Theoretical studies on the low-lying electronic states of the HSO neutral radical and its cation

Using the complete active space self-consistent field (CASSCF) method with large atomic natural orbital (ANO-L) basis set, four electronic states of the HSO neutral radical are optimized. The vertical transitions of the HSO neutral radical are investigated by using the same method under the basis set of ANO-L functions augmented with a series of adapted 1s1p1d Rydberg functions, through which eight valence states and eight Rydberg states are probed. Ionic states of the HSO neutral radical are extensively studied in both cases of the adiabatic and vertical ionization, from which the relatively complete understanding of ionization energies is given. To include further correlation effects, the second-order perturbation method (CASPT2) is implemented, and the comparison between CASSCF and CASPT2 methods is performed.