SiF_2自由基与异硫氰酸反应机理的理论研究

Theoreticalstudy of the reaction mechanism for SiF_2 radical with isothiocyanic acid

采用密度泛函理论B3LYP方法研究了SiF2自由基与异硫氰酸(HNCS)的反应机理,并在B3LYP/6-311++G**水平上对反应物、中间体、过渡态进行了全几何参数优化,通过频率分析和内禀反应坐标(IRC)确定中间体和过渡态的真实性.为了得到更精确的能量值,又用CCSD(T)/6-311++G**方法计算了在B3LYP/6-311++G**水平优化后的各个驻点的相对能量.根据统计热力学及用Winger校正的Eyring过渡态理论,利用自编程序,计算不同温度下低势垒反应的平衡常数和速率常数,并且通过电子密度拓扑分析讨论了化学反应过程中主要化学键的生成和断裂.计算结果表明,单重态的SiF2自由基与HNCS反应有6条可能的反应通道,其中反应通道SiF2+HNCS→IM1→TS1→IM2HSiF2NCS(P1)为主反应通道.

The reaction mechanism of SiF2 radical with isothiocyanic acid（HNCS） has been investigated by a B3LYP method of density functional theory, while the geometries and harmonic vibration frequen- cies of reactants, intermediates, transition states and products have been calculated at the B3LYP/6-311＋＋G＊＊ level. Intermediates and transition states were confirmed by the results of vibration analysis and the internal reaction coordinate（IRC） calculation. To obtain more precise energy result, stationary point energies were calculated at a CCSD （T）/6-311 ＋＋G＊＊//B3LYP/6-311＋＋ G＊＊level. In temperature range of 100 to 2300 K, the statistical thermodynamics and Eyring transition state theory with Winger correction are used to study the thermodynamic and kinetic characters of the channel with low energy barrier at 1.0 Arm, and the main chemical bond formation and breaking are discussed through Atoms in molecules （AIM）. The reaction SiF2→HNCS→IM1→TS1→IM2 HCF2 NCS（P1） was the main pathway with larger equilibrium constant and higher rate constant.