Ab initio quantum chemical study of the molecular and spectroscopic (infrared and Raman) properties of sulfur dioxide: Comparison with ozone

Using ab initio SCF, singles and doubles configuration interaction (CI-SD), and coupled pair functional (CPF) techniques with basis sets of triple zeta plus two polarization functions quality, the following properties have been computed for sulfur dioxide at its equilibrium geometry: dipole and quadrupole moments, electric field gradients at the nuclei, static and frequency dependent dipole polarizability (at λ = 5154 Å and λ = 6328 Å), dipole and polarizability derivatives, infrared absorption intensities, and Raman scattering activities. The properties, when calculated at the correlated level of theory have been evaluated by the energy derivative (ED) as well as the expectation value (EV) formalism. The results of the CPF(ED) calculations are in good agreement with the available experimental data and on the basis of additional two-configurational MCSCF studies the use of single reference CI-SD and CPF wave functions is judged to be justified. The analogous calculations on ozone serve to highlight the considerable differences between the two molecules, inasmuch as due to the considerably larger degree of near-degeneracy in O ₃, properties that involve mixing of the lowest ¹B ₂ excited state with the ¹A₁, ground state are predicted poorly at the SCF level as well as at the single reference CI-SD and CPF levels of theory.