An ab initio study on the ground and low-lying doublet electronic states of SbO₂

Geometry optimization and harmonic vibrational frequency calculations have been carried out on the low-lying doublet electronic states of antimony dioxide (SbO2) employing a variety of ab initio methods, including the complete active space self-consistent field/multireference configuration interaction and the RCCSD(T) methods. Both large and small core relativistic effective core potentials were used for Sb in these calculations, together with valence basis sets of up to aug-cc-pV5Z quality. Contributions from outer core correlation and off-diagonal spin-orbit interaction to relative electronic energies have been calculated. The ground electronic state of SbO2is determined to be the X̃2A1state, as is the case for dioxides of other lighter group 15 p-block (or group VA) elements. However, the Ã2B2and B̃2A2states are estimated to be only 4.1 and 10.7 kcal/mole above the X̃2A1state, respectively, at the complete basis set limit. Reliable vertical excitation energies from the X̃2A1state to low-lying excited states of SbO2have been computed with a view to assist future spectral assignments of the absorption and/or laser-induced fluorescence spectra of SbO2, when they become available.