Zhang Rui Ming, Truhlar Donald G, Xu Xuefei
Center for Combustion Energy, Department of Energy and Power Engineering, and Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China.
Department of Chemistry, Chemical Theory Center, and Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, MN 55455-0431, USA.
Research (Wash D C). 2019 May 29;2019:5373785. doi: 10.34133/2019/5373785. eCollection 2019.
We calculated the kinetics of chemical activation reactions of toluene with hydroxyl radical in the temperature range from 213 K to 2500 K and the pressure range from 10 Torr to the high-pressure limit by using multistructural variational transition state theory with the small-curvature tunneling approximation (MS-CVT/SCT) and using the system-specific quantum Rice-Ramsperger-Kassel method. The reactions of OH with toluene are important elementary steps in both combustion and atmospheric chemistry, and thus it is valuable to understand the rate constants both in the high-pressure, high-temperature regime and in the low-pressure, low-temperature regime. Under the experimental pressure conditions, the theoretically calculated total reaction rate constants agree well with the limited experimental data, including the negative temperature dependence at low temperature. We find that the effect of multistructural anharmonicity on the partition functions usually increases with temperature, and it can change the calculated reaction rates by factors as small as 0.2 and as large as 4.2. We also find a large effect of anharmonicity on the zero-point energies of the transition states for the abstraction reactions. We report that abstraction of H from methyl should not be neglected in atmospheric chemistry, even though the low-temperature results are dominated by addition. We calculated the product distribution, which is usually not accessible to experiments, as a function of temperature and pressure.
我们使用多结构变分过渡态理论结合小曲率隧道效应近似法（MS-CVT/SCT）以及系统特定的量子 Rice-Ramsperger-Kassel 方法，计算了在 213 K 至 2500 K 的温度范围和 10 Torr 至高压极限的压力范围内甲苯与羟基自由基的化学活化反应动力学。OH 与甲苯的反应在燃烧和大气化学中都是重要的基元反应步骤，因此了解高压、高温条件下以及低压、低温条件下的速率常数都很有价值。在实验压力条件下，理论计算得到的总反应速率常数与有限的实验数据吻合良好，包括低温下的负温度依赖性。我们发现多结构非谐性对配分函数的影响通常随温度升高而增大，它能使计算得到的反应速率变化 0.2 至 4.2 倍不等。我们还发现非谐性对抽象反应过渡态的零点能有很大影响。我们报告称，在大气化学中，即使低温结果以加成反应为主，从甲基上抽象出 H 的反应也不应被忽视。我们计算了通常实验难以获得的产物分布随温度和压力的变化情况。
