Multistructural Variational Reaction Kinetics of the Simplest Unsaturated Methyl Ester: H-Abstraction from Methyl Acrylate by H, OH, CH3, and HO2 Radicals
Multistructural Variational Reaction Kinetics of the Simplest Unsaturated Methyl Ester: H-Abstraction from Methyl Acrylate by H, OH, CH3, and HO2 Radicals
复制标题
最简单不饱和甲酯的多结构变分反应动力学：通过 H、OH、CH3 和 HO2 自由基从丙烯酸甲酯中进行 H 抽象
DOI：
10.1021/acs.jpca.1c01788
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发表时间：
2021
影响因子：
2.9
通讯作者：
Shengnian Luo
中科院分区：
文献类型：
--
作者：
Wenrui Li;Jun Li;Hongbo Ning;Yanlei Shang;Shengnian Luo
本文从理论上研究了甲基丙烯酸甲酯(MA)与H/OH/CH3/O2自由基的抽氢反应动力学。对于这些反应，首先使用几个密度泛函计算了反应能和势垒高度，并与耦合团簇CCSD(T)-F12/Jun-cc-pVTZ基准计算进行了比较。结合M062X/MAUG-CC-pVTZ方法的电子结构计算，用多结构正则变分过渡态理论和小曲率隧穿方法计算了500K-2000K的反应速率常数，变分效应在0.56K到1.0K之间，多结构扭转非简谐因子在0.004~4.57K之间，隧道系数在0.50K~4.70K之间。值得注意的是，对于MA+OH/HO2体系，考虑到反应物与过渡态之间存在反应物络合物(RCS)，我们进一步比较了低压极限(LPL)动力学模型和预平衡模型下的速率常数。LPL动力学模型将反应视为一步反应，忽略了RCS，预平衡模型考虑了RCS，将反应视为两步反应。在燃烧温度范围内，两种模型计算的速率常数基本一致，但在较低温度下有明显差异。此外，我们测定了支化比作为温度的函数，发现在低温和高温范围内，OH和H自由基对甲基位置(S3)的抽提分别占主导地位。此外，我们还用计算出的氢抽提速率常数对动力学模型进行了修正，以模拟MA的点火延迟时间。修正后的模型模拟结果与实验结果吻合较好。本工作所确定的准确反应动力学有助于了解和预测不饱和甲酯的消耗、支化分数和着火性能。
The H-abstraction reaction kinetics of methyl acrylate (MA) + H/OH/CH3/HO2radicals have been investigated theoretically in the present work. For these reactions, the reaction energies and barrier heights are first computed using several density functionals and compared to the coupled cluster CCSD(T)-F12/jun-cc-pVTZ benchmark calculations. The M062X/maug-cc-pVTZ method shows the best performance with the smallest mean unsigned deviation (MUD) of 0.42 kcal mol–1. Combined with the electronic structure calculations using the M062X/maug-cc-pVTZ method, the multistructural canonical variational transition-state theory (MS-CVT) with small-curvature tunneling (SCT) is employed to calculate the reaction rate constants at 500–2000 K. The variational effect is between 0.56 and 1.0, the multistructural torsional anharmonicity factor ranges from 0.004 to 4.57, and the tunneling coefficient is in the range of 0.5–4.70. Notably, given the existence of reactant complexes (RCs) between reactants and transition states for the reaction systems MA + OH/HO2, we further compare the rate constants under the low-pressure limit (LPL) kinetic model, which treats the reaction as a single-step process and neglects RCs, and the pre-equilibrium model, which takes RCs into account in the reaction and treats the reaction as a two-step process. The rate constants calculated by these two models are similar within the combustion temperature range, and apparent differences occur at lower temperatures. In addition, we determine the branching ratios as a function of temperature and find that the methyl site (S3) abstractions by OH and H radicals are dominant in the low- and high-temperature ranges, respectively. Moreover, we update the kinetic model with the calculated H-abstraction rate constants to simulate the ignition delay times of MA. The simulations of the updated model are in good agreement with experimental results. The accurate reaction kinetics determined in this work are useful for the understanding and prediction of consumption branching fractions and ignition properties of the unsaturated methyl esters.