物理化学学报 >> 2010, Vol. 26 >> Issue (01): 183-187.doi: 10.3866/PKU.WHXB20100132

量子化学及计算化学 上一篇    下一篇

甲硫醇和氢原子反应的从头算直接动力学

王永霞, 段雪梅, 王钦, 刘靖尧   

  1. 吉林大学理论化学研究所, 理论化学计算国家重点实验室, 长春 130023
  • 收稿日期:2009-09-25 修回日期:2009-11-09 发布日期:2009-12-29
  • 通讯作者: 刘靖尧 E-mail:ljy121@jlu.edu.cn

Direct Ab initio Dynamics on the Reaction o fMethanethiol and Hydrogen Atom

WANG Yong-Xia, DUAN Xue-Mei, Wang Qin, LIU Jing-Yao   

  1. State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, P. R. China
  • Received:2009-09-25 Revised:2009-11-09 Published:2009-12-29
  • Contact: LIU Jing-Yao E-mail:ljy121@jlu.edu.cn

摘要:

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.

关键词: 直接动力学, 从头算, G3(MP2), 速率常数, 变分过渡态理论

Abstract:

We studied the reaction of CH3SH+H theoretically using a dual-level direct dynamics method. Three reaction channels: two H-abstraction (from the —SH and —CH3 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 correction (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 contribution of H-abstraction fromthe—CH3 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=5.00×10-18T2.39exp(-119.81/T), which may be a useful expression for future experiments.

Key words: Direct dynamics, Ab initio, G3(MP2), Rate constant, Canonical variational transition state theory

MSC2000: 

  • O641