Under the case of a 248 nm photolysis UV-wavelength, it was suggested by experiments that, via a direct photolysis, the decomposition of HCNO molecule might occur, leading to some definite products for further observations. For these, theoretically a set of relative energies of the HCNO molecule was presented, to which ¹A' (0.00 kJ/mol), ³A' (255.01 kJ/mol), ³A" (282.37 kJ/mol) and ¹A" (341.59 kJ/mol) correspond, as our starting point to find some reasonable pathways for revealing the corresponding decomposition mechanism. As a direct result, it is shown that the main products are H＋(NCO), (HCN)＋O, and NH＋CO, which are in accordance with those suggested by experiments.

Key words: reaction mechanism, potential energy surface, HCNO