HNCS与C_2H(X^2Π)反应微观动力学的理论研究

Theoretical Study on the Mechanism and Dynamics for the Reaction of HNCS with C_2H(X^2Π) Radical

用量子化学密度泛函理论的UB3LYP/6-311+G鄢鄢方法和高级电子相关的UQCISD(T)/6-311+G鄢鄢方法研究了异硫氰酸(HNCS)与乙炔基自由基(C2H(X2Π))反应的微观机理.采用双水平直接动力学方法IVTST-M,获取反应的势能面信息,应用正则变分过渡态理论并考虑小曲率隧道效应,计算了在250～2500K温度范围内反应的速率常数.研究结果表明,HNCS与C2H(X2Π)反应为多通道、多步骤的复杂反应,共存在三个可能的反应通道,主反应通道为通过分子间H原子迁移,生成主要产物NCS+C2H2.反应速率常数随温度升高而增大,表现为正温度效应.速率常数计算中变分效果很小.在低温区隧道效应对反应速率的贡献较大,反应为放热反应.

The reaction mechanism of HNCS （isothiocyanic acid） and C2H（X^2π） radical has been investigated by using the density functional theory（DFT） at the B3LYP/6-311 ＋G^ ＊ ＊ level. The single point energies along the minimum energy path have been further refined at the UQCISD（T）/6-311＋G^＊＊ level. The dual-level direct dynamics method was employed to gain the information of potential energy surface for the reaction of HNCS with C2H（X^2π） radical. The rate constants were calculated over the temperature range of 250-2500 K by using variational transition state theory, and the small-curvature tunneling is included, The results show that the reaction mechanism of HNCS and C2H（X^2π） radical involves three path and NCS＋C2H2 are main products. It is found that the rate constants of the reaction are positively dependent on temperature. The variational effect for the rate constant calculation is very small in whole temperature range and the small-curvature tunnelling effect is only important in the lower temperature range. The reaction is exothermic.