Field-Theodore Terri E, Taylor Peter R
School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, China.
Phys Chem Chem Phys. 2022 Aug 17;24(32):19184-19198. doi: 10.1039/d2cp00995a.
The molecular species CHO represents a striking example of an astrochemical conundrum. With more than 60 structural isomers theoretically possible, to date only acrolein (CHCHCHO) has been identified in the Sgr B2(N) region of the interstellar medium (ISM). The topography of the singlet potential energy surface is complicated, with three low-lying minima predicted to be almost isoenergetic: and -acrolein, and methylketene (CHCHCO). Our CCSD(T)/cc-pVTZ calculations confirm that methylketene is energetically lower than -acrolein, lying only 1.9 kJ mol above the -isomer, which is the global minimum. In this respect, methylketene is a promising candidate for interstellar observation. Unfortunately, however, despite several searches its astronomical detection has been unsuccessful. To this end, the key question is whether in fact methylketene exists as a discrete chemical entity in the ISM at all? In this paper, we present a detailed examination of the CHO potential energy surface, with specific focus on formation pathways. CCSD(T)/cc-pVTZ calculations enable a more elaborate interpretation of reaction mechanisms than was published hitherto. Our results show that -propargyl alcohol and and -allenol emerge as interesting new targets for observational astronomers in TMC-1: given the recent discovery of the propargyl radical in this region, barrierless product channels involving OH˙ lend support to their candidacy as possible interstellar species. Finally, this work provides accurate spectral data of these three potential molecules, to be used for searches in interstellar space.
分子物种CHO是天体化学难题的一个显著例子。理论上可能有60多种结构异构体，迄今为止，仅在星际介质（ISM）的人马座B2（N）区域中鉴定出丙烯醛（CHCHCHO）。单重态势能面的地形很复杂，预计有三个低势能极小值几乎等能：顺式和反式丙烯醛以及甲基乙烯酮（CHCHCO）。我们的CCSD（T）/cc-pVTZ计算证实，甲基乙烯酮在能量上低于反式丙烯醛，仅比全局最小值反式异构体高1.9 kJ/mol。在这方面，甲基乙烯酮是星际观测的一个有前景的候选物。然而，不幸的是，尽管进行了几次搜索，其天文探测仍未成功。为此，关键问题是甲基乙烯酮在ISM中是否真的作为一种离散的化学实体存在？在本文中，我们对CHO势能面进行了详细研究，特别关注其形成途径。CCSD（T）/cc-pVTZ计算能够对反应机理进行比以往发表的更为详尽的解释。我们的结果表明，对于TMC-1中的观测天文学家来说，β-炔丙醇和顺式及反式烯丙醇成为了有趣的新目标：鉴于最近在该区域发现了炔丙基自由基，涉及OH˙的无势垒产物通道支持它们作为可能的星际物种的候选资格。最后，这项工作提供了这三种潜在分子的精确光谱数据，用于在星际空间中的搜索。
