Researcher basic information

• (BLANK)

• https://researchmap.jp/read0052174?lang=en

• https://jglobal.jst.go.jp/detail?JGLOBAL_ID=200901019614374455
• https://orcid.org/0000-0001-8408-2872
• http://www.lowtem.hokudai.ac.jp/astro/index.html

• https://orcid.org/0000-0001-8408-2872

• A-7451-2012

• 200901019614374455

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

• Natural Science, Space and planetary sciences
• Natural Science, Semiconductors, optical properties of condensed matter and atomic physics

• Master's degree program, Graduate School of Science
• Doctoral (PhD) degree program, Graduate School of Science

Research activity information

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

• Negative charge delivery in ice via proton-hole transfer
  Tsuge Masashi; Kitajima Kensei; Watanabe Naoki
  JSAP Review, 2026, n/a, The Japan Society of Applied Physics, 2026
  English, Water ice has been regarded as a “p-type semiconductor,” with the excess protons in ice serving as the positive charge carrier. Although ice is considered to be an insulator at very low temperatures, we recently found that ice has electrical conductivity via negative charge delivery even at temperatures around 10 K when simultaneously irradiated with ultraviolet photons and electrons, indicating that ice serves as an “n-type semiconductor” as well. Based on experimental and theoretical investigations, we propose that the carrier of the negative charge conductivity is the OH⁻ ion, called the proton-hole, and OH⁻ moves toward the interior of ice by repeated proton abstractions from neighboring H₂O molecules, namely the proton-hole transfer mechanism.
• Methylamine Formation on Amorphous Solid Water via the Diffusive CH ₃ + NH ₂ Reaction as Investigated by the Cs ⁺ Ion Pickup Method
  Arisa Iguchi; Masashi Tsuge; Hiroshi Hidaka; Yasuhiro Oba; Naoki Watanabe
  ACS Earth and Space Chemistry, American Chemical Society (ACS), 20 Nov. 2025
  Scientific journal
• Formation of Unsaturated Carbon Chains through Carbon Chemisorption on Solid CO
  Masashi Tsuge; Germán Molpeceres; Ryota Ichimura; Hideko Nomura; Kenji Furuya; Naoki Watanabe
  The Astrophysical Journal, 993, 2, 177, 177, American Astronomical Society, 31 Oct. 2025
  Scientific journal, Abstract
  
  The interaction of carbon atoms with solid carbon monoxide (CO) is a fundamental process in astrochemistry, influencing the formation of complex organic molecules in interstellar environments. This study investigates the adsorption and reaction mechanisms of carbon atoms on solid CO under cryogenic conditions, employing a combination of experimental techniques, including the combination of photostimulated desorption and resonance-enhanced multiphoton ionization and infrared spectroscopy, alongside quantum chemical calculations. The results reveal the formation of oxygenated carbon chains, such as CCO, C ₃ O ₂ , and C ₅ O ₂ , as well as CO ₂ . The findings highlight the role of chemisorption and subsequent reactions in driving molecular complexity on solid CO, with implications for the chemical evolution of interstellar ices and the potential formation of prebiotic molecules.
• 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
• 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,
  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,
  Hydrogen molecules have two nuclear spin isomers: ortho-H₂ and para-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, 01 Sep. 2021, [Peer-reviewed]
  English, Scientific journal
• 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,
  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, 01 Mar. 2021, [Peer-reviewed]
  English, Scientific journal
• 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, 03 Aug. 2020, [Peer-reviewed]
  English, Scientific journal
• 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, Mar. 2020, [Peer-reviewed]
  English, Scientific journal
• H-2 Ortho-Para Spin Conversion on Inhomogeneous Grain Surfaces
  Furuya Kenji; Aikawa Yuri; Hama Tetsuya; Watanabe Naoki
  ASTROPHYSICAL JOURNAL, 882, 2, 10 Sep. 2019, [Peer-reviewed]
  English, Scientific journal
• Nucleobase synthesis in interstellar ices
  Yasuhiro Oba; Yoshinori Takano; Hiroshi Naraoka; Naoki Watanabe; Akira Kouchi
  Nature Communications, 10, 1, 4413, Sep. 2019, [Peer-reviewed]
  English, Scientific journal
• 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, Jul. 2019, [Peer-reviewed]
  English, Scientific journal
• 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, Jun. 2019, [Peer-reviewed]
  English, Scientific journal
• 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
• 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 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
• 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, Nov. 2017, [Peer-reviewed]
  English, Scientific journal
• 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, Jul. 2017, [Peer-reviewed]
  English, Scientific journal
• 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, Mar. 2017, [Peer-reviewed]
  English, Scientific journal
• 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, 2017, [Peer-reviewed]
  English, International conference proceedings
• 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, Dec. 2016, [Peer-reviewed]
  English, Scientific journal
• 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, Oct. 2016, [Peer-reviewed]
  English, Scientific journal
• 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, Oct. 2016, [Peer-reviewed]
  English, Scientific journal
• 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), Aug. 2016, [Peer-reviewed]
  English, Scientific journal
• 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, Aug. 2016, [Peer-reviewed]
  English, Scientific journal
• 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), Jun. 2016, [Peer-reviewed]
  English, Scientific journal
• 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), Jun. 2016, [Peer-reviewed]
  English, Scientific journal
• 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 C₂H_{4 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, Jan. 2016, [Peer-reviewed]
  English, Scientific journal
• 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, Sep. 2015, [Peer-reviewed]
  English, Scientific journal
• 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, Aug. 2015, [Peer-reviewed]
  English, Scientific journal
• 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, Jun. 2015, [Peer-reviewed]
  English, Scientific journal
• 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, Nov. 2014, [Peer-reviewed]
  English, Scientific journal
• 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, Aug. 2014, [Peer-reviewed]
  English, Scientific journal
• 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, Jan. 2014, [Peer-reviewed]
  English, Scientific journal
• 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, 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, 2013, [Peer-reviewed], [Invited]
  English, International conference proceedings
• 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, 2013, [Peer-reviewed]
  English, International conference proceedings
• 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), Oct. 2012, [Peer-reviewed]
  English, Scientific journal
• 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), Apr. 2012, [Peer-reviewed]
  English, Scientific journal
• 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
• 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), Sep. 2011, [Peer-reviewed]
  English, Scientific journal
• 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, May 2011, [Peer-reviewed]
  English, Scientific journal
• 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, 2011, [Peer-reviewed]
  English, Scientific journal
• 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, 2011, [Peer-reviewed]
  English, Scientific journal
• 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, Oct. 2010, [Peer-reviewed]
  English, Scientific journal
• 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, May 2010, [Peer-reviewed]
  English, Scientific journal
• 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, Apr. 2010, [Peer-reviewed]
  English, Scientific journal
• 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, Apr. 2010, [Peer-reviewed]
  English, Scientific journal
• 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, Apr. 2010, [Peer-reviewed]
  English, Scientific journal
• 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 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, Sep. 2009, [Peer-reviewed]
  English, Scientific journal
• 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, Sep. 2009, [Peer-reviewed]
  English, Scientific journal
• 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, Sep. 2009, [Peer-reviewed]
  English, Scientific journal
• 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, Sep. 2009, [Peer-reviewed]
  English, Scientific journal
• 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, Aug. 2009, [Peer-reviewed]
  English, Scientific journal
• 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, Jul. 2009, [Peer-reviewed]
  English, Scientific journal
• 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, 2009, [Peer-reviewed]
  English, International conference proceedings
• 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
• 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, 2009, [Peer-reviewed]
  English, International conference proceedings
• 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, Scientific journal
• 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
• 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, Jul. 2008, [Peer-reviewed]
  English, Scientific journal
• 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, Jul. 2008, [Peer-reviewed]
  English, Scientific journal
• 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, Apr. 2008, [Peer-reviewed]
  English, Scientific journal
• 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, Apr. 2008, [Peer-reviewed]
  English, Scientific journal
• 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, Oct. 2007, [Peer-reviewed]
  English, Scientific journal
• 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, May 2007, [Peer-reviewed]
  English, Scientific journal
• 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, Apr. 2007, [Peer-reviewed]
  English, Scientific journal
• 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
• 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, Sep. 2006, [Peer-reviewed]
  English, Scientific journal
• 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, +, 2006, [Peer-reviewed]
  English, International conference proceedings
• 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, +, 2006, [Peer-reviewed]
  English, International conference proceedings
• 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, +, 2006, [Peer-reviewed]
  English, International conference proceedings
• 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, Jun. 2005, [Peer-reviewed]
  English, Scientific journal
• 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, May 2005, [Peer-reviewed]
  English, Scientific journal
• 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
• 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, Nov. 2004, [Peer-reviewed]
  English, Scientific journal
• 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, Oct. 2004, [Peer-reviewed]
  English, Scientific journal
• 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, May 2003, [Peer-reviewed]
  English, Scientific journal
• 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, Sep. 2002, [Peer-reviewed]
  English, Scientific journal
• 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, Jun. 2002, [Peer-reviewed]
  English, Scientific journal
• 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
• 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, Mar. 2002, [Peer-reviewed]
  English, Scientific journal
• 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, Feb. 2002, [Peer-reviewed]
  English, Scientific journal
• 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, Sep. 2001, [Peer-reviewed]
  English, Scientific journal
• 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, Oct. 2000, [Peer-reviewed]
  English, Scientific journal
• 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
• 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
• 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, Sep. 1998, [Peer-reviewed]
  English, Scientific journal
• 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, Apr. 1998, [Peer-reviewed]
  English, Scientific journal
• 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, Mar. 1998
  English, Scientific journal
• 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, Feb. 1998, [Peer-reviewed]
  English, Scientific journal
• 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, Feb. 1998, [Peer-reviewed]
  English, Scientific journal
• 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, Jun. 1997, [Peer-reviewed]
  English, Scientific journal
• 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, Jun. 1997, [Peer-reviewed]
  English, Scientific journal
• 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, Mar. 1997, [Peer-reviewed]
  English, Scientific journal
• 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, 1997, [Peer-reviewed]
  English, Scientific journal
• 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, 1997, [Peer-reviewed]
  English, 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
• 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
• 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, Aug. 1996, [Peer-reviewed]
  English, Scientific journal
• 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, May 1996, [Peer-reviewed]
  English, Scientific journal
• 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, Feb. 1996, [Peer-reviewed]
  English, Scientific journal
• 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
• 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, Dec. 1995, [Peer-reviewed]
  English, Scientific journal
• 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, May 1993, [Peer-reviewed]
  English, Scientific journal
• 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, May 1993, [Peer-reviewed]
  English, Scientific journal
• 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, Jun. 1992, [Peer-reviewed]
  English, Scientific journal

• 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
  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
  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
  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
  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
  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
  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
  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
• 宇宙の塵の化学：原子から分子・星・惑星系へ
  羽馬哲也; 香内晃; 渡部直樹, 化学と教育, 64, 282, 283, Dec. 2016, [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
  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
  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
  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
  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

• 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]

• 環境と人間, 2024年, 学士課程, 全学教育

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

• 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
  08 Mar. 2023 - 31 Mar. 2024
  渡部 直樹; NGUYEN THANH
  本研究の目的は，星や惑星誕生の場である星間分子雲に存在する固体微粒子，氷星間塵上での硫黄を含む分子の化学反応を実験的に検証し，宇宙における硫黄の化学進化をより詳細に理解することである。研究対象として，これまでに星間分子雲で観測されている硫黄を含む化学種，硫化カルボニル（OCS），メチルメルカプタン（CH3SH），二酸化硫黄（SO2）を選択した。超高真空（10-8Pa程度）チャンバー内で作製し，10ケルビン（K）に冷却されたアモルファス氷上にそれらの分子を蒸着し，水素原子との反応を検証した。反応はフーリエ変換型赤外吸収分光高度計でその場観測され，さらに氷から脱離する成分は四重極型質量分析計で分析された。
  いずれの分子も水素原子との反応には活性化エネルギー障壁が存在するため，通常10K程度の極低温では熱的に反応しえないが，量子トンネル効果による水素原子付加反応が進行した。OCSからはチオギ酸（HCOSH），SO2からはスルフィン酸（HSOOH）など，これまでの天文観測ではなじみのなかった硫黄を含む分子が生成し，CH3SHを含むいずれの分子も水素原子との反応で最終的に硫化水素（H2S）を生成した。硫化水素は水素原子との反応で容易にガス化するため，これらの硫黄を含む分子はいずれも氷星間塵上には固体として残りにくい化学種だと考えられる。これは，これまでの天文観測結果と極めて調和的である。
  上記の研究成果の大半は既に学術論文として公表され（Nguyen et al. 2021, 2023; The Astrophysical Journal），現時点でもう1報の論文投稿の準備がほぼ整っている。さらに，関連する化学反応を対象とした量子化学計算論文に実験データを提供し，実験と理論の両面で星間化学の発展に大きく貢献した。
  日本学術振興会, 特別研究員奨励費, 北海道大学, 22KF0001
• 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_,n=0-2) proceed in solid phase at 〜10K. The reaction rates of the substitution decrease as number of D atoms in methanol, n, increases
  3.We demonstrated for the first time that deuterium enrichment observed can be achieved partly by the grain-surface reactions. Our quantitative data shows that H-D substitution is more efficient to produce deuterated methanol than the successive deuterium addition to CO in a molecular cloud.
  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