HNCO+OH——NH~2+CO~2反应理论研究

用从头算UHF/6-31G基组研究了异氰酸和羟基生成氨基和二氧化碳即HNCO+OH--NH~2+CO~2的反应机理.优化得到了反应途径上的过渡态和中间体,并通过振动分析对过渡态和中间体进行了确认.在UMP4/6-31G水平上计算了它们的能量,同时对零点能进行了较正.计算结果表明:此反应是多步反应,先后通过3个过渡态(TS1,TS2,TS3),2个内旋转位垒(TSI,TSII),4个中间体(IM1,IM2,IM3,IM4),其中,IM3--TS2这一步为整个反应的决速步骤,速控步的活化能为202.388kJ/mol.与异氰酸和羟基作用的另一反应通道(即HNCO+OH--H~2O+NCO)的活化能(69.038kJ/mol)比较,可看出所研究反应通道为次要反应通道,这与实验结果是一致的。

Theoretical study of the reaction HNCO+OH--NH~2+CO~2

The mechanism of the reaction HNCO+OH--NH~2+CO~2 has been studied by using ab initio MO method. The geometries of reactants, transition states,intermediates and products have been optimized with UHF/6-31G basis set and verified by frequency analysis. Furthermore,the correlation energies are corrected by Mφller-Plesset perturbation theory up to 4th order. The zero-pint energies are also corrected. The results show that the reaction is a multi-step complex one. Along the reaction path there are three transition states, two internal rotational barriers and four intermediates. The step IM3--TS2 is the rate-controlling step. Moreover, the calculated activation energy for the rate controlling step of the reaction channel studied in this paper i.e. the E~a of the reaction channel HNCO+OH--NH~2+CO~2(202. 388kJ/mol) is much greater than that of the other reaction channel HNCO+OH--H~2O+NCO (which equals to 69.038kJ/mol). Hence, the latter reaction channel is the main product channel. This is in good agreement with the experimental results.