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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Predicted Chemical Activation Rate Constants for HO2 + CH2NH: The Dominant Role of a Hydrogen-Bonded Pre-reactive Complex
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Predicted Chemical Activation Rate Constants for HO2 + CH2NH: The Dominant Role of a Hydrogen-Bonded Pre-reactive Complex

机译：预测的HO2 + CH2NH的化学活化速率常数：氢键预反应复合物的主导作用

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摘要

The reaction of methanimine (CH2NH) with the hydroperoxy (HO2) radical has been investigated by using a combination of ab initio and density functional theory (CCSD(T)/CBSB7//B3LYP+Dispersion/CBSB7) and master equation calculations based on transition state theory (TST). Variational TST was used to compute both canonical (CVTST) and microcanonical (mu VTST) rate constants for barrierless reactions. The title reaction starts with the reversible formation of a cyclic prereactive complex (PRC) that is bound by similar to 11 kcal/mol and contains hydrogen bonds to both nitrogen and oxygen. The reaction path for the entrance channel was investigated by a series of constrained optimizations, which showed that the reaction is barrierless (i.e., no intrinsic energy barrier along the path). However, the variations in the potential energy, vibrational frequencies, and rotational constants reveal that the two hydrogen bonds are formed sequentially, producing two reaction flux bottlenecks (i.e., two transition states) along the reaction path, which were modeled using W. H. Miller's unified TST approach. The rate constant computed for the formation of the PRC is pressure dependent and increases at lower temperatures. Under atmospheric conditions, the PRC dissociates rapidly and its lifetime is too short for it to undergo significant bimolecular reaction with other species. A small fraction isomerizes via a cyclic transition state and subsequent reactions lead to products normally expected from hydrogen abstraction reactions. The kinetics of the HO2 + CH2NH reaction system differs substantially from the analogous isoelectronic reaction systems involving C2H4 and CH2O, which have been the subjects of previous experimental and theoretical studies.
机译：通过从头算和密度泛函理论（CCSD（T）/ CBSB7 // B3LYP + Dispersion / CBSB7）结合基于过渡的主方程计算，研究了甲胺（CH2NH）与氢过氧基（HO2）自由基的反应状态理论（TST）。变体TST用于计算无障碍反应的规范（CVTST）和微规范（μVTST）速率常数。标题反应从可逆形成环状预反应性络合物（PRC）开始，该环状预反应性络合物的结合力接近11 kcal / mol，并包含与氮和氧的氢键。通过一系列约束优化研究了入口通道的反应路径，这表明反应是无障碍的（即沿路径没有内在的能量屏障）。但是，势能，振动频率和旋转常数的变化表明，两个氢键是顺序形成的，沿反应路径产生了两个反应通量瓶颈（即两个过渡态），这是使用WH Miller统一的TST建模的方法。计算PRC形成的速率常数与压力有关，并且在较低温度下会增加。在大气条件下，PRC迅速解离，其寿命太短，无法与其他物种发生明显的双分子反应。一小部分通过环状过渡态异构化，随后的反应生成通常从氢提取反应中预期的产物。 HO2 + CH2NH反应系统的动力学与涉及C2H4和CH2O的类似等电子反应系统有很大的不同，后者已成为先前实验和理论研究的主题。

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