Investigation of the potential energy surfaces for the ground X̃ 1A1 and excited C̃ 1B2 electronic states of SO2

The stationary points along the dissociation path are investigated by means of high-level ab initio methods and the reliability of different methods is discussed. The multi-reference AQCC method using the ANO-type basis set is shown to give geometrical parameters and relative energies in very good agreement with experiment. At this level of theory, the C̃ 1B2(1A′) state has an asymmetrical equilibrium geometry and double-minimum potential with a barrier of 170 cm−1, in good agreement with experimental data.