Watanabe Naoki
| Institute of Low Temperature Science Frontier Ice and Snow Science | Professor |
Last Updated :2025/05/08
■Researcher basic information
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Researcher ID
- A-7451-2012
J-Global ID
Research Field
Educational Organization
- Master's degree program, Graduate School of Science
- Doctoral (PhD) degree program, Graduate School of Science
■Career
Career
- Apr. 2022 - Present
北海道大学低温科学研究所 所長 - Oct. 2009 - Present
Hokkaido University, 低温科学研究所, 教授 - Apr. 2018 - Mar. 2024
北海道大学ディスティングイッシュトプロフェッサー - Oct. 2020 - Mar. 2022
北海道大学総長補佐 - 2006 - Sep. 2009
Hokkaido University, Institute of Low Temperature Science, 准教授 - Jul. 1996 - 2006
Hokkaido University, Institute of Low Temperature Science, 助手 - Aug. 2000 - Aug. 2001
University College London, Department of Physics and Astronomy, 客員研究員 - Apr. 1994 - Jun. 1996
理化学研究所, 原子物理研究室, 基礎科学特別研究員 - Oct. 1993 - Mar. 1994
理化学研究所, 奨励研究員
Educational Background
Position History
■Research activity information
Papers
- Hydrogenation of HOCO and formation of interstellar CO2: A not so straightforward relation
Germán Molpeceres, Joan Enrique-Romero, Atsuki Ishibashi, Yasuhiro Oba, Hiroshi Hidaka, Thanja Lamberts, Yuri Aikawa, Naoki Watanabe
Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), 05 Mar. 2025
Scientific journal, Abstract
Carbon dioxide (CO2) is one of the most important interstellar molecules. While it is considered that it forms on the surface of interstellar dust grains, the exact contribution of different chemical mechanisms is still poorly constrained. Traditionally it is deemed that the CO + OH reaction occurring on top of ices is the main reaction path for its formation. Recent investigations showed that in reality the reaction presents a more complex mechanism, requiring an additional H-abstraction step. Building on our previous works, we carried out a detailed investigation of such H abstraction reactions with the hydrogen atom as a reactant for the abstraction reaction. We found an unconventional chemistry for this reaction, markedly depending on the isomeric form of the HOCO radical prior to reaction. The favored reactions are t-HOCO + H $\longrightarrow$ CO + H2O, c-HOCO + H $\longrightarrow$ CO2 + H2 and t/c-HOCO + H $\longrightarrow$ c/t-HCOOH. We estimate bounds for the rate constants of the less favored reaction channels, t-HOCO + H $\longrightarrow$ CO2 + H and c-HOCO + H $\longrightarrow$ CO + H2O, to be approximately 104 − 6 s−1. However, these estimates should be interpreted cautiously due to the significant role of quantum tunneling in these reactions and the complex electronic structure of the involved molecules, which complicates their study. Our findings underscore the need for detailed investigation into the chemistry of interstellar CO2 and pave the way for a reevaluation of its primary formation mechanisms in the interstellar medium. - Evidence for Jet/Outflow Shocks Heating the Environment around the Class I Protostellar Source Elias 29: FAUST XXI
Yoko Oya, Eri Saiga, Anna Miotello, Maria Koutoulaki, Doug Johnstone, Cecilia Ceccarelli, Claire J. Chandler, Claudio Codella, Nami Sakai, Eleonora Bianchi, Mathilde Bouvier, Steven Charnley, Nicolas Cuello, Marta De Simone, Logan Francis, Tomoyuki Hanawa, Izaskun Jiménez-Serra, Laurent Loinard, Francois Menard, Giovanni Sabatini, Charlotte Vastel, Ziwei Zhang, Yuri Aikawa, Felipe O. Alves, Nadia Balucani, Gemma Busquet, Paola Caselli, Emmanuel Caux, Spandan Choudhury, Francois Dulieu, Aurora Durán, Lucy Evans, Davide Fedele, Siyi Feng, Francesco Fontani, Tetsuya Hama, Eric Herbst, Shingo Hirano, Tomoya Hirota, Andrea Isella, Claudine Kahane, Bertrand Lefloch, Romane Le Gal, Hauyu Baobab Liu, Ana López-Sepulcre, Luke T. Maud, María José Maureira, Seyma Mercimek, George Moellenbrock, Shoji Mori, Hideko Nomura, Yasuhiro Oba, Ross O’Donoghue, Satoshi Ohashi, Yuki Okoda, Juan Ospina-Zamudio, Jaime Pineda, Linda Podio, Albert Rimola, Takeshi Sakai, Dominique Segura-Cox, Yancy Shirley, Brian Svoboda, Leonardo Testi, Serena Viti, Naoki Watanabe, Yoshimasa Watanabe, Yichen Zhang, Satoshi Yamamoto
The Astrophysical Journal, 980, 2, 263, 263, American Astronomical Society, 20 Feb. 2025
Scientific journal, Abstract
We have observed the late Class I protostellar source Elias 29 at a spatial resolution of 70 au with the Atacama Large Millimeter/submillimeter Array as part of the FAUST Large Program. We focus on the line emission of SO, while that of 34SO, C18O, CS, SiO, H13CO+, and DCO+ are used supplementarily. The spatial distribution of the SO rotational temperature (T rot(SO)) is evaluated by using the intensity ratio of its two rotational excitation lines. Besides in the vicinity of the protostar, two hot spots are found at a distance of 500 au from the protostar; T rot(SO) locally rises to 53 K at the interaction point of the outflow and the southern ridge, and 72 K within the southeastern outflow probably due to a jet-driven bow shock. However, the SiO emission is not detected at these hot spots. It is likely that active gas accretion through the disk-like structure and onto the protostar still continues even at this evolved protostellar stage, at least sporadically, considering the outflow/jet activities and the possible infall motion previously reported. Interestingly, T rot(SO) is as high as 20–30 K even within the quiescent part of the southern ridge apart from the protostar by 500–1000 au without clear kinematic indication of current outflow/jet interactions. Such a warm condition is also supported by the low deuterium fractionation ratio of HCO+ estimated by using the H13CO+ and DCO+ lines. The B-type star HD147889 ∼0.5 pc away from Elias 29, previously suggested as a heating source for this region, is likely responsible for the warm condition of Elias 29. - Chemical Pathways of SO2 with Hydrogen Atoms on Interstellar Ice Analogues
Thanh Nguyen, Yasuhiro Oba, W. M. C. Sameera, Kenji Furuya, Naoki Watanabe
The Astrophysical Journal, 01 Dec. 2024
Scientific journal - Signature of Proton-Hole Transfer in Hydrogen-Bonded Solids at 10 K
Kensei Kitajima, Yoichi Nakai, Masashi Tsuge, Naoki Watanabe
Journal of Physical Chemistry Letters, 15, 47, 11701, 11708, 28 Nov. 2024, [Peer-reviewed]
Scientific journal, Although proton transport in water ice is well understood, proton-hole transfer (PHT) involving proton abstraction by anions remains less explored. This study investigates PHT in H2S and NH3 solids at low temperatures, aiming to determine whether these solids exhibit negative charge transport similar to that in ice. In H2S and NH3 solids at 10 K, surface HS- and NH2- anions in hydrogen-bonded systems trigger negative current flow, providing a clear signature of PHT. This negative current is controlled by electron flow and 193 nm ultraviolet irradiation, which generates HS- and NH2- anions on the solid surfaces. In bilayer H2S/H2O and NH3/H2O solids, a significant negative current is observed only in the NH3/H2O solid, which is attributed to the exothermic proton abstraction by NH2- from H2O at the bilayer interface, a process not available for H2S on ice. This study is the first to demonstrate PHT-induced electrochemical behavior in hydrogen-bonded solids other than ice. - Methane Formation Efficiency on Icy Grains: Role of Adsorption States
Masashi Tsuge, Germán Molpeceres, Yuri Aikawa, Naoki Watanabe
The Astrophysical Journal, 973, 2, 80, 80, American Astronomical Society, 20 Sep. 2024, [Peer-reviewed]
Scientific journal, Abstract
Methane (CH4) is one of the major components of the icy mantle of cosmic dust prevalent in cold, dense regions of interstellar media, playing an important role in the synthesis of complex organic molecules and prebiotic molecules. Solid CH4 is considered to be formed via the successive hydrogenation of C atoms accreting onto dust: C + 4H → CH4. However, most astrochemical models assume this reaction on the ice mantles of dust to be barrierless and efficient, without considering the states of adsorption. Recently, we found that C atoms exist in either the physisorbed or chemisorbed state on compact amorphous solid water, which is analogous to an interstellar ice mantle. These distinct adsorption states considerably affect the hydrogenation reactivity of the C atom. Herein, we elucidate the reactivities of physisorbed and chemisorbed C atoms with H atoms via sequential deposition and codeposition processes. The results indicate that only physisorbed C atoms can produce CH4 on ice. Combining this finding with a previous estimate for the fraction of physisorbed C atoms on ice, we determined the upper limit for the conversion of C atoms into CH4 to be 30%. - Photodesorption efficiency of OH radical on the ice surface in the wavelength range from ultraviolet to visible
Ni-En Sie, Masashi Tsuge, Yoichi Nakai, Naoki Watanabe
Chemical Physics Letters, 848, 141384, 141384, Elsevier BV, Aug. 2024, [Peer-reviewed]
Scientific journal - Multiple chemical tracers finally unveil the intricate NGC 1333 IRAS 4A outflow system. FAUST XVI
Layal Chahine, Cecilia Ceccarelli, Marta De Simone, Claire J Chandler, Claudio Codella, Linda Podio, Ana López-Sepulcre, Nami Sakai, Laurent Loinard, Mathilde Bouvier, Paola Caselli, Charlotte Vastel, Eleonora Bianchi, Nicolás Cuello, Francesco Fontani, Doug Johnstone, Giovanni Sabatini, Tomoyuki Hanawa, Ziwei E Zhang, Yuri Aikawa, Gemma Busquet, Emmanuel Caux, Aurore Durán, Eric Herbst, François Ménard, Dominique Segura-Cox, Brian Svodoba, Nadia Balucani, Steven Charnley, François Dulieu, Lucy Evans, Davide Fedele, Siyi Feng, Tetsuya Hama, Tomoya Hirota, Andrea Isella, Izaskun Jímenez-Serra, Bertrand Lefloch, Luke T Maud, María José Maureira, Anna Miotello, George Moellenbrock, Hideko Nomura, Yasuhiro Oba, Satoshi Ohashi, Yuki Okoda, Yoko Oya, Jaime Pineda, Albert Rimola, Takeshi Sakai, Yancy Shirley, Leonardo Testi, Serena Viti, Naoki Watanabe, Yoshimasa Watanabe, Yichen Zhang, Satoshi Yamamoto
Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), 23 May 2024, [Peer-reviewed]
Scientific journal, Abstract
The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS 4A protobinary system. This analysis is based on ALMA observations of SiO(5–4), H2CO(30, 3–20, 3), and HDCO(41, 4–31, 3) with a spatial resolution of ∼150 au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS 4A1 and IRAS 4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterise the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS 4A1 exhibit extensions of 10″ and 13″ with position angles (PA) of 0○ and -12○, respectively, while those of IRAS 4A2 are more extended, spanning 18″ and 25″ with PAs of 29○ and 26○. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events. - Carbon Atom Condensation on NH3–H2O Ices. An Alternative Pathway to Interstellar Methanimine and Methylamine
Germán Molpeceres, Masashi Tsuge, Kenji Furuya, Naoki Watanabe, David San Andrés, Víctor M. Rivilla, Laura Colzi, Yuri Aikawa
The Journal of Physical Chemistry A, American Chemical Society (ACS), 06 May 2024, [Peer-reviewed]
Scientific journal - FAUST
G. Sabatini, L. Podio, C. Codella, Y. Watanabe, M. De Simone, E. Bianchi, C. Ceccarelli, C. J. Chandler, N. Sakai, B. Svoboda, L. Testi, Y. Aikawa, N. Balucani, M. Bouvier, P. Caselli, E. Caux, L. Chahine, S. Charnley, N. Cuello, F. Dulieu, L. Evans, D. Fedele, S. Feng, F. Fontani, T. Hama, T. Hanawa, E. Herbst, T. Hirota, A. Isella, I. Jímenez-Serra, D. Johnstone, B. Lefloch, R. Le Gal, L. Loinard, H. B. Liu, A. López-Sepulcre, L. T. Maud, M. J. Maureira, F. Menard, A. Miotello, G. Moellenbrock, H. Nomura, Y. Oba, S. Ohashi, Y. Okoda, Y. Oya, J. Pineda, A. Rimola, T. Sakai, D. Segura-Cox, Y. Shirley, C. Vastel, S. Viti, N. Watanabe, Y. Zhang, Z. E. Zhang, S. Yamamoto
Astronomy & Astrophysics, 684, L12, L12, EDP Sciences, 10 Apr. 2024, [Peer-reviewed]
Scientific journal, Context. The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems.
Aims. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems.
Methods. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH3OH, H2CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster.
Results. Methanol emission reveals an arc-like structure at ∼1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H2CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H2 column density of ∼7 × 1021 cm−2, a mass of ∼9 × 10−3 M⊙, and a lower limit on the dust spectral index of 1.4.
Conclusions. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues. - Determination of the Branching Ratio of CH3OH + OH Reaction on Water Ice Surface at 10 K
Atsuki Ishibashi, Hiroshi Hidaka, W. M. C. Sameera, Yasuhiro Oba, Naoki Watanabe
The Astrophysical Journal, 01 Jan. 2024, [Peer-reviewed]
Scientific journal - Surface diffusion of carbon atoms as a driver of interstellar organic chemistry
Masashi Tsuge, Germán Molpeceres, Yuri Aikawa, Naoki Watanabe
Nature Astronomy, SPRINGER NATURE, 14 Sep. 2023, [Peer-reviewed], [International Magazine]
Scientific journal, Many interstellar complex organic molecules (COMs) are believed to be produced on the surfaces of icy grains at low temperatures. Atomic carbon is considered responsible for the skeletal evolution processes, such as C–C bond formation, via insertion or addition reactions. Before reactions, C atoms must diffuse on the surface to encounter reaction partners; therefore, information on their diffusion process is critically important for evaluating the role of C atoms in the formation of COMs. In situ detection of C atoms on ice was achieved by a combination of photostimulated desorption and resonance-enhanced multiphoton ionization methods. We found that C atoms weakly bound to the ice surface diffused above approximately 30 K and produced C2 molecules. The activation energy for C-atom surface diffusion was experimentally determined to be 88 meV (1,020 K), indicating that the diffusive reaction of C atoms is activated at approximately 22 K on interstellar ice. The facile diffusion of C atoms at temperatures above 22 K on interstellar ice opens a previously overlooked chemical regime where the increase in complexity of COMs is driven by C atoms. Carbon addition chemistry can be an alternative source of chemical complexity in translucent clouds and protoplanetary disks with crucial implications in our current understanding on the origin and evolution of organic chemistry in our Universe. - Methanol Formation through Reaction of Low-energy CH3 + Ions with an Amorphous Solid Water Surface at Low Temperature
Y. Nakai, W. M. C. Sameera, K. Furuya, H. Hidaka, A. Ishibashi, N. Watanabe
The Astrophysical Journal, 01 Aug. 2023, [Peer-reviewed]
Scientific journal - Radical reactions on interstellar icy dust grains: Experimental investigations of elementary processes
Masashi TSUGE, Naoki WATANABE
Proceedings of the Japan Academy, Series B, 99, 4, 103, 130, Japan Academy, 28 Apr. 2023, [Peer-reviewed], [Invited]
Scientific journal - Surface Reaction of Methyl Mercaptan (CH3SH) with Hydrogen Atoms on Amorphous Solid Water
Thanh Nguyen, Yasuhiro Oba, W. M. C. Sameera, Kenji Furuya, Akira Kouchi, Naoki Watanabe
The Astrophysical Journal, 01 Feb. 2023, [Peer-reviewed]
Scientific journal - A systematic mechanistic survey on the reactions between OH radical and CH3OH on ice
W. M. C. Sameera, Avon P. Jayaweera, Atsuki Ishibashi, Hiroshi Hidaka, Yasuhiro Oba, Naoki Watanabe
Faraday Discussions, 245, 508, 518, Royal Society of Chemistry (RSC), 2023, [Peer-reviewed]
Scientific journal, Our systematic computational study suggests that the nature of the binding site or the reaction site has a significant effect on the computed binding energies or reaction barriers. - Direct Determination of the Activation Energy for Diffusion of OH Radicals on Water Ice
A. Miyazaki, M. Tsuge, H. Hidaka, Y. Nakai, N. Watanabe
The Astrophysical Journal Letters, 940, 1, L2, L2, American Astronomical Society, 14 Nov. 2022, [Peer-reviewed]
Scientific journal, Abstract
Using a combination of photostimulated desorption and resonance-enhanced multiphoton ionization methods, the behaviors of OH radicals on the surface of an interstellar ice analog were monitored at temperatures between 54 and 80 K. The OH number density on the surface of ultraviolet-irradiated compact amorphous solid water gradually decreased at temperatures above 60 K. Analyzing the temperature dependence of OH intensities with the Arrhenius equation, the decrease can be explained by the recombination of two OH radicals, which is rate-limited by thermal diffusion of OH. The activation energy for surface diffusion was experimentally determined for the first time to be 0.14 ± 0.01 eV, which is larger than or equivalent to those assumed in theoretical models. This value implies that the diffusive reaction of OH radicals starts to be activated at approximately 36 K on interstellar ice. - Chiral Ice Crystals in Space
Akira Kouchi, Takashi Shimonishi, Tomoya Yamazaki, Masashi Tsuge, Naoki Nakatani, Kenji Furuya, Hiromasa Niinomi, Yasuhiro Oba, Tetsuya Hama, Hiroyasu Katsuno, Naoki Watanabe, Yuki Kimura
Chirality - New Insights [Working Title], IntechOpen, 22 Aug. 2022
In book, We observed the formation of CO, CH3OH, and H2O ices using a cryogenic transmission electron microscope, to determine if chiral ice crystals could form under the conditions of interstellar molecular clouds and young stellar objects (protoplanetary disks) and to clarify the crystalline structure of these ices. Our results suggest that the following ice crystals are chiral: crystalline CO (α-CO) formed on amorphous H2O (a-H2O) grains in a 10-K molecular cloud, crystalline CH3OH formed by the heating of amorphous CH3OH on a-H2O grains at 40–60 K in young stellar objects, and several polymorphs of hydrogen-ordered cubic ice crystals formed by the heating of a-H2O at 80–100 K and direct condensation at 120–140 K in protoplanetary disks. We also investigated candidates for other chiral ices using published data. We found that NH3 I and NH3·H2O I are chiral at low temperature and pressure conditions. If one-handed circularly polarized light is irradiated during the nucleation of these chiral ice crystals, homochiral crystals can be formed. These results have important implications for the origin of interstellar organic molecule homochirality. - Diffusion Activation Energy and Desorption Activation Energy for Astrochemically Relevant Species on Water Ice Show No Clear Relation
Kenji Furuya, Tetsuya Hama, Yasuhiro Oba, Akira Kouchi, Naoki Watanabe, Yuri Aikawa
The Astrophysical Journal Letters, 01 Jul. 2022, [Peer-reviewed]
Scientific journal - Chemical and Physical Characterization of the Isolated Protostellar Source CB68: FAUST IV
Muneaki Imai, Yoko Oya, Brian Svoboda, Hauyu Baobab Liu, Bertrand Lefloch, Serena Viti, Yichen Zhang, Cecilia Ceccarelli, Claudio Codella, Claire J. Chandler, Nami Sakai, Yuri Aikawa, Felipe O. Alves, Nadia Balucani, Eleonora Bianchi, Mathilde Bouvier, Gemma Busquet, Paola Caselli, Emmanuel Caux, Steven Charnley, Spandan Choudhury, Nicolas Cuello, Marta De Simone, Francois Dulieu, Aurora Durán, Lucy Evans, Cécile Favre, Davide Fedele, Siyi Feng, Francesco Fontani, Logan Francis, Tetsuya Hama, Tomoyuki Hanawa, Eric Herbst, Shingo Hirano, Tomoya Hirota, Andrea Isella, Izaskun Jímenez-Serra, Doug Johnstone, Claudine Kahane, Romane Le Gal, Laurent Loinard, Ana López-Sepulcre, Luke T. Maud, María José Maureira, Francois Menard, Seyma Mercimek, Anna Miotello, George Moellenbrock, Shoji Mori, Nadia M. Murillo, Riouhei Nakatani, Hideko Nomura, Yasuhiro Oba, Ross O’Donoghue, Satoshi Ohashi, Yuki Okoda, Juan Ospina-Zamudio, Jaime Pineda, Linda Podio, Albert Rimola, Takeshi Sakai, Dominique Segura-Cox, Yancy Shirley, Vianney Taquet, Leonardo Testi, Charlotte Vastel, Naoki Watanabe, Yoshimasa Watanabe, Arezu Witzel, Ci Xue, Bo Zhao, Satoshi Yamamoto
The Astrophysical Journal, 934, 1, 70, 70, American Astronomical Society, 01 Jul. 2022, [Peer-reviewed]
Scientific journal, Abstract
The chemical diversity of low-mass protostellar sources has so far been recognized, and environmental effects are invoked as its origin. In this context, observations of isolated protostellar sources without the influence of nearby objects are of particular importance. Here, we report the chemical and physical structures of the low-mass Class 0 protostellar source IRAS 16544−1604 in the Bok globule CB 68, based on 1.3 mm Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of ∼70 au that were conducted as part of the large program FAUST. Three interstellar saturated complex organic molecules (iCOMs), CH3OH, HCOOCH3, and CH3OCH3, are detected toward the protostar. The rotation temperature and the emitting region size for CH3OH are derived to be 131 ± 11 K and ∼10 au, respectively. The detection of iCOMs in close proximity to the protostar indicates that CB 68 harbors a hot corino. The kinematic structure of the C18O, CH3OH, and OCS lines is explained by an infalling–rotating envelope model, and the protostellar mass and the radius of the centrifugal barrier are estimated to be 0.08–0.30 M⊙ and <30 au, respectively. The small radius of the centrifugal barrier seems to be related to the small emitting region of iCOMs. In addition, we detect emission lines of c-C3H2 and CCH associated with the protostar, revealing a warm carbon-chain chemistry on a 1000 au scale. We therefore find that the chemical structure of CB 68 is described by a hybrid chemistry. The molecular abundances are discussed in comparison with those in other hot corino sources and reported chemical models. - Penetration of Nonenergetic Hydrogen Atoms into Amorphous Solid Water and their Reaction with Embedded Benzene and Naphthalene
Masashi Tsuge, Akira Kouchi, Naoki Watanabe
The Astrophysical Journal, 933, 2, 138, 138, American Astronomical Society, 01 Jul. 2022, [Peer-reviewed]
Scientific journal, Abstract
Chemical processes on the surface of icy grains play an important role in the chemical evolution in molecular clouds. In particular, reactions involving nonenergetic hydrogen atoms accreted from the gaseous phase have been extensively studied. These reactions are believed to effectively proceed only on the surface of the icy grains; thus, molecules embedded in the ice mantle are not considered to react with hydrogen atoms. Recently, Tsuge et al. suggested that nonenergetic hydrogen atoms can react with CO molecules even in ice mantles via diffusive hydrogenation. This investigation was extended to benzene and naphthalene molecules embedded in amorphous solid water (ASW) in the present study, which revealed that a portion of these molecules could be fully hydrogenated in astrophysical environments. The penetration depths of nonenergetic hydrogen atoms into porous and nonporous ASW were determined using benzene molecules to be >50 and ∼10 monolayers, respectively (1 monolayer ≈ 0.3 nm). - Modelling the Radical Chemistry on Ice Surfaces: An Integrated Quantum Chemical and Experimental Approach
W. M. C. Sameera, Bethmini Senevirathne, Thanh Nguyen, Yasuhiro Oba, Atsuki Ishibashi, Masashi Tsuge, Hiroshi Hidaka, Naoki Watanabe
Frontiers in Astronomy and Space Sciences, 9, Frontiers Media SA, 30 May 2022, [Peer-reviewed]
Scientific journal, Heterogeneous radical processes on ice surfaces play a vital role in the formation of building blocks of the biologically relevant molecules in space. Therefore, quantitative mechanistic details of the radical binding and radical reactions on ices are crucial in rationalizing the chemical evolution in the Universe. The radical chemistry on ice surfaces was explored at low temperatures by combining quantum chemical calculations and laboratory experiments. A range of binding energies was observed for OH, HCO, CH3, and CH3O radicals binding on ices. Computed reaction paths of the radical reactions on ices, OCS + H and PH3 + D, explained the experimentally observed products. In both radical reactions, quantum tunnelling plays a key role in achieving the reactions at low temperatures. Our findings give quantitative insights into radical chemistry on ice surfaces in interstellar space and the planetary atmospheres. - Misaligned Rotations of the Envelope, Outflow, and Disks in the Multiple Protostellar System of VLA 1623–2417: FAUST. III
Satoshi Ohashi, Claudio Codella, Nami Sakai, Claire J. Chandler, Cecilia Ceccarelli, Felipe Alves, Davide Fedele, Tomoyuki Hanawa, Aurora Durán, Cécile Favre, Ana López-Sepulcre, Laurent Loinard, Seyma Mercimek, Nadia M. Murillo, Linda Podio, Yichen Zhang, Yuri Aikawa, Nadia Balucani, Eleonora Bianchi, Mathilde Bouvier, Gemma Busquet, Paola Caselli, Emmanuel Caux, Steven Charnley, Spandan Choudhury, Nicolas Cuello, Marta De Simone, Francois Dulieu, Lucy Evans, Siyi Feng, Francesco Fontani, Logan Francis, Tetsuya Hama, Eric Herbst, Shingo Hirano, Tomoya Hirota, Muneaki Imai, Andrea Isella, Izaskun Jímenez-Serra, Doug Johnstone, Claudine Kahane, Romane Le Gal, Bertrand Lefloch, Luke T. Maud, Maria Jose Maureira, Francois Menard, Anna Miotello, George Moellenbrock, Shoji Mori, Riouhei Nakatani, Hideko Nomura, Yasuhiro Oba, Ross O’Donoghue, Yuki Okoda, Juan Ospina-Zamudio, Yoko Oya, Jaime Pineda, Albert Rimola, Takeshi Sakai, Dominique Segura-Cox, Yancy Shirley, Brian Svoboda, Vianney Taquet, Leonardo Testi, Charlotte Vastel, Serena Viti, Naoki Watanabe, Yoshimasa Watanabe, Arezu Witzel, Ci Xue, Bo Zhao, Satoshi Yamamoto
The Astrophysical Journal, 927, 1, 54, 54, American Astronomical Society, 01 Mar. 2022, [Peer-reviewed]
Scientific journal,Abstract
We report a study of the low-mass Class 0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H13CO+ (J = 3–2), CS (J = 5–4), and CCH (N = 3–2) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circumbinary VLA 1623A disk, as well as the VLA 1623B disk. We found that the minor axis of the circumbinary disk of VLA 1623A is misaligned by about 12° with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circumbinary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be 5–16 au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circumbinary disk. The origin of its opposite gradient is also discussed. - UV-Induced Formation of Ice XI Observed Using an Ultra-High Vacuum Cryogenic Transmission Electron Microscope and its Implications for Planetary Science
Akira Kouchi, Yuki Kimura, Kensei Kitajima, Hiroyasu Katsuno, Hiroshi Hidaka, Yasuhiro Oba, Masashi Tsuge, Tomoya Yamazaki, Kazuyuki Fujita, Tetsuya Hama, Yukihiro Takahashi, Shunichi Nakatsubo, Naoki Watanabe
Frontiers in Chemistry, 9, Frontiers Media SA, 08 Dec. 2021, [Peer-reviewed]
Scientific journal, The occurrence of hydrogen atom-ordered form of ice Ih, ice XI, in the outer Solar System has been discussed based on laboratory experiments because its ferroelectricity influences the physical processes in the outer Solar System. However, the formation of ice XI in that region is still unknown due to a lack of formation conditions at temperatures higher than 72 K and the effect of UV-rays on the phase transition from ice I to ice XI. As a result, we observed the UV-irradiation process on ice Ih and ice Ic using a newly developed ultra-high vacuum cryogenic transmission electron microscope. We found that ice Ih transformed to ice XI at temperatures between 75 and 140 K with a relatively small UV dose. Although ice Ic partially transformed to ice XI at 83 K, the rate of transformation was slower than for ice Ih. These findings point to the formation of ice XI at temperatures greater than 72 K via UV irradiation of ice I crystals in the Solar System; icy grains and the surfaces of icy satellites in the Jovian and Saturnian regions. - Measurements of Ortho-to-para Nuclear Spin Conversion of H2 on Low-temperature Carbonaceous Grain Analogs: Diamond-like Carbon and Graphite
Masashi Tsuge, Akira Kouchi, Naoki Watanabe
The Astrophysical Journal, 923, 1, 71, 71, American Astronomical Society, 01 Dec. 2021, [Peer-reviewed]
Scientific journal,Abstract
Hydrogen molecules have two nuclear spin isomers:ortho -H2 andpara -H2. The ortho-to-para ratio (OPR) is known to affect chemical evolution as well as gas dynamics in space. Therefore, understanding the mechanism of OPR variation in astrophysical environments is important. In this work, the nuclear spin conversion (NSC) processes of H2 molecules on diamond-like carbon and graphite surfaces are investigated experimentally by employing temperature-programmed desorption and resonance-enhanced multiphoton ionization methods. For the diamond-like carbon surface, the NSC time constants were determined at temperatures of 10–18 K and from 3900 ± 800 s at 10 K to 750 ± 40 s at 18 K. Similar NSC time constants and temperature dependence were observed for a graphite surface, indicating that bonding motifs (sp3 or sp2 hybridization) have little effect on the NSC rates. - Successive H-atom Addition to Solid OCS on Compact Amorphous Solid Water
Thanh Nguyen, Yasuhiro Oba, W. M. C. Sameera, Akira Kouchi, Naoki Watanabe
The Astrophysical Journal, 01 Dec. 2021, [Peer-reviewed]
Scientific journal - Efficient Formation Pathway of Methyl Formate: The Role of OH Radicals on Ice Dust
A. Ishibashi, H. Hidaka, Y. Oba, A. Kouchi, N. Watanabe
The Astrophysical Journal Letters, 01 Nov. 2021, [Peer-reviewed]
Scientific journal - Transmission Electron Microscopy Study of the Morphology of Ices Composed of H2O, CO2, and CO on Refractory Grains
Akira Kouchi, Masashi Tsuge, Tetsuya Hama, Yasuhiro Oba, Satoshi Okuzumi, Sin-iti Sirono, Munetake Momose, Naoki Nakatani, Kenji Furuya, Takashi Shimonishi, Tomoya Yamazaki, Hiroshi Hidaka, Yuki Kimura, Ken-ichiro Murata, Kazuyuki Fujita, Shunichi Nakatsubo, Shogo Tachibana, Naoki Watanabe
The Astrophysical Journal, 918, 2, 45, 45, American Astronomical Society, 01 Sep. 2021, [Peer-reviewed]
Scientific journal - Experimental and Computational Studies on the Physicochemical Behavior of Phosphine Induced by Reactions with H and D Atoms on Interstellar Ice Grains
Thanh Nguyen, Yasuhiro Oba, W. M. C. Sameera, Akira Kouchi, Naoki Watanabe
The Astrophysical Journal, 918, 2, IOP PUBLISHING LTD, 01 Sep. 2021, [Peer-reviewed]
English, Scientific journal, Phosphine (PH3) is an important molecule in the chemistry of phosphorus (P)-bearing species in the interstellar medium. Interstellar PH3 is thought to primarily form on icy grains, where several surface processes may occur during and after its formation. To better understand the physicochemical behavior of PH3 on icy grains in dense molecular clouds, we performed experimental and computational studies on the reactions of phosphine with H and D atoms at low temperatures. We found that phosphine and its deuterated isotopologue PD3 are released into the gas phase from icy surfaces (porous amorphous, compact amorphous, and crystalline ice) via chemical desorption. Even though the effective desorption cross section did not vary between the different icy surfaces, the desorption fraction was smallest for porous amorphous ice. We confirmed that, at 10 K on icy surfaces, H-D substitution reactions of PH3 and D-H substitution reactions of PD3 occurred following reactions with D and H atoms, respectively. Because the activation barrier for the abstraction of H or D atoms from phosphine is similar to 1500 K, quantum tunneling should play a role at low temperatures. Under the present experimental conditions, the H-D substitution reaction of PH3 was slightly slower than the D-H substitution reaction of PD3. Therefore, the rates of the H-D and D-H substitution reactions should not be constrained by tunneling reactions but rather by other elementary processes such as atom diffusion on ice. Our experimental results suggest the possible presence of a deuterated phosphine isotopologue (PH2D) in PH3-rich interstellar environments. - Formation of chiral CO polyhedral crystals on icy interstellar grains
Akira Kouchi, Masashi Tsuge, Tetsuya Hama, Hiromasa Niinomi, Naoki Nakatani, Takashi Shimonishi, Yasuhiro Oba, Yuki Kimura, Sin-iti Sirono, Satoshi Okuzumi, Munetake Momose, Kenji Furuya, Naoki Watanabe
Monthly Notices of the Royal Astronomical Society, 505, 1, 1530, 1542, Oxford University Press (OUP), 03 Jun. 2021, [Peer-reviewed]
Scientific journal,ABSTRACT
The crystallinity and morphology of solid carbon monoxide (CO) on icy interstellar grains were examined by observing the deposition, crystallization, and UV and electrons irradiation of solid CO using transmission electron microscopy. Herein, we found that solid CO deposited in molecular clouds was crystalline, and that even if amorphous CO was deposited, amorphous CO crystallized within 103 yr at 10 K. Conversely, crystalline CO was not amorphized by UV rays or electron beam at 10 K. These results indicated the occurrence of chiral crystalline CO instead of amorphous CO in space. Furthermore, the large surface diffusion coefficients of CO on eamorphous H2O and crystalline CO at 10 K facilitated the morphological equilibration of crystalline CO. Bad wetting of crystalline CO with amorphous H2O proved that the morphology of the ice grains was not spherical with an onion-like structure, as hitherto assumed, but rather it was a polyhedral crystalline CO attached to amorphous H2O. This has important implications for phenomena associated with the collision and subsequent sticking between ice grains, surface chemical reactions, non-thermal desorption of molecules and the origin of homochirality in interstellar biomolecules. - Binding energies and sticking coefficients of H2 on crystalline and amorphous CO ice
G. Molpeceres, V. Zaverkin, N. Watanabe, J. Kästner
Astronomy & Astrophysics, {EDP} Sciences, Apr. 2021, [Peer-reviewed]
Scientific journal - FAUST. II. Discovery of a Secondary Outflow in IRAS 15398−3359: Variability in Outflow Direction during the Earliest Stage of Star Formation?
Yuki Okoda, Yoko Oya, Logan Francis, Doug Johnstone, Shu-ichiro Inutsuka, Cecilia Ceccarelli, Claudio Codella, Claire Chandler, Nami Sakai, Yuri Aikawa, Felipe O. Alves, Nadia Balucani, Eleonora Bianchi, Mathilde Bouvier, Paola Caselli, Emmanuel Caux, Steven Charnley, Spandan Choudhury, Marta De Simone, Francois Dulieu, Aurora Durán, Lucy Evans, Cécile Favre, Davide Fedele, Siyi Feng, Francesco Fontani, Tetsuya Hama, Tomoyuki Hanawa, Eric Herbst, Tomoya Hirota, Muneaki Imai, Andrea Isella, Izaskun Jímenez-Serra, Claudine Kahane, Bertrand Lefloch, Laurent Loinard, Ana López-Sepulcre, Luke T. Maud, María José Maureira, Francois Menard, Seyma Mercimek, Anna Miotello, George Moellenbrock, Shoji Mori, Nadia M. Murillo, Riouhei Nakatani, Hideko Nomura, Yasuhiro Oba, Ross O’Donoghue, Satoshi Ohashi, Juan Ospina-Zamudio, Jaime E. Pineda, Linda Podio, Albert Rimola, Takeshi Sakai, Dominique Segura-Cox, Yancy Shirley, Brian Svoboda, Vianney Taquet, Leonardo Testi, Charlotte Vastel, Serena Viti, Naoki Watanabe, Yoshimasa Watanabe, Arezu Witzel, Ci Xue, Yichen Zhang, Bo Zhao, Satoshi Yamamoto
The Astrophysical Journal, 910, 1, 11, 11, American Astronomical Society, 01 Mar. 2021, [Peer-reviewed]
English, Scientific journal, We have observed the very low-mass Class 0 protostar IRAS 15398-3359 at scales ranging from 50 to 1800 au, as part of the Atacama Large Millimeter/Submillimeter Array Large Program FAUST. We uncover a linear feature, visible in H2CO, SO, and (CO)-O-18 line emission, which extends from the source in a direction almost perpendicular to the known active outflow. Molecular line emission from H2CO, SO, SiO, and CH3OH further reveals an arc-like structure connected to the outer end of the linear feature and separated from the protostar, IRAS 15398-3359, by 1200 au. The arc-like structure is blueshifted with respect to the systemic velocity. A velocity gradient of 1.2 km s(-1) over 1200 au along the linear feature seen in the H2CO emission connects the protostar and the arc-like structure kinematically. SO, SiO, and CH3OH are known to trace shocks, and we interpret the arc-like structure as a relic shock region produced by an outflow previously launched by IRAS 15398-3359. The velocity gradient along the linear structure can be explained as relic outflow motion. The origins of the newly observed arc-like structure and extended linear feature are discussed in relation to turbulent motions within the protostellar core and episodic accretion events during the earliest stage of protostellar evolution. - Behavior of Hydroxyl Radicals on Water Ice at Low Temperatures
Masashi Tsuge, Naoki Watanabe
Accounts of Chemical Research, 54, 3, 471, 480, American Chemical Society ({ACS}), 02 Feb. 2021, [Peer-reviewed]
Scientific journal - Rapid Ortho-to-para Nuclear Spin Conversion of H2 on a Silicate Dust Surface
M. Tsuge, T. Namiyoshi, K. Furuya, T. Yamazaki, A. Kouchi, N. Watanabe
The Astrophysical Journal, 908, 2, 234, 234, American Astronomical Society, 01 Feb. 2021, [Peer-reviewed]
Scientific journal - Delivery of Electrons by Proton-Hole Transfer in Ice at 10 K: Role of Surface OH Radicals
Kensei Kitajima, Yoichi Nakai, W. M. C. Sameera, Masashi Tsuge, Ayane Miyazaki, Hiroshi Hidaka, Akira Kouchi, Naoki Watanabe
The Journal of Physical Chemistry Letters, 12, 1, 704, 710, American Chemical Society ({ACS}), 14 Jan. 2021, [Peer-reviewed]
Scientific journal - CH3O Radical Binding on Hexagonal Water Ice and Amorphous Solid Water
W. M. C. Sameera, Bethmini Senevirathne, Stefan Andersson, Muhsen Al-lbadi, Hiroshi Hidaka, Akira Kouchi, Gunnar Nyman, Naoki Watanabe
The Journal of Physical Chemistry A, 125, 1, 387, 393, American Chemical Society ({ACS}), 14 Jan. 2021, [Peer-reviewed]
Scientific journal - UV-ray irradiation never causes amorphization of crystalline CO2: A transmission electron microscopy study
Masashi Tsuge, Thanh Nguyen, Yasuhiro Oba, Tetsuya Hama, Akira Kouchi, Naoki Watanabe
Chemical Physics Letters, 760, 137999, 137999, Elsevier {BV}, Dec. 2020, [Peer-reviewed]
Scientific journal - Precometary organic matter: A hidden reservoir of water inside the snow line
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, Dec. 2020, [Peer-reviewed]
English, Scientific journal - Photostimulated desorption of OH radicals from amorphous solid water: Evidence for the interaction of visible light with an OH-ice complex
A. Miyazaki, N. Watanabe, W. M. C. Sameera, Y. Nakai, M. Tsuge, T. Hama, H. Hidaka, A. Kouchi
Physical Review A, 102, 5, American Physical Society (APS), 20 Nov. 2020, [Peer-reviewed]
Scientific journal - In vivo characterization of the structures of films of a fatty acid and an alcohol adsorbed on the skin surface
Tetsuya Hama, Akira Kouchi, Naoki Watanabe, Nobutaka Shioya, Takafumi Shimoaka, Takeshi Hasegawa
Biophysical Chemistry, 266, 106459, 106459, Elsevier BV, Nov. 2020, [Peer-reviewed]
Scientific journal - Quantitative Anisotropic Analysis of Molecular Orientation in Amorphous N2O at 6 K by Infrared Multiple-Angle Incidence Resolution Spectrometry
Tetsuya Hama, Atsuki Ishibashi, Akira Kouchi, Naoki Watanabe, Nobutaka Shioya, Takafumi Shimoaka, Takeshi Hasegawa
The Journal of Physical Chemistry Letters, 11, 18, 7857, 7866, American Chemical Society ({ACS}), 17 Sep. 2020, [Peer-reviewed]
Scientific journal - Diffusive Hydrogenation Reactions of CO Embedded in Amorphous Solid Water at Elevated Temperatures ∼70 K
Masashi Tsuge, Hiroshi Hidaka, Akira Kouchi, Naoki Watanabe
The Astrophysical Journal, 900, 2, 187, 187, American Astronomical Society, 15 Sep. 2020, [Peer-reviewed]
Scientific journal - An Experimental Study of Chemical Desorption for Phosphine in Interstellar Ice
Thanh Nguyen, Yasuhiro Oba, Takashi Shimonishi, Akira Kouchi, Naoki Watanabe
The Astrophysical Journal, 898, 2, IOP PUBLISHING LTD, 03 Aug. 2020, [Peer-reviewed]
English, Scientific journal, Phosphine (PH3), an important molecule for the chemistry of phosphorus (P)-bearing species in the interstellar medium (ISM) is considered to form primarily on interstellar grains. However, no report exists on the processes of PH(3)formation on grains. Here, we experimentally studied the reactions of hydrogen (H) atoms and PH(3)molecules on compact amorphous solid water, with a particular focus on the chemical desorption of PH(3)at 10-30 K. After exposure to H atoms for 120 minutes, up to 50% of solid PH(3)was lost from the icy surface. On the basis of experiments using deuterium atoms, it was concluded that the loss of PH(3)resulted from chemical desorption through the reactions PH3+ H -> PH2 + H(2)and/or PH2+ H -> PH3. The effective desorption cross-section was similar to 5 x 10(-17)cm(2), which is three times larger than that of hydrogen sulfide measured under similar experimental conditions. The present results suggest that the formation of PH3, and possibly PH(2)and PH, followed by their desorption from icy grains, may contribute to the formation of PN and PO in the gas phase, and thus may play a role in the P chemistry of the ISM. - Experimental Approach to Physicochemical Hydrogen Processes on Cosmic Ice Dust
Naoki Watanabe, Masashi Tsuge
Journal of the Physical Society of Japan, 15 May 2020
Scientific journal - Formation experiments of organic molecules by catalytic reactions in low-temperature and low-pressure environments
Yuki Kimura, Rikako Sato, AkiraTsuchiyama, YusukeTamenori, Tetsuya Hama, Hiroshi Hidaka, Naoki Watanabe, Akira Kouchi, Hiroko Nagahara
Low Temperature Science, 78, 79, 90, Mar. 2020, [Peer-reviewed] - Direct Measurements of Activation Energies for Surface Diffusion of CO and CO2 on Amorphous Solid Water Using In Situ Transmission Electron Microscopy
Akira Kouchi, Kenji Furuya, Tetsuya Hama, Takeshi Chigai, Takashi Kozasa, Naoki Watanabe
ASTROPHYSICAL JOURNAL LETTERS, 891, 1, IOP PUBLISHING LTD, Mar. 2020, [Peer-reviewed]
English, Scientific journal, 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. - H-2 Ortho-Para Spin Conversion on Inhomogeneous Grain Surfaces
Furuya Kenji, Aikawa Yuri, Hama Tetsuya, Watanabe Naoki
ASTROPHYSICAL JOURNAL, 882, 2, IOP PUBLISHING LTD, 10 Sep. 2019, [Peer-reviewed]
English, Scientific journal, We investigate the evolution of the ortho-to-para ratio of overall (gas + ice) H-2 via the nuclear spin conversion on grain surfaces coated with water ice under physical conditions that are relevant to star- and planet-forming regions. We utilize the rate equation model that considers adsorption of gaseous H-2 on grain surfaces, which have a variety of binding sites with a different potential energy depth, thermal hopping, desorption, and the nuclear spin conversion of adsorbed H-2. It is found that the spin conversion efficiency depends on the H-2 gas density and the surface temperature. As a general trend, enhanced H-2 gas density reduces the efficiency, while the temperature dependence is not monotonic; there is a critical surface temperature at which the efficiency is the maximum. At low temperatures, the exchange of gaseous and icy H-2 is inefficient (i.e., adsorbed H-2 does not desorb and hinders another gaseous H-2 to be adsorbed), while at warm temperatures, the residence time of H-2 on surfaces is too short for the spin conversion. Additionally, the spin conversion becomes more efficient with lowering the activation barriers for thermal hopping. We discuss whether the spin conversion on surfaces can dominate over that in the gas phase in star- and planet-forming regions. Finally, we establish a simple, but accurate way to implement the H-2 spin conversion on grain surfaces in existing gas-ice astrochemical models. - Nucleobase synthesis in interstellar ices
Yasuhiro Oba, Yoshinori Takano, Hiroshi Naraoka, Naoki Watanabe, Akira Kouchi
Nature Communications, 10, 1, 4413, Springer Science and Business Media {LLC}, Sep. 2019, [Peer-reviewed]
English, Scientific journal, The synthesis of nucleobases in natural environments, especially in interstellar molecular clouds, is the focus of a long-standing debate regarding prebiotic chemical evolution. Here we report the simultaneous detection of all three pyrimidine (cytosine, uracil and thymine) and three purine nucleobases (adenine, xanthine and hypoxanthine) in interstellar ice analogues composed of simple molecules including H2O, CO, NH3 and CH3OH after exposure to ultraviolet photons followed by thermal processes, that is, in conditions that simulate the chemical processes accompanying star formation from molecular clouds. Photolysis of primitive gas molecules at 10 K might be one of the key steps in the production of nucleobases. The present results strongly suggest that the evolution from molecular clouds to stars and planets provides a suitable environment for nucleobase synthesis in space. - Probing the Molecular Structure and Orientation of the Leaf Surface of Brassica oleracea L. by Polarization Modulation-Infrared Reflection-Absorption Spectroscopy
Hama, Tetsuya, Seki, Kousuke, Ishibashi, Atsuki, Miyazaki, Ayane, Kouchi, Akira, Watanabe, Naoki, Shimoaka, Takafumi, Hasegawa, Takeshi
PLANT AND CELL PHYSIOLOGY, 60, 7, 1567, 1580, OXFORD UNIV PRESS, Jul. 2019, [Peer-reviewed]
English, Scientific journal, 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. - Interactions of Atomic and Molecular Hydrogen with a Diamond-like Carbon Surface: H2 Formation and Desorption
Masashi Tsuge, Tetsuya Hama, Yuki Kimura, Akira Kouchi, Naoki Watanabe
The Astrophysical Journal, 878, 1, 23, IOP PUBLISHING LTD, Jun. 2019, [Peer-reviewed]
English, Scientific journal, The interactions of atomic and molecular hydrogen with bare interstellar dust grain surfaces are important for understanding H-2 formation at relatively high temperatures (>20 K). We investigate the diffusion of physisorbed H atoms and the desorption energetics of H-2 molecules on an amorphous diamond-like carbon (DLC) surface. From temperature-programmed desorption experiments with a resonance-enhanced multiphoton ionization (REMPI) method for H-2 detection, the H-2 coverage-dependent activation energies for H-2 desorption are determined. The activation energies decrease with increasing H-2 coverage and are centered at 30 meV with a narrow distribution. Using a combination of photostimulated desorption and REMPI methods, the time variations of the surface number density of H-2 following atomic and molecular hydrogen depositions are studied. From these measurements, we show that H-2 formation on a DLC surface is quite efficient, even at 20 K. A significant kinetic isotope effect for H-2 and D-2 recombination reactions suggests that H-atom diffusion on a DLC surface is mediated by quantum mechanical tunneling. In astrophysically relevant conditions, H-2 recombination due to physisorbed H-atoms is unlikely to occur at 20 K, suggesting that chemisorbed H atoms might play a role in H-2 formation at relatively high temperatures. - Behaviour of radicals on interstellar dust analogues
Naoki Watanabe
Proceedings of the International Astronomical Union, 15, S350, 116, 122, Cambridge University Press ({CUP}), Apr. 2019, [Peer-reviewed]
Scientific journal - Physico-chemical behavior of hydrogen sulfide induced by reactions with H and D atoms on different types of ice surfaces at low temperature
Yasuhiro Oba, Takuto Tomaru, Akira Kouchi, Naoki Watanabe
Astrophysical Journal, 874, 8pp, Apr. 2019, [Peer-reviewed]
English, Scientific journal - 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, [Peer-reviewed]
English, Scientific journal - Measurements of the Activation Energies for Atomic Hydrogen Diffusion on Pure Solid CO
Y. Kimura, M. Tsuge, V. Pirronello, A. Kouchi, N. Watanabe
The Astrophysical Journal, 858, L23, 5pp, American Astronomical Society, May 2018, [Peer-reviewed]
English, Scientific journal - The Ortho-to-para Ratio of Water Molecules Desorbed from Ice Made from Para-water Monomers at 11 K
Tetsuya Hama, Akira Kouchi, Naoki Watanabe
Astrophysical Journal Letters, 857, 2, 6pp, Institute of Physics Publishing, 20 Apr. 2018, [Peer-reviewed]
English, Scientific journal, 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. - An infrared measurement of chemical desorption from interstellar ice analogues
Y. Oba, T. Tomaru, T. Lamberts, A. Kouchi, N. Watanabe
Nature Astronomy, 2, 3, 228, 232, Nature Publishing Group, 01 Mar. 2018, [Peer-reviewed]
English, Scientific journal, 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. - In Situ Nondestructive Analysis of Kalanchoe pinnata Leaf Surface Structure by Polarization-Modulation Infrared Reflection-Absorption Spectroscopy
Tetsuya Hama, Akira Kouchi, Naoki Watanabe, Shinichi Enami, Takafumi Shimoaka, Takeshi Hasegawa
Journal of Physical Chemistry B, 121, 49, 11124, 11131, American Chemical Society, 14 Dec. 2017, [Peer-reviewed]
English, Scientific journal, 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. - Deuterium Fractionation upon the Formation of Hexamethylenetetramines through Photochemical Reactions of Interstellar Ice Analogs Containing Deuterated Methanol Isotopologues
Yasuhiro Oba, Yoshinori Takano, Hiroshi Naraoka, Akira Kouchi, Naoki Watanabe
ASTROPHYSICAL JOURNAL, 849, 2, 9pp, IOP PUBLISHING LTD, Nov. 2017, [Peer-reviewed]
English, Scientific journal, 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. - Liquid-like behavior of UV-irradiated interstellar ice analog at low temperatures.
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, Sep. 2017, [Peer-reviewed], [International Magazine]
English, Scientific journal, 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. - Fast crystalline ice formation at extremely low temperature through water/neon matrix sublimation
Tetsuya Hama, Shinnosuke Ishizuka, Tomoya Yamazaki, Yuki Kimura, Akira Kouchi, Naoki Watanabe, Toshiki Sugimoto, Valerio Pirronello
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 19, 27, 17677, 17684, ROYAL SOC CHEMISTRY, Jul. 2017, [Peer-reviewed]
English, Scientific journal, 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. - Simulations and spectra of water in CO matrices
Rafael Escribano, Emilio Artacho, Akira Kouchi, Tetusya Hama, Yuki Kimura, Hiroshi Hidaka, Naoki Watanabe
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 19, 10, 7280, 7287, ROYAL SOC CHEMISTRY, Mar. 2017, [Peer-reviewed]
English, Scientific journal, 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. - Deuterated hexamethylenetetramine formed by the photolysis of interstellar ice analogs
Oba Yasuhiro, Takano Yoshinori, Naraoka Hiroshi, Watanabe Naoki, Kouchi Akira
Abstracts of Annual Meeting of the Geochemical Society of Japan, 64, 131, 131, GEOCHEMICAL SOCIETY OF JAPAN, 2017
Japanese, - Ortho-to-para ratio of water desorbed from ice and its implications for astronomy and planetary science
Tetsuya Hama, Akira Kouchi, Naoki Watanabe
XXX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2017), 875, IOP PUBLISHING LTD, 2017, [Peer-reviewed]
English, International conference proceedings, 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. - Two-Step Process in Homogeneous Nucleation of Alumina in Supersaturated Vapor
Shinnosuke Ishizuka, Yuki Kimura, Tomoya Yamazaki, Tetsuya Hama, Naoki Watanabe, Akira Kouchi
CHEMISTRY OF MATERIALS, 28, 23, 8732, 8741, AMER CHEMICAL SOC, Dec. 2016, [Peer-reviewed]
English, Scientific journal, 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 - Negative catalytic effect of water on the reactivity of hydrogen abstraction from the C-H bond of dimethyl ether by deuterium atoms through tunneling at low temperatures
Yasuhiro Oba, Naoki Watanabe, Akira Kouchi
CHEMICAL PHYSICS LETTERS, 662, 14, 18, ELSEVIER SCIENCE BV, Oct. 2016, [Peer-reviewed]
English, Scientific journal, 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. - Hydrogen-deuterium substitution in solid ethanol by surface reactions at low temperatures
Yasuhiro Oba, Kazuya Osaka, Takeshi Chigai, Akira Kouchi, Naoki Watanabe
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 462, 1, 689, 695, OXFORD UNIV PRESS, Oct. 2016, [Peer-reviewed]
English, Scientific journal, 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. - DEUTERIUM FRACTIONATION DURING AMINO ACID FORMATION BY PHOTOLYSIS OF INTERSTELLAR ICE ANALOGS CONTAINING DEUTERATED METHANOL
Yasuhiro Oba, Yoshinori Takano, Naoki Watanabe, Akira Kouchi
ASTROPHYSICAL JOURNAL LETTERS, 827, 1, L18 (7pp), IOP PUBLISHING LTD, Aug. 2016, [Peer-reviewed]
English, Scientific journal, 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. - Matrix sublimation method for the formation of high-density amorphous ice
A. Kouchi, T. Hama, Y. Kimura, H. Hidaka, R. Escribano, N. Watanabe
CHEMICAL PHYSICS LETTERS, 658, 287, 292, ELSEVIER SCIENCE BV, Aug. 2016, [Peer-reviewed]
English, Scientific journal, 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. - Stepwise formation of H3O+(H2O)(n) in an ion drift tube: Empirical effective temperature of association/dissociation reaction equilibrium in an electric field
Yoichi Nakai, Hiroshi Hidaka, Naoki Watanabe, Takao M. Kojima
JOURNAL OF CHEMICAL PHYSICS, 144, 22, 224306(11pp), AMER INST PHYSICS, Jun. 2016, [Peer-reviewed]
English, Scientific journal, 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. - Surface Temperature Dependence of Hydrogen Ortho-Para Conversion on Amorphous Solid Water
Hirokazu Ueta, Naoki Watanabe, Tetsuya Hama, Akira Kouchi
PHYSICAL REVIEW LETTERS, 116, 25, 253201(5pp), AMER PHYSICAL SOC, Jun. 2016, [Peer-reviewed]
English, Scientific journal, 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. - 21pBE-13 Surface-temperature dependence of H_2-nuclear spin conversion on amorphous solid water
Ueta H., Watanabe N., Hama T., Kouchi A.
Meeting Abstracts of the Physical Society of Japan, 71, 742, 742, The Physical Society of Japan (JPS), 2016
Japanese - 20pAJ-3 Strong surface structural dependence in hydrogenation of aromatic hydrocarbon film
Hama T., Kouchi A., Watanabe N.
Meeting Abstracts of the Physical Society of Japan, 71, 2570, 2571, The Physical Society of Japan (JPS), 2016
Japanese - 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, [Peer-reviewed]
English, Scientific journal - Statistical ortho-to-para ratio of water desorbed from ice at 10 kelvin
Tetsuya Hama, Akira Kouchi, Naoki Watanabe
SCIENCE, 351, 6268, 65, 67, AMER ASSOC ADVANCEMENT SCIENCE, Jan. 2016, [Peer-reviewed]
English, Scientific journal, 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. - Signatures of Quantum-Tunneling Diffusion of Hydrogen Atoms on Water Ice at 10 K
K. Kuwahata, T. Hama, A. Kouchi, N. Watanabe
PHYSICAL REVIEW LETTERS, 115, 13, 133201, AMER PHYSICAL SOC, Sep. 2015, [Peer-reviewed]
English, Scientific journal, 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. - Study on Surface Diffusion of Hydrogen Atom on Amorphous Solid Water at Low Temperatures : A Key for Chemical Evolution in Space
Hama Tetsuya, Kouchi Akira, Watanabe Naoki
日本物理学会誌, 70, 8, 608, 613, The Physical Society of Japan (JPS), Aug. 2015, [Peer-reviewed]
Japanese, Scientific journal, Diffusion of hydrogen atom on cosmic dust is a key issue for the formation of interstellar hydrogen molecule, as well as chemical evolution in molecular clouds. Using the combination of Photon Stimulated Desorption (PSD) and Resonance Enhanced MultiPhoton Ionization (REMPI) techniques, we have investigated activation energy and mechanism of surface diffusion of hydrogen atom on amorphous solid water at low temperatures. - Chiral glycine formation on cold interstellar grains by quantum tunneling hydrogen-deuterium substitution reactions
Yasuhiro Oba, Naoki Watanabe, Yoshihiro Osamura, Akira Kouchi
CHEMICAL PHYSICS LETTERS, 634, 53, 59, ELSEVIER SCIENCE BV, Aug. 2015, [Peer-reviewed]
English, Scientific journal, 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. - Quantum tunneling observed without its characteristic large kinetic isotope effects
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, NATL ACAD SCIENCES, Jun. 2015, [Peer-reviewed]
English, Scientific journal, 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. - 21pBG-3 Reaction equilibria for stepwise formation of H_3O(H_2O)_n^+ cluster ions in an electric field of an ion drift tube
Nakai Yoichi, Hidaka Hiroshi, Watanabe Naoki, Kojima Takao M.
Meeting Abstracts of the Physical Society of Japan, 70, 632, 632, The Physical Society of Japan (JPS), 2015
Japanese - Quantum Tunneling Hydrogenation of Solid Benzene and Its Control via Surface Structure
Tetsuya Hama, Hirokazu Ueta, Akira Kouchi, Naoki Watanabe, Hiroto Tachikawa
JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 5, 21, 3843, 3848, AMER CHEMICAL SOC, Nov. 2014, [Peer-reviewed]
English, Scientific journal, 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. - Reaction kinetics and isotope effect of water formation by the surface reaction of solid H2O2 with H atoms at low temperatures
Yasuhiro Oba, Kazuya Osaka, Naoki Watanabe, Takeshi Chigai, Akira Kouchi
FARADAY DISCUSSIONS, 168, 185, 204, ROYAL SOC CHEMISTRY, Aug. 2014, [Peer-reviewed]
English, Scientific journal, 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. - Hydrogen isotopic substitution of solid methylamine through atomic surface reactions at low temperatures: A potential contribution to the D/H ratio of methylamine in molecular clouds
Yasuhiro Oba, Takeshi Chigai, Yoshihiro Osamura, Naoki Watanabe, Akira Kouchi
METEORITICS & PLANETARY SCIENCE, 49, 1, 117, 132, WILEY-BLACKWELL, Jan. 2014, [Peer-reviewed]
English, Scientific journal, 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. - Hydrogen isotopic composition of water formed by grain-surface reactions in molecular clouds
Oba Yasuhiro, Watanabe Naoki, Kouchi Akira
Abstracts of Annual Meeting of the Geochemical Society of Japan, 61, 168, 168, GEOCHEMICAL SOCIETY OF JAPAN, 2014
Japanese, 本講演では，星間塵表面反応で生成する水分子の水素同位体組成について，これまでの実験結果をもとに詳細な議論をおこなう。一般的に星間分子は分子生成時および分子生成後に重水素濃集可能であるが，水分子に関しては，極低温の星間塵表面では分子生成時に限定される。水分子は3つの経路でおもに生成するが，うち2つの生成反応は極低温では熱的におこりえず，量子力学的なトンネル効果が不可欠である。量子力学的トンネル反応には大きな同位体効果が期待されるため，生成する水分子の水素同位体組成を議論する際には注意が必要である。 - Surface Processes on Interstellar Amorphous Solid Water: Adsorption, Diffusion, Tunneling Reactions, and Nuclear-Spin Conversion
Tetsuya Hama, Naoki Watanabe
CHEMICAL REVIEWS, 113, 12, 8783, 8839, AMER CHEMICAL SOC, Dec. 2013, [Peer-reviewed]
English, Scientific journal - Nuclear spin temperatures of hydrogen and water molecules on amorphous solid water
N. Watanabe, T. Hama, A. Kouchi
AIP Conference Proceedings, 1543, 308, 316, 2013, [Peer-reviewed], [Invited]
English, International conference proceedings - Nuclear Spin Temperatures of Hydrogen and Water Molecules on Amorphous Solid Water
Naoki Watanabe, Tetsuya Hama, Akira Kouchi
FIRST INTERNATIONAL CONFERENCE ON CHEMICAL EVOLUTION OF STAR FORMING REGION AND ORIGIN OF LIFE (ASTROCHEM2012), 1543, 308, 316, AMER INST PHYSICS, 2013, [Peer-reviewed], [Invited]
English, International conference proceedings, 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. - Formation of deuterated formaldehyde on low temperature surfaces: isotope effect of quantum tunneling reactions
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, AMER INST PHYSICS, 2013, [Peer-reviewed]
English, International conference proceedings, 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. - THE MECHANISM OF SURFACE DIFFUSION OF H AND D ATOMS ON AMORPHOUS SOLID WATER: EXISTENCE OF VARIOUS POTENTIAL SITES
Tetsuya Hama, Kazuaki Kuwahata, Naoki Watanabe, Akira Kouchi, Yuki Kimura, Takeshi Chigai, Valerio Pirronello
ASTROPHYSICAL JOURNAL, 757, 2, 185, (12pp), IOP PUBLISHING LTD, Oct. 2012, [Peer-reviewed]
English, Scientific journal, 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. - WATER FORMATION THROUGH A QUANTUM TUNNELING SURFACE REACTION, OH + H-2, AT 10 K
Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
ASTROPHYSICAL JOURNAL, 749, 1, 67, (12pp), IOP PUBLISHING LTD, Apr. 2012, [Peer-reviewed]
English, Scientific journal, 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. - 星間分子雲での微粒子表面における水素の化学物理過程
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, [Peer-reviewed]
Japanese, Scientific journal - Experimental studies of surface reactions among OH radicals that yield H2O and CO2 at 40-60 K
Yasuhiro Oba, Naoki Watanabe, Akira Kouchi, Tetsuya Hama, Valerio Pirronello
Physical Chemistry Chemical Physics, 13, 35, 15792, 15797, 21 Sep. 2011, [Peer-reviewed]
English, Scientific journal, 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. - SPIN TEMPERATURE OF WATER MOLECULES DESORBED FROM THE SURFACES OF AMORPHOUS SOLID WATER, VAPOR-DEPOSITED AND PRODUCED FROM PHOTOLYSIS OF A CH4/O-2 SOLID MIXTURE
T. Hama, N. Watanabe, A. Kouchi, M. Yokoyama
ASTROPHYSICAL JOURNAL LETTERS, 738, 1, L15, (5pp), IOP PUBLISHING LTD, Sep. 2011, [Peer-reviewed]
English, Scientific journal, 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. - Translational and rotational energy measurements of desorbed water molecules in their vibrational ground state following 157 nm irradiation of amorphous solid water
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, ELSEVIER SCIENCE BV, May 2011, [Peer-reviewed]
English, Scientific journal, 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. - Experimental studies on the formation of carbon dioxide in interstellar molecular clouds
OBA Yasuhiro, WATANABE Naoki, KOUCHI Akira, HAMA Tetsuya, PIRRONELLO Valerio
Chikyukagaku, 45, 4, 213, 226, The Geochemical Society of Japan, 2011, [Peer-reviewed]
Japanese, Scientific journal, Since the first detection in interstellar medium in 1989, solid CO2 has been found in various lines of sight and regarded as one of the main constituent in icy grain mantles in interstellar clouds. Due to the low efficiency in the formation of CO2 in the gas phase and relatively high abundance of CO in icy grain mantles, it is generally accepted that CO2 forms on the surface of icy grain mantles in interstellar clouds. CO2 formation on/in icy grain mantles has been extensively studied experimentally, with the aid of energetic sources such as UV or cosmic-rays, and also without them. In this review, we summarize experimental results on the formation of CO2 on cold surfaces through energetic and non-energetic processes under the simulative conditions of interstellar molecular clouds. - Surface abundance change in vacuum ultraviolet photodissociation of CO2 and H2O mixture ices
Takashi Kinugawa, Akihiro Yabushita, Masahiro Kawasaki, Tetsuya Hama, Naoki Watanabe
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 35, 15785, 15791, ROYAL SOC CHEMISTRY, 2011, [Peer-reviewed]
English, Scientific journal, 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. - FTIR study of ammonia formation via the successive hydrogenation of N atoms trapped in a solid N-2 matrix at low temperatures
Hiroshi Hidaka, Motohiro Watanabe, Akira Kouchi, Naoki Watanabe
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 35, 15798, 15802, ROYAL SOC CHEMISTRY, 2011, [Peer-reviewed]
English, Scientific journal, 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. - Formation of ammonia molecules by H addition reactions to N atom on interstellar grain surfaces at low temperatures
Hidaka Hiroshi, Kouchi Akira, Watanabe Naoki
Abstracts of Annual Meeting of the Geochemical Society of Japan, 58, 292, 292, GEOCHEMICAL SOCIETY OF JAPAN, 2011
分子雲でアンモニア分子が生成される過程として提案されている，低温星間塵表面における窒素原子への水素原子付加反応の検証を実験的手法により行った．実験は，超高真空槽内に設置した低温基板（10K）にNおよびH原子を照射し，赤外吸収分光により生成分子の観測を行った．その結果，10Kという低温表面でも上記表面反応によりアンモニアが生成されることが明らかになった． - Isotope effect on the formation of H2O through surface reactions at low temperatures.
OBA YASUHIRO, WATANABE NAOKI, KOUCHI AKIRA
Abstracts of Annual Meeting of the Geochemical Society of Japan, 58, 291, 291, GEOCHEMICAL SOCIETY OF JAPAN, 2011
H2Oは星間塵アイスマントルの主要な構成成分である。H2Oはその存在量を気相反応のみでは説明できないことから，星間塵表面での反応で生成したと考えられている。本研究では，高密度星間分子雲で主要な経路だと考えられている，ヒドロキシルラジカル（OH)と水素分子(H2)の反応による，H2O生成に関する実験結果を紹介する。実験は，超高真空・極低温環境のアルミニウム基板表面でおこなった。 - 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, [Peer-reviewed]
English, Scientific journal - Experimental studies of surface reactions among OH radicals that yield H2O and CO2 at 40-60 K
Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
Phys. Chem. Chem. Phys., 13, 35, 15792, 15797, 2011, [Peer-reviewed]
English - FORMATION OF CARBONIC ACID (H2CO3) BY SURFACE REACTIONS OF NON-ENERGETIC OH RADICALS WITH CO MOLECULES AT LOW TEMPERATURES
Yasuhiro Oba, Naoki Watanabe, Akira Kouchi, Tetsuya Hama, Valerio Pirronello
ASTROPHYSICAL JOURNAL, 722, 2, 1598, 1606, IOP PUBLISHING LTD, Oct. 2010, [Peer-reviewed]
English, Scientific journal, 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. - DIRECT MEASUREMENTS OF HYDROGEN ATOM DIFFUSION AND THE SPIN TEMPERATURE OF NASCENT H-2 MOLECULE ON AMORPHOUS SOLID WATER
Naoki Watanabe, Yuki Kimura, Akira Kouchi, Takeshi Chigai, Tetsuya Hama, Valerio Pirronello
ASTROPHYSICAL JOURNAL LETTERS, 714, 2, L233, L237, IOP PUBLISHING LTD, May 2010, [Peer-reviewed]
English, Scientific journal, 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. - DIRECT EVIDENCE FOR AMMONIUM ION FORMATION IN ICE THROUGH ULTRAVIOLET-INDUCED ACID-BASE REACTION OF NH3 WITH H3O+
Eui-Seong Moon, Heon Kang, Yasuhiro Oba, Naoki Watanabe, Akira Kouchi
ASTROPHYSICAL JOURNAL, 713, 2, 906, 911, IOP PUBLISHING LTD, Apr. 2010, [Peer-reviewed]
English, Scientific journal, 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. - A desorption mechanism of water following vacuum-ultraviolet irradiation on amorphous solid water at 90 K
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, AMER INST PHYSICS, Apr. 2010, [Peer-reviewed]
English, Scientific journal, 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] - EXPERIMENTAL STUDY OF CO2 FORMATION BY SURFACE REACTIONS OF NON-ENERGETIC OH RADICALS WITH CO MOLECULES
Yasuhiro Oba, Naoki Watanabe, Akira Kouchi, Tetsuya Hama, Valerio Pirronello
ASTROPHYSICAL JOURNAL LETTERS, 712, 2, L174, L178, IOP PUBLISHING LTD, Apr. 2010, [Peer-reviewed]
English, Scientific journal, 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. - Experimental study of CO2 formation by surface reactions of non-energetic OH radicals with CO molecules
Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
Astrophys. J. Lett., 712, 2,Pt.2, L174, L178, 2010, [Peer-reviewed]
English, Scientific journal - Direct measurements of hydrogen atom diffusion and the spin temperature of nascent H2 molecule on amorphous solid water
N. Watanabe, Y. Kimura, A. Kouchi, T. Chigai, T. Hama, V. Pirronello
Astrophys. J. Lett., 714, 2,Pt.2, L233, L237, 2010, [Peer-reviewed]
English, Scientific journal - Direct measurements of hydrogen atom diffusion and the spin temperature of nascent H2 molecule on amorphous solid water
N. Watanabe, Y. Kimura, A. Kouchi, T. Chigai, T. Hama, V. Pirronello
Astrophys. J. Lett., 714, 2,Pt.2, L233, L237, 2010, [Peer-reviewed]
English - Direct evidence for ammonium ion formation in ice through ultraviolet-induced acid-base reaction of NH3 with H3O+
E-S. Moon, H. Kang, Y. Oba, N. Watanabe, A. Kouchi
Astrophys. J., 713, 2,Pt.1, 906, 911, 2010, [Peer-reviewed]
English - Experimental study of CO2 formation by surface reactions of non-energetic OH radicals with CO molecules
Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
Astrophys. J. Lett., 712, 2,Pt.2, L174, L178, 2010, [Peer-reviewed]
English - Hydrogen isotope exchange and H(D) atom addition reaction of solid formaldehyde on amorphous solid water at low temperatures
Hiroshi Hidaka, Motohiro Watanabe, Akira Kouchi, Naoki Watanabe
Journal of Physics: Conference Series, 194, 13, 132024, Institute of Physics Publishing, 24 Dec. 2009, [Peer-reviewed]
English, International conference proceedings, 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. - REACTION ROUTES IN THE CO-H2CO-d(n)-CH3OH-d(m) SYSTEM CLARIFIED FROM H(D) EXPOSURE OF SOLID FORMALDEHYDE AT LOW TEMPERATURES
H. Hidaka, M. Watanabe, A. Kouchi, N. Watanabe
ASTROPHYSICAL JOURNAL, 702, 1, 291, 300, IOP PUBLISHING LTD, Sep. 2009, [Peer-reviewed]
English, Scientific journal, 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. - Formation mechanisms of oxygen atoms in the O(D-1(2)) state from the 157 nm photoirradiation of amorphous water ice at 90 K
Tetsuya Hama, Akihiro Yabushita, Masaaki Yokoyama, Masahiro Kawasaki, Naoki Watanabe
JOURNAL OF CHEMICAL PHYSICS, 131, 11, 114510, AMER INST PHYSICS, Sep. 2009, [Peer-reviewed]
English, Scientific journal, 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] - Formation mechanisms of oxygen atoms in the O(D-1(2)) state from the 157 nm photoirradiation of amorphous water ice at 90 K
Tetsuya Hama, Akihiro Yabushita, Masaaki Yokoyama, Masahiro Kawasaki, Naoki Watanabe
JOURNAL OF CHEMICAL PHYSICS, 131, 11, 114511, AMER INST PHYSICS, Sep. 2009, [Peer-reviewed]
English, Scientific journal, 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] - Formation mechanisms of oxygen atoms in the O(P-3(J)) state from the 157 nm photoirradiation of amorphous water ice at 90 K
Tetsuya Hama, Akihiro Yabushita, Masaaki Yokoyama, Masahiro Kawasaki, Naoki Watanabe
JOURNAL OF CHEMICAL PHYSICS, 131, 11, 114511, AMER INST PHYSICS, Sep. 2009, [Peer-reviewed]
English, Scientific journal, 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] - FORMATION OF COMPACT AMORPHOUS H2O ICE BY CODEPOSITION OF HYDROGEN ATOMS WITH OXYGEN MOLECULES ON GRAIN SURFACES
Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
ASTROPHYSICAL JOURNAL, 701, 1, 464, 470, IOP PUBLISHING LTD, Aug. 2009, [Peer-reviewed]
English, Scientific journal, 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. - TRANSLATIONAL AND ROTATIONAL ENERGY MEASUREMENTS OF PHOTODESORBED WATER MOLECULES IN THEIR VIBRATIONAL GROUND STATE FROM AMORPHOUS SOLID WATER
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, IOP PUBLISHING LTD, Jul. 2009, [Peer-reviewed]
English, Scientific journal, 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, [Peer-reviewed]
Japanese, Scientific journal - Formation of water molecule by surface atomic reactions on interstellar grains at low temperatures
OBA Yasuhiro, MIYAUCHI Naoya, CHIGAI Takeshi, HIDAKA Hiroshi, WATANABE Naoki, KOUCHI Akira
Chikyukagaku, 43, 4, 117, 131, The Geochemical Society of Japan, 2009, [Peer-reviewed]
Japanese, Scientific journal, Formation of water by reaction of oxygen molecules (O2) with hydrogen atoms (H) were investigated at low temperatures (10-40 K) in order to reveal the possible reaction pathways to yield water on grain surfaces in molecular clouds. Two types of experiments for surface reaction between O2 and H were performed: one of which was that solid O2 was deposited onto the surface, followed by H irradiations to the O2, another of which was that gaseous O2 was continuously codeposited with H onto the surface and was reacted with each other. H2O (D2O) and H2O2 (D2O2) were quickly produced through successive reactions of O2 with H (D). Reaction kinetics and isotope effect are discussed for the former experiment. For the latter experiment, the dependence of compositions of the products on the temperature and O2/H ratio, and also the structure of the H2O ice produced are examined. - Production of multiply charged ions from the 4d photoionization of Cs+
Tetsuo Koizumi, Takao M. Kojima, Mutsumi Sano, Naoki Watanabe
14TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF HIGHLY CHARGED IONS (HCI 2008), 163, 1, 12099, IOP PUBLISHING LTD, 2009, [Peer-reviewed]
English, International conference proceedings, 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. - Nonenergetic reactions between atomic hydrogen and molecules on interstellar grain surfaces
N. Watanabe, A. Kouchi, H. Hidaka, Y. Oba, N. Miyauchi
Journal of Physics: Conference Series, 194, 1, 12044, (5pages), Institute of Physics Publishing, 2009, [Peer-reviewed]
English, International conference proceedings, 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. - Formation of CO2 molecules by a surface reaction CO+OH at low temperatures.
OBA Yasuhiro, WATANABE Naoki, HIDAKA Hiroshi, KOUCHI Akira, PIRRONELLO Varelio
Abstracts of Annual Meeting of the Geochemical Society of Japan, 56, 66, 66, GEOCHEMICAL SOCIETY OF JAPAN, 2009
二酸化炭素は分子雲中星間塵アイスマントルの主要な構成成分であるが、気相反応によってその存在量を説明することができないため、その生成には塵表面での反応が重要だと考えられている。これまでの研究では、UVなどの外部エネルギーをH2OやCOなどを含む混合氷に照射してCO2生成が確認されてきたが、外部エネルギー無しにCO2が生成するかどうかは明らかにされていなかった。本講演では、100Kに冷却されたOHラジカルとCOの固体表面上での反応でCO2生成が確認されたので、その結果について報告する。 - 1. Formation of interstellar ice by low temperature surface atomic reactions
A. Kouchi, Y. Oba, N. Miyauchi, H. Hidaka, N. Watanabe
Cryobiology, 59, 3, 370, Elsevier {BV}, 2009, [Peer-reviewed] - Nonenergetic reactions between atomic hydrogen and molecules on interstellar grain surfaces
N. Watanabe, A. Kouchi, H. Hidaka, Y. Oba, N. Miyauchi
J. Phys. Conf. Ser., 194, 1, 012044, (5pages), 2009, [Peer-reviewed]
English - Production of multiply charged ions from the 4d photoionization of Cs+
Tetsuo Koizumi, Takao M. Kojima, Mutsumi Sano, Naoki Watanabe
14TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF HIGHLY CHARGED IONS (HCI 2008), 163, 1, 012099, IOP PUBLISHING LTD, 2009, [Peer-reviewed]
English, International conference proceedings, 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. - Ice surface reactions: A key to chemical evolution in space
Naoki Watanabe, Akira Kouchi
PROGRESS IN SURFACE SCIENCE, 83, 10-12, 439, 489, PERGAMON-ELSEVIER SCIENCE LTD, Dec. 2008, [Peer-reviewed]
English, Scientific journal, 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. - Ice surface reactions: A key to chemical evolution in space
Naoki Watanabe, Akira Kouchi
Progress in Surface Science, 83, 10-12, 439, 489, Dec. 2008, [Peer-reviewed]
English, 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. - 332 極低温表面原子反応O2+Hによる水分子生成 : アモルファス氷の触媒効果(原始惑星系円盤II,オーラルセッション11)
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, 2008, 0, 93, 93, 日本惑星科学会, Nov. 2008
Japanese, Scientific journal - Measurements of energy partitioning in H-2 formation by photolysis of amorphous water ice
Akihiro Yabushita, Tetsuya Hama, Daisuke Iida, Noboru Kawanaka, Masahiro Kawasaki, Naoki Watanabe, Michael N. R. Ashfold, Hans-Peter Loock
ASTROPHYSICAL JOURNAL LETTERS, 682, 1, L69, L72, UNIV CHICAGO PRESS, Jul. 2008, [Peer-reviewed]
English, Scientific journal, We demonstrate experimentally that photodissociation of amorphous solid water at 100 K results in formation of H-2 molecules with an ortho/para ratio of g(OPR) = 3. Two distinct mechanisms can be identified: endothermic abstraction of a hydrogen atom from H2O by a photolytically produced H atom yields vibrationally cold H-2 products, whereas exothermic recombination of two H-atom photoproducts yields translationally and internally hot H-2. These results are in accord with predictions by molecular dynamics calculations and their astrophysical implications are discussed. - Release of hydrogen molecules from the photodissociation of amorphous solid water and polycrystalline ice at 157 and 193 nm
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, AMER INST PHYSICS, Jul. 2008, [Peer-reviewed]
English, Scientific journal, 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. - Structural effects of ice grain surfaces on the hydrogenation of CO at low temperatures
H. Hidaka, N. Miyauchi, A. Kouchi, N. Watanabe
CHEMICAL PHYSICS LETTERS, 456, 1-3, 36, 40, ELSEVIER SCIENCE BV, Apr. 2008, [Peer-reviewed]
English, Scientific journal, 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. - Formation of hydrogen peroxide and water from the reaction of cold hydrogen atoms with solid oxygen at 10 K
N. Miyauchi, H. Hidaka, T. Chigai, A. Nagaoka, N. Watanabe, A. Kouchi
CHEMICAL PHYSICS LETTERS, 456, 1-3, 27, 30, ELSEVIER SCIENCE BV, Apr. 2008, [Peer-reviewed]
English, Scientific journal, 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. - 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, [Peer-reviewed]
Japanese, Scientific journal - Formation of water from surface-atomic reactions at low temperatures
OBA YASUHIRO, MIYAUCHI NAOYA, CHIGAI TAKESHI, HIDAKA HIROSHI, WATANABE NAOKI, KOUCHI AKIRA
Abstracts of Annual Meeting of the Geochemical Society of Japan, 55, 371, 371, GEOCHEMICAL SOCIETY OF JAPAN, 2008
水分子は星間塵アイスマントル中で最も多く存在する分子であるが、その生成メカニズムはいまだはっきりしない。本研究では星間塵上表面原子反応による水分子生成反応の検証を行った。酸素分子を10Kに冷却された基板上に蒸着させ、そこに水素分子をプラズマ解離させて生成する水素原子を照射した。水素原子照射により酸素分子へ水素原子が付加され、過酸化水素、水の生成が確認された。これは酸素分子への水素原子逐次付加反応O2+H->HO2、HO2+H->H2O2、H2O2+H->H2O+OHが起こったことによる。 - Laboratory simulation of competition between hydrogenation and photolysis in the chemical evolution of H2O-CO ice mixtures
N. Watanabe, O. Mouri, A. Nagaoka, T. Chigai, A. Kouchi, V. Pirronello
ASTROPHYSICAL JOURNAL, 668, 2, 1001, 1011, UNIV CHICAGO PRESS, Oct. 2007, [Peer-reviewed]
English, Scientific journal, 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. - Temperature, composition, and hydrogen isotope effect in the hydrogenation of CO on amorphous ice surface at 10-20 K
H. Hidaka, A. Kouchi, N. Watanabe
JOURNAL OF CHEMICAL PHYSICS, 126, 20, 204707, AMER INST PHYSICS, May 2007, [Peer-reviewed]
English, Scientific journal, 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. - Effective rate constants for the surface reaction between solid methanol and deuterium atoms at 10 K
Akihiro Nagaoka, Naoki Watanabe, Akira Kouchi
JOURNAL OF PHYSICAL CHEMISTRY A, 111, 16, 3016, 3028, AMER CHEMICAL SOC, Apr. 2007, [Peer-reviewed]
English, Scientific journal, 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. - Interstellar amorphous ice ggrain: The role in chemical evolution
Naoki Watanabe, Akira Kouchi, Orie Mouri, Akihiro Nagaoka, Hiroshi Hidaka
Shinku/Journal of the Vacuum Society of Japan, 50, 4, 282, 290, 2007, [Peer-reviewed]
Japanese, Scientific journal, Surface reaction on interstellar ice grains is a key process for the chemical evolution in molecular clouds. We have performed a series of experiments to simulate the chemical evolution of the primordial CO molecule on the ice grains. Photochemical and hydrogen atom reactions of CO-H 2O binary ice at 15 K were studied because those are anticipated to be the most dominant chemical processes on the surface of grains. It was found that the photochemical reactions produce CO 2 with the highest yield, HCOOH, H 2CO, CH 3OH, and so on and that even at very low temperatures (much lower than activation energies), addition reactions of hydrogen atoms to CO proceed efficiently due to the tunneling effect and produce H 2CO and CH 3OH. Branching ratio of the yields in photochemical reactions strongly depends on the structure of ice, while hydrogen atom reactions are very sensitive to both the structure and temperature of ice. Considering the physical and chemical conditions of molecular clouds, the experimental results are consistent with the astronomical observation of ice grains. - Temperature, composition, and hydrogen isotope effect in the hydrogenation of CO on amorphous ice surface at 10 - 20 K
H. Hidaka, A. Kouchi, N. Watanabe
J. Chem. Phys., 126, 20, 204707, 2007, [Peer-reviewed]
English, Scientific journal - Dependence of the effective rate constants for the hydrogenation of CO on the temperature and composition of the surface
N. Watanabe, A. Nagaoka, H. Hidaka, T. Shiraki, T. Chigai, A. Kouchi
PLANETARY AND SPACE SCIENCE, 54, 11, 1107, 1114, PERGAMON-ELSEVIER SCIENCE LTD, Sep. 2006, [Peer-reviewed]
English, Scientific journal, 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, [Peer-reviewed]
Japanese, Scientific journal - 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, +, AMER INST PHYSICS, 2006, [Peer-reviewed]
English, International conference proceedings, 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, +, AMER INST PHYSICS, 2006, [Peer-reviewed]
English, International conference proceedings, 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
Naoki Watanabe, Hiroshi Hidaka, Akira Kouchi
ASTROCHEMISTRY: FROM LABORATORY STUDIES TO ASTRONOMICAL OBSERVATIONS, 855, 122, +, AMER INST PHYSICS, 2006, [Peer-reviewed]
English, International conference proceedings, Using cold atomic hydrogen and deuterium beams, hydrogenation and deuteration of solid CO on the surface of H2O ice were investigated in the surface-temperature range 8-20 K. In hydrogenation experiments, formaldehyde and methanol were produced efficiently by successive hydrogenation of CO below 20 K in conditions similar to those in molecular clouds. In deuteration experiments, we found, for the first time, that D2CO and CD3OD are formed from CO, with the reaction proceeding similarly to hydrogenation although at a much slower rate. From the attenuation curve of the parent CO at 15 K, the relative reaction rate of CO-deuteration to -hydrogenation was determined to be about 0.1. This isotope effect is considered to be due to tunneling reaction. - 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, [Peer-reviewed]
Japanese, Scientific journal - Observation of resonance structures in 4d photoionization of Eu
TM Kojima, FF Chen, M Kitajima, T Koizumi, Y Nakai, H Yamaoka, N Watanabe
JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, 144, 71, 74, ELSEVIER SCIENCE BV, Jun. 2005, [Peer-reviewed]
English, Scientific journal, 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. - H-D substitution in interstellar solid methanol: A key route for D enrichment
A Nagaoka, N Watanabe, A Kouchi
ASTROPHYSICAL JOURNAL, 624, 1, L29, L32, UNIV CHICAGO PRESS, May 2005, [Peer-reviewed]
English, Scientific journal, Deuterium enrichment of interstellar methanol is reproduced experimentally for the first time via grain-surface H-D substitution in solid methanol at an atomic D/H ratio of 0.1. Although previous gas-grain models successfully reproduce the deuterium enrichments observed in interstellar methanol molecules (D/H of up to 0.4, compared to the cosmic ratio of similar to 10(-5)), the models exclusively focus on deuterium fractionation resulting from the successive addition of atomic hydrogen/deuterium on CO. The mechanism proposed here represents a key route for deuterium enrichment that reproduces the high observed abundances of deuterated methanol, including multiple deuterations. - Laboratory Simulation of the Molecular Evolution on Interstellar Dusts
WATANABE Naoki, KOUCHI Akira
Butsuri, 60, 1, 39, 44, The Physical Society of Japan (JPS), 2005, [Peer-reviewed]
Japanese, Scientific journal, The evolution of CO molecules on the interstellar dusts was investigated expenmentally. The CO molecule was found to likely evolve into H_2CO and subsequently into CH_3OH by successive hydrogenation on the dusts even below 20K. In the center of dense molecular clouds, the hydrogenation would proceed via tunneling reactions and be more efficient than other processes such as photolysis and charged-particle bombardments. - 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, [Peer-reviewed]
Japanese, Scientific journal - Formation and deuterium fractionation of organic molecules on grain surfaces
Naoki Watanabe
Proceedings of the International Astronomical Union, 1, 231, 415, 426, Cambridge University Press, 2005, [Peer-reviewed]
English, Scientific journal, A series of experiments on the surface reactions of hydrogen and deuterium atoms with solid CO, formaldehyde (H2CO), and methanol (CH 3OH) has been performed. Successive hydrogenation of CO on surfaces at ∼10 K was found to proceed efficiently via tunneling to produce H 2CO and CH3OH on dust grains under the typical conditions of molecular clouds. Formation rates are strongly dependent on the surface temperature and composition. The role of surface reactions in the formation of deuterated formaldehyde and methanol was investigated. The deuterium fractionation of methanol observed in molecular clouds was reproduced experimentally via H-D substitution in solid methanol at an accreting atomic D/H ratio of 0.05-0.1. This is the first evidence that grain-surface reactions can be responsible for fractionation. We have determined several effective rate constants for hydrogenation, deuteration, and H-D substitution to construct the surface reaction network for CO, H2CO, CH3OH, deuterated formaldehyde, and deuterated methanol. © 2006 International Astronomical Union. - D-enrichment in molecular clouds: H-D substitution in solid methanol
Nagaoka Akihiro, Watanabe Naoki, Hidaka Hiroshi, Kouchi Akira
Abstracts for Annual Meeting of the Mineralogical Society of Japan, 2005, 136, 136, Japan Association of Mineralogical Sciences, 2005
Deuterium enrichment of interstellar methanol is reproduced experimentally for the first time via grain-surface H-D substitution in solid methanol at 10 K. The mechanism proposed here represents a key route for D-enrichment that reproduces the high observed abundances of deuterated methanol (D/H ratio of up to 0.4, compared to the cosmic ratio of about 10-5), including multiple deuterations. - Hydrogenation of CO on pure solid CO and CO-H2O mixed ice
N Watanabe, A Nagaoka, T Shiraki, A Kouchi
ASTROPHYSICAL JOURNAL, 616, 1, 638, 642, UNIV CHICAGO PRESS, Nov. 2004, [Peer-reviewed]
English, Scientific journal, Using a cold ( 30 K) atomic hydrogen beam, hydrogenation of CO on pure solid CO and CO-H2O mixed ice is investigated at temperatures below 20 K. Hydrogenation proceeds efficiently on both pure solid CO and CO-H2O mixed ice below 12 K, but the rate of reaction on pure CO decreases significantly at 15 K compared to CO-H2O mixed ice. Hydrogenation of CO at 12 K and above is found to be promoted by H2CO and H2O molecules on the CO surface. - Conversion of H2CO to CH3OH by reactions of cold atomic hydrogen on ice surfaces below 20 K
H Hidaka, N Watanabe, T Shiraki, A Nagaoka, A Kouchi
ASTROPHYSICAL JOURNAL, 614, 2, 1124, 1131, UNIV CHICAGO PRESS, Oct. 2004, [Peer-reviewed]
English, Scientific journal, 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, [Peer-reviewed]
Japanese, Scientific journal - 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, 2, 101, 106, 日本天文学会, 2004, [Peer-reviewed]
Japanese, Scientific journal - 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, [Peer-reviewed]
English, International conference proceedings - The dependence of H(2)CO and CH(3)OH formation on the temperature and thickness of H(2)O-CO ice during the successive hydrogenation of CO
N Watanabe, T Shiraki, A Kouchi
ASTROPHYSICAL JOURNAL, 588, 2, L121, L124, IOP PUBLISHING LTD, May 2003, [Peer-reviewed]
English, Scientific journal, 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. - An apparatus to determine the rovibrational distribution of molecular hydrogen formed by the heterogeneous recombination of H atoms on cosmic dust analogues
JSA Perry, JM Gingell, KA Newson, J To, N Watanabe, SD Price
MEASUREMENT SCIENCE AND TECHNOLOGY, 13, 9, 1414, 1424, IOP PUBLISHING LTD, Sep. 2002, [Peer-reviewed]
English, Scientific journal, 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. - Efficient formation of formaldehyde and methanol by the addition of hydrogen atoms to CO in H(2)O-CO ice at 10 K
N Watanabe, A Kouchi
ASTROPHYSICAL JOURNAL, 571, 2, L173, L176, IOP PUBLISHING LTD, Jun. 2002, [Peer-reviewed]
English, Scientific journal, 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. - Efficient formation of formaldehyde and methanol by the addition of hydrogen atoms to CO in H2O-CO ice at 10 K
Naoki Watanabe, Akira Kouchi
Astrophysical Journal, 571, 2, L173, L176, Institute of Physics Publishing, 01 Jun. 2002, [Peer-reviewed]
English, Scientific journal, 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. - Measurements of conversion rates of CO to CO2 in ultraviolet-induced reaction of amorphous D2O(H2O)/CO amorphouse ice
N Watanabe, A Kouchi
ASTROPHYSICAL JOURNAL, 567, 1, 651, 655, UNIV CHICAGO PRESS, Mar. 2002, [Peer-reviewed]
English, Scientific journal, The formation of carbon dioxide molecules from D2O(H2O)/CO binary ice induced by UV irradiation was studied experimentally. The measured conversion rate of CO CO2 to is about one order higher than previously reported rates. Our results imply that CO2 formation by the UV process is efficient even in a quiescent dense cloud. - Rapid growth of asteroids owing to very sticky interstellar organic grains
A Kouchi, T Kudo, H Nakano, M Arakawa, N Watanabe, SI Sirono, M Higa, N Maeno
ASTROPHYSICAL JOURNAL, 566, 2, L121, L124, UNIV CHICAGO PRESS, Feb. 2002, [Peer-reviewed]
English, Scientific journal, We experimentally found interstellar grains covered with organic matter in an asteroid belt, and more importantly, the organic matter played an essential role in the formation of the asteroids. The sticking threshold velocity of 5 m s(-1) of the millimeter-sized organic grains was several orders of magnitude higher than those of the coexisting silicate and ice grains. This indicated a very rapid coagulation of the very sticky organic grain aggregates and the formation of planetesimals in the asteroid region, covering even the early stage of the turbulent solar nebula. In contrast, there was no coagulation of the silicate and ice grains in the terrestrial and Jovian regions, respectively. - Measurements of conversion rates of CO to CO2 in Ultraviolet-induced reaction of D2O/CO amorphous ice
Naoki Watanabe, Akira Kouchi
Astrophys. J., 567, 1, 651, 655, 2002, [Peer-reviewed]
English - Absolute photoionization cross section measurements of Xe+ ions in the 4d threshold energy region
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, IOP PUBLISHING LTD, Sep. 2001, [Peer-reviewed]
English, Scientific journal, 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, [Peer-reviewed]
English, International conference proceedings - Measurements of D-2 yields from amorphous D2O ice by ultraviolet irradiation at 12 K
N Watanabe, T Horii, A Kouchi
ASTROPHYSICAL JOURNAL, 541, 2, 772, 778, UNIV CHICAGO PRESS, Oct. 2000, [Peer-reviewed]
English, Scientific journal, 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. - Measurements of D2 yields from D2O amorphous ice by ultraviolet irradiation at 12K
N. Watanabe, T. Horii, A. Kouchi
Astrophys. J., 541, 772, 779, 2000, [Peer-reviewed]
English - Dynamic properties of N and O 1s−1σu* shape resonances in N2 and CO2 molecules
A. A. Pavlychev, N. G. Fominykh, N. Watanabe, K. Soejima, E. Shigemasa, A. Yagishita
Physical Review Letters, 81, 17, 3623, 3626, 26 Oct. 1998, [Peer-reviewed]
English, Scientific journal, 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. - Dynamic properties of N and O 1s−1σu* shape resonances in N2 and CO2 molecules
A. A. Pavlychev, N. G. Fominykh, N. Watanabe, K. Soejima, E. Shigemasa, A. Yagishita
Physical Review Letters, 81, 17, 3623, 3626, 26 Oct. 1998, [Peer-reviewed]
English, Scientific journal, 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. - Photoion-yield spectra of Xe2+ in the 4d-threshold energy region
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, IOP PUBLISHING LTD, Sep. 1998, [Peer-reviewed]
English, Scientific journal, 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+. - Photoion yield spectroscopy in the 4d photoionization of Eu+
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, IOP PUBLISHING LTD, Apr. 1998, [Peer-reviewed]
English, Scientific journal, 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. - 4d photoionization of singly-charged ions
TM Kojima, M Oura, N Watanabe, Y Awaya, Y Itoh, T Koizumi, M Sano, F Koike
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 32, 3, 273, 279, KOREAN PHYSICAL SOC, Mar. 1998
English, Scientific journal, The relative partial photoion-yield spectra of A(2+) and A(3+) from the 4d photoionization of A(+) (A=Xe, Pa, and Eu) have been measured by using the ion-photon merged-beam technique in the 4d-photoionization energy region. A broad 'giant resonance' peak was observed for all three target species. The width of the resonance was wider in Xe+ and narrower in Eu+. Some apparent differences from the photoionization of neutral atoms were observed in the spectra for Xe+ and Ba+. For the Xe+ target, besides the giant-resonance peak at around 100 eV, a shoulder around 85 eV and sharp strong peaks at 55.4 and 56.1 eV were observed. By comparing the results with those from a multi-configuration Dirac-Fock (MCDF) calculation, the strong peaks were assigned as 4d --> 5p, and the shoulder and the main peak were assumed to be the 4d --> epsilon f resonance and the 4d5p --> 4fnp 'shake-up' transitions, respectively. In the case of Ba+, some prominent peaks on the rising slope of the giant resonance were observed in the spectra. On the contrary, in the Eu+ photoionization, the observed spectral shapes and peak positions were almost the same as those in neutral Eu case, except for the split peak of the giant resonance observed in the Eu2+ spectrum which showed a 'Beutler-Fano type' profile. This difference in the ionic state effect on the giant-resonance profile between Xe, Ba, and Eu is considered to be due to the difference of the depth of 'orbital collapse.' When the obtained giant resonance spectra ale compared to each other, the Z dependence of the resonance profile looks the same as that of the neutral lanthanides. Also our very recent results for the photoionization of Xe2+ and Xe3+ targets show vividly how a systematic change of the primary charge state affects the 4d giant resonance in an isonuclear sequence. These results are discussed in terms of the 'orbital collapse' picture. - Direct determination of partial wave contributions in the sigma* shape resonance of CO molecules
E Shigemasa, J Adachi, K Soejima, N Watanabe, A Yagishita, NA Cherepkov
PHYSICAL REVIEW LETTERS, 80, 8, 1622, 1625, AMERICAN PHYSICAL SOC, Feb. 1998, [Peer-reviewed]
English, Scientific journal, The first complete experiment for the C K-shell of CO molecules in the region of the sigma* shape resonance has been performed by detecting photoelectrons in coincidence with fragment ions. Four ratios of dipole matrix elements and four phase shift differences have been extracted from the experi mental data. Their analyses show that, in the sigma* shape resonance due to the l mixing, d and f partial waves give the main contribution to the cross section, and f and g waves give the main contribution to a rapid increase of phase shift by pi. - Direct determination of partial wave contributions in the sigma* shape resonance of CO molecules
E Shigemasa, J Adachi, K Soejima, N Watanabe, A Yagishita, NA Cherepkov
PHYSICAL REVIEW LETTERS, 80, 8, 1622, 1625, AMERICAN PHYSICAL SOC, Feb. 1998, [Peer-reviewed]
English, Scientific journal, The first complete experiment for the C K-shell of CO molecules in the region of the sigma* shape resonance has been performed by detecting photoelectrons in coincidence with fragment ions. Four ratios of dipole matrix elements and four phase shift differences have been extracted from the experi mental data. Their analyses show that, in the sigma* shape resonance due to the l mixing, d and f partial waves give the main contribution to the cross section, and f and g waves give the main contribution to a rapid increase of phase shift by pi. - Fixed-molecule 1s sigma(g,u) photoelectron angular distributions as a probe of sigma(g)* and sigma(u)* shape resonances of CO2
N Watanabe, J Adachi, K Soejima, E Shigemasa, A Yagishita, NG Fominykh, AA Pavlychev
PHYSICAL REVIEW LETTERS, 78, 26, 4910, 4913, AMERICAN PHYSICAL SOC, Jun. 1997, [Peer-reviewed]
English, Scientific journal, 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. - Fixed-molecule 1s sigma(g,u) photoelectron angular distributions as a probe of sigma(g)* and sigma(u)* shape resonances of CO2
N Watanabe, J Adachi, K Soejima, E Shigemasa, A Yagishita, NG Fominykh, AA Pavlychev
PHYSICAL REVIEW LETTERS, 78, 26, 4910, 4913, AMERICAN PHYSICAL SOC, Jun. 1997, [Peer-reviewed]
English, Scientific journal, 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. - Recoil-ion momentum distribution of single-electron capture to the ground and excited states in 0.5-1 MeV/u B-4+,B-5+-He collisions
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, IOP PUBLISHING LTD, Mar. 1997, [Peer-reviewed]
English, Scientific journal, 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, [Peer-reviewed]
Japanese, Scientific journal - Feasibility of photoionization of multi-charged ions and first test of a photon beam ion source(PHOBIS)with RIKEN EBIS(REBIS)
S.D. Kravis, N. Watanabe, Y. Awaya, M. Kimura, T. Kojima, K. Okuno, M. Oura
Physica Scripta, T71, 121, 126, 1997, [Peer-reviewed]
English, Scientific journal - 4d photoionization of multiply charged Xeq+ (q = 1-3) ions
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, ROYAL SWEDISH ACAD SCIENCES, 1997, [Peer-reviewed]
English, Scientific journal, 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. - Feasibility of photoionization of multi-charged ions and a first test of a PHOton Beam Ion Source (PHOBIS) with the RIKEN EBIS (REBlS)
SD Kravis, N Watanabe, Y Awaya, M Kimura, T Kojima, K Okuno, M Oura
PHYSICA SCRIPTA, T71, 121, 126, ROYAL SWEDISH ACAD SCIENCES, 1997, [Peer-reviewed]
English, Scientific journal, The importance, feasibility and method for measuring the photo-ionization cross-section of multi-charged ions using the RIKEN Electron Beam Ion Source (REBIS) is discussed. Specifically the cases for the 2 s and 1 s photo-ionization of Ar14+ is explored. It is concluded that such measurements are possible today and in future (3(rd) generation) synchrotron radiation facilities, and will be carried out upon modifications of the apparatus. Also described, is the first test of a PHOton Beam Ion Source using REBIS. It's potential advantage over other ion sources is that in the ion production mechanism photoionization the recoil ions obtain only near thermal energies to making ion beams with very low energy spread possible. - Feasibility of photoionization of multi-charged ions and first test of a photon beam ion source(PHOBIS)with RIKEN EBIS(REBIS)
S.D. Kravis, N. Watanabe, Y. Awaya, M. Kimura, T. Kojima, K. Okuno, M. Oura
Physica Scripta, T71, 121, 126, 1997, [Peer-reviewed]
English - Photoionization of 4d-electrons in singly charged Xe ions
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, 28 Nov. 1996, [Peer-reviewed]
English, Scientific journal, 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. - Single ionization of He by low-velocity protons and C6+: Ejected electron momentum distributions
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, AMERICAN PHYSICAL SOC, Aug. 1996, [Peer-reviewed]
English, Scientific journal, 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. - 4d photoionization of singly-charged Xe, Ba, and Eu ions
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, ELSEVIER SCIENCE BV, May 1996, [Peer-reviewed]
English, Scientific journal, 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. - Reactions of carbon-silicon binary cluster ions
Y Negishi, N Watanabe, H Shiromaru, Y Achiba, N Kobayashi
SURFACE REVIEW AND LETTERS, 3, 1, 661, 665, WORLD SCIENTIFIC PUBL CO PTE LTD, Feb. 1996, [Peer-reviewed]
English, Scientific journal, 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, [Peer-reviewed]
English - Reactions of carbon-silicon binary cluster ions
Y. Negishi, N. Watanabe, H. Shiromaru, Y. Achiba, N. Kobayashi
Surface Review and Letters, 3, 1, 661, 665, World Scientific Publishing Co. Pte Ltd, 1996, [Peer-reviewed]
English, Scientific journal, 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. - REACTION OF SICN+ (N=1-6) AND SICN- (N=2-4) WITH O-2 MOLECULES IN A RADIO-FREQUENCY ION-TRAP
Y NEGISHI, A KIMURA, N KOBAYASHI, H SHIROMARU, Y ACHIBA, N WATANABE
JOURNAL OF CHEMICAL PHYSICS, 103, 23, 9963, 9967, AMER INST PHYSICS, Dec. 1995, [Peer-reviewed]
English, Scientific journal, 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. - REACTIONS OF CARBON CLUSTER IONS STORED IN AN RF TRAP
N WATANABE, H SHIROMARU, Y NEGISHI, Y ACHIBA, N KOBAYASHI, Y KANEKO
ZEITSCHRIFT FUR PHYSIK D-ATOMS MOLECULES AND CLUSTERS, 26, 1, S252, S254, SPRINGER VERLAG, May 1993, [Peer-reviewed]
English, Scientific journal, Reactions of carbon cluster ions with O2 were studied by using an RF ion trap in which cluster ions of specific size produced by laser ablation could be stored selectively. Reaction rate constants for positive and negative carbon cluster ions were estimated. In the case of the positive cluster ions, these were consistent with the previous experimental results using FTMS. Negative carbon cluster ions C(n)- (n=4-8) were much less reactive than positive cluster ions. The C(n)O- products were seen only in n=4 and 6. - REACTIONS OF SCANDIUM CARBON BINARY CLUSTER IONS C(N)SC+ (N=2-6) WITH O-2 MOLECULES IN AN RF ION-TRAP
N WATANABE, H SHIROMARU, Y NEGISHI, Y ACHIBA, N KOBAYASHI, Y KANEKO
CHEMICAL PHYSICS LETTERS, 207, 4-6, 493, 497, ELSEVIER SCIENCE BV, May 1993, [Peer-reviewed]
English, Scientific journal, 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. - SIMULTANEOUS STORAGE OF HETEROCHARGED CARBON CLUSTER IONS IN AN RF TRAP
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, ELSEVIER SCIENCE BV, Jun. 1992, [Peer-reviewed]
English, Scientific journal, 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.
Other Activities and Achievements
- 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, Aug. 2019
AMER CHEMICAL SOC, English, Summary international conference - 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, Aug. 2019
AMER CHEMICAL SOC, English, Summary international conference - 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, Aug. 2019
AMER CHEMICAL SOC, English, Summary international conference - アモルファスMg2SiO4微粒子を覆った氷の光化学反応によるフォルステライト結晶の生成
香内晃, 木村勇気, 大場康弘, 羽馬哲也, 渡部直樹, 橘省吾, 土山明, 延寿里美, 大坪貴文, 日本地球惑星科学連合大会予稿集(Web), 2019, 2019 - 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, Mar. 2018
AMER CHEMICAL SOC, English, Summary international conference - H2 formation on interstellar dust grains: The viewpoints of theory, experiments, models and observations
Valentine Wakelam, Emeric Bron, Stephanie Cazaux, Francois Dulieu, Cécile Gry, Pierre Guillard, Emilie Habart, Liv Hornekær, Sabine Morisset, Gunnar Nyman, Valerio Pirronello, Stephen D. Price, Valeska Valdivia, Gianfranco Vidali, Naoki Watanabe, Molecular Astrophysics, 9, 1, 36, 01 Dec. 2017
Molecular hydrogen is the most abundant molecule in the universe. It is the first one to form and survive photo-dissociation in tenuous environments. Its formation involves catalytic reactions on the surface of interstellar grains. The micro-physics of the formation process has been investigated intensively in the last 20 years, in parallel of new astrophysical observational and modeling progresses. In the perspectives of the probable revolution brought by the future satellite JWST, this article has been written to present what we think we know about the H2 formation in a variety of interstellar environments., Elsevier B.V., English, Book review - 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, Apr. 2017
AMER CHEMICAL SOC, English, Summary international conference - Ortho-to-para ratio of water photodesorbed from ice at 10 K and the origin of interstellar water
Tetsuya Hama, Akira Kouchi, Naoki Watanabe, Journal of the Vacuum Society of Japan, 60, 7, 264, 274, 2017
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., Vacuum Society of Japan, Japanese, Book review - 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, [Peer-reviewed]
Japanese - 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, [Peer-reviewed]
Japanese - 固体芳香族炭化水素への水素・重水素原子付加から探る星間塵表面反応の速度論と同位体分別
羽馬哲也, 植田寛和, 渡部直樹, 香内晃, 地球化学, 50, 2, 33, 50, Jun. 2016, [Peer-reviewed]
Japanese - 27aCH-12 Current status for production of hydrated cluster ion using injected 4
Nakai Yoichi, Hidaka Hiroshi, Watanabe Naoki, Kojima Takao M., Meeting abstracts of the Physical Society of Japan, 69, 1, 175, 175, 05 Mar. 2014
The Physical Society of Japan (JPS), Japanese - 27aCH-13 Formation of water cluster ions by NO^+ injection into a drift tube filled with H_2O/buffer gases : effect of the metastable NO^+
Hidaka Hiroshi, Nakai Yoichi, Kojima Takao M., Watanabe Naoki, Meeting abstracts of the Physical Society of Japan, 69, 1, 175, 175, 05 Mar. 2014
The Physical Society of Japan (JPS), Japanese - 27aCH-5 H-D substitution of solid ethanol by quantum tunneling at low temperatures
Osaka K., Oba Y., Kouchi A., Watanabe N., Meeting abstracts of the Physical Society of Japan, 69, 1, 173, 173, 05 Mar. 2014
The Physical Society of Japan (JPS), Japanese - 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, Mar. 2014
AMER CHEMICAL SOC, English, Summary international conference - 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, Mar. 2014
AMER CHEMICAL SOC, English, Summary international conference - Current status for production of hydrated cluster ion using injected-ion drift tube 2 - production of water cluster ions
Nakai Yoichi, Hidaka Hiroshi, Watanabe Naoki, Kojima Takao M., Meeting abstracts of the Physical Society of Japan, 68, 2, 155, 155, 26 Aug. 2013
The Physical Society of Japan (JPS), Japanese - Isotope effect on the surface diffusion of hydrogen atom on ASW at low temperature
Kuwahata Kazuaki, Hama Tetsya, Hidaka Hiroshi, Kouchi Akira, Watanabe Naoki, Meeting abstracts of the Physical Society of Japan, 68, 2, 156, 156, 26 Aug. 2013
The Physical Society of Japan (JPS), Japanese - 26aEB-5 Isotope effect on the number density of hydrogen adatom on water ice during atomic irradiation
Kuwahata Kazuaki, Hama Tetsuya, Hidaka Hiroshi, Kouchi Akira, Watanabe Naoki, Meeting abstracts of the Physical Society of Japan, 68, 1, 182, 182, 26 Mar. 2013
The Physical Society of Japan (JPS), Japanese - Report of the Workshop on Interstellar Matter 2012
WATANABE N., Planetary People, 21, 4, 389, 391, 25 Dec. 2012
The Japanese Society for Planetary Sciences, Japanese - 24pAB-2 Experimental measurement of the nuclear spin temperature of thermally desorbed H_2O molecules from water ice
Hama Tetsuya, Watanabe Naoki, Kouchi Akira, Meeting abstracts of the Physical Society of Japan, 67, 1, 185, 185, 05 Mar. 2012
The Physical Society of Japan (JPS), Japanese - 24pAB-3 Current status for production of hydrated cluster ion using injected-ion drift tube 2 : production of water cluster ions
Nakai Yoichi, Hidaka Hiroshi, Watanabe Naoki, Kojima Takao M., Meeting abstracts of the Physical Society of Japan, 67, 1, 185, 185, 05 Mar. 2012
The Physical Society of Japan (JPS), Japanese - 24pAB-1 Measurements of the ortho/para ratio of H_2 formed by atomic hydrogen recombination on low temperature amorphous solid water : the time variation and isotope effect of that ratio
Kuwahata Kazuaki, Hama Tetsuya, Watanabe Naoki, Kouchi Akira, Meeting abstracts of the Physical Society of Japan, 67, 1, 185, 185, 05 Mar. 2012
The Physical Society of Japan (JPS), Japanese - 23pEA-1 Diffusion mechanism of hydrogen atoms adsorbed on water ice at low temperature
Hama Tetsuya, Watanabe Naoki, Kouchi Akira, Pirronello Valerio, Meeting abstracts of the Physical Society of Japan, 66, 2, 171, 171, 24 Aug. 2011
The Physical Society of Japan (JPS), Japanese - 24pEA-1 Current status for production of hydrated cluster ion using injected-ion drift tube
Nakai Yoichi, Hidaka Hiroshi, Watanabe Naoki, Kojima Takao M., Meeting abstracts of the Physical Society of Japan, 66, 2, 191, 191, 24 Aug. 2011
The Physical Society of Japan (JPS), Japanese - 22pGE-4 Reactions of atomic and molecular hydrogen on interstellar dust at low temperatures
Watanabe Naoki, Meeting abstracts of the Physical Society of Japan, 66, 2, 987, 987, 24 Aug. 2011
The Physical Society of Japan (JPS), Japanese - 28aRA-11 Ammonia formation by the successive hydrogenation of N atom in solid N_2 at low temperatures
Hidaka Hiroshi, Kouchi Akira, Watanabe Naoki, Meeting abstracts of the Physical Society of Japan, 66, 1, 220, 220, 03 Mar. 2011
The Physical Society of Japan (JPS), Japanese - 27pRB-6 Current status report of ion induced nucleation : Development of apparatus for production of hydrated cluster ion
Nakai Yoichi, Hidaka Hiroshi, Watanabe Naoki, Kojima Takao M., Meeting abstracts of the Physical Society of Japan, 66, 1, 213, 213, 03 Mar. 2011
The Physical Society of Japan (JPS), Japanese - 28aRA-12 Diffusion mechanism of hydrogen atoms adsorbed on water ice at low temperature
Hama Tetsuya, Watanabe Naoki, Kouchi Akira, Kimura Yuki, Pirronello V., Meeting abstracts of the Physical Society of Japan, 66, 1, 220, 220, 03 Mar. 2011
The Physical Society of Japan (JPS), Japanese - 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
English - 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, [Peer-reviewed]
English - 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, Mar. 2010
AMER CHEMICAL SOC, English, Summary international conference - 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, Mar. 2010
AMER CHEMICAL SOC, English, Summary international conference - Formation of amorphous H2O ice from the reactions of cold H atoms with solid O2 at 10 K
A. Kouchi, N. Watanabe, H. Hidaka, N. Miyauchi, Y. Oba, T. Chigai, Astron. Soc. Pacific Conf. Ser., 414, 338, 346, 2010, [Peer-reviewed]
English - 210 Formation of ammonia molecules by reactions of H and N atoms on the low temperature surfaces
Hidata H., Watanabe M., Kouchi A., Watanabe N., Abstracts Fall Meeting of the Japanese Society for Planetary Sciences, 2009, 38, 38, 28 Sep. 2009
The Japanese Society for Planetary Sciences, Japanese - P202 Clarification of the key routes for deuteration of formaldehyde on icy grain surface
渡辺 元浩, 日高 宏, 渡部 直樹, 香内 晃, Abstracts Fall Meeting of the Japanese Society for Planetary Sciences, 2009, 87, 87, 28 Sep. 2009
The Japanese Society for Planetary Sciences, Japanese - 27pZB-7 Diffusion and desorption of hydrogen atoms on amorphous solid water at very low temperatures
Watanabe Naoki, Kouchi Akira, Kimura Yuki, Meeting abstracts of the Physical Society of Japan, 64, 2, 96, 96, 18 Aug. 2009
The Physical Society of Japan (JPS), Japanese - 24aRB-6 Hydrogen atom addition reaction on surface of low temperature oxygen molecular solid
Miyauchi N., Hidaka H., Nagaoka A., Watanabe N., Kouchi A., Meeting abstracts of the Physical Society of Japan, 63, 1, 166, 166, 29 Feb. 2008
The Physical Society of Japan (JPS), Japanese - 24aRB-7 Structural effects office surfaces on the hydrogenation of CO at low temperature
Hidaka H., Miyauchi N., Kouchi A., Watanabe N., Meeting abstracts of the Physical Society of Japan, 63, 1, 166, 166, 29 Feb. 2008
The Physical Society of Japan (JPS), Japanese - 19pXH-6 Surface reaction of methanol molecule with deuterium atoms at 10 K
Nagaoka A., Hidaka H., Kouchi A., Watanabe N., Meeting abstracts of the Physical Society of Japan, 62, 1, 149, 149, 28 Feb. 2007
The Physical Society of Japan (JPS), Japanese - 19pXH-7 Isotope effect on H/D atom addition reaction to CO on amorphous ice surfaces at low temperatures
Hidaka H., Nagaoka A., Kouchi A., Watanabe N., Meeting abstracts of the Physical Society of Japan, 62, 1, 149, 149, 28 Feb. 2007
The Physical Society of Japan (JPS), Japanese - Deuterium fractionation in interstellar methanol by grain-surface reactions
NAGAOKA Akihiro, WATANABE Naoki, HIDAKA Hiroshi, KOUCHI Akira, Planetary people, 15, 1, 4, 11, 25 Mar. 2006
The Japanese Society for Planetary Sciences, Japanese - 28pYB-5 Chemical reactions on the surface of amorphous ice : chemical evolution on interstellar ice dusts
Watanabe N., Kouchi A., Nagaoka A., Hidaka H., Meeting abstracts of the Physical Society of Japan, 61, 1, 886, 886, 04 Mar. 2006
The Physical Society of Japan (JPS), Japanese - Formation of Methanol by the addition of Hydrogen atoms to Formaldehyde on Formaldehyde ice
Hidaka H., Shiraki T., Watanabe N., Kouchi A., Meeting abstracts of the Physical Society of Japan, 58, 2, 104, 104, 15 Aug. 2003
The Physical Society of Japan (JPS), Japanese - Atomic and molecular processes on interstellar dusts
Watanabe Naoki, Meeting abstracts of the Physical Society of Japan, 58, 2, 134, 134, 15 Aug. 2003
The Physical Society of Japan (JPS), Japanese - Multi-Peak Structures Observed in the 4d Giant Resonance of Eu^+
Kojima T. M., Chen F., Kitajima M., Koizumi T., Nakai Y., Yamaoka H., Watanabe N., Meeting abstracts of the Physical Society of Japan, 58, 1, 154, 154, 06 Mar. 2003
The Physical Society of Japan (JPS), Japanese - Molecular evolution on interstellar dusts at a very low temperature
Watanabe Naoki, Meeting abstracts of the Physical Society of Japan, 57, 2, 129, 129, 13 Aug. 2002
The Physical Society of Japan (JPS), Japanese - P01 MEASUREMENTS OF CONVERSION RATES OF CO TO CO_2 IN UV INDUCED REACTION OF D_2O/CO AMORPHOUS ICE
渡部 直樹, 香内 晃, Abstracts Fall Meeting of the Japanese Society for Planetary Sciences, 2001, 57, 57, 06 Oct. 2001
The formation of carbon dioxide molecules from D_2O/CO binary ice induced by UV irradiation have been studied experimentally. The measured conversion rate of CO to CO_2 is about one order higher than previously reported ones. Our results imply that the CO_2 formation by the UV process can be efficient even in a quiescent dense cloud., The Japanese Society for Planetary Sciences, Japanese - UV-PHOTOSTIMULATED PRODUCTION OF D_2 MOLECULES FROM AMORPHOUS D_2O ICE AT 10K
WATANABE Naoki, HORII Toshikazu, KOUCHI Akira, Atomic collision research in Japan, 24, 141, 142, Nov. 1998
English - Formation of D_2 molecules from D_2O amorphous ice by uv irradiation
WATANABE N., HORII T., KOUCHI A., Meeting abstracts of the Physical Society of Japan, 53, 2, 897, 897, 05 Sep. 1998
The Physical Society of Japan (JPS), Japanese - About the Validity of Expected Utility Maximisation
Watanabe Naoki, Mita business review, 31, 2, 53, 72, 25 Jun. 1988
Keio University, Japanese
Lectures, oral presentations, etc.
- Experimental approach to fast ortho to para nuclear spin conversion of hydrogen molecule on dust grain analogues
Naoki Watanabe
COSPAR 2021, Chemical Evolution and Origin of Life, English, Invited oral presentation
29 Jan. 2021 - 01 Feb. 2021, [Invited] - Clarifying a proton-hole transfer in ice by the new method of OH detection
Naoki Watanabe
Frontier of structures and dynamics of water by advanced spectroscopic techniques, 27 Oct. 2020, English, Invited oral presentation
[Invited] - Behavior of OH radical on ice
Naoki Watanabe
Water in the Universe in the ACS National Meeting, English, Invited oral presentation
25 Aug. 2019 - 29 Aug. 2019, [Invited] - Ortho-to-Para Ratios in water and H2 desorbed from ice --Experimental view--
Naoki Watanabe
Astrochemistry: From nanometers to megaparsecs - A symposium in honour of John H. Black, English, Invited oral presentation
24 Jun. 2019 - 28 Jun. 2019, [Invited] - Behavior of OH Radical on an Ice Surface at Low Temperatures
Naoki Watanabe
35th Symposium on Chemical Kinetics and Dynamics, English, Invited oral presentation
05 Jun. 2019 - 07 Jun. 2019, [Invited] - Detection of OH radicals on amorphous solid water
Naoki Watanabe
IAU Symposium 350 Laboratory Astrophysics: From Observations to Interpretation, English, Invited oral presentation
14 Apr. 2019 - 29 Apr. 2019, [Invited] - Infrared measurements on efficient chemical desorption of hydrogen sulfide from amorphous solid water
Naoki Watanabe
Oxygen in Space, English, Invited oral presentation
16 Oct. 2018 - 17 Oct. 2018, [Invited] - 星間塵表面の化学：重水素濃集に果たす役割
渡部 直樹
日本地球化学会年会, 11 Sep. 2018, Japanese, Invited oral presentation
[Invited], [Domestic Conference] - Measurements of activation energies for diffusion of hydrogen atom on pure CO solid
N. Watanabe
European Conference On Surface Science (ECOSS34), 26 Aug. 2018, English, Invited oral presentation
[Invited], [International presentation] - Infrared Measurements of Efficient Chemical Desorption of Hydrogen Sulfide from Amorphous Solid Water
N. Watanabe
COSPAR 2018, The Evolving Chemical Universe: from proto-stars to the Origin of Life, 26 Jul. 2018, English, Invited oral presentation
[Invited], [International presentation] - Surface Chemistry of the ISM: Experimental Approach to grain surface processes
N. Watanabe
The Olympian Symposium 2018 Gas and stars from milli- to mega- parsecs, 01 May 2018, English, Invited oral presentation
[Invited], [International presentation] - Strong temperature dependence of H2 nuclear spin conversion on ice: what controls the rate?
Naoki Watanabe
Dust and Ice Particles Spectroscopy and Scattering, English, Invited oral presentation
25 Sep. 2017 - 28 Sep. 2017, [Invited] - H 2ortho-para conversion on amorphous solid water
N. Watanabe
International Conference on Photonic Electronic and Atomic Collisions(ICPEAC2017), 26 Jul. 2017, English, Invited oral presentation
[Invited], [International presentation] - 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
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－, 06 Jul. 2017, Japanese, Invited oral presentation
[Invited], [Domestic Conference] - Ortho-to-para nuclear spin conversion of H2 on ice: a key to chemical evolution in space
Naoki Watanabe
XXXVI BIENNAIAL MEETING OF THE SPANISh ROYAL SOCIETY OF CHEMISTRY, 25 Jun. 2017, English, Invited oral presentation
[Invited], [International presentation] - Physicochemical processes on Ice Dust towards Deuterium Enrichment
N. Watanabe
International Symposium on Molecular Spectroscopy, 19 Jun. 2017, English, Invited oral presentation
[Invited], [International presentation] - Physicohemical Processes on ice dust towards deuterium enrichment
N.Watanabe
International Symposium on Molecular Spectroscopy 72ND MEETING, 19 Jun. 2017, English, Invited oral presentation
[Invited], [International presentation] - Ortho-to-para ratios of hydrogen molecules desorbed from ice at around 10 K: What happens on cosmic ice dust?
N. Watanabe, H. Ueta, T. Hama, A. Kouchi
The 253thAmerican Chemical Society National Meeting, 02 Apr. 2017, English, Invited oral presentation
[Invited], [International presentation] - Strong temperature dependence of ortho-to-para conversion of H2 on amorphous solid water at around 10 K
N. Watanabe
EUROPEAN CONFERNCE ON LABORATORY ASTROPHYSICS (ECLA2016) GAS ON THE ROCKS, 21 Nov. 2016, English, Oral presentation
Madrid, Spain, [Invited], [International presentation] - Experimental approach to hydrogen chemistry on grain surfaces: molecular formation
N. Watanabe
Center for Astrochemical Studies Seminar, 12 Oct. 2016, English, Invited oral presentation
Max-Planck-Institut für extraterrestrische Physik, Germany, [Invited], [International presentation] - Experimental approach to ortho-to-para ratio of hydrogen and water molecules desorbed from ice at around 10 K
Naoki Watanabe
Workshop on Astrochemistry in Star and Planet Formation, 16 Feb. 2016, English, Invited oral presentation
Riken, Saitama, Japan, [Invited], [International presentation] - Deuterium chemistry and nuclear spin conversion on grain surfaces: implication to deuterium enrichment
N. Watanabe
From clouds to protoplanetary disk: the astrochemical link, 05 Oct. 2015, English, Invited oral presentation
Hans Harnack Haus, Berlin, Germany, [Invited], [International presentation] - Grain Surface Chemistry: What Happens Without Photons and Ions
N. Watanabe
A symposium to honor Lou Allamandola’s Contributions to the Molecular Universe, 13 Sep. 2015, English, Invited oral presentation
Annapolis, MD, USA, [Invited], [International presentation] - Role of Tunneling in the Formation and Deuterium Enrichment of Molecules on Dust Grains
Naoki Watanabe
Astrobiology Science Conference 2015, English, Invited oral presentation
15 Jun. 2015 - 19 Jun. 2015, [Invited] - Experimental Approach to Chemistry of Cosmic Dust
N. Watanabe
COST Action Our Astrochemical History CM1401, 25 May 2015, English, Invited oral presentation
The Czech Republic, [Invited], [International presentation] - Experimental approach to nonenergetic physicochemical processes on icy grains
Naoki Watanabe
Icy Grain Chemistry for Formation of Complex Organic Molecules: From Molecular Clouds to Protoplanetary Disks, Comets and Meteorites, 05 Mar. 2015, Japanese, Invited oral presentation
Tokyo Institute of Technology, Japan, [Invited], [International presentation] - What controls the diffusion mechanism of hydrogen atom on ice?
Naoki Watanabe
Second Workshop on Experimental Laboratory Astrophysics, English, Invited oral presentation
23 Feb. 2015 - 26 Feb. 2015, [Invited] - Nuclear spin temperatures of hydrogen and water molecules formed and trapped on ice
Naoki Watanabe
Nuclear Spin Effects in Astrochemistry 2014, English, Invited oral presentation
09 Jun. 2014 - 11 Jun. 2014, [Invited] - Diffusion of hydrogen atom on amorphous solid water: Thermal or tunneling?
N. Watanabe
247th ACS Chemistry & Materials for Energy, 16 Mar. 2014, English, Invited oral presentation
Dallas, USA, [Invited], [International presentation] - Physics and chemistry of hydrogen on cosmic dust: diffusion, spin temperatures, and water formation
N. Watanabe, T. Hama, H. Hidaka, Y. Kimura, A. Kouchi, Y. Oba, V. Pirronello
First Workshop on Experimental Laboratory Astrophysics, Feb. 2013, English, Invited oral presentation
Kauai, Hawaii, [Invited], [International presentation] - Physicochemical Processes of Hydrogen on Ice: A Key for Chemical Evolution in Space
N. Watanabe
2nd International Symposium on Hierarchy and Holism, Feb. 2013, English, Invited oral presentation
Tokyo, Japan, [Invited], [International presentation] - Surface diffusion mechanism of atomic hydrogen and the ortho/para ratio of nascent H2 molecule on amorphous solid water at around 10 K
N. Watanabe
International Lorentz Center Workshop: Dynamical Phenomena at Surfaces: The Role of Complexity, Nov. 2012, English
Leiden, The Netherlands, [Invited] - Grain surface processes at very low temperatures: hydrogen diffusion and tunneling reactions
N. Watanabe
Gordon Research Conference, Radiation Driven Processes in Physics, Chemistry, Biology, and Industry, Jul. 2012, English
New Hampshire, USA, [Invited] - Spin temperatures of hydrogen and water molecules on amorphous solid water
N.Watanabe
ASTROCHEM 2012, Jul. 2012, English
Kolkata, India, [Invited] - Hydrogen processes on dust grains: H atom diffusion and water formation
N.Watanabe
30th COSPAR Scientific Assembly, Jul. 2012, English
Mysore, India, [Invited] - Hydrogen chemistry on cold grain surfaces
N.Watanabe
XVIIIth Symposium on Atomic, Cluster, and Surface Physics, Jan. 2012, English
Alpe d'Huez, France, [Invited] - Hydrogen tunneling reaction and its isotope effect at a low temperature ice surface: Origin of deuterium enrichments in interstellar formaldehyde and methanol
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）, Jul. 2011, English
Vancouver, Canada, [Invited] - Ice surface chemistry of hydrogen atom in space
N. Watanabe, H. Hidaka, T. Hama, A. Kouchi, T. Chigai, Y. Kimura
27th European Conference on Surface Science, ECOSS 27, Aug. 2010, English
Groningen, the Netherlands, [Invited] - Surface processes of atomic hydrogen at very low temperatures relevant to astrochemistry
N. Watanabe
24th International Conference on Atomic Collisions in Solids ICACS- 24, Jul. 2010, English
Krak?w, Poland, [Invited] - Chemistry of atomic hydrogen on interstellar ice grains at very low temperatures
N. Watanabe, H. Hidaka, A. Kouchi, T. Hama, Y. Kimura
Western Pacific Geophysics Meeting, Jun. 2010, English
Taipei, Taiwan, [Invited] - Physicochemical processes of atomic hydrogen on amorphous solid water at very low temperatures
N. Watanabe, A. Kouchi, H. Hidaka, Y. Kimura, T. Hama
239th American Chemical Society National Meeting & Exposition, Mar. 2010, English
San Francisco, USA, [Invited] - Ice surface reactions: its role in chemical evolution in space
N.Watanabe
ILTS International Symposium "Frontier of Low Temperature Science", Sapporo, Nov. 2009, English
Sapporo, [Invited] - Tunneling reactions of atomic hydrogen and molecules on amorphous solid water at very low temperatures
N. Watanabe
Horiba-ISSP International Symposium on “Hydrogen and water in condensed matter physics”, Oct. 2009, English
Chiba, [Invited] - Nonenergetic reactions between hydrogen and molecules On Interstellar Grain Surfaces
N. Watanabe
XXVI International Conference on Photonic, Electronic, and Atomic Collisions, Jul. 2009, English
Michigan, USA, [Invited] - Reactions of hydrogen atoms and molecules on amorphous solid water at very low temperatures
N. Watanabe
Gordon Research Conferences, Physics & Chemistry of Matrix-Isolated Species, Jul. 2009, English
Oxford, UK, [Invited] - Experimental approach to grain surface reactions of hydrogen and deuterium atoms
N.Watanabe
International Lorentz Center Workshop: Interstellar Surfaces: From Laboratory to Models, Oct. 2008, English
Leiden, Holland, [Invited] - Grain surface chemistry: fractionation routes
N. Watanabe
The Molecular Univers: an International Meeting on Physics and Chemistry of the Intersteller Medium, May 2008, English
Arcachon, France, [Invited] - Simultaneous irradiation experiments of H2O-CO binary ice with UV photons and cold H atoms
N. Watanabe, A. Nagaoka, O. MouriI, A. Kouchi, V. Pirronello
Asia-Oceania Geosciences Society Annual Meeting, Aug. 2007, English
Bangkok, Thailand, [Invited] - Laboratory study of chemical processes on interstellar ice grains
N. Watanabe, A. Nagaoka, H. Hidaka, A. Kouchi
XXIV International Union of Feodesy and Geophysics (IUGG) General Assembly, Jul. 2007, English
Perguia, Italy, [Invited] - Reactions of hydrogen and deuterium atoms with CO, formaldehyde, and methanol on ice grains
N.Watanabe
International Astrophysics and Astrochemistry Meeting: Molecules in Space & Laboratory, May 2007, English
Paris, France, [Invited] - Formation of simple organic molecules by Hydrogenation on grain surfaces
N. Watanabe
International Astronomical Union Symposium: Astrochemistry,, Aug. 2005, English
California,USA, [Invited] - Formation of deuterated methanol by surface reactions at 10 K
N. Watanabe, A. Nagaoka, A. Kouchi
Asia-Oceania Geosciences Society Annual Meeting, Jun. 2005, English
Singapore, [Invited] - Evolution of CO molecule on dusts in dense core: formation of H2CO and CH3OH
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-, Mar. 2005, English
Sapporo, [Invited]
Affiliated academic society
Research Themes
- Exploration of the possibility of hydrated silicate formation in early stage of molecular clouds
Grants-in-Aid for Scientific Research
01 Apr. 2024 - 31 Mar. 2027
中井 陽一, 渡部 直樹
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Institute of Physical and Chemical Research, 24K00699 - ラジカルの拡散が活性化させる星間塵表面での分子進化：複雑有機分子生成の鍵
科学研究費助成事業 基盤研究(A)
01 Apr. 2022 - 31 Mar. 2027
渡部 直樹, 柘植 雅士, Sameera W.M.C.
日本学術振興会, 基盤研究(A), 北海道大学, 22H00159 - Theoretical astrochemistry based on microscopic processes in the gas and solid phases
Grants-in-Aid for Scientific Research
19 Nov. 2020 - 31 Mar. 2025
相川 祐理, 古家 健次, 高柳 敏幸, 山崎 祥平, 花輪 知幸, 吉田 直紀, 渡部 直樹
Japan Society for the Promotion of Science, Grant-in-Aid for Transformative Research Areas (A), The University of Tokyo, 20H05847 - Next Generation Astrochemistry: Transformative Action Based on Understandings of Microscopic Chemical Processes
Grants-in-Aid for Scientific Research
19 Nov. 2020 - 31 Mar. 2025
坂井 南美, 橘 省吾, 中野 祐司, 相川 祐理, 今田 裕, 渡部 直樹
低温低密度の単純な環境を前提としてきた星間化学を刷新し、惑星系形成領域のように、ガスや固体物質の組成が劇的に変化する広範な物理環境に対応できる強固な学術基盤を構築するための領域全体の連携を支援した。大きく異なる分野の融合研究を推進する計画であるため、分野間の相互研究理解が極めて重要である。そのために、下記３つの手法で相互理解を深めた。
①話題提供：総括班会議での運営議論の後、各班代表から新たな課題となりつつあるテーマや、重要なテーマの紹介を行ってもらい、議論を行った。各班の研究計画への他班からのフィードバックとしての役割を担った。
②セミナー：各班の研究テーマの背景にある基本的知見を、学生などを含めた他班の若手までもが理解しなければ、真の意味での融合・共同研究は難しい。このため、修士学生でもわかりやすいように日本語での基礎セミナーを1－2ヶ月に1度のペースで開催し始めた。また、参加できなかったメンバーのために、期間を定めて動画の公開も行った。
③ミクロ班会合：素過程理解に基づく学理の再構築のためには、どのような分子や化学反応素過程に着目すべきかを、逐次議論していくことが重要となる。そのために、より踏み込んだ詳細議論を行う場として、1-2ヶ月に1度のペースで開始した。
これらに加え、協力研究者である渡部直樹教授を連携コーディネータとし、班間での議論促進に取り組んだ。例として、2021年11月(コロナにより約1年延期)にInternational workshop on interstellar matterを開催した。150名もの異分野研究者が集い、非常に活発に分野をまたぐテーマについての議論が行われた。 なお、コロナ禍であったため、国外からの招聘や出張旅費の計画は臨機応変に組替えを行った。具体的には、オンライン議論促進アプリ・ソフトの活用や動画記録でのセミナー開催などが挙げられる。
Japan Society for the Promotion of Science, Grant-in-Aid for Transformative Research Areas (A), Institute of Physical and Chemical Research, 20H05844 - 極低温星間塵表面における有機硫黄分子の化学反応
科学研究費助成事業
18 Nov. 2021 - 31 Mar. 2024
渡部 直樹, NGUYEN THANH
本研究は，極低温の星間塵表面における有機硫黄分子の化学反応を実験的に調べることを目的としている。本年は，硫黄を含む化合物の中で唯一固体として検出されている星間分子：硫化カルボニル（OCS)に着目し，星間塵表面でのH原子との反応性を調べた。真空中で10ケルビンに冷却したアモルファスH2O氷上に固体OCSを作製し，水素原子と反応させたところ，生成物としてCO, H2S, H2CO, およびCH3OHが検出された。量子化学計算により，氷とOCS分子の結合エネルギーや各種表面反応の活性化エネルギーを求めたところ，これらを生成する過程として，OCS + H → OCSHが始めに生じ,その後，さらに水素原子付加反応 OCSH + H → H2S + COが生じる連続反応であることがわかった。H2CO, CH3OHは左記の反応で生成したCOにH原子がさらに逐次付加して生成したものである。また，最近の天文観測で星間空間に見つかっているHC(O)SHが，氷星間塵表面でHCOとSHラジカルとの反応により生成しうることが初めて示唆された。この反応経路はこれまで知られていなかった新たな生成機構を示すものである。また，本研究により，比較的な簡単なOCS分子から，外部からのエネルギーを必要としないH原子付加反応により，多様な分子が生成されることが分かった。また，S含有物として，もっとも存在度が高いと思われるH2Sが最終生成物として残ることが明らかになった。
日本学術振興会, 特別研究員奨励費, 北海道大学, 21F21319 - Chemical evolution on cosmic dust: approach from elementary processes
Grants-in-Aid for Scientific Research Grant-in-Aid for Specially Promoted Research
25 Apr. 2017 - 31 Mar. 2022
Watanabe Naoki
Using novel experimental methods and quantum chemical calculations, we demonstrated various physicochemical processes on the surfaces of cosmic dust analogues, which play an important role in evolution of molecules in space. Notable findings were mode on (1) formation and desorption process of some organic molecules and sulfer- and phosphorous-containing molecules; (2) deuterium fractionation of molecules; (3) nuclear-spin conversion of hydrogen molecules on dust. Furthermore, direct observation of amorphous ice at around 10 K was first successful with cryogenic transmission electron microscope and atomic force microscope.
Japan Society for the Promotion of Science, Grant-in-Aid for Specially Promoted Research, Hokkaido University, 17H06087 - 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
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
01 Apr. 2017 - 31 Mar. 2018
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, Grant-in-Aid for Scientific Research (A), Hokkaido University, 17H01169 - Mechanisms of formation and isotope fractionation of interstellar molecules on cosmic dust
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)
31 May 2012 - 31 Mar. 2017
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, Grant-in-Aid for Scientific Research (S), Hokkaido University, 24224012 - Experiments on io-induced nucleation to clarify a new mechanism of cosmic dust formation
Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
01 Apr. 2014 - 31 Mar. 2016
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, Grant-in-Aid for Challenging Exploratory Research, Hokkaido University, 26610137 - Development of ultrahigh vacuum (UHV) transmission electron microscope for in-situ observation of ice
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
21 Oct. 2013 - 31 Mar. 2016
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, Grant-in-Aid for Scientific Research (A), Hokkaido University, 25247086 - Quantitative investigation for ion-induced nucleation under non-equilibrium conditions of association/dissociation reactions: experimental approaches for elementary formation processes
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
01 Apr. 2013 - 31 Mar. 2016
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, Grant-in-Aid for Scientific Research (B), Institute of Physical and Chemical Research, 25287148 - Quantitative elucidation for ion induced nucleation in the atmosphere: Approach through the experiments for elementary processes
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
01 Apr. 2010 - 31 Mar. 2013
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), The Institute of Physical and Chemical Research, 22540498 - 星間塵表面反応:分子進化と同位体分別機構の新展開
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
2012 - 2012
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, Grant-in-Aid for Scientific Research (A), Hokkaido University, 24244083 - Observation of surface structure of amorphous ice and role of amorphous ice in surface atomic reactions at low temperatures
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
2010 - 2012
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, Grant-in-Aid for Scientific Research (B), Hokkaido University, 22340157 - Ice surface processes: tunneling reactions and isotope fractionation
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research a proposed research project)
2009 - 2011
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, Grant-in-Aid for Scientific Research on Innovative Areas (Research a proposed research project), Hokkaido University, 21200048 - Deuterium fractionation of water molecule via grain surface reactions at very low temperatures
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
2009 - 2011
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, Grant-in-Aid for Scientific Research (C), Hokkaido University, 21540502 - Evaluation of catalytic effect of amorphous ice on the surface atomic reactions
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)
2005 - 2009
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, Grant-in-Aid for Scientific Research (S), Hokkaido University, 17104006 - Role of cosmic-grain surface reactions in the deuterium fractionationof interstellar molecules
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
2007 - 2008
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, Grant-in-Aid for Scientific Research (B), Hokkaido University, 19340167 - Experimental and theoretical studies of the evolution from dust to exoplanets
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas
2004 - 2008
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
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Priority Areas, Hokkaido University, 16077203 - 星間塵表面における重水素濃縮機構
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas
2004 - 2005
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Priority Areas, Hokkaido University, 16036201 - Surface reactions of atoms and the mechanism of deuterium fractionation on inter Stellar dusts at the very low temperature
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
2004 - 2005
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_
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), HOKKAIDO UNIVERSITY, 16340145 - UV-induced diamond formation in interstellar clouds
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
2003 - 2004
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 15340180 - Development of electrostatic accelerator for ice dust and the aggregates
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
2001 - 2003
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), HOKKAIDO UNIVERSITY, 13554015 - Collisional sticking of organic grains in the solar nebula
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
2000 - 2001
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), HOKKAIDO UNIVERSITY, 12440142 - The observation of the growth and ifrured absorption for dust particles ecclosed in a small scale space
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
1999 - 2000
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), HOKKAIDO UNIVERSITY, 11640470 - Development of comet nucleus simulation experiments
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
1998 - 1999
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Institute of Low Temperature Science, HOKKAIDO UNIVERSITY, 10554027 - Structure and physical properties of impure amorphous interstellar icy grains
Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
1997 - 1999
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.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), HOKKAIDO UNIVERSITY, 09304050 - アモルファス氷星間塵上での水素分子生成機構
Grants-in-Aid for Scientific Research Grant-in-Aid for Encouragement of Young Scientists (A)
1997 - 1998
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。
Japan Society for the Promotion of Science, Grant-in-Aid for Encouragement of Young Scientists (A), Hokkaido University, 09740371 - The development of a simulation device for the nucleation in the primordial solar nebula.
Grants-in-Aid for Scientific Research
1996 - 1998
YAMAMOTO Tetsuo, ABE Tsutomu, WATANABE Naoki
In order to investigate the mechanism of the nucleation of solid particles and its role in the evolution of the solar system materials, we have developed an experimental apparatus that simulates the non-equilibrium homogeneous nucleation from simple molecules to polymerized clusters. Condensable gas species are collimated in molecular beams and introduced into a high-vacuum chamber. A pulsed beam of the controlled environmental gas supplied from another vacuum port crosses the previous molecular beams. This method makes the necessary conditions of the cluster formation fulfilled in a localized area of the chamber and suffices the quantitative analysis of the nucleation and condensation. We have obtained the following results during this three-year grant-in-aid project
(1) We have built a system that enables the cluster formation in a clean environment A vibration-free ultra-high vacuum system have been installed.
(2) We have modified a gas effusion device for high vacuum and high temperature to truncate a mili-second small pulses out of the high-temperature gas mixture. The test of the device was satisfactory.
(3) We have developed a TOF mass spectrometer for an in-situ analysis of the polymerized cluster that formed by multiple collisions.
(4) In order to improve the emittance from the excimer laser device purchased with a Heisei 8 grant-in-aid, we have obtained a necessary local energy flux with a use of focal lens of high transmission.
(5) Following the above developments, we have performed a laboratory experiment of the non-equilibrium homogeneous nucleation. We were able to observe clusters of low mass range, but polymerized clusters of high mass range were too small in abundance to be detected. A higher laser energy flux and a much larger mass flux of the condensable gas from the effusion device will be necessary to accomplish this task..
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), HOKKAIDO UNIVERSITY, 08554016 - 原子・イオン・分子の光電離過程の研究
Competitive research funding - アモルファス氷表面上における原子・分子素過程
Competitive research funding - Study on Atomic,ionic,and Molecular Photoionization processes
Competitive research funding - Atomic and Molecular Processes on Amorphous ice surface
Competitive research funding
