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 1Δg)+S(1D). The spectroscopic properties of the X 3Σg-, a 1Δg, and b 1Σg+ 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 C2v-D3h (open-cyclic) isomerization energy of S3 to be 4.4±0.5 kcal/mol. [ABSTRACT FROM AUTHOR]