Elucidation of the unified mechanism of molecular nuclear-spin-conversion with use of rotationally resolved spectroscopy

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K05424
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 32010:Fundamental physical chemistry-related
• Research Institution: Japan Atomic Energy Agency
• Principal Investigator: Yamakawa Koichiro 国立研究開発法人日本原子力研究開発機構, 原子力科学研究部門 原子力科学研究所 先端基礎研究センター, 研究副主幹 (60633279)
• Co-Investigator(Kenkyū-buntansha): 福谷 克之 東京大学, 生産技術研究所, 教授 (10228900)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 核スピン転換

Outline of Final Research Achievements

Molecules including the hydrogen nuclei in the rotationally symmetric positions are classified into nuclear spin isomers, according to the quantum number of their resultant spin. In the present work, we targeted at the fundamental molecules of hydrogen, water, ammonia, and methane, and observed the interconversion between the nuclear spin isomers by using rotationally resolved spectroscopy. We isolated hydrogen in condensed layers of carbon dioxide, and detected weak infrared absorption by polarized hydrogen. The conversion rate was determined from its time development. In addition, we investigated the oxygen-isotope effect on the conversion rate of water molecules, and found the abnormal temperature dependence of the conversion rate of ammonia. Furthermore, we analyzed the time evolution of the infrared spectrum of crystalline methane on the basis of the nuclear spin conversion, and determined the assignments of absorption signals in a combination-tone region.

Free Research Field

分子分光

Academic Significance and Societal Importance of the Research Achievements

核スピン転換の研究は，分子と凝縮系との間の磁気相互作用とエネルギー授受の究明という基礎物理学的観点，水素の効率的な液化貯蔵に代表される産業的観点，そして宇宙における天体の熱履歴の解明という天文学的観点から，重要な意義を持つ．本研究で行った一連の実験によって，水素，水，アンモニア，メタンという基本的な分子の核スピン転換特性が明らかになり，転換メカニズムの理解が大きく進んだ．さらに，核スピン転換の解析がスペクトルを解釈する上でも有用であることが，本研究により示された．