Measurements of Ortho-to-para Nuclear Spin Conversion of H2 on Low-temperature Carbonaceous Grain Analogs: Diamond-like Carbon and Graphite
Measurements of Ortho-to-para Nuclear Spin Conversion of H2 on Low-temperature Carbonaceous Grain Analogs: Diamond-like Carbon and Graphite
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DOI：
10.3847/1538-4357/ac2a33
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发表时间：
2021-09
期刊：
影响因子：
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通讯作者：
M. Tsuge;A. Kouchi;N. Watanabe
中科院分区：
文献类型：
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作者：
M. Tsuge;A. Kouchi;N. Watanabe
氢分子有两种核自旋异构体：正h2和对h2。正对对位比（OPR）已知会影响化学演化以及空间中的气体动力学。因此，了解天体物理环境中OPR变化的机制是很重要的。本文采用程序升温解吸和共振增强多光子电离的方法，研究了H2分子在类金刚石碳和石墨表面的核自旋转换过程。类金刚石表面的NSC时间常数在10 - 18 K和10 K时（3900±800 s）至18 K时（750±40 s）测定。在石墨表面观察到类似的NSC时间常数和温度依赖性，表明键基序（sp3或sp2杂化）对NSC速率的影响很小。
Hydrogen molecules have two nuclear spin isomers: ortho-H2 and para-H2. The ortho-to-para ratio (OPR) is known to affect chemical evolution as well as gas dynamics in space. Therefore, understanding the mechanism of OPR variation in astrophysical environments is important. In this work, the nuclear spin conversion (NSC) processes of H2 molecules on diamond-like carbon and graphite surfaces are investigated experimentally by employing temperature-programmed desorption and resonance-enhanced multiphoton ionization methods. For the diamond-like carbon surface, the NSC time constants were determined at temperatures of 10–18 K and from 3900 ± 800 s at 10 K to 750 ± 40 s at 18 K. Similar NSC time constants and temperature dependence were observed for a graphite surface, indicating that bonding motifs (sp3 or sp2 hybridization) have little effect on the NSC rates.