HNCS与CX(X=H,F,Cl)自由基反应的理论研究

Theoretical Studies on the Mechanism for the Reaction of HNCS with CX (X=H, F, Cl) Radical

用量子化学密度泛函理论的UB3LYP方法 ,在 6 3 1+G 水平上按BERNY能量梯度解析法全参数优化了HNCS与CX(X =H ,F ,Cl)反应势能面上各驻点的几何构型 ,通过同一水平的振动频率分析确认了中间体和过渡态 ,并得到各驻点的零点能校正 (Ezpc) .通过内禀反应坐标 (IRC)计算确认了反应物、中间体、过渡态和产物的相关性并得到最小能量途径(MEP) .为了得到体系势能面的更准确信息 ,在各驻点的UB3LYP/6 3 1+G 构型基础上 ,又进行了UQCISD(T) /6 3 11+G 水平上的单点能计算 ,得到体系的势能面信息和可能的反应机理 .应用变分过渡态理论及最小能量途径半经典绝热基态(MEPSAG)、小曲率半经典绝热基态 (SCSAG)隧道效应校正的方法计算了标题反应在 2 5 0～ 15 0 0K温度范围内的速率常数 .研究结果表明 ,HNCS与CX自由基反应是通过分子间H原子迁移及N—C键的断裂 ,生成产物CS +NCXH .

DFr-UB3LYP was used to calculate the geometries of reactants, intermediates, transition states and products for HNCS + CX (X = H, F, Cl) reaction on the 6-31 + G * level. The transiton states and intermediates of the reaction were verified by frequency analysis. The relationship among reactants, transition states, intermediates and products was affirmed by IRC (intrinsic reaction coordinate) calculation. The energies along the MEP ( minimum. energy path) were further refined at the UQCISD ( T)/6-311 + G * * level. The kinetics of the tide reaction was studied by using the 'direct dynamics' method of variational transition-state theory. The rate constants of the title reaction were calculated for the range of temperature 250 similar to 1500 K. In the calculation, we considered the tunneling correction. The tunneling correction was calculated by using the centrifugal-dominant small curvature semiclassical adiabatic ground-state (CD-SCSAG) method. The results show that the reaction mechanism of the title reactions involves five steps. The reaction pathway is reactants --> IMn1 --> TSn1 --> IMn2 --> TSn2--> products. These reactions are exothermic.