甲硫醇和氢原子反应的从头算直接动力学

利用双水平直接动力学方法对反应CH3SH+H的微观机理和动力学性质进行了理论研究.对于此反应的三个反应通道,即—SH和—CH3基团上的两个氢提取通道及一个取代通道,在MP2/6-311+G(d,p)水平上优化得到了各稳定点的结构及振动频率,并在G3(MP2)水平上进行了单点能量计算以获得更精确的能量信息;在此基础上运用结合小曲率隧道效应校正的变分过渡态理论(CVT/SCT)计算了各反应通道在220-1000 K温度区间的速率常数.计算结果表明提取—SH基团上H的反应通道R1在整个反应温度区间都是主要通道,而随着温度的升高,低温下的次要反应通道——取代通道R3变得越来越重要,并且在高温下将成为一个竞争的反应通道;提取—CH3基团上H的反应通道(R2)由于具有较高的反应能垒,因而,其对总反应速率常数的贡献可以忽略.计算得到的总反应速率常数与已有的实验值符合得很好,进而我们预测了该反应在220-1000 K温度范围内速率常数的表达式为:k=5.00×10-18T2.39exp(-119.81/T),为将来的实验研究提供参考.

Direct Ab initio Dynamics on the Reaction of Methanethiol and Hydrogen Atom

We smdied the reaction of CH_3SH+H theoretically using a dual-level direct dynamics method.Three reaction channels:two H-abstraction(from the-SH and-CH_3 groups) and one substitution channels,were found.Optimized geometries,frequencies,and energies of the stationary points as well as extra points along the minimum energy path were calculated at the MP2/6-311+G(d,p)level of theory.The potential energy profiles were then refined by single-point energy calculations at the G3(MP2) level.Furthermore,the rate constants of all three channels were evaluated by canonical variational transition state theory(CVT) with the small-curvature tunneling effect conection(SCT) over the wide temperature range of 220-1000 K These calculations show that H-abstraction from the-SH group(R1)is the major channel for the title reaction over the whole temperature range.The substitution channel(R3)is a minor pathway at low temperatures and becomes more important as the temperature increases.This would be a competitive channel at high temperature while the contribufion of H-abstraction from the-CH_3 group(R2)to the overall rate constant is almost negligible because of its high energy barrier.The calculated CVT/SCT rate constants agree well with the available experimental values.The three-parameter rate-temperature expression for the total reaction over the whole temperature range of 220-1000 K is shown to be k=5.00×10~(-18)T~(2.39)exp(-119.81/T),which may be a useful expression for future experiments.