博士（理学）, 岡山大学

自然科学一般, 宇宙惑星科学

修士課程, 理学院

博士課程, 理学院

2026年04月, 文部科学省, 令和8年度科学技術分野の文部科学大臣表彰 科学技術賞
太陽系始原物質に含まれる有機物とその起源に関する研究
大場康弘

2023年05月, 日本地球惑星科学連合, 第5回西田賞
星間物質および太陽系物質の有機的な化学進化に関する研究
大場康弘

2017年12月, 地球化学研究協会, 地球化学研究協会学術賞｢進歩賞｣
新しい実験手法による安定同位体比を使用した炭素質隕石中の有機物と模擬星間分子の研究
大場康弘

2010年, 日本有機地球化学会, 2010年度日本有機地球化学会研究奨励賞（田口賞）「
炭素質隕石中有機化合物の安定同位体組成とその同位体分別プロセスに関する研究
大場康弘

Distribution of purine and pyrimidine bases in Antarctic carbonaceous meteorites
Yasuhiro Oba; Takuto Tomaru; Toshiki Koga; Yoshihiro Furukawa; Sako Sunami; Toshihiro Yoshimura; Yuta Hirakawa; Nanako O. Ogawa; Naohiko Ohkouchi; Keiko Kuwamoto; Yoshinori Takano; Hiroshi Naraoka
Geochimica et Cosmochimica Acta, 2026年08月
研究論文（学術雑誌）

FAUST XXXI. Grain properties and variability of three sources in GSS 30
Q. Yang; H. Baobab Liu; S. Feng; C. J. Chandler; F. Fontani; N. Sakai; Y. Oya; T. Hanawa; C. Codella; C. Ceccarelli; I. Jiménez-Serra; L. Cacciapuoti; E. Bianchi; M. Bouvier; M. De Simone; A. Isella; D. Johnstone; L. Loinard; G. Sabatini; Y. Shirley; Y. Aikawa; M. J. Maureira; P. Caselli; F. Menard; N. Balucani; E. Caux; S. Charnley; N. Cuello; F. Dulieu; L. Evans; D. Fedele; T. Hama; E. Herbst; T. Hirota; B. Lefloch; A. López-Sepulcre; L. T. Maud; A. Miotello; G. Moellenbrock; H. Nomura; Y. Oba; S. Ohashi; Y. Okoda; J. Pineda; L. Podio; A. Rimola; T. Sakai; D. Segura-Cox; B. Svoboda; L. Testi; C. Vastel; S. Viti; N. Watanabe; Y. Watanabe; Y. Zhang; Z. E. Zhang; F. O. Alves; S. Yamamoto
Astronomy & Astrophysics, 711, A117, A117, EDP Sciences, 2026年07月07日, ［査読有り］
英語, 研究論文（学術雑誌）, Aims . To advance our understanding of dust properties in class 0/I young stellar objects, it is essential to resolve and characterize their structures at multiple wavelengths and investigate how both grain growth and environmental factors shape their spectral properties.

Methods . We present 0.″5 angular resolution ALMA observations of the GSS 30 complex at 1.2–3.0 mm, collected as part of the FAUST large programme, with a linear resolution of 69 au. We analysed the dust continuum emission and performed model fitting to constrain the dust mass and the disk structure.

Results . For IRS3, the spectral index increases radially from 2.0 at the centre to 2.5 at the disk edge. In contrast, it decreases from 2.0 to as low as 1.6–1.8 along the outflow direction. An asymmetric distribution shows α as low as 1.6 to the northeastern blueshifted lobe, possibly due to cold outer envelope dust obscuring warmer inner regions. Spectral energy distribution fitting indicates maximum dust grain sizes of tens of microns and a dust mass of 650–1510 M _⊕ . IRS1 is connected with an extended structure to the north-east. It may be an outflow–disk complex or a trailing structure associated with a circumbinary disk, although we cannot rule out the possibility that it could also be a gas streamer accreting onto IRS1. At the centre of IRS1, the spectral index is < 0.8, which is consistent with marginally optically thick free-free emission. IRS2 exhibits brightness variations over 420 seconds of observation, with a multi-epoch comparison suggesting a flare lasting tens of minutes, indicating magnetic activity in the central star.

Conclusions . This study presents a detailed millimetre multi-wavelength analysis of the GSS 30 IRS3 and IRS1 systems, highlighting the crucial role of environmental factors – specifically dust obscuration and the connecting streamer structures – in shaping the observed morphology of these early-stage disks. We also find that the IRS2 exhibits millimetre variability, which may originate from magnetic flares at the surface of the protostar.

Direct observation of organic molecules in asteroid ryugu revealed by high-resolution atomic force microscope
Kota Iwata; Yasuhiro Oba; Hiroshi Naraoka; Hikaru Yabuta; Shogo Tachibana; Yoshiaki Sugimoto
Nature Communications, 2026年04月14日
研究論文（学術雑誌）

Distribution of extraterrestrial nucleobases, other N-heterocycles, and their precursors in a sample from asteroid Bennu
Yasuhiro Oba; Toshiki Koga; Yoshinori Takano; Hiroshi Naraoka; Yuta Hirakawa; Sako Sunami; Yoshihiro Furukawa; Tomoya Yamazaki; Takuto Tomaru; Jason P. Dworkin; Daniel P. Glavin; Harold C. Connolly, Jr; Dante S. Lauretta
Communications Chemistry, 2026年04月02日
研究論文（学術雑誌）

A complete set of canonical nucleobases in the carbonaceous asteroid (162173) Ryugu
Toshiki Koga; Yasuhiro Oba; Yoshinori Takano; Hiroshi Naraoka; Nanako O. Ogawa; Kazunori Sasaki; Hajime Sato; Toshihiro Yoshimura; Naohiko Ohkouchi
Nature Astronomy, 2026年03月16日
研究論文（学術雑誌）

Experimental and computational studies of the hydrogenation of carbon disulfide (CS2) on ice analogues
Thanh Nguyen; Germán Molpeceres; Yasuhiro Oba; Marcelino Agúndez; Gisela Esplugues; José Cernicharo; Naoki Watanabe
Monthly Notices of the Royal Astronomical Society, 2026年03月14日
研究論文（学術雑誌）

Methanol Formation via the Radical–Radical Reaction of OH and CH3 Radicals Undergoing Transient Diffusion on Ice at 10 to 60 K
Arisa Iguchi; Hiroshi Hidaka; Atsuki Ishibashi; Masashi Tsuge; Yasuhiro Oba; Naoki Watanabe
The Astrophysical Journal, 2026年02月20日
研究論文（学術雑誌）

Bio-essential sugars in samples from asteroid Bennu
Yoshihiro Furukawa; Sako Sunami; Yoshinori Takano; Toshiki Koga; Yuta Hirakawa; Yasuhiro Oba; Hiroshi Naraoka; Daisuke Saigusa; Takaaki Yoshikawa; Satoru Tanaka; Daniel P. Glavin; Jason P. Dworkin; Harold C. Connolly, Jr.; Dante S. Lauretta
Nature Geoscience, 2026年01月
研究論文（学術雑誌）

Methylamine Formation on Amorphous Solid Water via the Diffusive CH3 + NH2 Reaction as Investigated by the Cs+ Ion Pickup Method
Arisa Iguchi; Masashi Tsuge; Hiroshi Hidaka; Yasuhiro Oba; Naoki Watanabe
ACS Earth and Space Chemistry, 2025年12月18日
研究論文（学術雑誌）

FAUST XXIII. SiO outflow in the protobinary system L483
T. Hirota; B. Lefloch; Y. Oya; M. Bouvier; S. Charnley; I. Jiménez-Serra; A. López-Sepulcre; A. Miotello; J. Ospina-Zamudio; C. Vastel; S. Viti; C. J. Chandler; B. Svoboda; C. Ceccarelli; C. Codella; N. Sakai; Y. Aikawa; N. Balucani; E. Bianchi; P. Caselli; E. Caux; N. Cuello; M. De Simone; F. Dulieu; L. Evans; D. Fedele; S. Feng; F. Fontani; T. Hama; T. Hanawa; E. Herbst; A. Isella; D. Johnstone; H. B. Liu; L. Loinard; L. T. Maud; M. J. Maureira; F. Menard; G. Moellenbrock; H. Nomura; Y. Oba; S. Ohashi; Y. Okoda; J. Pineda; L. Podio; A. Rimola; G. Sabatini; T. Sakai; D. Segura-Cox; Y. Shirley; L. Testi; N. Watanabe; Y. Watanabe; Y. Zhang; S. Yamamoto
Astronomy and Astrophysics, 695, A278, A278, EDP Sciences, 2025年03月27日, ［査読有り］
研究論文（学術雑誌）, Context. While protostellar outflows are important in terms of mass accretion and angular momentum transport in star formation processes, high-resolution observations of outflows in protobinary systems are still sparse.

Aims. We aim to reveal outflow structures traced by millimeter SiO emission in a low-mass protobinary system, L483.

Methods. We observed the SiO (J = 5−4) line in L483 with the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the large program FAUST (Fifty AU STudy of the chemistry in the disk/envelope systems of Solar-like protostars). The spatial and spectral resolutions were 0.39^′′×0.30^′′ (780 au×60 au) and 122 kHz (0.17 km s⁻¹ at 217 GHz), respectively. The spectral lines of SO, CS, and C¹⁸O were also used to study the physical and dynamical properties of the SiO emitting regions.

Results. Two SiO emission peaks are identified in the central part of L483, which have offsets of 100 au and 200 au toward the northeast (SiO-peak) and north (SiO-N), respectively, from the continuum peak. The SiO-peak shows only blueshifted emission with a broad linewidth of 5 km s⁻¹, while that of SiO-N corresponds to the systemic velocity. Furthermore, weak and compact SiO emission components are distributed up to 2400 au away from the continuum position. They have narrow linewidths of ∼1 km s⁻¹. One of these components is a blueshifted isolated emission feature, 2400 au northeast of the continuum peak, NE-cloud, located outside the east-west outflow lobes. The SiO abundances relative to H₂ are 10⁻¹⁰−10⁻⁹ and 10⁻¹⁰ in the central part and more widely distributed components, respectively. These are intermediate values between those of strongly shocked regions caused by high-velocity outflows and quiescent molecular clouds.

Conclusions. The central SiO emission could be interpreted as either two different outflows driven by both protostars or as an outflow ejected from one of the circumstellar disks in the binary system. The NE-cloud region is most likely explained as a remnant of an old shock produced by past outflow activity, as has been proposed for the low-mass protostar IRAS 15398–3359. The complex structures of the outflows traced by the SiO line could reflect dynamical processes of the newly formed protobinary system in L483.

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), 2025年03月05日
研究論文（学術雑誌）, 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.

Compound-Specific Carbon and Nitrogen Isotopic Analyses of Underivatized Pyrimidine and Purine Nucleobases
Toshiki Koga; Yoshinori Takano; Nanako O. Ogawa; Emily H. Hollingsworth; Yasuhiro Oba; Naohiko Ohkouchi
ACS Earth and Space Chemistry, 9, 3, 424, 432, American Chemical Society (ACS), 2025年03月03日
研究論文（学術雑誌）

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, 2025年02月20日
研究論文（学術雑誌）, 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.

Hydrogenation of acetaldehyde on interstellar ice analogs results in limited destruction
G. Molpeceres; T. Nguyen; Y. Oba; N. Watanabe
Astronomy & Astrophysics, 2025年02月
研究論文（学術雑誌）

Abundant ammonia and nitrogen-rich soluble organic matter in samples from asteroid (101955) Bennu
Daniel P. Glavin; Jason P. Dworkin; Conel M.O.D. Alexander; José C. Aponte; Allison A. Baczynski; Jessica J. Barnes; Hans A. Bechtel; Eve L. Berger; Aaron S. Burton; Paola Caselli; Angela H. Chung; Simon J. Clemett; George D. Cody; Gerardo Dominguez; Jamie E. Elsila; Kendra K. Farnsworth; Dionysis I. Foustoukos; Katherine H. Freeman; Yoshihiro Furukawa; Zack Gainsforth; Heather V. Graham; Tommaso Grassi; Barbara Michela Giuliano; Victoria E. Hamilton; Pierre Haenecour; Philipp R. Heck; Amy E. Hofmann; Christopher H. House; Yongsong Huang; Hannah H. Kaplan; Lindsay P. Keller; Bumsoo Kim; Toshiki Koga; Michael Liss; Hannah L. McLain; Matthew A. Marcus; Mila Matney; Timothy J. McCoy; Ophélie M. McIntosh; Angel Mojarro; Hiroshi Naraoka; Ann N. Nguyen; Michel Nuevo; Joseph A. Nuth; Yasuhiro Oba; Eric T. Parker; Tanya S. Peretyazhko; Scott A. Sandford; Ewerton Santos; Philippe Schmitt-Kopplin; Frederic Seguin; Danielle N. Simkus; Anique Shahid; Yoshinori Takano; Kathie L. Thomas-Keprta; Havishk Tripathi; Gabriella Weiss; Yuke Zheng; Nicole G. Lunning; Kevin Righter; Harold C. Connolly; Dante S. Lauretta
Nature Astronomy, 2025年
研究論文（学術雑誌）

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, 2024年12月01日
研究論文（学術雑誌）

Proposed Importance of HOCO Chemistry: Inefficient Formation of CO2 from CO and OH Reactions on Ice Dust
Atsuki Ishibashi; Germán Molpeceres; Hiroshi Hidaka; Yasuhiro Oba; Thanja Lamberts; Naoki Watanabe
The Astrophysical Journal, 2024年12月01日
研究論文（学術雑誌）

FAUST XVII. Super deuteration in the planet-forming system IRS 63 where the streamer strikes the disk
L. Podio; C. Ceccarelli; C. Codella; G. Sabatini; D. Segura-Cox; N. Balucani; A. Rimola; P. Ugliengo; C. J. Chandler; N. Sakai; B. Svoboda; J. Pineda; M. De Simone; E. Bianchi; P. Caselli; A. Isella; Y. Aikawa; M. Bouvier; E. Caux; L. Chahine; S. B. Charnley; N. Cuello; F. Dulieu; L. Evans; D. Fedele; S. Feng; F. Fontani; T. Hama; T. Hanawa; E. Herbst; T. Hirota; I. Jiménez-Serra; D. Johnstone; B. Lefloch; R. Le Gal; L. Loinard; H. Baobab 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; T. Sakai; Y. Shirley; L. Testi; C. Vastel; S. Viti; N. Watanabe; Y. Watanabe; Y. Zhang; Z. E. Zhang; S. Yamamoto
Astronomy & Astrophysics, 688, L22, L22, EDP Sciences, 2024年08月09日
研究論文（学術雑誌）, Context. Recent observations suggest that planet formation starts early, in protostellar disks of ≤10⁵ yr, which are characterized by strong interactions with the environment, such as through accretion streamers and molecular outflows.

Aims. To investigate the impact of such phenomena on the physical and chemical properties of a disk, it is key to understand what chemistry planets inherit from their natal environment.

Methods. In the context of the ALMA large program Fifty AU Study of the chemistry in the disk/envelope system of solar-like protostars (FAUST), we present observations on scales from ∼1500 au to ∼60 au of H₂CO, HDCO, and D₂CO toward the young planet-forming disk IRS 63.

Results. The H₂CO probes the gas in the disk as well as in a large scale streamer (∼1500 au) impacting onto the southeast disk side. We detected for the first time deuterated formaldehyde, HDCO and D₂CO, in a planet-forming disk and HDCO in the streamer that is feeding it. These detections allowed us to estimate the deuterium fractionation of H₂CO in the disk: [HDCO]/[H₂CO] ∼ 0.1 − 0.3 and [D₂CO]/[H₂CO] ∼ 0.1. Interestingly, while HDCO follows the H₂CO distribution in the disk and in the streamer, the distribution of D₂CO is highly asymmetric, with a peak of the emission (and [D]/[H] ratio) in the southeast disk side, where the streamer crashes onto the disk. In addition, D₂CO was detected in two spots along the blue- and redshifted outflow. This suggests that (i) in the disk, HDCO formation is dominated by gas-phase reactions in a manner similar to H₂CO, while (ii) D₂CO is mainly formed on the grain mantles during the prestellar phase and/or in the disk itself and is at present released in the gas phase in the shocks driven by the streamer and the outflow.

Conclusions. These findings testify to the key role of streamers in the buildup of the disk concerning both the final mass available for planet formation and its chemical composition.

Primordial aqueous alteration recorded in water-soluble organic molecules from the carbonaceous asteroid (162173) Ryugu
Yoshinori Takano; Hiroshi Naraoka; Jason P. Dworkin; Toshiki Koga; Kazunori Sasaki; Hajime Sato; Yasuhiro Oba; Nanako O. Ogawa; Toshihiro Yoshimura; Kenji Hamase; Naohiko Ohkouchi; Eric T. Parker; José C. Aponte; Daniel P. Glavin; Yoshihiro Furukawa; Junken Aoki; Kuniyuki Kano; Shin-ichiro M. Nomura; Francois-Regis Orthous-Daunay; Philippe Schmitt-Kopplin; Aogu Furusho; Minako Hashiguchi; Kazuhiko Fukushima; Dan Aoki; Hannah L. McLain; Jamie E. Elsila; Heather V. Graham; John M. Eiler; Norbert Hertkorn; Alexander Ruf; Cédric Wolters; Junko Isa; Véronique Vuitton; Roland Thissen; Saburo Sakai; Haruna Sugahara; Hajime Mita; Yoshito Chikaraishi; Takaaki Yoshikawa; Satoru Tanaka; Mayu Morita; Morihiko Onose; Daisuke Araoka; Fumie Kabashima; Kosuke Fujishima; Hajime Sato; Tomoya Yamazaki; Yuki Kimura; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Kanako Sakamoto; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tatsuaki Okada; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Sei-ichiro Watanabe; Yuichi Tsuda; Shogo Tachibana
Nature Communications, 15, 1, Springer Science and Business Media LLC, 2024年07月10日
研究論文（学術雑誌）, Abstract

We report primordial aqueous alteration signatures in water-soluble organic molecules from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 spacecraft of JAXA. Newly identified low-molecular-weight hydroxy acids (HO-R-COOH) and dicarboxylic acids (HOOC-R-COOH), such as glycolic acid, lactic acid, glyceric acid, oxalic acid, and succinic acid, are predominant in samples from the two touchdown locations at Ryugu. The quantitative and qualitative profiles for the hydrophilic molecules between the two sampling locations shows similar trends within the order of ppb (parts per billion) to ppm (parts per million). A wide variety of structural isomers, including α- and β-hydroxy acids, are observed among the hydrophilic molecules. We also identify pyruvic acid and dihydroxy and tricarboxylic acids, which are biochemically important intermediates relevant to molecular evolution, such as the primordial TCA (tricarboxylic acid) cycle. Here, we find evidence that the asteroid Ryugu samples underwent substantial aqueous alteration, as revealed by the presence of malonic acid during keto–enol tautomerism in the dicarboxylic acid profile. The comprehensive data suggest the presence of a series for water-soluble organic molecules in the regolith of Ryugu and evidence of signatures in coevolutionary aqueous alteration between water and organics in this carbonaceous asteroid.

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 Svoboda; 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, 531, 2, 2653, 2668, Oxford University Press (OUP), 2024年05月23日
研究論文（学術雑誌）, 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 characterize 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 arcsec with position angles (PA) of 0° and -12°, respectively, while those of IRAS 4A2 are more extended, spanning 18 and 25 arcsec 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.

Enantioselective three-dimensional high-performance liquid chromatographic determination of amino acids in the Hayabusa2 returned samples from the asteroid Ryugu
Aogu Furusho; Chiharu Ishii; Takeyuki Akita; Mai Oyaide; Masashi Mita; Hiroshi Naraoka; Yoshinori Takano; Jason P. Dworkin; Yasuhiro Oba; Toshiki Koga; Kazuhiko Fukushima; Dan Aoki; Minako Hashiguchi; Hajime Mita; Yoshito Chikaraishi; Naohiko Ohkouchi; Nanako O. Ogawa; Saburo Sakai; Daniel P. Glavin; Jamie E. Elsila; Eric T. Parker; José C. Aponte; Hannah L. McLain; Francois-Regis Orthous-Daunay; Véronique Vuitton; Roland Thissen; Cédric Wolters; Philippe Schmitt-Kopplin; Alexander Ruf; Junko Isa; Norbert Hertkorn; John M. Eiler; Toshihiro Yoshimura; Haruna Sugahara; Heather V. Graham; Yoshihiro Furukawa; Daisuke Araoka; Satoru Tanaka; Takaaki Yoshikawa; Fumie Kabashima; Kazunori Sasaki; Hajime Sato; Tomoya Yamazaki; Morihiko Onose; Mayu Morita; Yuki Kimura; Kuniyuki Kano; Junken Aoki; Kosuke Fujishima; Shin-ichiro Nomura; Shogo Tachibana; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Hisayoshi Yurimoto; Kanako Sakamoto; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Tatsuaki Okada; Sei-ichiro Watanabe; Yuichi Tsuda; Kenji Hamase
Journal of Chromatography Open, 100134, 100134, Elsevier BV, 2024年05月
研究論文（学術雑誌）

Abundant extraterrestrial purine nucleobases in the Murchison meteorite: Implications for a unified mechanism for purine synthesis in carbonaceous chondrite parent bodies
Toshiki Koga; Yoshinori Takano; Yasuhiro Oba; Hiroshi Naraoka; Naohiko Ohkouchi
Geochimica et Cosmochimica Acta, 2024年01月
英語, 研究論文（学術雑誌）

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, 2024年01月01日
研究論文（学術雑誌）, Abstract
The CH3O and CH2OH radicals can be important precursors of complex organic molecules (COMs) in interstellar dust. The COMs presumably originating from these radicals were abundantly found in various astronomical objects. Because each radical leads to different types of COMs, determining the abundance ratio of CH3O to CH2OH is crucial for a better understanding of the chemical evolution into various COMs. Recent work suggested that the reaction between CH3OH and OH on ice dust plays an important role in forming CH3O and CH2OH radicals. However, quantitative details on the abundance of these radicals have not been presented to date. Herein, we experimentally determined the branching ratio (CH3O/CH2OH) resulting from the CH3OH + OH reaction on the water ice surface at 10 K to be 4.3 ± 0.6. Furthermore, the CH3O product in the reaction would participate in subsequent diffusive reactions even at a temperature as low as 10 K. This fact should provide critical information for COMs formation models in cold molecular clouds.

Investigating the impact of x-ray computed tomography imaging on soluble organic matter in the Murchison meteorite: Implications for Bennu sample analyses
Daniel P. Glavin; Scott A. Eckley; José C. Aponte; Eve L. Berger; Aaron S. Burton; Jason P. Dworkin; Jamie E. Elsila; Frank T. Ferguson; Yoshihiro Furukawa; Heather V. Graham; Toshiki Koga; Michael Liss; Hannah L. McLain; Hiroshi Naraoka; Yasuhiro Oba; Eric T. Parker; Kevin Righter; Philippe Schmitt-Kopplin; Danielle N. Simkus; Yoshinori Takano; Harold C. Connolly; Dante S. Lauretta
Meteoritics and Planetary Science, 59, 1, 105, 133, 2024年01月
英語, 研究論文（学術雑誌）

Abundant extraterrestrial purine nucleobases in the Murchison meteorite: Implications for a unified mechanism for purine synthesis in carbonaceous chondrite parent bodies
Toshiki Koga; Yoshinori Takano; Yasuhiro Oba; Hiroshi Naraoka; Naohiko Ohkouchi
Geochimica et Cosmochimica Acta, 365, 253, 265, Elsevier BV, 2024年01月
研究論文（学術雑誌）

Polycyclic aromatic hydrocarbons in samples of Ryugu formed in the interstellar medium.
Sarah S Zeichner; José C Aponte; Surjyendu Bhattacharjee; Guannan Dong; Amy E Hofmann; Jason P Dworkin; Daniel P Glavin; Jamie E Elsila; Heather V Graham; Hiroshi Naraoka; Yoshinori Takano; Shogo Tachibana; Allison T Karp; Kliti Grice; Alex I Holman; Katherine H Freeman; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Kanako Sakamoto; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tatsuaki Okada; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Sei-Ichiro Watanabe; Yuichi Tsuda; Kenji Hamase; Kazuhiko Fukushima; Dan Aoki; Minako Hashiguchi; Hajime Mita; Yoshito Chikaraishi; Naohiko Ohkouchi; Nanako O Ogawa; Saburo Sakai; Eric T Parker; Hannah L McLain; Francois-Regis Orthous-Daunay; Véronique Vuitton; Cédric Wolters; Philippe Schmitt-Kopplin; Norbert Hertkorn; Roland Thissen; Alexander Ruf; Junko Isa; Yasuhiro Oba; Toshiki Koga; Toshihiro Yoshimura; Daisuke Araoka; Haruna Sugahara; Aogu Furusho; Yoshihiro Furukawa; Junken Aoki; Kuniyuki Kano; Shin-Ichiro M Nomura; Kazunori Sasaki; Hajime Sato; Takaaki Yoshikawa; Satoru Tanaka; Mayu Morita; Morihiko Onose; Fumie Kabashima; Kosuke Fujishima; Tomoya Yamazaki; Yuki Kimura; John M Eiler
Science (New York, N.Y.), 382, 6677, 1411, 1416, 2023年12月22日, ［国際誌］
英語, 研究論文（学術雑誌）, Polycyclic aromatic hydrocarbons (PAHs) contain ≲20% of the carbon in the interstellar medium. They are potentially produced in circumstellar environments (at temperatures ≳1000 kelvin), by reactions within cold (~10 kelvin) interstellar clouds, or by processing of carbon-rich dust grains. We report isotopic properties of PAHs extracted from samples of the asteroid Ryugu and the meteorite Murchison. The doubly-13C substituted compositions (Δ2×13C values) of the PAHs naphthalene, fluoranthene, and pyrene are 9 to 51‰ higher than values expected for a stochastic distribution of isotopes. The Δ2×13C values are higher than expected if the PAHs formed in a circumstellar environment, but consistent with formation in the interstellar medium. By contrast, the PAHs phenanthrene and anthracene in Ryugu samples have Δ2×13C values consistent with formation by higher-temperature reactions.

Soluble organic matter Molecular atlas of Ryugu reveals cold hydrothermalism on C-type asteroid parent body
Philippe Schmitt-Kopplin; Norbert Hertkorn; Mourad Harir; Franco Moritz; Marianna Lucio; Lydie Bonal; Eric Quirico; Yoshinori Takano; Jason P. Dworkin; Hiroshi Naraoka; Shogo Tachibana; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Hisayoshi Yurimoto; Kanako Sakamoto; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Tatsuaki Okada; Sei-ichiro Watanabe; Yuichi Tsuda; Kenji Hamase; Aogu Furusho; Minako Hashiguchi; Kazuhiko Fukushima; Dan Aoki; José C. Aponte; Eric T. Parker; Daniel P. Glavin; Hannah L. McLain; Jamie E. Elsila; Heather V. Graham; John M. Eiler; Alexander Ruf; Francois-Regis Orthous-Daunay; Junko Isa; Véronique Vuitton; Roland Thissen; Nanako O. Ogawa; Saburo Sakai; Toshihiro Yoshimura; Toshiki Koga; Haruna Sugahara; Naohiko Ohkouchi; Hajime Mita; Yoshihiro Furukawa; Yasuhiro Oba
Nature Communications, 14, 1, Springer Science and Business Media LLC, 2023年10月16日
研究論文（学術雑誌）, Abstract

The sample from the near-Earth carbonaceous asteroid (162173) Ryugu is analyzed in the context of carbonaceous meteorites soluble organic matter. The analysis of soluble molecules of samples collected by the Hayabusa2 spacecraft shines light on an extremely high molecular diversity on the C-type asteroid. Sequential solvent extracts of increasing polarity of Ryugu samples are analyzed using mass spectrometry with complementary ionization methods and structural information confirmed by nuclear magnetic resonance spectroscopy. Here we show a continuum in the molecular size and polarity, and no organomagnesium molecules are detected, reflecting a low temperature and water-rich environment on the parent body approving earlier mineralogical and chemical data. High abundance of sulfidic and nitrogen rich compounds as well as high abundance of ammonium ions confirm the water processing. Polycyclic aromatic hydrocarbons are also detected in a structural continuum of carbon saturations and oxidations, implying multiple origins of the observed organic complexity, thus involving generic processes such as earlier carbonization and serpentinization with successive low temperature aqueous alteration.

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年09月20日, ［国際誌］
英語, 研究論文（学術雑誌）, 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.

Chemical evolution of primordial salts and organic sulfur molecules in the asteroid 162173 Ryugu.
Toshihiro Yoshimura; Yoshinori Takano; Hiroshi Naraoka; Toshiki Koga; Daisuke Araoka; Nanako O Ogawa; Philippe Schmitt-Kopplin; Norbert Hertkorn; Yasuhiro Oba; Jason P Dworkin; José C Aponte; Takaaki Yoshikawa; Satoru Tanaka; Naohiko Ohkouchi; Minako Hashiguchi; Hannah McLain; Eric T Parker; Saburo Sakai; Mihoko Yamaguchi; Takahiro Suzuki; Tetsuya Yokoyama; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Kanako Sakamoto; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tatsuaki Okada; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Sei-Ichiro Watanabe; Yuichi Tsuda; Shogo Tachibana
Nature communications, 14, 1, 5284, 5284, Springer Science and Business Media LLC, 2023年09月18日, ［国際誌］
英語, 研究論文（学術雑誌）, Abstract

Samples from the carbonaceous asteroid (162173) Ryugu provide information on the chemical evolution of organic molecules in the early solar system. Here we show the element partitioning of the major component ions by sequential extractions of salts, carbonates, and phyllosilicate-bearing fractions to reveal primordial brine composition of the primitive asteroid. Sodium is the dominant electrolyte of the salt fraction extract. Anions and NH₄⁺ are more abundant in the salt fraction than in the carbonate and phyllosilicate fractions, with molar concentrations in the order SO₄²⁻> Cl⁻> S₂O₃²⁻> NO₃⁻> NH₄⁺. The salt fraction extracts contain anionic soluble sulfur-bearing species such as S_n-polythionic acids (n < 6), C_n-alkylsulfonates, alkylthiosulfonates, hydroxyalkylsulfonates, and hydroxyalkylthiosulfonates (n < 7). The sulfur-bearing soluble compounds may have driven the molecular evolution of prebiotic organic material transforming simple organic molecules into hydrophilic, amphiphilic, and refractory S allotropes.

Ryugu asteroid sample return provides a natural laboratory for primordial chemical evolution.
Yasuhiro Oba; Yoshinori Takano; Jason P Dworkin; Hiroshi Naraoka
Nature communications, 14, 1, 3107, 3107, 2023年05月30日, ［国際誌］
英語, 研究論文（学術雑誌）, The samples returned from near-Earth asteroid (162173) Ryugu provide a pristine record of the 4.6 billion years since the birth of the Solar System. The Hayabusa2 initial analysis team has integrated a range of analytical techniques to investigate Ryugu’s organic chemistry. Here, we highlight their latest findings, the potential questions which may be answered, and provide an overview of new prospects in the decade to come.

Uracil in the carbonaceous asteroid (162173) Ryugu.
Yasuhiro Oba; Toshiki Koga; Yoshinori Takano; Nanako O Ogawa; Naohiko Ohkouchi; Kazunori Sasaki; Hajime Sato; Daniel P Glavin; Jason P Dworkin; Hiroshi Naraoka; Shogo Tachibana; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Kanako Sakamoto; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tatsuaki Okada; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Sei-Ichiro Watanabe; Yuichi Tsuda
Nature communications, 14, 1, 1292, 1292, Springer Science and Business Media LLC, 2023年03月21日, ［国際誌］
英語, 研究論文（学術雑誌）, Abstract

The pristine sample from the near-Earth carbonaceous asteroid (162173) Ryugu collected by the Hayabusa2 spacecraft enabled us to analyze the pristine extraterrestrial material without uncontrolled exposure to the Earth’s atmosphere and biosphere. The initial analysis team for the soluble organic matter reported the detection of wide variety of organic molecules including racemic amino acids in the Ryugu samples. Here we report the detection of uracil, one of the four nucleobases in ribonucleic acid, in aqueous extracts from Ryugu samples. In addition, nicotinic acid (niacin, a B₃ vitamer), its derivatives, and imidazoles were detected in search for nitrogen heterocyclic molecules. The observed difference in the concentration of uracil between A0106 and C0107 may be related to the possible differences in the degree of alteration induced by energetic particles such as ultraviolet photons and cosmic rays. The present study strongly suggests that such molecules of prebiotic interest commonly formed in carbonaceous asteroids including Ryugu and were delivered to the early Earth.

Soluble organic molecules in samples of the carbonaceous asteroid (162173) Ryugu.
Hiroshi Naraoka; Yoshinori Takano; Jason P Dworkin; Yasuhiro Oba; Kenji Hamase; Aogu Furusho; Nanako O Ogawa; Minako Hashiguchi; Kazuhiko Fukushima; Dan Aoki; Philippe Schmitt-Kopplin; José C Aponte; Eric T Parker; Daniel P Glavin; Hannah L McLain; Jamie E Elsila; Heather V Graham; John M Eiler; Francois-Regis Orthous-Daunay; Cédric Wolters; Junko Isa; Véronique Vuitton; Roland Thissen; Saburo Sakai; Toshihiro Yoshimura; Toshiki Koga; Naohiko Ohkouchi; Yoshito Chikaraishi; Haruna Sugahara; Hajime Mita; Yoshihiro Furukawa; Norbert Hertkorn; Alexander Ruf; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Kanako Sakamoto; Shogo Tachibana; Harold C Connolly Jr; Dante S Lauretta; Masanao Abe; Toru Yada; Masahiro Nishimura; Kasumi Yogata; Aiko Nakato; Miwa Yoshitake; Ayako Suzuki; Akiko Miyazaki; Shizuho Furuya; Kentaro Hatakeda; Hiromichi Soejima; Yuya Hitomi; Kazuya Kumagai; Tomohiro Usui; Tasuku Hayashi; Daiki Yamamoto; Ryota Fukai; Kohei Kitazato; Seiji Sugita; Noriyuki Namiki; Masahiko Arakawa; Hitoshi Ikeda; Masateru Ishiguro; Naru Hirata; Koji Wada; Yoshiaki Ishihara; Rina Noguchi; Tomokatsu Morota; Naoya Sakatani; Koji Matsumoto; Hiroki Senshu; Rie Honda; Eri Tatsumi; Yasuhiro Yokota; Chikatoshi Honda; Tatsuhiro Michikami; Moe Matsuoka; Akira Miura; Hirotomo Noda; Tetsuya Yamada; Keisuke Yoshihara; Kosuke Kawahara; Masanobu Ozaki; Yu-Ichi Iijima; Hajime Yano; Masahiko Hayakawa; Takahiro Iwata; Ryudo Tsukizaki; Hirotaka Sawada; Satoshi Hosoda; Kazunori Ogawa; Chisato Okamoto; Naoyuki Hirata; Kei Shirai; Yuri Shimaki; Manabu Yamada; Tatsuaki Okada; Yukio Yamamoto; Hiroshi Takeuchi; Atsushi Fujii; Yuto Takei; Kento Yoshikawa; Yuya Mimasu; Go Ono; Naoko Ogawa; Shota Kikuchi; Satoru Nakazawa; Fuyuto Terui; Satoshi Tanaka; Takanao Saiki; Makoto Yoshikawa; Sei-Ichiro Watanabe; Yuichi Tsuda
Science (New York, N.Y.), 379, 6634, eabn9033, American Association for the Advancement of Science (AAAS), 2023年02月24日, ［国際誌］
英語, 研究論文（学術雑誌）, The Hayabusa2 spacecraft collected samples from the surface of the carbonaceous near-Earth asteroid (162173) Ryugu and brought them to Earth. The samples were expected to contain organic molecules, which record processes that occurred in the early Solar System. We analyzed organic molecules extracted from the Ryugu surface samples. We identified a variety of molecules containing the atoms CHNOS, formed by methylation, hydration, hydroxylation, and sulfurization reactions. Amino acids, aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-heterocyclic compounds were detected, which had properties consistent with an abiotic origin. These compounds likely arose from an aqueous reaction on Ryugu’s parent body and are similar to the organics in Ivuna-type meteorites. These molecules can survive on the surfaces of asteroids and be transported throughout the Solar System.

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, 2023年02月01日, ［査読有り］
研究論文（学術雑誌）, Abstract
Methyl mercaptan (CH3SH) is one of the S-bearing organic compounds found in the interstellar medium (ISM). In this study, we investigated the surface reactions of solid CH3SH with H atoms on amorphous solid water using experimental and computational methods to examine their physicochemical behavior in the ISM. Consequently, the primary product was discovered to be CH4. As the computational studies show that the dominant reaction pathway is H + CH3SH → CH3 + H2S, the observed CH4 would result from H addition to CH3. As relatively minor routes, the H abstraction processes from the –CH3 and –SH functional groups of CH3SH, giving rise to CH2SH and CH3S radicals, are confirmed. Although these radicals may form CH3SH again by reactions with H atoms, the loss of CH3SH from the ice surface by chemical desorption would be minor.

FAUST V. Hot methanol in the [BHB2007] 11 protobinary system; hot corino versus shock origin
C. Vastel; F. Alves; C. Ceccarelli; M. Bouvier; I. Jiménez-Serra; T. Sakai; P. Caselli; L. Evans; F. Fontani; R. Le Gal; C. J. Chandler; B. Svoboda; L. Maud; C. Codella; N. Sakai; A. Lόpez-Sepulcre; G. Moellenbrock; Y. Aikawa; N. Balucani; E. Bianchi; G. Busquet; E. Caux; S. Charnley; N. Cuello; M. De Simone; F. Dulieu; A. Durân; D. Fedele; S. Feng; L. Francis; T. Hama; T. Hanawa; E. Herbst; T. Hirota; M. Imai; A. Isella; D. Johnstone; B. Lefloch; L. Loinard; M. Maureira; N. M. Murillo; S. Mercimek; S. Mori; F. Menard; A. Miotello; R. Nakatani; H. Nomura; Y. Oba; S. Ohashi; Y. Okoda; J. Ospina-Zamudio; Y. Oya; J. E. Pineda; L. Podio; A. Rimola; D. Segura Cox; Y. Shirley; L. Testi; S. Viti; N. Watanabe; Y. Watanabe; A. Witzel; C. Xue; Y. Zhang; B. Zhao; S. Yamamoto
Astronomy & Astrophysics, 664, A171, A171, EDP Sciences, 2022年08月29日
研究論文（学術雑誌）, Aims. Methanol is a ubiquitous species commonly found in the molecular interstellar medium. It is also a crucial seed species for the build-up of chemical complexity in star forming regions. Thus, understanding how its abundance evolves during the star formation process and whether it enriches the emerging planetary system is of paramount importance.

Methods. We used new data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar protostars) to study the methanol line emission towards the [BHB2007] 11 protobinary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disc has previously been detected.

Results. Twelve methanol lines have been detected with upper energies in the [45–537] K range along with one ¹³CH₃OH transition and one methyl formate (CH₃OCHO) line blended with one of the methanol transitions. The methanol emission is compact (FWHM ~ 0.5″) and encompasses both protostars, which are separated by only 0.2″ (28 au). In addition, the overall methanol line emission presents three velocity components, which are not spatially resolved by our observations. Nonetheless, a detailed analysis of the spatial origin of these three components suggests that they are associated with three different spatial regions, with two of them close to 11B and the third one associated with 11A. A radiative transfer analysis of the methanol lines gives a kinetic temperature of [100–140] K, an H₂ volume density of 10⁶–10⁷ cm⁻³ and column density of a few 10¹⁸ cm⁻² in all three components with a source size of ~0.15″. Thus, this hot and dense gas is highly enriched in methanol with an abundance as high as 10⁻⁵. Using previous continuum data, we show that dust opacity can potentially completely absorb the methanol line emission from the two binary objects.

Conclusions. Although we cannot firmly exclude other possibilities, we suggest that the detected hot methanol is resulting from the shocked gas from the incoming filaments streaming towards [BHB2007] 11A and B, respectively. Higher spatial resolution observations are necessary to confirm this hypothesis.

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, 2022年08月22日
論文集(書籍)内論文, 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.

The spatial distribution of soluble organic matter and its relationship to minerals in the asteroid (162173) Ryugu.
Minako Hashiguchi; Dan Aoki; Kazuhiko Fukushima; Hiroshi Naraoka; Yoshinori Takano; Dworkin P. Jason; Aponte C. Jose; Elsila E. Jamie; Eiler M. John; Yoshihiro Furukawa; Aogu Furusho; Glavin P. Daniel; Heather V. Graham; Kenji Hamase; Hertkorn Norbert; Junko Isa; Toshiki Koga; McLain L. Hannah; Hajime Mita; Yasuhiro Oba; Nanako O. Ogawa; Naohiko Ohkouchi; Francois-Regis Orthous-Daunay; Eric T. Parker; Ruf Alexander; Saburo Sakaki; Schmitt-Kopplin Philippe; Haruna Sugahara; Thissen Roland; Vuitton Véronique; Cédric Wolters; Toshihiro Yoshimura; Hisayoshi Yurimoto; Tomoki Nakamura; Takaaki Noguchi; Ryuji Okazaki; Hikaru Yabuta; Kanako Sakamoto; Shogo Tachibana; Toru Yada; Masahiro Nishimura; Aiko Nakato; Akiko Miyazaki; Kasumi Yogata; Masanao Abe; Tomohiro Usui; Makoto Yoshikawa; Takanao Saiki; Satoshi Tanaka; Fuyuto Terui; Satoru Nakazawa; Sei-ichiro Watanabe; Yuichi Tsuda
Research Square Platform LLC, 2022年07月25日
Abstract

We performed in-situ analysis on a ~1 mm-sized Ryugu grain A0080 returned by the Hayabusa2 spacecraft to investigate the relationship of soluble organic matter (SOM) to minerals. The DESI-HRMS (desorption electrospray ionization-high resolution mass spectrometry) imaging using methanol spray identified more than 200 soluble organic compounds, which were assigned as CHN, CHO, CHO-Na (sodium adducted), and CHNO in molecular composition. Heterogeneous spatial distribution was observed for different compound classes of SOM as well as among the same alkylated homologues on the sample surface. The A0080 sample showed similar mineralogy to that of CI chondrite and contained two different lithologies, which are rich in magnetite, pyrrhotite, and dolomite (lithology 1) and poor in those minerals (lithology 2). CHN compounds were relatively concentrated in lithology 1 than in lithology 2, on the other hand, CHO, CHO-Na, and CHNO compounds were distributed in both lithologies. Such different spatial distribution of SOM is the result of interaction of the SOM with minerals, during precipitation of the SOM via fluid activity, or could be due to difference in transportation efficiencies of SOMs in aqueous fluid. However, organic-related ions measured by ToF-SIMS did not coincide with the spatial distribution revealed by DESI-HRMS imaging, indicating that the ToF-SIMS data would be mainly derived from methanol-insoluble organic matter in A0080. Alkylated homologues of CHN compounds with large C number appeared more abundant in lithology 2 than lithology 1. In contrast, fragments of the Murchison meteorite showed different features to of A0080, implying different formation or growth mechanisms for the alkylated CHN compounds by interaction with fluid and minerals on Murchison parent body and asteroid Ryugu. This difference might be mainly attributed to the carbonate grains, which would have played as a catalyst for CH₂ growth of CHN compounds. Future in-situ analysis of CI chondrite will provide more reliable constraints for the history of soluble organic compounds in asteroid Ryugu.

Hydrogen abstraction reactions in formic and thioformic acid isomers by hydrogen and deuterium atoms
G. Molpeceres; I. Jiménez-Serra; Y. Oba; T. Nguyen; N. Watanabe; J. García de la Concepción; B. Maté; R. Oliveira; J. Kästner
Astronomy & Astrophysics, 2022年07月
研究論文（学術雑誌）, Context. The isomerism of molecules in the interstellar medium and the mechanisms behind it are essential questions in the chemistry of organic molecules in space. In the particular case of simple formic and thioformic acids, the low temperatures found in molecular clouds indicate that cis-trans isomerization in the gas-phase must be impeded. Reactions taking place on top of interstellar dust grains may explain the isomer interconversion at low temperatures.
Aims. We studied the isomerization processes of formic and thioformic acid that are likely to take place on the surface of interstellar dust grains after being initiated by H abstraction reactions. Similarly, deuterium enrichment of the acids can occur by the same mechanism. Our objective is to shed light on both topics to expand our understanding of the key precursors of organic molecules in space.
Methods. We determined the rate constants for the H abstraction reactions as well as the binding energies for the acids on water ice using ab initio calculations and the instanton method for calculating the rate constants, including quantum tunneling. In addition, we tested the viability of the deuteration of formic acid with tailored experiments and looked for it on the L1544 source.
Results. For formic acid, there is a clear dependence of the H abstraction reactions on the isomer of the reactant, with rate constants at ~50 K that differ by five orders of magnitude. Correspondingly, we did not observe the trans-cis reaction in our experiments. In the case of thioformic acid, a very similar cis-trans reactivity is found for abstraction reactions at the thiol (-SH) group in contrast to a preferential reactivity that is found when abstractions take place at the -CH moiety. We found comparable binding energies for both isomers with average binding energies of around −6200 and −3100 K for formic and thioformic acid, respectively. Our binding energy calculations show that the reactions are precluded for specific orientations, affecting the overall isomerization rate. For H abstractions initiated by deuterium atoms, we found very similar trends, with kinetic isotope effects varying in most cases between 13 and 20.
Conclusions. Our results support the cis-trans interconversion of cis-formic acid on dust grains, suggesting that such an acid should not withstand the conditions found on these objects. On the other hand, the trans isomer is very resilient. Both isomers of thioformic acid are much more reactive. A non-trivial chemistry is behind the apparent excess of its trans isomer that is found in cold molecular clouds and star-forming regions due to a subtle combination of preferential reactivity and binding with the surface. In light of our results, all the deuterated counterparts of thioformic acid are viable molecules to be present on the ISM. In contrast, only the trans isomer of deuterated formic acid is expected, for which we provide upper bounds of detection. Given the mechanisms presented in this paper, other mechanisms must be at play to explain the tiny fraction of cis-formic acid observed in interstellar cold environments, as well as the current trans-DCOOH and trans-HCOOD abundances in hot-corinos.

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, 2022年07月01日
研究論文（学術雑誌）, Abstract
The activation energies for desorption (E
des) and for surface diffusion (E
sd) of adsorbed molecules on dust grains are two of the most important parameters for the chemistry in the interstellar medium. Although E
des is often measured by laboratory experiments, the measurement of E
sd is sparse. Due to the lack of data, astrochemical models usually assume a simple scaling relation, E
sd = f
E
des, where f is a constant, irrespective of the adsorbed species. Here, we experimentally measure E
sd for CH4, H2S, OCS, CH3OH, and CH3CN on water-ice surfaces using an ultrahigh-vacuum transmission electron microscope. Compiling the measured E
sd values and E
des values from the literature, we find that the value of f ranges from ∼0.2 to ∼0.7, depending on the species. Unless f (or E
sd) for the majority of species is available, a natural alternative approach for astrochemical models is running multiple simulations, varying f for each species randomly. In this approach, ranges of molecular abundances predicted by multiple simulations, rather than abundances predicted by each simulation, are important. We here run 10,000 simulations of astrochemical models of molecular clouds and protostellar envelopes, randomly assigning a value of f for each species. In the former case, we identify several key species whose E
sd most strongly affects the uncertainties of the model predictions; E
sd for those species should be investigated in future laboratory and quantum chemical studies. In the latter case, uncertainties in the E
sd of many species contribute to the uncertainties in the model predictions.

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, 2022年07月01日
研究論文（学術雑誌）, 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.

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, 2022年05月30日
研究論文（学術雑誌）, 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.

Identifying the wide diversity of extraterrestrial purine and pyrimidine nucleobases in carbonaceous meteorites.
Yasuhiro Oba; Yoshinori Takano; Yoshihiro Furukawa; Toshiki Koga; Daniel P Glavin; Jason P Dworkin; Hiroshi Naraoka
Nature communications, 13, 1, 2008, 2008, Springer Science and Business Media LLC, 2022年04月26日, ［国際誌］
英語, 研究論文（学術雑誌）, Abstract

The lack of pyrimidine diversity in meteorites remains a mystery since prebiotic chemical models and laboratory experiments have predicted that these compounds can also be produced from chemical precursors found in meteorites. Here we report the detection of nucleobases in three carbonaceous meteorites using state-of-the-art analytical techniques optimized for small-scale quantification of nucleobases down to the range of parts per trillion (ppt). In addition to previously detected purine nucleobases in meteorites such as guanine and adenine, we identify various pyrimidine nucleobases such as cytosine, uracil, and thymine, and their structural isomers such as isocytosine, imidazole-4-carboxylic acid, and 6-methyluracil, respectively. Given the similarity in the molecular distribution of pyrimidines in meteorites and those in photon-processed interstellar ice analogues, some of these derivatives could have been generated by photochemical reactions prevailing in the interstellar medium and later incorporated into asteroids during solar system formation. This study demonstrates that a diversity of meteoritic nucleobases could serve as building blocks of DNA and RNA on the early Earth.

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, 2022年03月01日
研究論文（学術雑誌）,
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.

Quantifying the Chemical Desorption of H₂S and PH₃ from Amorphous Water-ice Surfaces
Kenji Furuya; Yasuhiro Oba; Takashi Shimonishi
The Astrophysical Journal, 926, 2, 171, 171, American Astronomical Society, 2022年02月01日
研究論文（学術雑誌）, Abstract

Nonthermal desorption of molecules from icy grain surfaces is required to explain molecular line observations in the cold gas of star-forming regions. Chemical desorption is one of the nonthermal desorption processes and is driven by the energy released by chemical reactions. After an exothermic surface reaction, the excess energy is transferred to products’ translational energy in the direction perpendicular to the surface, leading to desorption. The desorption probability of product species, especially that of product species from water-ice surfaces, is not well understood. This uncertainty limits our understanding of the interplay between gas-phase and ice-surface chemistry. In the present work, we constrain the desorption probability of H₂S and PH₃ per reaction event on porous amorphous solid water (ASW) by numerically simulating previous laboratory experiments. Adopting the microscopic kinetic Monte Carlo method, we find that the desorption probabilities of H₂S and PH₃ from porous ASW per hydrogen-addition event of the precursor species are 3% ± 1.5% and 4% ± 2%, respectively. These probabilities are consistent with a theoretical model of chemical desorption proposed in the literature if ∼7% of energy released by the reactions is transferred to the translational excitation of the products. As a byproduct, we find that approximately 70% (40%) of adsorption sites for atomic H on porous ASW should have a binding energy lower than ∼300 K (∼200 K). The astrochemical implications of our findings are briefly discussed.

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, 2021年12月01日, ［査読有り］
研究論文（学術雑誌）, Abstract
Carbonyl sulfide (OCS) is an abundant sulfur (S)-bearing species in the interstellar medium. It is present not only in the gas phase, but also on interstellar grains as a solid; therefore, OCS very likely undergoes physicochemical processes on icy surfaces at very low temperatures. The present study experimentally and computationally investigates the reaction of solid OCS with hydrogen (H) atoms on amorphous solid water at low temperatures. The results show that the addition of H to OCS proceeds via quantum tunneling, and further addition of H leads to the formation of carbon monoxide (CO), hydrogen sulfide (H2S), formaldehyde (H2CO), methanol (CH3OH), and thioformic acid (HC(O)SH). These experimental results are explained by our quantum chemical calculations, which demonstrate that the initial addition of H to the S atom of OCS is the most predominant, leading to the formation of OCS-H radicals. Once the formed OCS-H radical is stabilized on ice, further addition of H to the S atom yields CO and H2S, while that to the C atom yields HC(O)SH. We have also confirmed, in a separate experiment, the HC(O)SH formation by the HCO reactions with the SH radicals. The present results would have an important implication for the recent detection of HC(O)SH toward G+0.693–0.027.

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, 921, 1, American Astronomical Society, 2021年11月01日
英語, 研究論文（学術雑誌）

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
ASTROPHYSICAL JOURNAL, 918, 2, 2021年09月
英語, 研究論文（学術雑誌）

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
ASTROPHYSICAL JOURNAL, 918, 2, 2021年09月
英語, 研究論文（学術雑誌）

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, 2021年07月
英語, 研究論文（学術雑誌）

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 Duran; Lucy Evans; Cecile Favre; Davide Fedele; Siyi Feng; Francesco Fontani; Tetsuya Hama; Tomoyuki Hanawa; Eric Herbst; Tomoya Hirota; Muneaki Imai; Andrea Isella; Izaskun Jimenez-Serra; Claudine Kahane; Bertrand Lefloch; Laurent Loinard; Ana Lopez-Sepulcre; Luke T. Maud; Maria Jose 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
ASTROPHYSICAL JOURNAL, 910, 1, 2021年03月
英語, 研究論文（学術雑誌）

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, 799851, 799851, Frontiers Media SA, 2021年12月08日, ［国際誌］
英語, 研究論文（学術雑誌）, 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.

Analytical development of seamless procedures on cation-exchange chromatography and ion-pair chromatography with high-precision mass spectrometry for short-chain peptides
Yoshinori Takano; Yasuhiro Oba; Satoshi Furota; Hiroshi Naraoka; Nanako Ogawa; Thomas M. Blattmann; Naohiko Ohkouchi
International Journal of Mass Spectrometry, 116529, 116529, Elsevier BV, 2021年01月, ［査読有り］
研究論文（学術雑誌）

Extraterrestrial hexamethylenetetramine in meteorites-a precursor of prebiotic chemistry in the inner solar system.
Yasuhiro Oba; Yoshinori Takano; Hiroshi Naraoka; Yoshihiro Furukawa; Daniel P Glavin; Jason P Dworkin; Shogo Tachibana
Nature communications, 11, 1, 6243, 6243, 2020年12月07日, ［査読有り］, ［筆頭著者, 責任著者］, ［国際誌］
英語, 研究論文（学術雑誌）

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, 2020年12月, ［査読有り］
研究論文（学術雑誌）

An Experimental Study of Chemical Desorption for Phosphine in Interstellar Ice
Thanh Nguyen; Yasuhiro Oba; Takashi Shimonishi; Akira Kouchi; Naoki Watanabe
ASTROPHYSICAL JOURNAL LETTERS, 898, 2, 2020年08月, ［査読有り］
英語, 研究論文（学術雑誌）

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; Tetsuya Hama; Yasuhiro Oba; Yuki Kimura; Naoki Watanabe; Akira Kouchi
Scientific reports, 10, 1, 7755, 7755, 2020年05月08日, ［査読有り］, ［国際誌］
英語, 研究論文（学術雑誌）, The origin and evolution of solar system bodies, including water on the Earth, have been discussed based on the assumption that the relevant ingredients were simply silicates and ices. However, large amounts of organic matter have been found in cometary and interplanetary dust, which are recognized as remnants of interstellar/precometary grains. Precometary organic matter may therefore be a potential source of water; however, to date, there have been no experimental investigations into this possibility. Here, we experimentally demonstrate that abundant water and oil are formed via the heating of a precometary-organic-matter analog under conditions appropriate for the parent bodies of meteorites inside the snow line. This implies that H2O ice is not required as the sole source of water on planetary bodies inside the snow line. Further, we can explain the change in the oxidation state of the Earth from an initially reduced state to a final oxidized state. Our study also suggests that petroleum was present in the asteroids and is present in icy satellites and dwarf planets.

FAUST I. The hot corino at the heart of the prototypical Class i protostar L1551 IRS5
Bianchi, E.; Ch; ler, C.J.; Ceccarelli, C.; Codella, C.; Sakai, N.; Lopez-Sepulcre, A.; Maud, L.T.; Moellenbrock, G.; Svoboda, B.; Watanabe, Y.; Sakai, T.; Menard, F.; Aikawa, Y.; Alves, F.; Balucani, N.; Bouvier, M.; Caselli, P.; Caux, E.; Charnley, S.; Choudhury, S.; De Simone, M.; Dulieu, F.; Duran, A.; Evans, L.; Favre, C.; Fedele, D.; Feng, S.; Fontani, F.; Francis, L.; Hama, T.; Hanawa, T.; Herbst, E.; Hirota, T.; Imai, M.; Isella, A.; Jimenez-Serra, I.; Johnstone, D.; Kahane, C.; Lefloch, B.; Loinard, L.; Maureira, M.J.; Mercimek, S.; Miotello, A.; Mori, S.; Nakatani, R.; Nomura, H.; Oba, Y.; Ohashi, S.; Okoda, Y.; Ospina-Zamudio, J.; Oya, Y.; Pineda, J.; Podio, L.; Rimola, A.; Segura Cox, D.; Shirley, Y.; Taquet, V.; Testi, L.; Vastel, C.; Viti, S.; Watanabe, N.; Witzel, A.; Xue, C.; Zhang, Y.; Zhao, B.; Yamamoto, S.
Monthly Notices of the Royal Astronomical Society: Letters, 498, 1, L87, L92, Oxford University Press, 2020年
英語, 研究論文（学術雑誌）

Nucleobase synthesis in interstellar ices
Y. Oba; Y. Takano; H. Naraoka; N. Watanabe; A. Kouchi
Nature Communications, 10, 4413, 2019年09月, ［査読有り］
英語, 研究論文（学術雑誌）

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
The Astrophysical Journal, 874, 2, 8pp, 2019年04月01日, ［査読有り］
英語, 研究論文（学術雑誌）

なぜ宇宙空間の分子はガス状で存在できるのか？星間塵上の化学反応によるガスの放出を放出を実証
渡部直樹; 大場康弘
化学, 73, 2018年06月, ［査読有り］
日本語, 研究論文（学術雑誌）

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, 2018年03月01日, ［査読有り］
英語, 研究論文（学術雑誌）

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, 2017年11月, ［査読有り］
英語, 研究論文（学術雑誌）

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, 2017年09月, ［査読有り］, ［国際誌］
英語, 研究論文（学術雑誌）, 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.

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, 2016年10月, ［査読有り］
英語, 研究論文（学術雑誌）

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, 2016年10月, ［査読有り］
英語, 研究論文（学術雑誌）

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), 2016年08月, ［査読有り］
英語, 研究論文（学術雑誌）

Chiral glycine formation on cold interstellar grains by quantum tunneling hydrogen–deuterium substitution reactions
Y. Oba; N. Watanabe; Y. Osamura; A.Kouchi
Chem. Phys. Lett., 634, 53, 59, 2015年08月, ［査読有り］
英語, 研究論文（学術雑誌）

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, 2014年08月, ［査読有り］
英語, 研究論文（学術雑誌）

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, 2014年01月, ［査読有り］
英語, 研究論文（学術雑誌）

Octanol-water partition coefficients (Kow) vs. Ph for fluorescent dye tracers (fluorescein, eosin y), and implications for hydrologic tracer tests
Oba, Y.; Poulson, S.R.
Geochemical Journal, 46, 6, 517, 520, 2012年, ［査読有り］
英語, 研究論文（学術雑誌）

Water formation through a quantum tunneling surface reaction, OH + H 2, at 10K
Oba, Y.; Watanabe, N.; Hama, T.; Kuwahata, K.; Hidaka, H.; Kouchi, A.
Astrophysical Journal, 749, 1, 67, (12pp), 2012年, ［査読有り］
英語, 研究論文（学術雑誌）

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, 12, 662, 668, 2012年
日本語, 研究論文（学術雑誌）

星間分子雲における二酸化炭素生成に関する実験的研究
大場 康弘; 渡部 直樹; 香内 晃; 羽馬 哲也; ピロネロ バレリオ
地球化学, 45, 4, 213, 226, 日本地球化学会, 2011年12月, ［査読有り］
日本語, 研究論文（学術雑誌）, 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.

炭素質隕石中有機化合物の安定同位体組成とその同位体分別プロセスに関する研究
Yasuhiro Oba
Researches in Organic Geochemistry, 27, 103, 115, 2011年09月, ［査読有り］
日本語, 研究論文（学術雑誌）

Formation of H₂O ice through the surface reaction O₂ + H at low temperatures: Reaction kinetics and structure of the ice
Y. Oba; N. Miyauchi; T. Chigai; H. Hidaka; N. Watanabe; A. Kouchi
Physics and Chemistry of ice 2010, 369, 378, 2011年, ［査読有り］
英語, 研究論文（国際会議プロシーディングス）

Experimental studies of surface reactions among OH radicals that yield H2O and CO2 at 40-60 K
Oba, Yasuhiro; Watanabe, Naoki; Kouchi, Akira; Hama, Tetsuya; Pirronello, Valerio
Physical Chemistry Chemical Physics, 13, 35, 2011年
研究論文（学術雑誌）

Formation of carbonic acid (H2CO3) by surface reactions of non-energetic OH radicals with CO molecules at low temperatures
Oba, Y.; Watanabe, N.; Kouchi, A.; Hama, T.; Pirronello, V.
Astrophysical Journal, 722, 2, 1598, 1606, 2010年10月, ［査読有り］
英語, 研究論文（学術雑誌）

Experimental study of co2 formation by surface reactions of non-energetic oh radicals with co molecules
Oba, Y.; Watanabe, N.; Kouchi, A.; Hama, T.; Pirronello, V.
Astrophysical Journal Letters, 712, 2 PART 2, L174, L178, 2010年04月, ［査読有り］
英語, 研究論文（学術雑誌）

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, 2010年04月, ［査読有り］
英語, 研究論文（学術雑誌）

Diel behavior of stable isotopes of dissolved oxygen and dissolved inorganic carbon in rivers over a range of trophic conditions, and in a mesocosm experiment
Stephen R. Parker; Christopher H. Gammons; Simon R. Poulson; Michael D. DeGrandpre; Charmaine L. Weyer; M. Garrett Smith; John N. Babcock; Yasuhiro Oba
CHEMICAL GEOLOGY, 269, 1-2, 22, 32, 2010年01月, ［査読有り］
英語, 研究論文（学術雑誌）

Vertical carbon isotope change in acetate in a surface sediment from the northwestern Pacific Ocean
Masanori Kaneko, Yasuhiro Oba, Hiroshi Naraoka
Researches in Organic Geochemistry, 26, 73, 79, 2010年, ［査読有り］
英語, 研究論文（学術雑誌）

Oxygen isotope fractionation of dissolved oxygen during abiological reduction by aqueous sulfide
Oba, Y.; Poulson, S.R.
Chemical Geology, 268, 3-4, 226, 232, 2009年11月, ［査読有り］
英語, 研究論文（学術雑誌）

Formation of compact amorphous H2O ice by codeposition of hydrogen atoms with oxygen molecules on grain surfaces
Oba, Y.; Miyauchi, N.; Hidaka, H.; Chigai, T.; Watanabe, N.; Kouchi, A.
Astrophysical Journal, 701, 1, 464, 470, 2009年07月, ［査読有り］
英語, 研究論文（学術雑誌）

Nonenergetic reactions between atomic hydrogen and molecules on interstellar grain surfaces
N. Watanabe; A. Kouchi; H. Hidaka; Oba Y; N. Miyauchi
Journal of Physics: Conference Series, 194, 1, 012044, 2009年, ［査読有り］
英語, 研究論文（国際会議プロシーディングス）

Formation of amorphous H₂O ice from the reactions of cold H atoms with solid O₂ at 10K
A. Kouchi; N. Watanabe; H. Hidaka; N. Miyauchi; Oba Y; T. Chigai
Cosmic Dust-Near & Far, ASP Conference Series, 414, 338, 2009年, ［査読有り］
英語, 研究論文（国際会議プロシーディングス）

極低温星間塵表面原子反応による水分子生成
大場 康弘; 宮内 直弥; 千貝 健; 日高 宏; 渡部 直樹; 香内 晃
地球化学, 43, 4, 117, 131, 日本地球化学会, 2009年, ［査読有り］
日本語, 研究論文（学術雑誌）, 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.

Nonenergetic reactions between atomic hydrogen and molecules on interstellar grain surfaces
N.Watanabe; A.Kouchi; H.Hidaka; Y.Oba; N.Miyauchi
XXVI International Conference on Photonic, Electronic and Atomic Collisions, Journal of Physics: Conference Series, 194, 12044, 2009年, ［査読有り］
英語, 研究論文（学術雑誌）

Oxygen isotope fractionation of dissolved oxygen during reduction by ferrous iron
Oba, Y.; Poulson, S.R.
Geochimica et Cosmochimica Acta, 73, 1, 13, 24, 2009年, ［査読有り］
英語, 研究論文（学術雑誌）

Elemental and isotope behavior of macromolecular organic matter from CM chondrites during hydrous pyrolysis
Oba, Y.; Naraoka, H.
Meteoritics and Planetary Science, 44, 7, 943, 953, 2009年, ［査読有り］
英語, 研究論文（学術雑誌）

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年, ［査読有り］

Carbon and hydrogen isotopic fractionation of low molecular weight organic compounds during ultraviolet degradation
Oba, Y.; Naraoka, H.
Organic Geochemistry, 39, 5, 501, 509, 2008年, ［査読有り］
英語, 研究論文（学術雑誌）

ガスクロマトグラフ/同位体比質量分析計による分子レベル安定同位体比分析法
力石 嘉人; 大場 康弘
Researches in Organic Geochemistry, 23/24, 99, 122, 日本有機地球化学会, 2008年, ［査読有り］
日本語, 研究論文（学術雑誌）, One of the most powerful techniques in the molecular isotope studies is compound-specific isotope analysis (CSIA) by gas chromatograph/isotope ratio mass spectrometer (GC/IRMS), which allows a rapid and precise determination of stable carbon, nitrogen, and hydrogen (and oxygen) isotopic compositions of individual compounds even in complex mixture of components. After commercial production of GC/IRMS in the 1990s, CSIA has explosively been used for many fields of studies, particularly among the organic geochemical community as a powerful tool for tracing sources and delivery of organic compounds in geological and geographical samples and for reconstructing paleoenvironments. However, it is also true that fundamental analytical parameters of GC/IRMS has not been known extensively, which often leads to unreliable determination of the isotopic compositions. Unfortunately, based on such unreliable determination, several studies have unconsciously reported essentially inaccurate data and associated discussion. Therefore, in this paper, we review a brief outline of GC/IRMS and associated methodologies, and summarize the instrumental factors influencing accuracy and precision of the isotope measurements. We hope that this paper is useful for applying CSIA to future studies.

Carbon and hydrogen isotope fractionation of acetic acid during degradation by ultraviolet light
Yasuhiro Oba; Hiroshi Naraoka
GEOCHEMICAL JOURNAL, 41, 2, 103, 110, 2007年, ［査読有り］
英語, 研究論文（学術雑誌）

Carbon isotopic composition of acetic acid generated by hydrous pyrolysis of macromolecular organic matter from the Murchison meteorite
Y.Oba; H.Naraoka
Meteoritics and Planetary Science, 41, 8, 1175, 1181, 2006年08月, ［査読有り］
英語, 研究論文（学術雑誌）

Site-specific carbon isotope analysis of aromatic carboxylic acids by elemental analysis/pyrolysis/isotope ratio mass spectrometry
Oba, Y.; Naraoka, H.
Rapid Communications in Mass Spectrometry, 20, 24, 3649, 3653, 2006年, ［査読有り］
英語, 研究論文（学術雑誌）

A different behavior of hydrogen isotope exchange in aqueous solutions between two PAH isomers (fluoranthene and pyrene)
Y.Oba; H.Naraoka
Researches in Organic Geochemistry, 18, 29, 35, 日本有機地球化学会, 2003年, ［査読有り］
英語, 研究論文（学術雑誌）, Compound-specific hydrogen isotope analysis of polycyclic aromatic hydrocarbons (PAHs) has been established at sub-nano molar level, using gas chromatography/pyrolysis/isotope ratio mass spectrometry (GC/pyrolysis/IRMS). The analytical precision of δD value is generally less than a few ‰ at >2nmol (i.e. 20ng H) injection of pyrene and fluoranthene calibrated with co-injected 30ng H of phenanthrene and chrysene.
Hydrogen isotope exchange of pyrene and fluoranthene with water under neutral and acidic conditions was examined with relevance to hydrogen isotopic distribution of individual PAHs in carbonaceous chondrites. Hydrogen isotope exchange between PAH and water hardly occurred at 170℃ under neutral pH condition for 2 days. However, under acidic condition (pH=2), the isotope exchange reaction occurred, where hydrogens have exchanged more easily between pyrene and water relative to between fluoranthene and water. The kinetically different behavior between pyrene and fluoranthene coincides with the two-series PAH formation mechanisms in carbonaceous chondrites inferred from carbon isotopic compositions of PAH.

炭素質小惑星リュウグウと太陽系物質科学:軽元素および分子レベル解析法の高度化と今後の展望
高野淑識; 小川奈々子; 吉村寿紘; 古賀俊貴; 坂井三郎; 大河内直彦; 大場康弘; 古川善博, 環境と測定技術, 52, 1, 2025年

炭素質小惑星Bennu試料からのアミノ酸・核酸塩基検出とその意義
大場康弘; 古賀俊貴; 高野淑識; 古川善博; 奈良岡浩; DWORKIN Jason P.; GLAVIN Daniel P.; CONNOLLY Harold C., Jr.; CONNOLLY Harold C., Jr.; CONNOLLY Harold C., Jr.; LAURETTA Dante S., 環境と測定技術, 52, 7, 2025年

Inversion of surface voltage on H2O films affecting sublimation of CO underlayer
Atsuki Ishibashi; Yasuhiro Oba; Tetsuya Hama; Akira Kouchi; Naoki Watanabe, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 258, 2019年08月
英語, 研究発表ペーパー・要旨（国際会議）

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年

Reaction experiments on H exposure of solid methanol at low temperatures
Yukiko Yarnall; Hiroshi Hidaka; Yasuhiro Oba; Tetsuya Hama; Akira Kouchi; Naoki Watanabe, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 255, 2018年03月
英語, 研究発表ペーパー・要旨（国際会議）

低温光化学反応による分子雲での有機物形成・進化
Piani Laurette; 橘 省吾; 羽馬 哲也; 菅原 いよ; 大場 康弘; 田中 秀和; 木村 勇気; 三宅 亮; 松 野 淳也; 土山 明; 圦本 尚義; 香内 晃, 日本地球惑星科学連合2016年大会, 2016年

27aCH-5 極低温固体エタノールの水素-重水素トンネル置換反応(27aCH 原子分子(原子・分子一般),領域1(原子分子・量子エレクトロニクス・放射線))
尾坂 和哉; 大場 康弘; 香内 晃; 渡部 直樹, 日本物理学会講演概要集, 69, 1, 173, 173, 2014年03月05日
一般社団法人日本物理学会, 日本語

Role of quantum tunneling for the formation of H2O by reaction of H-2 with OH on interstellar grains
Yasuhiro Oba; Naoki Watanabe; Tetsuya Hama; Kazuaki Kuwahata; Hiroshi Hidaka; Akira Kouchi, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 247, 2014年03月
英語, 研究発表ペーパー・要旨（国際会議）

Formation of H₂O ice through the surface reaction O₂ + H at low temperatures: Reaction kinetics and structure of the ice
Y.Oba; N.Miyauchi; T.Chigai; H.Hidaka; N.Watanabe; A.Kouchi, Physics and Chemistry of ice 2010, 369, 378, 2011年, ［査読有り］
英語, 研究発表ペーパー・要旨（国際会議）

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年, ［査読有り］
英語, 研究発表ペーパー・要旨（国際会議）

「有機化合物の安定同位体比を用いた有機地球化学的研究の発展とその応用」によせて(<特集>有機化合物の安定同位体比を用いた有機地球化学的研究の発展とその応用(Part I))
力石 嘉人; 大場 康弘, Researches in organic geochemistry, 26, 1, 1, 2010年12月24日
日本有機地球化学会, 日本語

Nonenergetic reactions between atomic hydrogen and molecules on interstellar grain surfaces
N. Watanabe; A. Kouchi; H. Hidaka; Y. Oba; N. Miyauchi, XXVI INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS, 194, 012044, 2009年, ［査読有り］
英語, 研究発表ペーパー・要旨（国際会議）

Formation of amorphous H₂O ice from the reactions of cold H atoms with solid O₂ at 10K
A.Kouchi; N.Watanabe; H.Hidaka; N.Miyauchi; Y.Oba; T.Chigai, Cosmic Dust-Near & Far, ASP Conference Series, 414, 338, 2009年, ［査読有り］
英語, 研究発表ペーパー・要旨（国際会議）

332 極低温表面原子反応O_2+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, 93, 93, 2008年11月01日
日本惑星科学会, 日本語

Incorporation of hydrous oxygen into insoluble organic matter (IOM) of murchison
Yasuhiro Oba; Hiroshi Naraoka, METEORITICS & PLANETARY SCIENCE, 43, 7, A119, A119, 2008年07月
英語, 研究発表ペーパー・要旨（国際会議）

Search for Nucleobases in Antarctic Carbonaceous Meteorites
大場康弘
JPGU2026, 2026年05月29日
［招待講演］

Laboratory studies on the surface reactions of sulfur-bearing molecules on amorphous solid water
大場康弘
Pacifichem2025, 2025年12月18日
［招待講演］

A possible connection between interstellar and solar-system sulfur chemistry
大場康弘
Astrochemistry on grain surfaces: The Journey of Dust, Ice, and Sulfur in Space, 2025年10月16日
［招待講演］

Nucleobases and other nitrogen-containing molecules in samples from asteroid Bennu
大場康弘
European Astronomical Society Annual Meeting, 2025年06月24日
［招待講演］

Detection of nucleobases and other N-heterocycles in the sample returned from asteroid (101955) Bennu
大場康弘
JpGU2024, 2024年05月27日
［招待講演］

Chemical Evolution from the Interstellar Medium to the Solar System: Insight from the Analysis of Asteroidal Materials
大場康弘
ISM2023, 2023年11月10日
［招待講演］

Chemical evolution from molecular clouds to star-forming regions, and beyond
大場康弘
Chemical Processes in Solar-type Star-Forming Regions, 2023年06月08日
［招待講演］

Detection of nucleobases in extraterrestrial materials using liquid chromatography coupled with ultra high-resolution mass spectrometry
大場康弘
JPGU2023, 2023年
［招待講演］

Nucleobases in space: insights from meteorite analyses and laboratory experiments
大場康弘
計算アストロバイオロジー2022, 2022年11月11日
［招待講演］

星間塵表面における化学反応素過程研究の最前線
大場康弘
日本地球化学会第68回年会, 2021年09月07日, 口頭発表（招待・特別）
［招待講演］

Recent advances in analytical techniques for the identification of specific COMs in photochemically-processed interstellar ice analogs
Yasuhiro Oba
43rd COSPAR Scientific Assembly, 2021年01月31日, 英語, 口頭発表（招待・特別）
［招待講演］

H2S, why you no solid at 10 K? -Nonthermal desorption from interstellar icy grains
大場康弘
JPGU 2018 Meeting, 2018年05月22日, 英語, 口頭発表（招待・特別）
［招待講演］, ［国際会議］

Experimental studies on the surface reaction of hydrogen sulfide with deuterium atoms on amorphous solid water at 10 K
大場康弘
ACS Spring National Meeting, 2018年03月21日, 英語, 口頭発表（招待・特別）
［招待講演］, ［国際会議］

Formation of chiral glycine by surface reactions of normal glycine with deuterium atoms at 10 K
大場康弘
Astrophysical Ices in the Lab (AILab), 2016年03月08日, 英語, 口頭発表（招待・特別）
［招待講演］, ［国際会議］

Formation of H2O ice on cold interstellar grains: Reaction kinetics and the structure of ice
大場康弘
Center for Astrochemical Studies Seminar, 2015年10月13日, 英語, 口頭発表（招待・特別）
［招待講演］, ［国際会議］

Co-evolution of water and organics via surface reactions on interstellar grains
大場康弘
JPGU 2013 Meeting, 2013年05月22日, 日本語, 口頭発表（招待・特別）
［招待講演］, ［国内会議］

Formation of H₂O ice on cold interstellar grains: reaction kinetics and the structure of ice
Y. Oba
Workshop on Ice and Water Films, 2013年05月06日, 英語, 口頭発表（招待・特別）
Seoul National Univ., ［招待講演］, ［国際会議］

Structure of H₂O ice formed by surface reactions of oxygen molecules with hydrogen atoms at low temperatures
Y. Oba; N. Miyauchi; H. Hidaka; T. Chigai; N. Watanabe; A. Kouchi
12th International Conference on the Physics and Chemistry of Ice, 2010年09月, 英語
Sapporo, Hokkaido,Japan, ［招待講演］, ［国内会議］

Structure of H₂O ice formed by surface reactions of oxygen molecules with hydrogen atoms at low temperatures
Y. Oba; N. Miyauchi; H. Hidaka; T. Chigai; N. Watanabe; A. Kouchi
12th International Conference on the Physics and Chemistry of Ice, 2010年09月, 英語
Sapporo, Hokkaido,Japan, ［招待講演］, ［国内会議］

Formation of compact amorphous water ice by surface atomic reactions at low temperatures
A. Kouchi; Y. Oba; N. Miyahchi; H. Hidaka; T. Chigai; N. Watanabe
2010 Western Pacific Geophysics Meeting, 2010年06月, 英語
Taipei, Taiwan, ［招待講演］

Formation of compact amorphous H₂O ice by a reaction of hydrogen atoms with oxygen molecules at low temperatures
Y. Oba; N. Miyauchi; T. Chigai; H. Hidaka; N. Watanabe; A. Kouchi
Gordon Research Conferences, Matrix-Isolated Species, Physics & Chemistry Of, 2009年07月, 英語
Magdalen College, Oxford, UK

Formation of interstellar ice by low temperature surface atomic reactions
A. Kouchi; Y. Oba; N. Miyahchi; H. Hidaka; N. Watanabe
CRYO2009, 2009年07月, 英語
Sapporo,Hokkaido,Japan

Effective formation of H₂O by the H-addition to solid O₂ on amorphous D₂O ice
Y. Oba; N. Miyauchi; T. Chigai; H. Hidaka; N. Watanabe; A. Kouchi
Workshop on Interstellar Matter 2008, 2008年09月, 英語
Sapporo, Hokkaido,Japan

Incorporation of hydrous oxygen into insoluble organic matter (IOM) of Murchison
Y. Oba; H. Naraoka
71th Annual Meeting of the Meteoritical Society, 2008年07月, 英語
Matsue, Shimane,Japan

Isotopic variation of macromolecular organic matter from CM chondrites during hydrous pyrolysis
Y. Oba; H. Naraoka
31th Symposium on Antarctic Meteorites, 2007年06月, 英語
Tokyo, Japan

Carbon and hydrogen isotopic fractionations of organic compounds during UV degradation
Y. Oba; H. Naraoka
16th Annual V. M. Goldschmidt Conference, 2006年08月, 英語
Melbourne, Australia

Intramolecular carbon isotopic distribution of macromolecular organic matter in carbonaceous chondrites (CM)
Y. Oba; H. Naraoka
68th Annual Meeting of the Meteoritical Society, 2005年09月, 英語
Gatlinburg, TN, USA

Carbon and hydrogen isotopic compositions of acetic acid derived from macromolecular organic matter in the Murchison
Y. Oba; H. Naraoka
29th Symposium on Antarctic Meteorites, 2005年06月, 英語
Tokyo, Japan

A different behavior of hydrogen isotope exchange between two PAH isomers (fluoranthen and pyrene)
Y. Oba; H. Naraoka
13th Annual V. M. Goldschmidt Conference, 2003年09月
Kurashiki, Okayama, Japan

宇宙低温物質科学特論, 2024年, 修士課程, 理学院

地球外有機分子を材料とした原始地球環境での核酸合成
科学研究費助成事業
2025年04月01日 - 2028年03月31日
大場 康弘; 古賀 俊貴; 岡村 秀紀; 高野 淑識; Sameera W.M.C.
日本学術振興会, 基盤研究(A), 北海道大学, 25H00677

地球外物質中「プロト核酸塩基」の検出とその生成メカニズム解明
科学研究費助成事業
2023年04月01日 - 2025年03月31日
大場 康弘
日本学術振興会, 学術変革領域研究(A), 北海道大学, 23H03980

原始地球上での核酸合成に関する新展開：地球外からの材料供給の可能性に迫る
科学研究費助成事業 基盤研究(A)
2021年04月05日 - 2025年03月31日
大場 康弘; 高野 淑識
今年度は，（１）炭素質隕石から核酸塩基など，核酸の材料となりうる窒素複素環化合物の検出，（２）星間分子雲環境を模擬した光化学反応による分子生成およびその熱水反応による分子進化，という２点について研究を遂行した。
まず（１）の炭素質隕石からの窒素複素環化合物検出について，マーチソン隕石，マレー隕石，タギッシュレイク隕石という３種の炭素質隕石から，高温や強酸などを使用しない温和な抽出方法を駆使することにより，これまでに検出された例があったグアニンとアデニン，ウラシルだけでなく，シトシン，チミンというDNA，RNAに含まれる主要核酸塩基５種すべてを検出することに初めて成功した。さらにこれら５種以外にも５－メチルシトシンなど複数の核酸塩基が合計１８種検出された。先行研究では，炭素質隕石中では核酸塩基のバリエーションは乏しく，アミノ酸や炭化水素類と比べて検出された分子種が非常に少ないことが謎であったが，本研究によって核酸塩基類も多様な分子分布を示すことが明らかになった。これらの核酸塩基以外にも核酸の材料となりうる複素環化合物が検出され，これらの隕石中有機物が原始地球上での遺伝機能発現に寄与したと期待される。
（２）の模擬実験生成物について，水やメタノール，アンモニアを主成分とした混合氷を１０ケルビンに冷却し，真空紫外光を照射したのちに室温まで温度を上げると，黄色がかった複雑有機物の生成が確認された。その後，生成物をアモルファスケイ酸塩（MgSiO3）と水とともに１００℃で加熱すると，アミノ酸や複素環化合物など種々の有機化合物が検出された。これらのプロセスは星間分子雲での星誕生および惑星系形成後の熱水プロセスを模擬したものであり，宇宙における分子進化に重要な役割を担うことが強く示唆された。
日本学術振興会, 基盤研究(A), 北海道大学, 21H04501

ヘキサメチレンテトラミンがつなぐ星間分子雲と太陽系の分子進化
科学研究費助成事業
2021年09月10日 - 2023年03月31日
大場 康弘
今年度は，水，アンモニア，一酸化炭素（CO)，メタノールを含む模擬星間塵氷への真空紫外光照射によるヘキサメチレンテトラミン（HMT)生成実験をおこなった。その際，反応基板温度を10ケルビン（K)と77Kの2種類設定し，生成量の温度依存性を検証した。その結果，反応基板温度が低いほうがHMT生成量が低い（10Kの1/10程度）ことが明らかになった。反応基板温度の違いが及ぼす影響のうち，もっとも顕著なのがCOが基板上に吸着可能かどうかである。つまり，77KではCOが基板に吸着できず，光化学反応に関与できないことが，HMT生成を制約していると結論できる。
星間分子雲で生成したHMTが，星形成後の熱水プロセスでどのように変化するのかを明らかにするために，10Kでの光化学反応で作製したHMTを含む複雑有機物合物をアモルファスケイ酸塩粉末と水とともに100℃で加熱した。10日程度加熱すると大半のHMTは分解されてしまった。一方，アミノ酸をはじめとする種々の有機化合物がその加熱によって生成することが，液体クロマトグラフ－飛行時間型質量分析計による分析で確かめられた。従来の研究では，光化学反応で生成した複雑有機物を分析操作中に意図的に酸加水分解したとき，もしくはHMTをギ酸や酢酸など有機酸とともに加熱したときにアミノ酸生成が確認されていた。本研究では，光化学反応のみで生成した有機物を加熱するだけでアミノ酸が生成可能であることがわかった。これは，HMTが現実的な小惑星環境でもアミノ酸生成の材料となることを強く示唆した。
日本学術振興会, 学術変革領域研究(A), 北海道大学, 21H05414

宇宙における未知の分子進化プロセスの探求：可視光による光化学反応
科学研究費助成事業 挑戦的研究(萌芽)
2021年07月09日 - 2023年03月31日
大場 康弘
今年度は２種類の実験を行った。まず光学活性なアミノ酸であるアラニンに，様々な金属・鉱物の存在下，波長532nmの可視円偏光を照射して，アラニンの光学異性体組成が変化するか検証した。可視光照射ののち，アラニンを塩酸で抽出し，塩化チオニル，ブタノール，塩化ピバロイルなどの試薬を用いて化学的な処理を施した。最終的にガスクロマトグラフ質量分析計でアラニン存在量を分析した。用いた触媒としては直径10nm, 25nmの金チューブやダイヤモンド粉末，窒化炭素である。しかしいずれの条件でも可視光レーザーを最長80時間程度照射したものの，アラニンの光学異性体組成に明確な変化は見られなかった。
続いて，研究室の都合上，上記の実験で使っていた可視光レーザーシステムの使用を断念し，小型レーザーシステムを新たに構築した。そして可視光照射対象をアラニンからヘキサメチレンテトラミン（HMT)に変更した。HMT水溶液を作成し，これをサンプル基板に滴下後乾燥させ，真空チャンバー内で可視光レーザー（波長532nm or 785nm，いずれも10mW)を10日間照射した。その際，金属や鉱物ナノ粒子の存在の有無による変化の違いを検証した。触媒として窒化炭素を用いたときには光の照射によるHMTの変化は明確に検出されなかった。また，ガラス基板に蒸着した鉄ナノ粒子（直径50nm程度）上で同様の操作をおこなったものの，HMTに変化は見られなかった。一方，ガラス基板に直径20nm程度の金ナノ粒子を蒸着して，そのうえで同様の操作を行ったところ，金ナノ粒子非存在下では検出されない新たな生成物が検出された。現在その生成物の素性を解析中だが，表面プラズモン共鳴を利用した光化学反応がHMTで起きたことは間違いないだろう。
日本学術振興会, 挑戦的研究(萌芽), 北海道大学, 21K18639

星間塵表面における分子進化の解明：素過程からのアプローチ
科学研究費助成事業 特別推進研究
2017年04月25日 - 2022年03月31日
渡部 直樹; 大場 康弘; 杉本 敏樹; 中井 陽一
超高真空実験槽中に氷星間塵表面を擬似したアモルファス氷表面を作製し，紫外線照射で生成したのOHラジカルの表面拡散の活性化エネルギーを求めることに，世界で初めて成功した（渡部，宮崎，羽馬）。また，OHラジカルの吸着状態と脱離メカニズムを明らかにした。これらの成果には，新たに雇用した研究補助者（WMC Sameera）の量子化学計算によるところが大きい。この結果を発表すべく，論文の執筆を始めた。
星間塵表面物質のひとつである炭素質表面を，グラファイトディスクのレーザーアブレーションにより真空実験槽内でその場作製し，その構造と作製条件の依存性を，透過型電子顕微鏡を用いて調べ，いつでも最適な試料表面を作製するノウハウを確立した（柘植，木村）。
極低温超高真空原子間力顕微鏡の特性を調べた。観測する基板が9～10Kの極低温に到達すること，それを維持出来る熱負荷の確認を行った。極低温下でシリコン結晶を観測することができ基本的な運転を習熟した。（日高，香内）。
氷表面上に分子イオンが吸着した際の生成物を検出するイオンピックアップ装置の立ち上げを行った。冷凍基板および赤外分光計，イオン源を超高真空槽に設置し，極低温氷の作製など予備実験を行った（渡部，大場，中井）
杉本は京都大学から分子科学研究所への異動に伴い，装置の移設・再構築を行った。また，分光測定中の振動ノイズを軽減するため，希釈冷凍機から液体ヘリウム貯め込み式の冷却方式への転換作業を進めた。氷表面に対する和周波発生振動分光を行ったところ，表面特有の水素結合構造を有する液晶相が熱力学的な安定相として氷表面に存在することを発見した。
日本学術振興会, 特別推進研究, 北海道大学, 17H06087

星間分子から隕石有機物へ：重水素存在度を指標とした分子進化プロセス解明
若手研究（A)
2017年04月 - 2021年03月
大場康弘
研究代表者, 競争的資金

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
科学研究費助成事業 基盤研究(A)
2017年04月01日 - 2018年03月31日
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。
日本学術振興会, 基盤研究(A), 北海道大学, 17H01169

光化学反応による星間分子の重水素濃集度の変化
新学術領域研究（研究領域提案型：公募研究）
2016年04月 - 2018年03月
大場康弘
研究代表者, 競争的資金

星間塵表面での分子進化と新しい同位体分別機構
科学研究費助成事業 基盤研究(S)
2012年05月31日 - 2017年03月31日
渡部 直樹; 日高 宏; 大場 康弘; 羽馬 哲也; 香内 晃
星間分子雲における分子生成・進化・同位体分別（化学進化）を明らかにすることは、太陽系の物質起源を研究するうえで重要である。本研究では、化学進化の鍵を握る、極低温下における氷星間塵表面でのトンネル反応による分子生成・重水素濃集プロセスを定量的な実験で調べた。氷表面での水素原子拡散係数と拡散メカニズム、水分子などの基本分子や始原的有機分子の生成・重水素濃集の反応経路やと化学進化に果たす役割を明らかにした。
日本学術振興会, 基盤研究(S), 北海道大学, 24224012

星間分子雲における硫黄の化学進化
若手研究（A)
2014年04月 - 2017年03月
大場康弘
研究代表者, 競争的資金

氷生成過程のその場観察・構造解析のための極低温超高真空透過型電子顕微鏡の開発
科学研究費助成事業 基盤研究(A)
2013年10月21日 - 2016年03月31日
香内 晃; 日高 宏; 大場 康弘; 羽馬 哲也; 千貝 健; 渡部 直樹; 木村 勇気; 都丸 隆行
氷の構造（ミクロ～マクロ）を解析するための超高真空極低温透過型電子顕微鏡を開発した．鏡体内で制御された条件での氷の作製が可能であり，氷に紫外線を照射することもできる．
本装置を用いて以下の研究を行った．(1)アモルファス氷のミクロな欠陥構造を初めて直接観察した．(2)氷Ih，氷Icへ75-100Kで紫外線を照射することにより，氷XIが生成されることを発見した．一方，アモルファス氷では相転移は観察されなかった．(3)CO:H2O=10:1-50:1を10Kで蒸着しその後温度を上昇させCOを昇華させると，高密度アモルファス氷が生成されることを見出した．この方法をマトリックス昇華法と命名した．
日本学術振興会, 基盤研究(A), 北海道大学, 25247086

星間塵表面反応による有機分子の重水素濃集：炭素鎖伸長による濃集度の変化
新学術領域研究（研究領域提案型：公募研究）
2014年04月 - 2016年03月
大場康弘
研究代表者, 競争的資金

星間分子雲における極低温表面原子反応によるアミノ酸の重水素濃集機構の解明
科学研究費助成事業 研究活動スタート支援
2012年08月31日 - 2014年03月31日
大場 康弘
本研究では，星間分子雲における化学進化で重要な役割を担う星間塵表面反応による，アミノ酸の重水素濃集に関する研究をおこなった。もっとも単純なアミノ酸であるグリシンを超高真空反応チャンバー内に設置した反応基板（12K）に蒸着し，重水素原子と反応させた。FTIRやNMRで反応生成物を分析したところ，グリシンの重水素置換体の生成が確認された。反応には高い活性化エネルギーが存在するため，極低温での重水素置換体生成には量子力学的なトンネル効果が重要だと考えられる。本研究では，アミノ酸が星間分子雲における極低温表面原子反応によって重水素濃集可能であることを示した。
日本学術振興会, 研究活動スタート支援, 北海道大学, 24840001

星間分子雲における極低温表面原子反応によるアミノ酸の重水素農集機構の解明
研究活動スタート支援
2012年08月 - 2014年03月
大場康弘
研究代表者, 競争的資金

極低温星間塵表面原子反応によるアミノ酸の生成機構
科学研究費助成事業 特別研究員奨励費
2009年 - 2011年
大場 康弘
メチルアミンの部分重水素置換体,CH_3ND_2およびCD_3NH_2を用いて,それぞれをH原子およびD原子と反応させ,各置換基のH-DおよびD-H交換速度を求めた。メチルアミンのメチル基のH-D交換,D-H交換,そしてアミノ基のH-D交換,D-H交換速度定数をそれぞれRc_,Rc_,Rn_,Rn_とすると,Rc_D > Rc_ >> Rn_ > Rn_という関係が得られた。同じ置換基のH-DおよびD-H交換速度を比較すると,H-D交換,つまりD濃縮反応のほうが速いことが明らかになった。また,CH_3NH_2全体のH-D交換反応,およびCD_3ND_2全体のD-H交換反応の速度定数をそれぞれR_,R_,とすると,R_〓Rc_,R_〓Rc_という関係が成立した。これはメチル基の水素交換速度がメチルアミン全体の水素交換速度を支配していることを意味する。これは,メチル基・アミノ基の水素交換が同時に起きているためだといえる。
メチルアミンのD(H)濃縮反応は,D(H)原子によるH(D)引き抜き反応→D(H)原子付加反応によって進行すると考えられる。たとえば(1)CH_3NH_2 + D→CH_2NH_2 + HD,(2)CH_2NH_2 + D→CH_2DNH_2のように進む。反応(2)はラジカル同士の反応であるため,速やかに進む。一方,反応(1)には分子からH(D)原子を引き抜く際に,2000-5000Kというエネルギー障壁が存在する。～10Kという極低温では反応(1)に必要なエネルギーを得ることは難しく,熱的に反応は進行しない。したがって,反応(1)は量子的なトンネル効果によって進行したと結論できる。
本研究で,メチルアミンは水素同位体交換しやすい分子であることがわかった。これは,星間分子雲の重水素濃集モデルで見積もられている最大のD/H原子比(～0.05)と,R_R_の比(R_/R_たとえば～2at 10K)を考慮すると,星間分子雲でのメチルアミンは水素交換反応によってそのD/H比が10^<-2>オーダーであることを示唆する。これは,星間分子雲に存在するメタノールやホルムアルデヒドの高いD/H比(～10^<-2>-10^<-1>)に匹敵する。いまだメチルアミンの重水素置換体の存在は星間空間で確認されていないが,今後の発見が期待される。
日本学術振興会, 特別研究員奨励費, 北海道大学, 09J02374

地球外有機分子の多次元同位体組成解析による化学進化メカニズムの解明
科学研究費助成事業 特別研究員奨励費
2005年 - 2006年
大場 康弘
低分子有機化合物(酢酸、プロピオン酸、メタノール、アセトニトリル、ベンゼン、アセトン)に高圧水銀ランプから発せられる紫外線を照射し、その分解に伴う炭素・水素同位体分別を明らかにした。各化合物は紫外線照射時間とともに分解が進み、アセトンが最も早く分解した。また、酢酸とプロピオン酸もアセトンについで分解が早かった。これら3種類の化合物はその構造に炭素-酸素二重結合(カルボニル基)をもつことから、カルボニル基は本研究で用いた紫外線をより効率よく吸収することが示された。各化合物の半減期は17から550分であった。
各化合物は分解とともに炭素・水素同位体比ともに大きくなった。炭素同位体分別係数は0.9968から0.9875、水素同位体分別係数は0.9890から0.9406であった。分解速度の順序と炭素・水素同位体分別係数の大きさの順序には相関は見られず、化学的に安定な化合物が同位体的に安定であるというわけではないことが明らかになった。
分解に伴う同位体分別の大きさの順序が炭素、水素でまったく異なった。これは同位体分別のメカニズムが炭素と水素でまったく異なることを示唆する。例えば水素同位体分別の場合は、水素ラジカルなどの化学的に活性種が紫外線照射により生成し、それが化合物と反応することで分解・同位体比変化が起こるというメカニズムが想定されるが、炭素同位体分別の場合には考えにくい。したがって、分解のされやすさだけでなく、化学的に活性な分子種の種類や量にも同位体比変化は依存している可能性がある。
このように有機化合物の紫外線分解は、宇宙空間や地球大気中など紫外線に富む環境では有機化合物の同位体組成に影響を及ぼすひとつの要因となりうることが示された。
日本学術振興会, 特別研究員奨励費, 岡山大学, 05J03562

星間塵表面原子反応によるアミノ酸前駆物質の生成機構
若手研究（B)
大場康弘
研究代表者, 競争的資金