The equilibrium structures, harmonic vibrational frequencies and binding energies of ClONO2-H2O and HONO2-H2O complexes have been investigated with ab initio MP2 and density functional B3LYP methods. The B3LYP method performs better than MP2 methods in predicting the vibrational frequencies of both ClONO2 and HONO2. It is found that the ClONO2-H2O complex possesses a near C-s symmetry structure. The ZPE corrected binding energies determined at B3LYP/6-311++G(2df,2p) level for ClONO2-H2O and HONO2-H2O complexes are 2.2 and 7.2 kcal mol(-1), respectively. A possible surface based heterogeneous reaction mechanism of ClONO2 on water-ice surface is proposed.