CH_3S自由基H迁移异构化及脱H_2反应的直接动力学研究

Direct Dynamics Studies on the Isomerization and H_2 Elimination Reaction of CH_3S

采用密度泛函方法(MPW1PW91)在6-311G(d,p)基组水平上研究了CH3S自由基H迁移反应CH3S→CH2SH(R1),脱H2反应CH3S→HCS+H2(R2)以及脱H2产物HCS异构化反应HCS→CSH(R3)的微观动力学机理.在QCISD(t)/6-311++G(d,p)//MPW1PW91/6-311G(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)分别计算了各反应在200～2000K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.结果表明,反应R1,R2和R3的势垒?E≠分别为160.69,266.61和241.63kJ/mol,R1为反应的主通道.低温下CH3S比CH2SH稳定,高温时CH2SH比CH3S更稳定.另外,速率常数计算结果显示,量子力学隧道效应在低温段对速率常数的计算有显著影响,而变分效应在计算温度段内对速率常数的影响可以忽略.

The isomerization reaction of CH3S→CH2SH （R 1）, H2 elimination reaction of CH3S→HCS ＋ H2 （R2） and the isomerization reaction of HCS→CSH （R3） have been studied by using the density functional theory. Geometries, harmonic vibrational frequencies of all stationary points and the minimum energy paths for the title reactions were calculated at the MPW1PW91 level in conjunction with the 6-311G（d,p） basis set. In order to obtain more reliable energies, higher level energy calculations for the stationary points and se- lected points were carried out at the QCISD（t）/6-311 ＋ ＋G（d,p）//MPW1PW91/6-311G（d,p）＋ZPE levels. The rate constants of the reactions were evaluated by means of the classical transition state theory, the canonical variational transition state theory, and canonical variational transition state theory incorporating small-curvature tunneling correction in the temperature range of 200-2000 K. The results show that the energy barriers of the reactions R1, R2 and R3 are 160.69, 266.61 and 241.63 kJ/mol, respectively, and the reaction R1 is the dominant reaction channel. CH3S radical is more stable than CH2SH in low temperature region, while the latter is more stable in high temperature region. The tunneling effect is significant and the variational effect is small for the calculated rate constants.