The reaction of H+ SO2→HO + SO was theoretically investigated sing ab initio MOmethods, and HF/TZV (d, p) level of theory was employed to locate stationary points which werethen characterized by calculation of the vibrational frequencies. Energies were estimated at the optimized geometries using MP2/TZV (d, p) calculations. The results show that the caIculated geometries- frequencies. and thermochemical data were in good agreement with available experi-mental values. The IRC calculations confirmed that nonplanar HSO2 and HOSO adducts shouldbe more reasonable than those of planar conformation. The reaction of H + SO2 → HO + SO was theoretically investigated sing ab initio MOmethods, and HF / TZV (d, p) level of theory was employed to locate stationary points which werethen characterized by calculation of the vibrational frequencies. Energies were estimated at the The results show that the caIculated geometries- frequencies. and thermochemical data were in good agreement with available experi-mental values. The results of the show that the caIculated geometries- frequencies. and thermochemical data were in good agreement with available experi- mental values. The IRC calculations that that nonplanar HSO2 and HOSO adducts shouldbe more reasonable than those of planar conformation.