Ab initio calculations of the ionization spectrum of SO₂

The ionization spectrum of sulfur dioxide has been successfully studied by using the symmetry-adapted-cluster configuration-interaction (SAC-CI) general-R and SD-R methods and the basis set correlation-consistent polarized valence triple-zeta (cc-pVTZ). The SAC-CI general-R method reproduces the experimental spectrum well for both the main peaks and the satellite peaks of ionization spectrum of SO_2. The sequence of ionic states corresponding to main peaks of SO_2 has been re-determined according to the SAC-CI conclusions and it is reordered as \tilde X ^\rm 2A_1 , \tilde A^\rm 2B_\rm 2 , \tilde B ^\rm 2A_\rm 2 , \tilde C^\rm 2B_\rm 1 , \tilde D ^\rm 2A_\rm 1 , \tilde E^\rm 2B_\rm 2 and \tilde F^\rm 2A_1 . Besides, the equilibrium structures and adiabatic ionization potentials (AIPs) of ionic states of main peaks of SO_2 are calculated by using the SAC-CI SD-R method.