Tan Ting, Yang Xueliang, Ju Yiguang, Carter Emily A
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Phys Chem Chem Phys. 2016 Feb 14;18(6):4594-607. doi: 10.1039/c5cp07282d.
The kinetics of hydrogen abstraction by five radicals (H, CH3, O((3)P), OH, and HO2) from a biodiesel surrogate, methyl propanoate (MP), is theoretically investigated. We employ high-level ab initio quantum chemistry methods, coupled-cluster singles and doubles with perturbative triples correction (CCSD(T)) and multi-reference singles and doubles configuration interaction (MRSDCI) with the Davidson-Silver (DS) correction, and obtain chemically accurate reaction energetics. Overall, MRSDCI + DS predicts comparable energetics to CCSD(T) for MP + H/CH3/O/OH. The rate constants are computed using transition state theory (TST-Rice-Ramsperger-Kassel-Marcus theory) in conjunction with the separable-hindered-rotor approximation, variable reaction coordinate TST, and the multi-structure all-structure (MS-AS) approach. A simplified method, semi-multi-structure, is also employed for MP + OH/HO2, and the rate coefficients with this less expensive method are in good agreement with the results obtained with the MS-AS method. The fitted modified Arrhenius expressions are provided over a temperature range of 250 to 2000 K. The predicted rate coefficients for MP + OH agree remarkably well with experimental data over a wide temperature range. Branching ratio analysis of all the studied reactions shows that abstractions of the secondary H atoms within MP are expected to dominate the consumption of fuel at low temperatures, and the contributions of abstractions from the two methyl groups increase with temperature for all abstracting radicals.
从理论上研究了5种自由基（H、CH₃、O((³)P)、OH和HO₂）从生物柴油替代物丙酸甲酯（MP）中夺取氢的动力学。我们采用高水平的从头算量子化学方法，即耦合簇单双激发并带有微扰三激发校正（CCSD(T)）以及带有戴维森 - 西尔弗（DS）校正的多参考单双激发组态相互作用（MRSDCI），并获得化学精度的反应能量学。总体而言，对于MP + H/CH₃/O/OH反应，MRSDCI + DS预测的能量学与CCSD(T)相当。速率常数使用过渡态理论（TST - 赖斯 - 兰斯伯格 - 卡塞尔 - 马库斯理论）结合可分离受阻转子近似、变反应坐标TST以及多结构全结构（MS - AS）方法进行计算。对于MP + OH/HO₂反应，还采用了一种简化方法，即半多结构方法，并且这种成本较低方法得到的速率系数与MS - AS方法得到的结果吻合良好。在250至2000 K的温度范围内给出了拟合的修正阿仑尼乌斯表达式。在很宽的温度范围内，MP + OH反应预测的速率系数与实验数据非常吻合。对所有研究反应的分支比分析表明，在低温下，MP中仲氢原子的夺取预计主导燃料的消耗，并且对于所有夺取自由基，来自两个甲基的夺取贡献随温度升高而增加。
