The reaction path of isocyanic acid (HNCO) with carbon-hydrogen radicals CH, CH_2 and CH_3 have been investigated by using UMP2 method at 6-311 g(d, p) level. The geometries of the stationary points and the changes of molecular structure along the reaction path are discussed. Furthermore, the UQCISD (T, full) single-point energy calculations were performed on the geometries optimized at UMP2/6-311G (d, p) level. For the reactions of HNCO with CH_2 and HNCO with CH_3, we found that the formation of new C-H bond concerted with the break of old N-H bond along the IRC, and that there was a weak hydrogen-bond hypermolecular complex on the reactant side for the both reactions. However, for the reaction of HNCO with CH there were two stable molecular complexes HN(CH)CO and H_2CNCO on the reactant side and the product side, respectively.

Key words: ISOCYANIC ACID, FREE RADICAL, CONFIGURATION, HYDROGEN BONDS, SUPERMOLECULAR STRUCTURE