羟基自由基与乙烯反应的化学动力学模拟

使用电子结构理论计算和直接动力学模拟对羟基自由基与乙烯反应体系进行了理论研究．在高水平的CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVDZ上获得了包括羟基加成和氢抽取在内的多种反应通道的准确势能面信息，并在此基础上对OH+C₂H₄发展了一套准确性较高的MSINDO半经验哈密顿参数．特定反应参数哈密顿(SRP-MSINDO)能准确的再现高水平从头算结果．在2～10 kcal/mol的碰撞能应用SRP-MSINDO对OH+C₂H₄反应进行了直接准经典轨线模拟，获得的反应截面表明羟基加成反应为主导地位．另外，激发函数的模拟结果表明羟基加成是一个无势垒的捕获过程，而氢抽取则对应活化过程，这与两条反应通道的过渡态能量紧密相关．研究发现对OH+C₂H₄发展准确的半经验哈密顿需要考虑弥散矫正，这对准确描述分子间的长程吸引尤为重要

Chemical Dynamics Simulations of the Hydroxyl Radical Reaction with Ethene

We present a theoretical study of the reaction of the hydroxyl radical with ethene using electronic structure calculations and direct-dynamics simulations. High-accuracy electronic structure calculations at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVDZ level have been carried out to characterize the representative regions of the potential energy surface of various reaction pathways, including OH-addition and H-abstraction. These ab initio calculations have been employed to derive an improved set of parameters for the MSINDO semiempirical Hamiltonian specific to the OH+C₂H₄ reaction. The specific-reaction-parameter Hamilto-nian captures the ab initio data accurately, and has been used to perform direct quasiclas-sical trajectory simulations of the OH+C₂H₄ reaction at collision energies in the range of 2?10 kcal/mol. The calculated cross sections reveal that the OH-addition reaction domi-nates at all energies over H-abstraction. In addition, the excitation function of addition is reminiscent of a barrierless capture process, while that for abstraction corresponds to an activated one, and these trends can be connected to the transition-state energies of both reactions. We note that the development of an accurate semiempirical Hamiltonian for the OH+C₂H₄ reaction in this work required the inclusion of empirical dispersion corrections, which will be important in future applications for which long-range intermolecular attraction becomes significant