Perrero Jessica, Enrique-Romero Joan, Martínez-Bachs Berta, Ceccarelli Cecilia, Balucani Nadia, Ugliengo Piero, Rimola Albert
Departament de Química, Universitat Autònoma de Barcelona, Bellaterra, 08193 Catalonia, Spain.
Dipartimento di Chimica and Nanostructured Interfaces and Surfaces (NIS) Centre, Università degli Studi di Torino, via P. Giuria 7, 10125 Torino, Italy.
ACS Earth Space Chem. 2022 Mar 17;6(3):496-511. doi: 10.1021/acsearthspacechem.1c00369. Epub 2022 Mar 7.
Ethanol (CHCHOH) is a relatively common molecule, often found in star-forming regions. Recent studies suggest that it could be a parent molecule of several so-called interstellar complex organic molecules (iCOMs). However, the formation route of this species remains under debate. In the present work, we study the formation of ethanol through the reaction of CCH with one HO molecule belonging to the ice as a test case to investigate the viability of chemical reactions based on a "radical + ice component" scheme as an alternative mechanism for the synthesis of iCOMs, beyond the usual radical-radical coupling. This has been done by means of DFT calculations adopting two clusters of 18 and 33 water molecules as ice models. Results indicate that CHCHOH can potentially be formed by this proposed reaction mechanism. The reaction of CCH with HO on the water ice clusters can be barrierless (because of the help of boundary icy water molecules acting as proton-transfer assistants), leading to the formation of vinyl alcohol precursors (HCCOH and CHCHOH). Subsequent hydrogenation of vinyl alcohol yielding ethanol is the only step presenting a low activation energy barrier. We finally discuss the astrophysical implications of these findings.
乙醇（CH₃CH₂OH）是一种相对常见的分子，常在恒星形成区域被发现。最近的研究表明，它可能是几种所谓星际复杂有机分子（iCOMs）的母体分子。然而，该物种的形成途径仍存在争议。在本工作中，我们研究了通过CCH与一个属于冰的HO分子反应来形成乙醇，以此作为一个测试案例，以研究基于“自由基 + 冰成分”方案的化学反应作为合成iCOMs的替代机制的可行性，这一机制不同于常见的自由基 - 自由基耦合。这是通过采用由18个和33个水分子组成的两个团簇作为冰模型的密度泛函理论计算来完成的。结果表明，CH₃CH₂OH有可能通过这种提出的反应机制形成。CCH与水冰团簇上的HO反应可以是无势垒的（由于边界冰水分子作为质子转移辅助剂的帮助），导致形成乙烯醇前体（H₂CCOH和CH₃CHOH）。随后乙烯醇氢化生成乙醇是唯一呈现低活化能垒的步骤。我们最后讨论了这些发现的天体物理学意义。
