Zasimov Pavel V, Sanochkina Elizaveta V, Tyurin Daniil A, Feldman Vladimir I
Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia.
Phys Chem Chem Phys. 2023 Aug 23;25(33):21883-21896. doi: 10.1039/d3cp02834h.
Ethanol (CHOH) is one of the most common alcohol molecules observed in various space media (molecular clouds, star formation regions, and, highly likely, interstellar ices), where it is exposed to light and ionizing radiation, leading to more complex organic molecules and eventually to the biologically important species. To better understand the radiation-induced evolution of ethanol molecules in icy media, we have examined the transformations of isolated CHOH and CDOH under the action of X-rays and vacuum ultraviolet (VUV) radiation in solid inert matrices (Ne, Ar, Kr, and Xe) at 4.4 K using Fourier transform infrared (FTIR) spectroscopy. The results obtained with X-ray irradiation demonstrate the formation of a variety of radiolysis products corresponding to dehydrogenation (CHCHOH˙, CHCHO, CHCHOH, CHCO˙, HCCO-H, HCCO, HCCO˙, CCO) and C-C bond rupture (HCO, HCO˙, CO, CH, and CH˙). The absorptions of the CHCHOH˙ radical related to the CCO stretching (the bands at 1249.1, 1247.0, 1246.2, and 1245.1 cm, in Ne, Ar, Kr, and Xe, respectively) were first tentatively characterized on the basis of comparison with available computational data. In addition, the CH⋯HO complex, which corresponds to dehydrogenation, was found followed by C-O bond cleavage. The results were confirmed by experiments with isotopic substitution. It was found that dehydrogenation strongly predominated in a xenon matrix, while skeleton bond rupture is more feasible in neon and argon. The matrix effect was attributed to a significant role of "hot" reaction channels in neon and argon, which are efficiently quenched due to relaxation in more polarizable xenon. The VUV photolysis (185 nm) in Ar and Xe matrices yields a similar set of products, except for CHCHOH˙ and CHCHOH, which were not found (the nonobservation of the former species may be explained by its efficient secondary photolysis). The plausible mechanisms of product formation and astrochemical implications of the results are discussed.
乙醇（CH₃CH₂OH）是在各种空间介质（分子云、恒星形成区域，极有可能还有星际冰）中观测到的最常见的酒精分子之一，在这些介质中它会受到光和电离辐射的作用，从而形成更复杂的有机分子，并最终形成具有生物学重要性的物种。为了更好地理解冰介质中乙醇分子的辐射诱导演化，我们使用傅里叶变换红外（FTIR）光谱研究了在4.4 K的固体惰性基质（Ne、Ar、Kr和Xe）中，孤立的CH₃CH₂OH和CD₃CD₂OH在X射线和真空紫外（VUV）辐射作用下的转变。X射线辐照得到的结果表明形成了多种辐解产物，对应于脱氢反应（CH₂CHOH˙、CH₂CHO、CH₂CHOH、CH₂CO˙、HCCO-H、HCCO、HCCO˙、CCO）和C-C键断裂（HCO、HCO˙、CO、CH₃、CH˙）。与CCO伸缩相关的CH₂CHOH˙自由基的吸收（在Ne、Ar、Kr和Xe中分别位于1249.1、1247.0、1246.2和1245.1 cm⁻¹处的谱带）首先通过与现有计算数据比较进行了初步表征。此外，发现了对应于脱氢反应的CH⋯HO络合物，随后是C-O键断裂。同位素取代实验证实了这些结果。发现在氙基质中脱氢反应占主导，而在氖和氩中骨架键断裂更易发生。基质效应归因于氖和氩中“热”反应通道的重要作用，由于在极化率更高的氙中弛豫，这些通道被有效淬灭。在Ar和Xe基质中的VUV光解（185 nm）产生了一组类似的产物，但未发现CH₂CHOH˙和CH₂CHOH（未观察到前一种物质可能是由于其有效的二次光解）。讨论了产物形成的可能机制以及结果的天体化学意义。
