Abstract: Ab initio UMP2 method was used to study the reaction mechanism of CH3 radical with HNCO. The geometric configurations of reactants, products, intermediates and transition states were optimized at UMP2(full)/6-311＋＋G** level. The results show that the reaction of CH3 radical with HNCO has three pathways: (1) CH3 radical reacts with HNCO to form a hydrogen-bond complex M of which the relative stable energy is 4.56 kJ•mol－1,and then forms another complex M′through a transition state TS, and breaks down into CH4 and NCO radical in the end. (2) CH3 radical reacts with HNCO to form a stable trans- intermediate (trans-int), then through a transition state (trans-ts) breaks down into CH3NH and CO. (3) CH3 radical reacts with HNCO to form a stable cis-intermediate (cis-int), and then through a transition state(cis-ts) breaks down into CH3NH and CO. Comparing the activation energy of the three pathways, we can draw a conclusion that the pathway of forming CH4 and NCO radical is more feasible.

Key words: HNCO, Radical reaction, Ab initio UMP2 method, Hydrogen-bond complex