Electronic structures of the S2O and S3 isomers: an ab initio CI study

The electronic structures of the S₂O and S₃ isomers have been dealt with by the multireference double-excitation (MRD) configuration-interaction (CI) calculations, using contracted 5s3p1d] and 4s2p1d] basis functions for the S and O atoms, respectively. The ground-state geometries for the SOS (symmetric chain), S₂O (symmetric ring) and SSO (unsymmetric chain) are optimized, and their vertical singlet excitation energies are calculated. It is found that SSO is the most stable of the three isomers and that the ground state (¹A₁) of the S₂O (ring) is correlated with the excited states of SOS (2¹A₁) and SSO (3¹A). The chain and ring isomers of S₃ have been treated in a similar manner. Energetics for the ring closure of the O₃, SO₂, SSO and S₃ chain molecules are discussed on a unified ground.Dedicated to Professor J. Koutecký on the occasion of his 65th birthdayPresented at the 5th International Congress on Quantum Chemistry, Montréal, August 1985