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Rapid Ortho-to-para Nuclear Spin Conversion of H2 on a Silicate Dust Surface

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Title: Rapid Ortho-to-para Nuclear Spin Conversion of H2 on a Silicate Dust Surface
Authors: Tsuge, M Browse this author
Namiyoshi, T Browse this author
Furuya, K Browse this author
Yamazaki, T Browse this author
Kouchi, A Browse this author
Watanabe, N Browse this author
Issue Date: 26-Feb-2021
Publisher: The American Astronomical Society
Journal Title: The Astrophysical Journal
Volume: 908
Issue: 2
Start Page: 234
Publisher DOI: 10.3847/1538-4357/abd9c0
Abstract: The H2 molecule has two nuclear spin isomers, the so-called ortho and para isomers. Nuclear spin conversion (NSC) between these states is forbidden in the gas phase. The energy difference between the lowest ortho and para states is as large as 14.7 meV, corresponding to ~170 K. Therefore, each state of H2 differently affects not only the chemistry but also the macroscopic gas dynamics in space; thus, the ortho-to-para abundance ratio (OPR) of H2 has significant impacts on various astronomical phenomena. For a long time, the OPR of nascent H2 upon formation on dust grains has been assumed to have a statistical value of 3 and to gradually equilibrate in the gas phase at the temperature of the circumstances. Recently, the NSC of H2 was experimentally revealed to occur on water ice at very low temperatures and thus incorporated into gas–dust chemical models. However, H2 molecules should form well before dust grains are coated by water ice. Information about how the OPR of H2 behaves on bare silicate dust before ice-mantle formation is lacking. Knowing the influence of the OPR of H2 is desirable, if the OPR changes even on a bare silicate surface within an astronomically meaningful timescale. We report the first laboratory measurements of the NSC of H2 physisorbed on amorphous silicate (Mg2SiO4) at temperatures up to 18 K. The conversion was found to occur very rapidly.
Rights: This is the Accepted Manuscript version of an article accepted for publication in Astrophysical journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at 10.3847/1538-4357/abd9c0.
Type: article (author version)
Appears in Collections:低温科学研究所 (Institute of Low Temperature Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 柘植 雅士

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