CH3CH2S自由基H迁移异构化及裂解反应的理论研究

采用密度泛函方法(B3LYP)在6-311+G(d,p)基组水平上研究了CH3CH2S自由基H迁移异构化以及裂解反应的微观动力学机理. 在QCISD(T)/6-311++G(d,p)//B3LYP/6-311+G(d,p)+ZPE水平上进行了单点能校正. 利用经典过渡态理论(TST)与变分过渡态理论(CVT)分别计算了在200~2000 K温度区间内的速率常数kTST和kCVT, 同时获得了经小曲率隧道效应模型(SCT)校正后的速率常数kCVT/SCT. 研究结果表明, CH3CH2S自由基1,2-H迁移、1,3-H迁移、C—C键断裂和β-C—H键断裂反应的势垒ΔE≠分别为149.74, 144.34, 168.79和198.29 kJ/mol. 当温度低于800 K时, 主要发生1,2-H迁移反应, 高于1800 K时, 主要表现为C—C键断裂反应, 在1300—1800 K范围内, 1,3-H迁移反应是优势通道, 在计算的整个温度段内, β-C—H键断裂反应可以忽略.

Theoretical Studies on the CH3CH2S Radical Hydrogen Shift Isomerization and Dissociation Reaction

Density functional theory B3LYP/6-311+G(d,p) method was employed to reveal the micro-kine-tic character of the hydrogen shift isomerization and dissociation reaction of the CH3CH2S. In order to obtain more reliable energies, the single point calculations were carried out at the QCISD(T)/6-311++G(d,p) level of theory. The rate constants of the reactions were evaluated by means of the canonical variational transition-state theory(CVT) conjunction with small- curvature tunneling(SCT) correction over a wide range of temperature 200—2000 K at the QCISD(T)/6-311++G(d,p)//B3LYP/6-311+G(d,p) level. In this study, the potential barriers ΔE≠ of the 1,2-H shift, 1,3-H shift, C—C dissociation and β-C—H dissociation reactions of the CH3CH2S radical are 149.74, 144.34, 168.79 and 198.29 kJ/mol, respectively. The 1,2-H shift is the major reaction process when temperature is lower than 800 K, and C—C dissociation reaction became the dominant when temperature is higher than 1800 K, and 1,3-H shift is the major pathway when temperature is between 1300 and 1800 K. The β-C—H dissociaton reacton always play a minor role over the whole temperature region.