Ground and low-lying excited states of SO2 studied by the SAC/SAC-CI method

The SAC (Symmetry-adapted-cluster)/SAC-CI (Symmetry-adapted-cluster configuration interaction) method is applied for studying the properties of the ground and eight low-lying excited states of SO2. Firstly, the geometry of the ground state of SO2 is optimized by SAC method using many different basis sets. The calculated results are in agreement with the experiments, and the conclusion suggests that the basis sets 6-311+G (2df) and cc-pVTZ are the better suitable ones for the calculation of SO2 in the SAC method and the 3d function plays an important role in SO2. Then eight low-lying excited states of SO2 are optimized at SAC-CI/cc-pVTZ level and the adiabatic excitation energies of the low-lying excited states are also got based on the energy of ground state. Comparing with the available data, the equilibrium geometries and adiabatic excitation energies are in well agreement with the experimental values. Finally, based on the equilibrium geometry of the ground state X˜1A1, the vertical excitation energies, transition dipole moments and oscillation strengths of the eight excited states are also got at SAC-CI/cc-pVTZ level.