An ab initio study of the low-lying electronic states of S3.

Accurate calculations of the low-lying singlet and triplet electronic states of thiozone, S₃, have been carried out using large multireference configuration interaction wave functions. Cuts of the full potential energy surfaces along the stretching and bending coordinates have been presented, together with the vertical excitation spectra. The strong experimentally observed absorption around 395 nm is assigned to the 1 ¹B₂ state, which correlates to ground state products. Absorption at wavelengths shorter than 260 nm is predicted to lead to singlet excited state products, S₂ (a ¹Δ_g)+S(¹D). The spectroscopic properties of the X ³Σ_g^-, a ¹Δ_g, and b ¹Σ_g⁺ electronic states of the S₂ radical have also been accurately characterized in this work. The investigations of the low-lying electronic states were accompanied by accurate ground state coupled cluster calculations of the thermochemistry of both S₂ and S₃ using large correlation consistent basis sets with corrections for core-valence correlation, scalar relativity, and atomic spin-orbit effects. Resulting values for D₀(S₂+S) and ∑D₀ for S₃ are predicted to be 61.3 and 162.7 kcal/mol, respectively, with conservative uncertainties of ±1 kcal/mol. Analogous calculations predict the C_2v-D_3h (open-cyclic) isomerization energy of S₃ to be 4.4±0.5 kcal/mol. [ABSTRACT FROM AUTHOR]