Ab initio calculations on low-lying electronic states of Sb O^-₂and Franck-Condon simulation of its photodetachment spectrum

Geometry optimization and harmonic vibrational frequency calculations have been carried out on the low-lying singlet and triplet electronic states of the antimony dioxide anion (Sb O2-) employing a variety of ab initio methods. Both large-core and small-core relativistic effective core potentials were used for Sb in these calculations, together with valence basis sets of up to augmented correlation-consistent polarized-valence quintuple-zeta (aug-cc-pV5Z) quality. The ground electronic state of Sb O2- is determined to be the X̃ A11 state, with the ã B13 state, calculated to be ∼48 kcal mole-1 (2.1 eV) higher in energy. Further calculations were performed on the X̃ A12, Ã B22, and B̃ A22 states of Sb O2 with the aim to simulating the photodetachment spectrum of Sb O2-. Potential energy functions (PEFs) of the X̃ A11 state of Sb O2- and the X̃ A12, Ã B22, and B̃ A22 states of Sb O2 were computed at the complete-active-space self-consistent-field multireference internally contracted configuration interaction level with basis sets of augmented correlation-consistent polarized valence quadruple-zeta quality. Anharmonic vibrational wave functions obtained from these PEFs were used to compute Franck-Condon factors between the X̃ A11 state of Sb O2- and the X̃ A12, Ã B22, and B̃ A22 states of Sb O2, which were then used to simulate the photodetachment spectrum of Sb O2-, which is yet to be recorded experimentally.