Recent astronomical observations of both isomers E and Z of imines such as cyanomethanimine, ethanimine and 2-propyn-1-imine, have revealed that the abundances in the ISM of these isomers differ by factors of ~3-10. Several theories have been proposed to explain the observed behavior, but none of them successfully explains the [E]/[Z] ratios. In this work we present a detailed study of the kinetics of the one-step E-Z isomerization reactions of cyanomethanimine, ethanimine and 2-propyn-1-imine under interstellar conditions (in the 10-400 K temperature range). This reaction was previously thought to be non-viable in the ISM due to its associated high-energy barrier (about 13,000 K). In this Letter, we show that considering the multidimensional small curvature tunneling approximation, the tunneling effect enables the isomerization even at low temperatures. This is due to the fact that the representative tunneling energy lies in the vibrational ground state of the least stable isomer up to approximately 150 K, making the reaction constants of the isomerization from the least stable to the most stable isomer basically constant. The predicted [E]/[Z] ratios are almost the same as those reported from the astronomical observations for all imines observed. This study demonstrates that the [E]/[Z] ratio of imines in the ISM strongly depends on their relative stability.
Isomers in Interstellar Environments (I): The Case of Z- and E-Cyanomethanimine
在这项工作中，我们提出的Z-和E-氰基甲亚胺（HNCHCN），这两者都是可能的前体的核碱基腺嘌呤的化学研究的结果。对氢原子参与的反应进行了量子化学从头计算。我们发现，H + Z/E-HNCHCN导致H-加成以及H-$_2$ -提取的反应通过类似的短程势垒进行，双分子速率系数为$\sim10^{-17}$ cm $^{3}$ s $^{-1}$。这些结果随后被纳入天体化学模型，并用于模拟巨大的分子云G+0.693。从这些模型中获得的计算丰度与以前的观测数据进行了比较，发现是在良好的协议，与$\sim3$的预测[Z/E]比-略小于以前推导出的值$6.1\pm2.4$。我们发现，在我们的模拟中的[Z/E]比主要是由于离子分子的破坏率驱动的两个构象的不同的永久偶极子。基于这些结果，我们提出了一个通用的经验法则，估计在星际环境中的异构体的丰度。
Formation of HNC and HCN isomers in molecular plasmas revealed by frequency comb and quantum cascade laser spectroscopy
Leibniz Institute for Plasma Science and Technology (INP)（莱布尼兹等离子体科学与技术研究所）；Department of Mathematics and Physics, University of Campania “Luigi Vanvitelli”（坎帕尼亚路易吉范维泰利大学数学与物理系）；Italian Aerospace Research Centre (CIRA)（意大利航空航天研究中心）
Gas-phase chemistry of $\mathrm{C}_3\mathrm{H}_3^+$: a key building block for carbon mass growth in space
Université Paris-Saclay（巴黎萨克雷大学）；CNRS（法国国家科学研究中心）；Institut des Sciences Moléculaires d’Orsay（奥赛分子科学学院）；Université Bordeaux（波尔多大学）；Bordeaux INP（波尔多国立应用理工学院）；ISM, UMR 5255（波尔多分子科学研究所，联合研究单位5255）；SOLEIL（索莱尔同步辐射中心）；Institut de Chimie Physique, UMR8000（物理化学研究所，联合研究单位8000）；Department of Physics, University of Trento（特伦托大学物理系）
A theoretical investigation of the reaction between the amidogen, NH, and the ethyl, C2H5, radicals: a possible gas-phase formation route of interstellar and planetary ethanimine
