Emtiaz Shahnewaz M, Toriello Francis, He Jiao, Vidali Gianfranco
Physics Department, Syracuse University, Syracuse, New York 13244, United States.
Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany.
J Phys Chem A. 2022 Mar 31;126(12):1973-1979. doi: 10.1021/acs.jpca.2c00287. Epub 2022 Mar 18.
Mid-infrared studies of fundamental modes of ices of pure CH and its mixtures with polar (HO) and nonpolar (e.g., N) molecules are essential in order to learn the state of aggregation and thermal history of ices present in the interstellar medium and outer solar system bodies. Such data will be useful in the interpretation of observational data from the James Webb Space Telescope. Using an ultrahigh vacuum apparatus, we conducted reflection-absorption infrared spectroscopy measurements in the mid-IR range of pure methane ice and methane-containing ice mixtures of interest to interstellar and solar system ice chemistry, e.g., with HO and N molecules. We found that nuclear spin conversion (NSC) in solid methane and its crystalline structures is affected─in different ways─by the presence of HO and N. Specifically, we found a relationship between the thickness and the solid-state ordering transformation in methane thin films. This new study of the NSC of pure CH ice and of the CH:HO ice mixture at 7 K is carried out in relation to the segregation of HO using the ν and ν IR inactive modes of methane. The diffusion of N and CH in the CH:N ice mixture with temperature cycling has been studied to obtain the relationship between IR features and the state of aggregation of the ice.
对纯CH冰及其与极性分子（如HO）和非极性分子（如N）混合物的基本模式进行中红外研究，对于了解星际介质和外太阳系天体中冰的聚集状态和热历史至关重要。这些数据将有助于解释詹姆斯·韦布空间望远镜的观测数据。我们使用超高真空装置，对纯甲烷冰以及对星际和太阳系冰化学感兴趣的含甲烷冰混合物（例如与HO和N分子的混合物）在中红外范围内进行了反射吸收红外光谱测量。我们发现，固体甲烷及其晶体结构中的核自旋转换（NSC）会受到HO和N的存在的影响，且影响方式不同。具体而言，我们发现了甲烷薄膜厚度与固态有序转变之间的关系。这项关于7K下纯CH冰和CH:HO冰混合物的NSC的新研究，是利用甲烷的ν和ν红外非活性模式，针对HO的偏析进行的。通过对CH:N冰混合物中N和CH随温度循环的扩散进行研究，以获得红外特征与冰的聚集状态之间的关系。
