH-radical diffusion on water ice surface
    Ayane Miyazaki, Naoki Watanabe, W. M. C. Sameera, Tetsuya Hama, Hiroshi Hidaka, Akira Kouchi  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  258-  2019/08  [Not refereed][Not invited]
  • Behavior of OH radical on ice
    Naoki Watanabe, Ayane Miyazaki, W. M. C. Sameera, Tetsuya Hama, Akira Kouchi  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  258-  2019/08  [Not refereed][Not invited]
  • Reaction experiments on H exposure of solid methanol at low temperatures
    Yukiko Yarnall, Hiroshi Hidaka, Yasuhiro Oba, Tetsuya Hama, Akira Kouchi, Naoki Watanabe  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  255-  2018/03  [Not refereed][Not invited]
  • Ortho-to-para ratios of hydrogen molecules desorbed from ice at around 10 K: What happens on cosmic ice dust?
    Naoki Watanabe, Hirokazu Ueta, Tetsuya Hama, Akira Kouchi  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  253-  2017/04  [Not refereed][Not invited]
  • Tetsuya Hama, Akira Kouchi, Naoki Watanabe  Journal of the Vacuum Society of Japan  60-  (7)  264  -274  2017  [Not refereed][Not invited]
     
    Chemistry of interstellar H2O is essential for understanding the formation of stars and planetary systems because of the ubiquity of H2O in space. The abundance ratio of nuclear spin isomers (the ortho-to-para ratio, OPR) can be a key for interstellar water chemistry, when assuming that the OPR desorbed from ice is closely related to the ice formation temperature. However, the above assumption has not been experimentally validated. Here, we report that H2O photodesorbed from ice at 10 K shows a statistical OPR of 3, even when the ice is produced in situ by hydrogenation of O2, a known formation process of interstellar H2O. This invalidates the hypothesis for relation between OPR and temperature. Reinterpretation of previous observations is necessary to improve our understanding of interstellar chemistry and the formation of the solar system and comets.
  • 超高真空極低温透過型電子顕微鏡の開発─氷のその場観察をめざして─
    香内晃, 日高宏, 羽馬哲也, 木村勇気, 渡部直樹, 中坪俊一, 藤田和之, 新堀邦夫, 池田正幸  雪氷  2017  [Refereed][Not invited]
  • 星間塵表面における量子トンネル水素付加反応:その同位体効果と表面構造依存
    羽馬哲也, 渡部直樹, 香内晃  触媒  2017  [Refereed][Not invited]
  • 羽馬哲也, 香内晃, 渡部直樹  化学と教育  64-  282  -283  2016/12  [Refereed][Not invited]
  • 羽馬哲也, 植田寛和, 渡部直樹, 香内晃  地球化学  50-  (2)  33  -50  2016/06  [Refereed][Not invited]
  • Role of quantum tunneling for the formation of H2O by reaction of H-2 with OH on interstellar grains
    Yasuhiro Oba, Naoki Watanabe, Tetsuya Hama, Kazuaki Kuwahata, Hiroshi Hidaka, Akira Kouchi  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  247-  2014/03  [Not refereed][Not invited]
  • Diffusion of hydrogen atom on amorphous solid water: Thermal or tunneling?
    Naoki Watanabe, Kazuaki Kuwahata, Tetsuya Hama, Akira Kouchi  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  247-  2014/03  [Not refereed][Not invited]
  • Formation of H2O Ice through the Surface Reaction O2 + H at Low Temperatures: Reaction Kinetics and Structure of the Ice
    Oba, Y, Miyauchi, N, Chigai, T, Hidaka, H, Watanabe, N, Kouchi, A  Physics and Chemistry of Ice 2010, eds. Y. Furukawa, G. Sazaki, T. Uchida, N. Watanabe, Hokkaido University Press, Sapporo, ISBN: 978-4-8329-0361-6  361  -368  2011  [Not refereed][Not invited]
  • Sequential hydrogenation of molecular oxygen on cold surfaces: reaction kinetics and structure of formed H2O ice
    Y.Oba, N.Miyauchi, H.Hidaka, T.Chigai, N.Watanabe, A.Kouchi  Proceedings of the International Astronomical Union  280-  2011  [Refereed][Not invited]
  • Ammonia formation by the successive hydrogenation of N atoms trapped in solid N-2 at 10 K
    Hiroshi Hidaka, Motohiro Watanabe, Akira Kouchi, Naoki Watanabe  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  239-  2010/03  [Not refereed][Not invited]
  • Physicochemical processes of atomic hydrogen on amorphous solid water at very low temperatures
    Naoki Watanabe, Akira Kouchi, Hiroshi Hidaka, Yuki Kimura, Tetsuya Hama  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  239-  2010/03  [Not refereed][Not invited]
  • A. Kouchi, N. Watanabe, H. Hidaka, N. Miyauchi, Y. Oba, T. Chigai  Astron. Soc. Pacific Conf. Ser.  414-  338  -346  2010  [Refereed][Not invited]

Awards & Honors

  • 2020/04 令和2年度 科学技術分野の文部科学大臣表彰 科学技術賞 研究部門

Research Grants & Projects

  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Specially Promoted Research
    Date (from‐to) : 2017/04 -2022/03 
    Author : 渡部 直樹, 大場 康弘, 杉本 敏樹, 中井 陽一
     
    超高真空実験槽中に氷星間塵表面を擬似したアモルファス氷表面を作製し,紫外線照射で生成したのOHラジカルの表面拡散の活性化エネルギーを求めることに,世界で初めて成功した(渡部,宮崎,羽馬)。また,OHラジカルの吸着状態と脱離メカニズムを明らかにした。これらの成果には,新たに雇用した研究補助者(WMC Sameera)の量子化学計算によるところが大きい。この結果を発表すべく,論文の執筆を始めた。 星間塵表面物質のひとつである炭素質表面を,グラファイトディスクのレーザーアブレーションにより真空実験槽内でその場作製し,その構造と作製条件の依存性を,透過型電子顕微鏡を用いて調べ,いつでも最適な試料表面を作製するノウハウを確立した(柘植,木村)。 極低温超高真空原子間力顕微鏡の特性を調べた。観測する基板が9~10Kの極低温に到達すること,それを維持出来る熱負荷の確認を行った。極低温下でシリコン結晶を観測することができ基本的な運転を習熟した。(日高,香内)。 氷表面上に分子イオンが吸着した際の生成物を検出するイオンピックアップ装置の立ち上げを行った。冷凍基板および赤外分光計,イオン源を超高真空槽に設置し,極低温氷の作製など予備実験を行った(渡部,大場,中井) 杉本は京都大学から分子科学研究所への異動に伴い,装置の移設・再構築を行った。また,分光測定中の振動ノイズを軽減するため,希釈冷凍機から液体ヘリウム貯め込み式の冷却方式への転換作業を進めた。氷表面に対する和周波発生振動分光を行ったところ,表面特有の水素結合構造を有する液晶相が熱力学的な安定相として氷表面に存在することを発見した。
  • 星間分子雲初期に起こるケイ酸塩星間塵表面での分子進化
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2017/04 -2018/03 
    Author : 渡部 直樹, 大場 康弘
     
    本研究は,未解明になっている,星間塵表面に氷マントルが生成される以前の,ケイ酸塩星間塵表面での分子生成,重水素濃集に着目し,化学・物理素過程を系統的かつ定量的な実験で調べ,星間塵上での分子進化の解明を目指すものである。採択と同時に,研究の根幹をなす,新たなケイ酸塩試料作製装置開発に向け,真空ポンプ,真空部品などを購入した。また,表面を原子間力顕微鏡で評価するため,カンチレバーチップを購入した。同時に,プラズマ放電による鉱物サンプル試料の作製を業者に依頼した。ケイ酸塩試料作製装置の開発は引き続き行っているところだが,業者に作製を依頼したサンプル試料がかなり高品質であることが分かった。 また,採択直後に東京理科大学にて,本研究課題についての研究討論を行い,本課題の独創性や重要性をアピールすることができた。 その後,すぐに現在実施中の特別推進研究が採択されたため,本研究課題の実施は7月28日をもって終了した。しかし,上記の取り組みは特別推進研究に引き継がれるため,基盤研究Aで行った討論,整備した装置類は将来にわたって有効に活用される。
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)
    Date (from‐to) : 2012/05 -2017/03 
    Author : WATANABE NAOKI, KOUCHI Akira
     
    Formation and isotope fractionation of molecules in molecular clouds are very important as the initial stage of chemical evolution toward planetary system. The aim of this project was to clarify the role of physicochemical processes on cosmic ice dust at very low temperatures which are keys in chemical evolution. We have experimentally demonstrated mechanisms of elementary processes for molecular formation and deuteration on ice at around 10 K. We determined diffusion-rates of hydrogen (deuterium) atoms on amorphous ice and formation (and deuteration) pathways and those reaction rates for water and some primordial organic molecules.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    Date (from‐to) : 2014/04 -2016/03 
    Author : Watanabe Naoki, UETA Hirokazu
     
    Interstellar dust particles play an important role in chemical evolution of interstellar matter. Although the details of dust formation are still unknown, it is generally believed that they form in the gas phase via homogeneous nucleation. In contrast, the present study focuses on inhomogeneous ion-induced nucleation in the gas phase in which activation barriers for cluster formation decrease significantly by ion-ion induced dipole interaction. We have constructed an rf ion trap to study the cluster ion formation as the first stage of nucleation. We have been successful in storing several kinds of molecular ions and clusters and monitoring the successive reaction in the rf trap.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2013/10 -2016/03 
    Author : Kouchi Akira, HIDAKA Hiroshi, OBA Yasuhiro, HAMA Tetsuya, CHIGAI Takeshi, WATANABE Naoki, KIMURA Yuki, TOMARU Takayuki
     
    An ultrahigh vacuum (UHV) transmission electron microscope for in-situ observation of ice has been developed. We use a single tilt liquid He cooling holder for specimen cooling to 4 K. Two ports are directed to the specimen surface for in-situ studies: gas-inlet, and UV irradiation. Results of preliminary observation are as follows: (1) Macroscopic defect structure of vapor-deposited amorphous ice are observed at first time. (2) Formation of ice XI by UV irradiation onto ices Ih and Ic are observed at 75-100 K. On the other hand, no structural change has been observed by UV irradiation onto amorphous ice. (3) Formation of high-density amorphous ice by CO matrix sublimation method has been developed.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2013/04 -2016/03 
    Author : NAKAI Yoichi, WATANABE Naoki, KOJIMA Takao, HIDAKA Hiroshi
     
    We performed stable and precise measurements compared with previous studies for Gibbs free energy changes of stepwise association reactions of a water molecule to H3O+(H2O)n ions using a ion drift tube with a selected ion injection. Furthermore, an empirical effective temperature of the reaction equilibrium constants was obtained for association/dissociation reactions of a water molecule to/from H3O+(H2O)n ions in a pure water vapor. The effective temperature means a representative physical quantity of collision energy influenced by an electric field. It was found that a new parameter describing electric field dependence of the effective temperature presumably reflects structures of H3O+(H2O)n ions. We also performed R&D of ion handling methods in an RF ion trap, such as an ion mass selection, in order to make use of RF ion traps for cluster formation experiments.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2010/04 -2013/03 
    Author : NAKAI Yoichi, WATANABE Naoki, KOJIMA Takao, HIDAKA Hiroshi
     
    Experimental study for cluster ion formation, early stages of ion induced nucleation, has been performed. We developed the experimental equipment, in which the region for production of initial ions is separated from that for generation of cluster ions, in order to define the reaction paths. Gibbs free energy changes for the stepwise association of an H2O molecule were measured for H3O+(H2O)n cluster ions and our method has provided more stable and precise results compared with previous measurements. In the use of initial NO+ ions, we have reduced influence of metastable NO+ ions in produced initial ions, using hydrogen buffer gas.
  • 星間塵表面反応:分子進化と同位体分別機構の新展開
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2012 -2012 
    Author : 渡部 直樹, 日高 宏, 羽馬 哲也
     
    本研究は,極低温下での星間塵表面反応素過程の詳細を実験的に調べ,星間分子雲での分子進化と同位体分別における星間塵の役割を明らかにすることを主たる目的としている.本研究課題が採択されると同時に,始原天体に関する国際会議(新潟),原始太陽系における鉱物・水・有機物に関する国際シンポジウム(東京)および日本地球惑星科学連合大会(千葉幕張)に出席し,星間塵表面における水分子および始原有機分子生成に関する研究の現状報告を行ない,同位体濃集プロセスに関する情報収集・議論を通して本研究の重要性や独創性を充分アピールすることができた. 現有実験装置の改良も本研究課題の重要な目的である。まず気相の原子・分子を検出する装置を駆動するための電源ユニット(NIM標準ビン電源,クリアパス社製)を購入し,信号検出系の改善に取り組み始めた.改良は現時点でも引き続き行っているところだが,これにより,実験の際の信号/ノイズ比が向上し,さらに規則的に現れる電気的なノイズを除去することが可能になると予想され、実験値の精度向上等大きな効果が期待される. その後すぐに現在実施中の基盤研究Sが採択されたため,本研究課題の実施は5月31日をもって終了した.しかし,上記の取り組みは基盤研究Sに引き継がれるため,基盤研究Aで行った発表・研究議論,整備した物品は、将来にわたって有効に活用される.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2010 -2012 
    Author : KOUCHI Akira, WATANABE Naoki, HIDAKA Hiroshi
     
    An ultrahigh vacuum low temperature atomic force microscope for in-situ deposition of amorphous ice and for observation of ice surface has been developed. We have succeeded to observe the surface structure of amorphous ice and found that the surface of amorphous ice is very porous. This might cause the catalytic properties of amorphous ice in surface atomic reactions.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research a proposed research project)
    Date (from‐to) : 2009 -2011 
    Author : WATANABE Naoki, HIDAKA Hiroshi
     
    Ice surface reactions relevant to chemical evolution and deuterium fractionation were experimentally investigated. Activation energies for ice-surface diffusion of H and D atoms were determined. It was found that effective mass of reaction system is a control-factor of tunneling reactions. The reactivities of tunneling reactions related to deuterium fraction of formaldehyde can be well explained by the effective masses. A novel route of CO_2 formation on the ice surface was found.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2009 -2011 
    Author : WATANABE Naoki, HIDAKA Hiroshi
     
    Water molecule formation and its deuterium fractionation via surface tunneling reactions were investigated experimentally, relevant to chemical evolution in a molecular cloud. We found that H_2O molecule is produced by tunneling reaction, OH + H_2, at very low temperature surfaces and that, from the isotope effect on the above reaction, the formation of OD is essential for deuterium fractionation of water rather than HD or D_2 formation.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)
    Date (from‐to) : 2005 -2009 
    Author : KOUCHI Akira, WATANABE Naoki
     
    Surface atomic reactions on interstellar grains at low temperatures are investigated experimentally using newly developed experimental setup. Formation mechanisms of H_2, H_2O, CO_2, H_2CO, and CH_3OH are clarified. Measurement of sticking coefficient of H-atoms onto amorphous water ice enables us to deduce reaction rate constants. We also showed that amorphous water ice enhances reactivity at higher temperatures compared with pure solid reactants.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2007 -2008 
    Author : WATANABE Naoki, HIDAKA HIROSHI
     
    星間分子の重水素濃集プロセスとして研究代表者らが提唱している極低温星間塵表面反応を, 実験により定量的に評価した. 特に, 高度な重水素濃集が観測で確認されているホルムアルデヒド, メタノールの重水素化表面反応に焦点をあて, 重要な反応経路について実効的な反応速度定数を決定し, 上記分子種に関する重水素濃集の星間塵表面反応ネットワークを完成させた.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas
    Date (from‐to) : 2004 -2008 
    Author : YAMAMORO Tetsuo
     
    惑星系円盤におけるダストの衝突進化と熱進化の素過程,観測結果を読み解くうえで重要な光学に関する研究,ダスト生成とその後続解析実験,ダスト衝突実験,氷表面における分子反応等,物質進化の総合的研究を展開した.加えて,この分野の研究基盤形成にも貢献した.研究グループの交流を促進し,国内の関連研究グループの組織化を図り,研究コミュニティー形成を積極的に推進した
  • 星間塵表面における重水素濃縮機構
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas
    Date (from‐to) : 2004 -2005 
    Author : 渡部 直樹, 香内 晃
     
    本研究では,これまで全く情報の無かった星間塵表面における星間分子の重水素濃集過程を実験的に調べることを目的としている.本年度は以下のことを明らかにした. ホルムアルデヒド(H_2CO)における重水素濃集過程を調べるために,10KのH_2O氷(疑似星間塵表面)上でCO+DおよびH_2CO+D,D_2CO+Hの表面反応を定性的に調べた.その結果,すべての反応で重水素(D)原子を含む重水素体ホルムアルデヒドが生成された.実験条件から推測すると,これらの反応はすべて宇宙空間で起こりうることが解った.大雑把な見積もりでは重水素体を生成するのにもっとも速い反応はH_2CO+Dの系に見られるH-D置換反応である.しかし,一度重水素体が生成してもH原子との反応でD原子が再びH原子に入れ替わる反応(D_2CO+H→・・→H_2CO)も見られたことから,ホルムアルデヒドにおけるH-D置換反応が結果として重水素濃集過程になりうるかどうかを見極めるにはより定量的な実験が必要であることがわかった.
  • Surface reactions of atoms and the mechanism of deuterium fractionation on inter Stellar dusts at the very low temperature
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2004 -2005 
    Author : WATANABE Naoki, KOUCHI Akira
     
    This project was carried out for the purpose of obtaining the reaction channels and rates of the formation of interstellar molecules via surface reactions of atoms and also revealing the origin of deuterium enrichment in methanol molecules observed. We summarize the results of our research as follows. 1.The rate of addition of deuterium atoms to solid CO molecule is as slow as one-tenths of that of hydrogen addition, indicating that the deuterium addition is unlikely for the first step of the deuterium enrichment of methanol. 2.We confirmed that H-D substitution reactions in CH_3OH-d_n(CH_3OH-d_n+D→CH_3OH-d_,n=0-2) proceed in solid phase at 〜10K. The reaction rates of the substitution decrease as number of D atoms in methanol, n, increases 3.We demonstrated for the first time that deuterium enrichment observed can be achieved partly by the grain-surface reactions. Our quantitative data shows that H-D substitution is more efficient to produce deuterated methanol than the successive deuterium addition to CO in a molecular cloud.
  • UV-induced diamond formation in interstellar clouds
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2003 -2004 
    Author : KOUCHI Akira, ARAKAWA Masahiiko, WATANABE Naoki
     
    New formation routes of diamond in interstellar clouds and parent bodies of carbonaceous chondrites are found based on laboratory experiments. It is shown that diamond precursor nucleated as a result of UV photolysis of interstellar ice mixtures in molecular clouds, and grew with further UV irradiation in diffuse clouds. The present study supports the occurrence of diamonds in interstellar clouds, and suggests that diamond is ubiquitous in space. Furthermore, we performed experiments on the aqueous alteration and the subsequent thermal metamorphism of organic materials formed in molecular cloud, and found that diamonds formed by this process in the parent bodies of carbonaceous chondrites. The various characteristics of nano-diamonds in chondrites and interplanetary dusts are well explained by these new formation routes.
  • Development of electrostatic accelerator for ice dust and the aggregates
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2001 -2003 
    Author : ARAKAWA Masahiko, WATANABE Naoki, MAENO Norikazu
     
    We have developed an electrostatic accelerator to launch a ice dust and ice aggregates at a wide range of velocities from cm/s to km/s. The ice sample launched was prepared by a condensation, method : a cold copper plate cooled by liquid nitrogen was subjected to an air saturated with water vapor at -10℃. The condensed icy dust is an almost spherical shape with the size of 10 μm, Ice aggregates were grown by collecting each ice dust under high electric field more than 100 V/cm. The aggregate was charged under the electric field, so that it was launched by the electrostatic attraction. The relationship between the electric field and the velocity is derived as follows for the aggregates of 500μm.: V_i=0.25(V_/d)^<0.9> (m/s), V_i: velocity, V_o: Voltage, d: distance between electrodes (d=2.5mm). The launch velocity is strongly affected by the air drag for the small aggregates, so we have set a vacuum chamber to eliminate the gas drag to the aggregates in the acceleration. We also used a longer acceleration tube to avoid disruption of the aggregates by the strong attraction force. As a result we have achieved 20m/s for 500μm aggregate at the electric field of 1kV/mm and 1 bar. In the evacuated condition of 0.1 bar, the launched velocity increased about 3 to 4 times higher than that of 1 bar at the same electric field strength. This means that it could be possible to achieve more than 100 m/s for ice aggregate of 500 μm at 1kV/mm.
  • Collisional sticking of organic grains in the solar nebula
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2000 -2001 
    Author : KOUCHI Akira, WATANABE Seiichiro, WATANABE Naoki, ARAKAWA Masahiko
     
    Heating and collision experiments were performed involving interstellar organic material analogue to determine the distribution of interstellar organic material in the proto solar nebula and to investigate the growth of organic grains. We found that there were interstellar organic grains in 2.1-3.0 AU, silicate grains <2.1 AU, and ice grains>3.0 AU. We also found that gas evaporated at around 2.2 AU is very reductive. The organic material in 2.1-3.0 AU is very sticky ; the sticking threshold velocity of the mm-size organic grains is 5 m/s. This shows a very rapid coagulation of organic grain aggregates, the formation of planetesimals even the early stage of the turbulent accretion disk. The planetesimals in this region become achondrites' parent bodies. In contrast, the formation of planetesimals in <2.1 AU and >3.0 AU occur when passive disk is formed, because silicate and ice grains are not sticky. The planetesimals in <2.1 AU and >3.0 AU become ordinary and carbonaceous chondrites' parent bodies, respectively. In these framework, we discuss a redox state of chondrites, an oxygen isotope composition of meteorites and planets, and the formation of chondrules. We have succeded to give an explanation for various sequences among meteorites and planets by the heliocentric distance only : the sequence from the sun is the Earth, Mars, LL, L, H, E, Aubrite, HED, Acapulcoite, Ureilite, CO, CV, CM, CI.
  • The observation of the growth and ifrured absorption for dust particles ecclosed in a small scale space
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 1999 -2000 
    Author : ARAKAWA Masahiko, KOUCHI Akira, WATANABE Naoki
     
    The purpose of this study is to clarify the growth process of cosmic dusts in the interstellar space and to determine the optical property of the cosmic dusts in the laboratory. Our final goal of this experiment is that we observe the growth process of the dust particles in collision with time when various kinds of small dusts are enclosed in a small vacuum space for a long time. The chosen materials are ices, organic matters and silicates, and their sizes are from 0.1 to 1 mm. We also intend to analyze these dusts by using a infrared absorption method. In this term, we have finished to develop the instrument to enclose the dust particles, which is the most important part of this experiment, moreover we estimated the adhesion strength among the organic dust particles. We succeeded to enclose molecular ions for several hours by means of the developed instrument of dust enclosure, so called RF ion trap instrument in ultra-high vacuum chamber. This instrument has characteristics that there are 4 holes of the diameter of 5mm at the ion trap electrode necessary to observe the interior and that the electric gun is set as a lower electrode. We did a preliminary test with molecular ions, then we developed the impedance matching instrument for high frequency electric field in order to arrange the experimental conditions to enclose the dust particles. We improved our electrodes for the ion trap according to these preliminary tests. Before we try to enclose the organic dusts, we studied the adhesion force of ethylene glycol particles, which particles were formed by a spray, at 200 K.The adhesion force was measured by a flowing method. As a result, the adhesion force of the organic matter was concluded to be several orders of magnitudes larger than that of silicate particles.
  • Development of comet nucleus simulation experiments
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 1998 -1999 
    Author : KOUCHI Akira, WATANABE Naoki
     
    We have developed new methods for making amorphous icy grains: 1 ) CO sublimation-induced disruption method First, we deposited CO sample of 10 mm thickness. Second, thin film of amorphous water ice was deposited on the CO. After deposition, the substrate was heated by turning off the helium refrigerator. At temperatures around 30 K, corresponding to CO sublimation temperatures, the sublimation of CO occurred violently, and this caused the disruption of the thin film of amorphous water ice. 2) Continuous production method by fast codeposition of HィイD22ィエD2O and COィイD22ィエD2. We found that continuous disruption of ice film occurred during the deposition , when deposition rate is larger than 3x10ィイD1-9ィエD1 m/s and when thickness of the film is larger than critical thickness. In both method, we collected amorphous icy grains falling from the substrate using grain collector. These methods enables us to perform better comet nucleus simulation experiments than hitherto performed.
  • Structure and physical properties of impure amorphous interstellar icy grains
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 1997 -1999 
    Author : AKIRA Kouichi, WATANABE Naoki
     
    The following research was carried out on the formation and metamorphism of amorphous icy grains and origin and evolution of comets using newly developed ultrahigh-vacuum very low temperature atomic force microscope and existing equipments : 1) By irradiating the ultraviolet rays onto amorphous ice thin film, we analyze the formation of hydrogen molecule quantitatively. In addition, the reaction cross section was measured, and the reaction mechanism was decided. 2) The measurements on physical properties of impure amorphous ices were carried out. The thermal conductivity of impure amorphous ice was found to be 2-3 orders of magnitude smaller than that of the amorphous ice without the defect. As a result of the differential thermal analysis, we found that the crystallization of amorphous ices including impurities were endothermic reaction. 3) There results clearly shows that the some properties of impure amorphous ices strongly depends on their defect structure in amorphous ices. 4) On the basis of the above results, we have calculated the thermal history of comet nucleus. We found that runaway crystallization considered until now could not be occurred in the actual comet nucleus.
  • アモルファス氷星間塵上での水素分子生成機構
    Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Encouragement of Young Scientists (A)
    Date (from‐to) : 1997 -1998 
    Author : 渡部 直樹
     
    本研究の目的は、アモルファス氷星間塵上での水素分子生成機構の解明である。そのうち、期間内にアモルファス氷への紫外線照射による水素分子生成を定性的、かつ定量的に調べ、その生成メカニズムを明らかにした。具体的には以下の通りである。 1. 紫外線照射による水素分子生成の確認:10K基板に蒸着法により生成されたアモルファス重水氷に126nm、172nmの紫外線を照射し、昇温脱離法により光反応生成物を分析した。その結果、重水素分子の生成が確認された。 2. 重水素分子の生成メカニズム:生成量の波長依存性、光量依存性を調べたところ、重水素分子は、重水分子の第一電子励起状態を経由した、1光子過程の光反応により生成されることが強く示唆された。 3. 重水素分子生成量の定量化:氷厚、紫外線照射時間を変えて生成量の変化を調べた。生成量は50〜150Åの範囲で膜厚に比例し、照射時間40分付近で飽和を始め、120分(星間空間10^6yに相当)で生成量は重水分子の数%になった。この照射時間の範囲では逆反応は観測されなかったことから、生成反応は氷固体内部よりも、むしろ氷内部の裂け目や孔の表面で起きているものと考えられる。以上のことから、紫外線による水素分子生成は星間空間で支配的とは言えないまでも無視できない過程であり、星間空間で観測された「氷内水素分子」の生成過程として有力な生成反応であることが分かった。
  • 原子・イオン・分子の光電離過程の研究
  • アモルファス氷表面上における原子・分子素過程
  • Study on Atomic,ionic,and Molecular Photoionization processes
  • Atomic and Molecular Processes on Amorphous ice surface

Educational Activities

Teaching Experience

  • Advanced Course in Planetary Material Science
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : アモルファス氷,結晶氷,星間塵,彗星,氷天体
  • Environment and People
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 地球環境、雪氷、大気、海洋、生態系、生物、光合成、耐寒性、宇宙の氷、分子進化

Campus Position History

  • 2018年4月1日 
    2020年3月31日 
    低温科学研究所副所長

Position History

  • 2018年4月1日 
    2020年3月31日 
    低温科学研究所副所長


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