AB-INITIO STUDIES OF THE LOWEST SINGLET AND TRIPLET POTENTIAL-ENERGY SURFACES OF CO2S

Portions of the lowest singlet and triplet potential energy surfaces of CO2S were investigated by ab initio self-consistent field methods with the inclusion of electron correlation by Moller-Plesset perturbation theory. Earlier experiments indicated that the reaction of oxygen atoms with carbonyl sulphide occurred by a direct stripping mechanism to form the products CO(1SIGMA+) and SO(3SIGMA-). This reaction may proceed on the singlet potential energy surface through an OCSO intermediate. This singlet surface lies approximately 60 kcal mol-1 below the triplet and the barrier heights leading to the OCSO singlet minima are less than 30 kcal mol-1. Multiple intersystem crossings are required to connect ground state reactants to products as both have triplet multiplicity in contrast to the singlet intermediates. Two sets of bent cis and trans triplet structures were located, the SCOO and OCOS isomers, both of which are considerably higher in energy than the singlet species. Another series of low-lying singlet structures was found and these include the lowest energy intermediate on either surface, an asymmetric ring isomer with sulphur, oxygen and carbon forming a three-membered ring and a carbonyl group.