Researcher Database

OBA YASUHIRO
Institute of Low Temperature Science Frontier Ice and Snow Science
Assistant Professor

Researcher Profile and Settings

Affiliation

  • Institute of Low Temperature Science Frontier Ice and Snow Science

Job Title

  • Assistant Professor

J-Global ID

Research Areas

  • Natural sciences / Space and planetary science

Academic & Professional Experience

  • 2015/04 - Today Hokkaido University Institute of Low Temperature Science
  • 2012/04 - 2015/03 Hokkaido University Institute of Low Temperature Science
  • 2009/04 - 2012/03 日本学術振興会特別研究員(PD)
  • 2008/04 - 2009/03 Hokkaido University Institute of Low Temperature Science
  • 2007/04 - 2008/03 University of Nevada-Reno (USA) 博士研究員

Research Activities

Published Papers

  • Hideyuki Nakano, Naoki Hirakawa, Yasuhiro Matsubara, Shigeru Yamashita, Takuo Okuchi, Kenta Asahina, Ryo Tanaka, Noriyuki Suzuki, Hiroshi Naraoka, Yoshinori Takano, Shogo Tachibana, Tetsyua Hama, Yasuhiro Oba, Yuki Kimura, Naoki Watanabe, Akira Kouchi
    Scientific Reports 10 7755  2020/12 [Refereed][Not invited]
  • Thanh Nguyen, Yasuhiro Oba, Takashi Shimonishi, Akira Kouchi, Naoki Watanabe
    ASTROPHYSICAL JOURNAL LETTERS 898 (2) 2041-8205 2020/08 [Refereed][Not invited]
     
    Phosphine (PH3), an important molecule for the chemistry of phosphorus (P)-bearing species in the interstellar medium (ISM) is considered to form primarily on interstellar grains. However, no report exists on the processes of PH(3)formation on grains. Here, we experimentally studied the reactions of hydrogen (H) atoms and PH(3)molecules on compact amorphous solid water, with a particular focus on the chemical desorption of PH(3)at 10-30 K. After exposure to H atoms for 120 minutes, up to 50% of solid PH(3)was lost from the icy surface. On the basis of experiments using deuterium atoms, it was concluded that the loss of PH(3)resulted from chemical desorption through the reactions PH3+ H -> PH2 + H(2)and/or PH2+ H -> PH3. The effective desorption cross-section was similar to 5 x 10(-17)cm(2), which is three times larger than that of hydrogen sulfide measured under similar experimental conditions. The present results suggest that the formation of PH3, and possibly PH(2)and PH, followed by their desorption from icy grains, may contribute to the formation of PN and PO in the gas phase, and thus may play a role in the P chemistry of the ISM.
  • Nucleobase synthesis in interstellar ices
    Y. Oba, Y. Takano, H. Naraoka, N. Watanabe, A. Kouchi
    Nature Communications 10 4413  2019/09 [Refereed][Not invited]
  • Physico-chemical behavior of hydrogen sulfide induced by reactions with H and D atoms on different types of ice surfaces at low temperature
    Y. Oba, T. Tomaru, A. Kouchi, N. Watanabe
    Astrophysical Journal 874 8pp  2019/04 [Refereed][Not invited]
  • 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 2018/06 [Refereed][Not invited]
  • Y. Oba, T. Tomaru, T. Lamberts, A. Kouchi, N. Watanabe
    Nature Astronomy 2 (3) 228 - 232 2397-3366 2018/03/01 [Refereed][Not invited]
     
    In molecular clouds at temperatures as low as 10 K, all species except hydrogen and helium should be locked in the heterogeneous ice on dust grain surfaces. Nevertheless, astronomical observations have detected over 150 different species in the gas phase in these clouds. The mechanism by which molecules are released from the dust surface below thermal desorption temperatures to be detectable in the gas phase is crucial for understanding the chemical evolution in such cold clouds. Chemical desorption, caused by the excess energy of an exothermic reaction, was first proposed as a key molecular release mechanism almost 50 years ago 1 . Chemical desorption can, in principle, take place at any temperature, even below the thermal desorption temperature. Therefore, astrochemical network models commonly include this process 2,3 . Although there have been a few previous experimental efforts 4-6, no infrared measurement of the surface (which has a strong advantage to quantify chemical desorption) has been performed. Here, we report the first infrared in situ measurement of chemical desorption during the reactions H + H2S → HS + H2 (reaction 1) and HS + H → H2S (reaction 2), which are key to interstellar sulphur chemistry 2,3 . The present study clearly demonstrates that chemical desorption is a more efficient process for releasing H2S into the gas phase than was previously believed. The obtained effective cross-section for chemical desorption indicates that the chemical desorption rate exceeds the photodesorption rate in typical interstellar environments.
  • Yasuhiro Oba, Yoshinori Takano, Hiroshi Naraoka, Akira Kouchi, Naoki Watanabe
    ASTROPHYSICAL JOURNAL 849 (2) 9pp  0004-637X 2017/11 [Refereed][Not invited]
     
    Hexamethylenetetramine (HMT) is a representative product after the photolysis of interstellar ice analogs containing methanol followed by warming-up to room temperature. Since interstellar methanol is often significantly enriched in deuterium (D), the HMT photoproduct is expected to inherit D atoms from deuterated methanol. However, D fractionation upon the formation of HMT is not well understood, especially when it is produced from partly deuterated methanol isotopologues such as CH2DOH and CH3OD. Here, we experimentally studied the composition of deuterated HMT (d(n)-HMT, where n is the number of D atoms) at the isotopologue level formed by the photolysis of ice mixtures containing deuterated methanol, CH2DOH or CH3OD, at 10 or 77 K. The analyses were performed using a state-of-the-art high-resolution mass spectrometer coupled with a compoundspecific separation technique. The formation of dn-HMT (n = 0-8) was confirmed under all experimental conditions. In addition, methyl-and hydroxyl-substituted HMT and their deuterated isotopologues were also obtained in the products. The deuterium enrichment was outstanding when CH2DOH was used rather than CH3OD, and when photolysis was performed at 77 K rather than 10 K. We found that the deuteration level of the formed HMT far exceeded that of the reactants under the present experimental conditions. These results obtained during stable isotope probing of deuterium strongly suggest that HMT can play a role as an organic pool of interstellar D atoms. These may be distributed into other chemical species through molecular evolution in space.
  • Shogo Tachibana, Akira Kouchi, Tetsuya Hama, Yasuhiro Oba, Laurette Piani, Iyo Sugawara, Yukiko Endo, Hiroshi Hidaka, Yuki Kimura, Ken-Ichiro Murata, Hisayoshi Yurimoto, Naoki Watanabe
    Science advances 3 (9) eaao2538  2017/09 [Refereed][Not invited]
     
    Interstellar ice is believed to be a cradle of complex organic compounds, commonly found within icy comets and interstellar clouds, in association with ultraviolet (UV) irradiation and subsequent warming. We found that UV-irradiated amorphous ices composed of H2O, CH3OH, and NH3 and of pure H2O behave like liquids over the temperature ranges of 65 to 150 kelvin and 50 to 140 kelvin, respectively. This low-viscosity liquid-like ice may enhance the formation of organic compounds including prebiotic molecules and the accretion of icy dust to form icy planetesimals under certain interstellar conditions.
  • Yasuhiro Oba, Naoki Watanabe, Akira Kouchi
    CHEMICAL PHYSICS LETTERS 662 14 - 18 0009-2614 2016/10 [Refereed][Not invited]
     
    We report an experimental study on the catalytic effect of solid water on the reactivity of hydrogen abstraction (H-abstraction) from dimethyl ether (DME) in the low-temperature solid DME-H2O complex. When DME reacted with deuterium atoms on a surface at 15-25 K, it was efficiently deuterated via successive tunneling H-abstraction and deuterium (D)-addition reactions. The 'effective rate constant for DME-H2O + D was found to be about 20 times smaller than that of pure DME + D. This provides the first evidence that the presence of solid water has a negative catalytic effect on tunneling H-abstraction reactions. (C) 2016 Elsevier B.V. All rights reserved.
  • Yasuhiro Oba, Kazuya Osaka, Takeshi Chigai, Akira Kouchi, Naoki Watanabe
    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 462 (1) 689 - 695 0035-8711 2016/10 [Refereed][Not invited]
     
    Ethanol (CH3CH2OH) is one of the most abundant complex organic molecules in star-forming regions. Despite its detection in the gas phase only, ethanol is believed to be formed by low temperature grain-surface reactions. Methanol, the simplest alcohol, has been a target for observational, experimental, and theoretical studies in view of its deuterium enrichment in the interstellar medium; however, the deuterium chemistry of ethanol has not yet been an area of focus. Recently, deuterated dimethyl ether, a structural isomer of ethanol, was found in star forming regions, indicating that deuterated ethanol can also be present in those environments. In this study, we performed laboratory experiments on the deuterium fractionation of solid ethanol at low temperatures through a reaction with deuterium (D) atoms at 10 K. Hydrogen (II)-D substitution, which increases the deuteration level, was found to occur on the ethyl group but not on the hydroxyl group. In addition, when deuterated ethanol (e.g. CD3CD2OD) solid was exposed to H atoms at 10 K, D-H substitution that reduced the deuteration level occurred on the ethyl group. Based on the results, it is likely that deuterated ethanol is present even under H-atom-dominant conditions in the interstellar medium.
  • Yasuhiro Oba, Yoshinori Takano, Naoki Watanabe, Akira Kouchi
    ASTROPHYSICAL JOURNAL LETTERS 827 (1) L18(7pp)  2041-8205 2016/08 [Refereed][Not invited]
     
    Deuterium (D) atoms in interstellar deuterated methanol might be distributed into complex organic molecules through molecular evolution by photochemical reactions in interstellar grains. In this study, we use a state-of-the-art high-resolution mass spectrometer coupled with a high-performance liquid chromatography system to quantitatively analyze amino acids and their deuterated isotopologues formed by the photolysis of interstellar ice analogs containing singly deuterated methanol CH2DOH at 10 K. Five amino acids (glycine, alpha-alanine, beta-alanine, sarcosine, and serine) and their deuterated isotopologues whose D atoms are bound to carbon atoms are detected in organic residues formed by photolysis followed by warming up to room temperature. The abundances of singly deuterated amino acids are in the range of 0.3-1.1 relative to each nondeuterated counterpart, and the relative abundances of doubly and triply deuterated species decrease with an increasing number of D atoms in a molecule. The abundances of amino acids increase by a factor of more than five upon the hydrolysis of the organic residues, leading to decreases in the relative abundances of deuterated species for alpha-alanine and beta-alanine. On the other hand, the relative abundances of the deuterated isotopologues of the other three amino acids did not decrease upon hydrolysis, indicating different formation mechanisms of these two groups upon hydrolysis. The present study facilitates both qualitative and quantitative evaluations of D fractionation during molecular evolution in the interstellar medium.
  • Yasuhiro Oba, Naoki Watanabe, Yoshihiro Osamura, Akira Kouchi
    CHEMICAL PHYSICS LETTERS 634 53 - 59 0009-2614 2015/08 [Refereed][Not invited]
     
    We report experimental evidence that chiral glycine (NH2CHDCOOH) is formed by the surface reaction of normal glycine (NH2CH2COOH) solid with deuterium (D) atom at 12K under the simulative conditions of interstellar molecular clouds. Chiral glycine formation is most likely initiated by the tunneling abstraction reaction of H atom by D atom followed by the addition of D atom to the glycine radical (NH2CHCOOH). Given that chiral glycine can form in such a primordial low-temperature environment, it might source molecular chirality as molecular clouds evolve into planetary systems. (C) 2015 Elsevier B.V. All rights reserved.
  • Yasuhiro Oba, Kazuya Osaka, Naoki Watanabe, Takeshi Chigai, Akira Kouchi
    FARADAY DISCUSSIONS 168 185 - 204 1359-6640 2014/08 [Refereed][Not invited]
     
    We performed laboratory experiments on the formation of water and its isotopologues by surface reactions of hydrogen peroxide (H2O2) with hydrogen (H) atoms and their deuterated counterparts (D2O2, D) at 10-30 K. High-purity H2O2 (>95%) was prepared in situ by the codeposition of molecular oxygen and H atoms at relatively high temperatures (45-50 K). We determined that the high-purity H2O2 solid reacts with both H and deuterium (D) atoms at 10-30 K despite the large activation barriers (similar to 2000 K). Moreover, the reaction rate for H atoms is approximately 45 times faster than that for D atoms at 15 K. Thus, the observed large isotope effect indicates that these reactions occurred through quantum tunneling. We propose that the observed HDO/H2O ratio in molecular clouds might be a good tool for the estimation of the atomic D/H ratio in those environments.
  • Yasuhiro Oba, Takeshi Chigai, Yoshihiro Osamura, Naoki Watanabe, Akira Kouchi
    METEORITICS & PLANETARY SCIENCE 49 (1) 117 - 132 1086-9379 2014/01 [Refereed][Not invited]
     
    We experimentally studied hydrogen (H)-deuterium (D) substitution reactions of solid methylamine (CH3NH2) under astrophysically relevant conditions. We also calculated the potential energy surface for the H-D substitution reactions of methylamine isotopologues using quantum chemical methods. Despite the relatively large energy barrier of more than 18kJmol(-1), CH3NH2 reacted with D atoms to yield deuterated methylamines at 10K, suggesting that the H-D substitution reaction proceeds through quantum tunneling. Deuterated methylamines reacted with H atoms as well. On the basis of present results, we propose that methylamine has potential for D enrichment through atomic surface reactions on interstellar grains at very low temperatures in molecular clouds. D enrichment would occur in particular in the methyl group of methylamine.
  • Y.Oba, N.Watanabe, T.Hama, K.Kuwahata, H.Hidaka, A.Kouchi
    The Astrophysical Journal 749 (1) 67 - (12pp) 2012 [Refereed][Not invited]
  • 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 0388-5321 2012 [Not refereed][Not invited]
  • 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 0386-4073 2011/12 [Refereed][Not invited]
  • Y.Oba
    Researches in Organic Geochemistry 27 103 - 115 1344-9915 2011/09 [Refereed][Not invited]
  • 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 [Refereed][Not invited]
  • Y.Oba, N.Watanabe, A.Kouchi, T.Hama, V.Pirronello
    The Astrophysical Journal 722 (2,Pt.1) 1598 - 1606 0004-637X 2010/10 [Refereed][Not invited]
  • Oba Y, Watanabe N, Kouchi A, Hama T, Pirronello V
    The Astrophysical Journal 712 (2,Pt.2) L174 - L178 0004-637X 2010/04 [Refereed][Not invited]
  • Eui-Seong Moon, Heon Kang, Yasuhiro Oba, Naoki Watanabe, Akira Kouchi
    ASTROPHYSICAL JOURNAL 713 (2) 906 - 911 0004-637X 2010/04 [Refereed][Not invited]
     
    We present direct evidence for ammonium ion (NH4+) formation through ultraviolet (UV) photolysis of NH3-H2O mixture ice that does not contain acids. NH4+ forms by the reaction of NH3 with protonic defects (H3O+) in the UV-photolyzed ice. Our observations may explain the deficient counter-anions in interstellar ice relative to the abundance of NH4+. Also, H3O+ may play an important role in the acid-base chemistry of interstellar ice in UV-irradiating environments. IR absorption results suggest that NH4+ is a potential contributor to the interstellar 6.85 mu m band but is not a dominant component.
  • 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 0009-2541 2010/01 [Refereed][Not invited]
     
    Rates of diel (24-h) biogeochemical processes in rivers and their effect on daily changes in the concentration of metals and metalloids have been well documented in the literature over the last 20 years. Investigations into the effects of these processes on aquatic systems and the underlying mechanisms that control the processes can significantly improve our understanding of how natural aquatic environments function and will respond to changing environmental conditions and anthropogenic impacts. Daily changes in the rates of biogeochemical processes have, more recently, been shown to influence the stable isotope composition of dissolved oxygen and dissolved inorganic carbon in natural waters. Here we present a comprehensive picture of the persistence and reproducibility of diel cycles of the (18)O composition of dissolved molecular oxygen (delta(18)O-DO) and the (13)C composition of dissolved inorganic carbon (delta(13)C-DIC) across five Montana, USA rivers investigated over a 4-year period. A mesocosm experiment showed the same behavior in delta(13)O-DO and delta(13)C-DIC as seen in riverine settings across light and dark periods. A cross plot of delta(18)O-DO and delta(13)C-DIC from each stream exhibits a clockwise elliptical pattern which is attributed to the daily changes in the balance of metabolic rates as well as air-water gas exchange. The amplitude of the change in the isotope composition is shown to be directly related to the trophic state of the river and a relationship between net productivity and diel changes in delta(18)O-DO and delta(13)C-DIC is presented. This relationship between trophic status with delta(18)O-DO, delta(13)C-DIC and production emphasizes the significance of how rates of biogeochemical processes in natural systems can influence the daily changes in the composition of surface waters. (c) 2009 Elsevier B.V. All rights reserved.
  • Kaneko, M, Oba Y, Naraoka, H
    Res.Org.Geochem. 26 73 - 79 2010 [Refereed][Not invited]
  • Oba Y, Poulson S.R
    ChemicalGeology 268 (3-4) 226 - 232 0009-2541 2009/11 [Refereed][Not invited]
  • Oba Y, Miyauchi N, Chigai T, Hidaka H, Watanabe N, Kouchi A
    The Astrophysical Journal 701 (1) 464 - 470 2009/07 [Refereed][Not invited]
  • N. Watanabe, A. Kouchi, H. Hidaka, Oba Y, N. Miyauchi
    Journal of Physics: Conference Series 194 (1) 012044  2009 [Refereed][Not invited]
  • 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 [Refereed][Not invited]
  • 大場 康弘, 宮内 直弥, 千貝 健, 日高 宏, 渡部 直樹, 香内 晃
    地球化学 43 117 - 131 0386-4073 2009 [Refereed][Not invited]
  • 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 [Refereed][Not invited]
  • Y.Oba, S.R.Poulson
    Geochimica et Cosmochimica Acta 73 (1) 13 - 24 0016-7037 2009 [Refereed][Not invited]
  • Y.Oba, H.Naraoka
    Meteoritics and Planetary Science 44 (7) 943 - 953 2009 [Refereed][Not invited]
  • A. Kouchi, Y. Oba, N. Miyauchi, H. Hidaka, N. Watanabe
    Cryobiology Elsevier {BV} 59 (3) 370  2009 [Refereed][Not invited]
  • Oba Y, Naraoka H
    Organicgeochemistry 39 (5) 501 - 509 0146-6380 2008 [Refereed][Not invited]
  • 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 2008 [Refereed][Not invited]
  • Yasuhiro Oba, Hiroshi Naraoka
    GEOCHEMICAL JOURNAL 41 (2) 103 - 110 0016-7002 2007 [Refereed][Not invited]
     
    Low molecular-weight carboxylic acids, such as acetic and propionic acids, are abundant organic compounds in carbonaceous chondrites, and are generally enriched in heavy stable isotopes (i.e., C-13 and D) relative to terrestrial organic compounds. In this study, we have determined carbon and hydrogen isotopic fractionation of acetic acid, and site-specific carbon isotopic fractionation of acetic acid, during degradation by ultraviolet (UV) light. Acetic acid became enriched in C-13 and D with increased UV exposure times. The isotopic fractionation factors (alpha) of total, methyl and carboxyl carbon of acetic acid were 0.9922, 1.0022 and 0.9823 respectively, and the alpha value for hydrogen was 0.9875. These results suggest that UV degradation could be a process for yielding C-13- and D-enrichnient of acetic acid in natural environments.
  • Y.Oba, H.Naraoka
    Meteoritics and Planetary Science 41 (8) 1175 - 1181 2006/08 [Refereed][Not invited]
  • Oba Y, Naraoka H
    Rapid Communications in Mass Spectrometry 20 (24) 3649 - 3653 0951-4198 2006 [Refereed][Not invited]
  • Y.Oba, H.Naraoka
    Researches in Organic Geochemistry 18 29 - 35 1344-9915 2003 [Refereed][Not invited]

Conference Activities & Talks

  • H2S, why you no solid at 10 K? -Nonthermal desorption from interstellar icy grains  [Invited]
    OBA YASUHIRO
    JPGU 2018 Meeting  2018/05
  • Experimental studies on the surface reaction of hydrogen sulfide with deuterium atoms on amorphous solid water at 10 K  [Invited]
    OBA YASUHIRO
    ACS Spring National Meeting  2018/03
  • Formation of chiral glycine by surface reactions of normal glycine with deuterium atoms at 10 K  [Invited]
    OBA YASUHIRO
    Astrophysical Ices in the Lab (AILab)  2016/03
  • Formation of H2O ice on cold interstellar grains: Reaction kinetics and the structure of ice  [Invited]
    OBA YASUHIRO
    Center for Astrochemical Studies Seminar  2015/10
  • Co-evolution of water and organics via surface reactions on interstellar grains  [Invited]
    OBA YASUHIRO
    JPGU 2013 Meeting  2013/05
  • Formation of H2O ice on cold interstellar grains: reaction kinetics and the structure of ice  [Invited]
    Y. Oba
    Workshop on Ice and Water Films  2013/05  Seoul National Univ.
  • Laboratory study of solid H2O formation trhough quantum tunneling reaction OH + H2 at 10 K  [Not invited]
    Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    Dynamical Phenomena at Surfaces: The Role of Complexity  2012/11  Leiden, Netherland
  • Water formation by OH + H2 on grain surfaces at 10 K: large isotope effects by quantum tunneling  [Not invited]
    Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    Workshop on Interstellar Matter 2012  2012/10
  • Deuterium fractionation of methylamine through atomic grain-surface reactions at low temperatures: implication for the possible D/H ratio in molecular clouds  [Not invited]
    Y. Oba, T. Chigai, N. Watanabe, A. Kouchi
    Workshop on Interstellar Matter 2012  2012/10  Sapporo, Hokkaido, Japan
  • Formation of solid H2O through surface reactions of H2 with OH radicals produced by microwave-induced H2O plasma  [Not invited]
    Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    Gordon Research Conference, Radiation Chemisty  2012/07  Andover, NH, USA
  • Surface chemical reactions to the formation of solid H2O and its isotopologues on interstellar grains at 10 K  [Not invited]
    Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    Asteroids, Comets, Meteors (ACM) 2012  2012/05  Niigata, JAPAN
  • Hydrogen isotope substitution of solid methylamine (CH3NH2) on a low-temperature surface  [Not invited]
    Y. Oba, N. Watanabe, T. Hama, K. Kuwahata, H. Hidaka, A. Kouchi
    Asteroids, Comets, Meteors (ACM) 2012  2012/05  Niigata, JAPAN
  • Low-temperature surface reactions of non-energetic OH radicals of astrophysical interest  [Not invited]
    Y. Oba, N. Watanabe, T. Hama, A. Kouchi, V. Pirronello
    SASP 2012  2012/01  Alpe d'Huez, France
  • Isotope effect on the formation of H2O isotopologues by quantum tunneling reactions of H2/HD/D2 with non-energetic OH/OD radicals at low temperatures  [Not invited]
    Y. Oba, N. Watanabe, A. Kouchi
    MATRIX 2011  2011/07  UBC, Vancouver, Canada
  • Sequential hydrogenation of molecular oxygen on cold surfaces: reaction kinetics and structure of formed H2O ice  [Not invited]
    Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
    IAU symposium 280, The Molecular Universe  2011/05  Toledo, Spain
  • Neutral radical-molecule reactions CO + OH on cold interstellar ices  [Not invited]
    Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    IAU symposium 280, The Molecular Universe  2011/05  Toledo, Spain
  • Experimental studies on surface reactions of CO molecules with cold OH radicals at 10-40 K  [Not invited]
    Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    Pacifichem 2010  2010/12  Honolulu, Hawaii, USA
  • Structure of H2O ice formed by surface reactions of oxygen molecules with hydrogen atoms at low temperatures  [Invited]
    Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
    12th International Conference on the Physics and Chemistry of Ice  2010/09  Sapporo, Hokkaido,Japan
  • Structure of H2O ice formed by surface reactions of oxygen molecules with hydrogen atoms at low temperatures  [Invited]
    Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
    12th International Conference on the Physics and Chemistry of Ice  2010/09  Sapporo, Hokkaido,Japan
  • Formation of CO2 and H2CO3 through non-energetic surface reactions at low temperatures  [Not invited]
    Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    Workshop on Interstellar Matter 2010  2010/09  Sapporo, Hokkaido,Japan
  • Formation of compact amorphous water ice by surface atomic reactions at low temperatures  [Invited]
    A. Kouchi, Y. Oba, N. Miyahchi, H. Hidaka, T. Chigai, N. Watanabe
    2010 Western Pacific Geophysics Meeting  2010/06  Taipei, Taiwan
  • Formation of compact amorphous water ice by surface atomic reactions at low temperatures  [Invited]
    A. Kouchi, Y. Oba, N. Miyahchi, H. Hidaka, T. Chigai, N. Watanabe
    2010 Western Pacific Geophysics Meeting  2010/06  Taipei, Taiwan
  • Surface reactions of CO molecules with OH radicals at low temperatures  [Not invited]
    Y. Oba, N. Watanabe, A. Kouchi, T. Hama, V. Pirronello
    2010 Western Pacific Geophysics Meeting  2010/06  Taipei, Taiwan
  • Surface reactions of hydrogen atoms with oxygen molecules at low temperatures: A potential route for the H2O formation in space  [Not invited]
    Y. Oba, N. Miyauchi, H. Hidaka, T. Chigai, N. Watanabe, A. Kouchi
    Horiba-ISSP International Symposium on "Hydrogen and water in condensed matter physics"  2009/10  Chiba, Japan
  • Formation of compact amorphous H2O ice by a reaction of hydrogen atoms with oxygen molecules at low temperatures  [Not invited]
    Y. Oba, N. Miyauchi, T. Chigai, H. Hidaka, N. Watanabe, A. Kouchi
    Gordon Research Conferences, Matrix-Isolated Species, Physics & Chemistry Of  2009/07  Magdalen College, Oxford, UK
  • Formation of interstellar ice by low temperature surface atomic reactions  [Not invited]
    A. Kouchi, Y. Oba, N. Miyahchi, H. Hidaka, N. Watanabe
    CRYO2009  2009/07  Sapporo,Hokkaido,Japan
  • Effective formation of H2O by the H-addition to solid O2 on amorphous D2O ice  [Not invited]
    Y. Oba, N. Miyauchi, T. Chigai, H. Hidaka, N. Watanabe, A. Kouchi
    Workshop on Interstellar Matter 2008  2008/09  Sapporo, Hokkaido,Japan
  • Incorporation of hydrous oxygen into insoluble organic matter (IOM) of Murchison  [Not invited]
    Y. Oba, H. Naraoka
    71th Annual Meeting of the Meteoritical Society  2008/07  Matsue, Shimane,Japan
  • Isotopic variation of macromolecular organic matter from CM chondrites during hydrous pyrolysis  [Not invited]
    Y. Oba, H. Naraoka
    31th Symposium on Antarctic Meteorites  2007/06  Tokyo, Japan
  • Carbon and hydrogen isotopic fractionations of organic compounds during UV degradation  [Not invited]
    Y. Oba, H. Naraoka
    16th Annual V. M. Goldschmidt Conference  2006/08  Melbourne, Australia
  • Intramolecular carbon isotopic distribution of macromolecular organic matter in carbonaceous chondrites (CM)  [Not invited]
    Y. Oba, H. Naraoka
    68th Annual Meeting of the Meteoritical Society  2005/09  Gatlinburg, TN, USA
  • Carbon and hydrogen isotopic compositions of acetic acid derived from macromolecular organic matter in the Murchison  [Not invited]
    Y. Oba, H. Naraoka
    29th Symposium on Antarctic Meteorites  2005/06  Tokyo, Japan
  • A different behavior of hydrogen isotope exchange between two PAH isomers (fluoranthen and pyrene)  [Not invited]
    Y. Oba, H. Naraoka
    13th Annual V. M. Goldschmidt Conference  2003/09  Kurashiki, Okayama, Japan

MISC

  • E. Bianchi, C. J. Chandler, C. Ceccarelli, C. Codella, N. Sakai, A. López-Sepulcre, L. T. Maud, G. Moellenbrock, B. Svoboda, Y. Watanabe, T. Sakai, F. Ménard, Y. Aikawa, F. Alves, N. Balucani, M. Bouvier, P. Caselli, E. Caux, S. Charnley, S. Choudhury, M. De Simone, F. Dulieu, A. Durán, L. Evans, C. Favre, D. Fedele, S. Feng, F. Fontani, L. Francis, T. Hama, T. Hanawa, E. Herbst, T. Hirota, M. Imai, A. Isella, I. Jiménez-Serra, D. Johnstone, C. Kahane, B. Lefloch, L. Loinard, M. J. Maureira, S. Mercimek, A. Miotello, S. Mori, R. Nakatani, H. Nomura, Y. Oba, S. Ohashi, Y. Okoda, J. Ospina-Zamudio, Y. Oya, J. Pineda, L. Podio, A. Rimola, D. Segura Cox, Y. Shirley, V. Taquet, L. Testi, C. Vastel, S. Viti, N. Watanabe, A. Witzel, C. Xue, Y. Zhang, B. Zhao, S. Yamamoto  2020/07/20  [Not refereed][Not invited]
     
    The study of hot corinos in Solar-like protostars has been so far mostly limited to the Class 0 phase, hampering our understanding of their origin and evolution. In addition, recent evidence suggests that planet formation starts already during Class I phase, which, therefore, represents a crucial step in the future planetary system chemical composition. Hence, the study of hot corinos in Class I protostars has become of paramount importance. Here we report the discovery of a hot corino towards the prototypical Class I protostar L1551 IRS5, obtained within the ALMA Large Program FAUST. We detected several lines from methanol and its isopotologues ($^{13}$CH$_{\rm 3}$OH and CH$_{\rm 2}$DOH), methyl formate and ethanol. Lines are bright toward the north component of the IRS5 binary system, and a possible second hot corino may be associated with the south component. The methanol lines non-LTE analysis constrains the gas temperature ($\sim$100 K), density ($\geq$1.5$\times$10$^{8}$ cm$^{-3}$), and emitting size ($\sim$10 au in radius). All CH$_{\rm 3}$OH and $^{13}$CH$_{\rm 3}$OH lines are optically thick, preventing a reliable measure of the deuteration. The methyl formate and ethanol relative abundances are compatible with those measured in Class 0 hot corinos. Thus, based on the present work, little chemical evolution from Class 0 to I hot corinos occurs.
  • Inversion of surface voltage on H2O films affecting sublimation of CO underlayer
    Atsuki Ishibashi, Yasuhiro Oba, Tetsuya Hama, Akira Kouchi, Naoki Watanabe  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  258-  2019/08  [Not refereed][Not invited]
  • Reaction experiments on H exposure of solid methanol at low temperatures
    Yukiko Yarnall, Hiroshi Hidaka, Yasuhiro Oba, Tetsuya Hama, Akira Kouchi, Naoki Watanabe  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  255-  2018/03  [Not refereed][Not invited]
  • 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  [Not refereed][Not invited]
  • Role of quantum tunneling for the formation of H2O by reaction of H-2 with OH on interstellar grains
    Yasuhiro Oba, Naoki Watanabe, Tetsuya Hama, Kazuaki Kuwahata, Hiroshi Hidaka, Akira Kouchi  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  247-  2014/03  [Not refereed][Not invited]
  • 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  [Refereed][Not invited]
  • Laboratory investigations of physico-chemical processes occurring in icy mantles on interstellar dust grains
    V. Pirronello, M. Accolla, T. Hama, H. Hidaka, A. Kouchi, G. Manico, Y. Oba, N. Watanabe  Physics and Chemistry of ice 2010  361  -368  2011  [Refereed][Not invited]
  • N. Watanabe, A. Kouchi, H. Hidaka, Y. Oba, N. Miyauchi  XXVI INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS  194-  012044  2009  [Refereed][Not invited]
     
    Reactions of atomic hydrogen with CO and O-2 on amorphous solid water (ASW), relevant to chemical evolution on cosmic ice dust, were experimentally investigated at around 10 K. Successive addition of hydrogen atoms to CO and O-2 produces H2CO, CH3OH, and H2O2, H2O, respectively. At such low temperatures, some of hydrogen additions such as H + CO -> HCO proceed via tunneling reactions rather than thermally-activated reactions. Effective reaction rates and isotope effect of the tunneling reactions to produce HCO and H2O were measured. The surface of ASW was found to enhance the effective rate of hydrogen addition to CO at relatively higher temperatures, namely around 20 K.
  • 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  [Refereed][Not invited]
  • Incorporation of hydrous oxygen into insoluble organic matter (IOM) of murchison
    Yasuhiro Oba, Hiroshi Naraoka  METEORITICS & PLANETARY SCIENCE  43-  (7)  A119  -A119  2008/07  [Not refereed][Not invited]

Awards & Honors

  • 2017/12 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 
    受賞者: 大場康弘
  • 2010 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 
    受賞者: 大場康弘

Research Grants & Projects

  • 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)
    Date (from‐to) : 2017/04 -2021/03 
    Author : 大場康弘
  • 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)
    Date (from‐to) : 2016/04 -2018/03 
    Author : 大場康弘
  • 星間分子雲における硫黄の化学進化
    若手研究(A)
    Date (from‐to) : 2014/04 -2017/03 
    Author : 大場康弘
  • 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)
    Date (from‐to) : 2014/04 -2016/03 
    Author : 大場康弘
  • 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
    Date (from‐to) : 2012/08 -2014/03 
    Author : 大場康弘
  • 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)
    Author : 大場康弘


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