Potential energy surfaces for low-lying electronic states of SO2

The potential energy surfaces for the nine low-lying electronic states of SO2 have been constructed by using the multi-reference second order perturbation theory (MRPT2) with the basis set cc-pVTZ. The optimized geometries and the adiabatic excitation energies of these states are in good agreement with experiments and previous calculations. The crossings and avoided crossings displayed in the potential energy surfaces are expounded.