C(3P) + CH3OCH3 反应的低温动力学研究：速率常数、氢原子产物产率和天体化学意义,ACS Earth and Space Chemistry

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C(3P) + CH3OCH3 反应的低温动力学研究：速率常数、氢原子产物产率和天体化学意义
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2024-04-11 , DOI: 10.1021/acsearthspacechem.4c00014
Kevin M. Hickson ₁ , Jean-Christophe Loison ₁ , Valentine Wakelam ₂

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处于基电子态的原子碳 C( ³ P) 预计在致密分子云的演化过程中以高丰度存在。因此，它与其他星际物种的反应可能会对这些区域的化学成分产生强烈影响。在此，我们报告了 C( ³ P) 与二甲醚 CH ₃ OCH ₃之间反应的研究结果，该反应最近在暗云 TMC-1 中检测到。使用连续超音速流反应器进行实验来研究该反应的动力学，该反应器分别采用脉冲激光光解和脉冲激光诱导荧光来产生和检测原子自由基。该过程的速率常数在 50 至 296 K 之间测量，同时还在 75-296 K 范围内对产物原子氢产率进行了额外测量。为了更好地理解实验结果，使用统计速率理论来计算相同温度范围内的速率常数，并提供对主要产品渠道的了解。这些模拟基于 C ₃ H ₆ O 分子基三重态的量子化学计算，使我们能够获得潜在势能表面的最重要特征。测量的速率常数随着温度下降而增加，在 50 K 时达到k _{C + CH ₃ OCH ₃} = 7.5 × 10 ^–11 cm ³ s ^–1的值，而测得的低 H 原子产率支持了理论预测：反应产物为 CH ₃ + CH ₃ + CO。使用致密星际云的气体颗粒模型，采用速率常数k的表达式，测试了该反应对星际 CH ₃ OCH ₃和相关物质丰度的影响。( T ) = α( T /300) ^β，其中 α = 1.27 × 10 ^–11且 β = -1.01。这些模拟预测，C( ³ P) + CH ₃ OCH ₃反应使早期和中期云龄的气相CH ₃ OCH ₃丰度降低一个数量级以上。

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A Low-Temperature Kinetic Study of the C(3P) + CH3OCH3 Reaction: Rate Constants, H Atom Product Yields, and Astrochemical Implications

Atomic carbon in its ground electronic state, C(³P), is expected to be present at high abundances during the evolution of dense molecular clouds. Consequently, its reactions with other interstellar species could have a strong influence on the chemical composition of these regions. Here, we report the results of an investigation of the reaction between C(³P) and dimethyl ether, CH₃OCH₃, which was recently detected in dark cloud TMC-1. Experiments were performed to study the kinetics of this reaction using a continuous supersonic flow reactor employing pulsed laser photolysis and pulsed laser-induced fluorescence for atomic radical generation and detection, respectively. Rate constants for this process were measured between 50 and 296 K, while additional measurements of the product atomic hydrogen yields were also performed over the 75–296 K range. To better understand the experimental results, statistical rate theory was used to calculate rate constants over the same temperature range and to provide insight on the major product channels. These simulations, based on quantum chemical calculations of the ground triplet state of the C₃H₆O molecule, allowed us to obtain the most important features of the underlying potential energy surface. The measured rate constant increases as the temperature falls, reaching a value of k_{C+CH₃OCH₃} = 7.5 × 10^–11 cm³ s^–1 at 50 K, while the low measured H atom yields support the theoretical prediction that the major reaction products are CH₃ + CH₃ + CO. The effects of this reaction on the abundances of interstellar CH₃OCH₃ and related species were tested using a gas-grain model of dense interstellar clouds, employing an expression for the rate constant, k(T) = α(T/300)^β, with α = 1.27 × 10^–11 and β = −1.01. These simulations predict that the C(³P) + CH₃OCH₃ reaction decreases gas-phase CH₃OCH₃ abundances by more than an order of magnitude at early and intermediate cloud ages.

更新日期：2024-04-11

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