A new type of chemical reaction within icy grains

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01139
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Hokkaido University
• Principal Investigator: Masashi Tsuge 北海道大学, 低温科学研究所, 助教 (60454211)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 原子拡散 / 化学進化 / 氷星間塵 / 星間分子雲 / 炭素原子

Outline of Final Research Achievements

In the chemical evolution processes occurring within low temperature molecular clouds, it has been demonstrated that chemical reactions on icy grain surface play significant roles. Recently, we found that hydrogen atoms can penetrate into ice mantles and, therefore, they can induce chemical processes without photons and cosmic rays.The aims of this work were as follows: One is to quantify the penetration depths of H-atoms into porous and nonporous amorphous solid water (ASW). The other is to investigate whether atoms other than hydrogen can penetrate into ice or not.
We found that hydrogen atoms penetrate more than 30 nm into porous-ASW and 2-3 nm into nonporous-ASW, where the latter type of ASW is considered relevant to molecular cloud conditions. Carbon atoms were found to diffuse on the surface of ASW at temperatures 20-40 K, indicating that they can penetrate into ASW through cracks.

Free Research Field

物理化学

Academic Significance and Societal Importance of the Research Achievements

星間分子雲内での標準的な化学進化モデルでは、氷表面に吸着する原子種は氷内部における分子生成に影響を与えないとされてきた。我々が見出した「氷内部への原子の侵入」という全く新しい反応プロセスは「光や宇宙線を必要としない氷内部の分子進化プロセス」と言い換えることができ、既存の極低温分子雲における分子進化モデルに大きな変更を要請するという学術的意義を持つ。
本研究で、一部の炭素原子は極低温の条件下でも氷表面を動き回ることを明らかした。本発見は、氷微粒子上で炭素原子が様々な分子種と化学反応を起こし大きな有機分子を生成しうることを示唆しており、宇宙における複雑有機分子形成メカニズムの解明に大きく寄与する。