自动反应路径搜索揭示了星际 CH3OCH3 和 HCOOCH3 的能量有利合成,ACS Earth and Space Chemistry

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自动反应路径搜索揭示了星际 CH3OCH3 和 HCOOCH3 的能量有利合成
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2023-08-17 , DOI: 10.1021/acsearthspacechem.3c00117
Yu Komatsu _{1,

2} , Kenji Furuya ₂

Affiliation

最近的天文观测表明，星际复杂有机分子（COM）即使在寒冷环境（~10 K）中也存在，而传统上在高质量和低质量附近的热气体（≳100 K）中检测到了各种星际COM。质量原恒星。然而，每个星际 COM 的形成途径仍然很大程度上不清楚。在这项工作中，我们证明了基于过渡态理论的自动反应路径搜索不需要预先确定的路径，有助于研究气相中星际 COM 的形成路径。对电子基态的详尽研究有助于阐明低温下 COM 的复杂化学形成途径。在这里，我们研究了二甲醚（CH ₃ OCH ₃）和甲酸甲酯（HCOOCH ₃），它们经常在恒星形成区域的冷和热气体中检测到。我们通过中性物质之间的反应确定了CH ₃ OCH ₃的无障碍放热形成路径；CH ₃ O + CH ₃ → H ₂ CO···CH ₄ → CH ₃ OCH ₃是我们的自动反应路径搜索构建的大型化学网络中最有效的路径，与之前的研究相当。对于 HCOOCH ₃，我们获得了中性物质之间反应引发的复杂途径；HCOO和CH ₃生成HCOOCH ₃及其异构体无需外加能量。_{然而，我们还确定了产生CO 2} + CH ₄和CH ₃ COOH的竞争反应分支，这比形成HCOOCH ₃更有效。_{因此，与CH 3} OCH ₃形成相比，通过中性物质之间的反应气相形成HCOOCH ₃的效率不高。

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The Automated Reaction Pathway Search Reveals the Energetically Favorable Synthesis of Interstellar CH3OCH3 and HCOOCH3

Recent astronomical observations have shown that interstellar complex organic molecules (COMs) exist even in cold environments (∼10 K), while various interstellar COMs have conventionally been detected in hot gas (≳100 K) in the vicinity of high-mass and low-mass protostars. However, the formation pathway of each interstellar COM remains largely unclear. In this work, we demonstrate that an automated reaction path search based on transition state theory, which does not require predetermined pathways, is helpful for investigating the formation pathways of interstellar COMs in the gas phase. The exhaustive search within the electronic ground states helps elucidate the complex chemical formation pathways of COMs at low temperatures. Here we examine the formation pathways of dimethyl ether (CH₃OCH₃) and methyl formate (HCOOCH₃), which are often detected in the cold and hot gas of star-forming regions. We have identified a barrierless and exothermic formation path of CH₃OCH₃ by reaction between neutral species; CH₃O + CH₃ → H₂CO···CH₄ → CH₃OCH₃ is the most efficient path in the large chemical network constructed by our automated reaction path search and is comparable to those of previous studies. For HCOOCH₃, we obtain complex pathways initiated from reactions between neutral species; HCOO and CH₃ generate HCOOCH₃ and its isomers without external energy. However, we also identified competing reaction branches producing CO₂ + CH₄ and CH₃COOH, which would be more efficient than the formation of HCOOCH₃. Thus, the gas-phase formation of HCOOCH₃ through reactions between neutral species would not be efficient compared to CH₃OCH₃ formation.

更新日期：2023-08-17

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