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

Portions of the lowest singlet and triplet potential energy surfaces o f CO2S were investigated by ab initio self-consistent field methods wi th the inclusion of electron correlation by Moller-Plesset perturbatio n theory. Earlier experiments indicated that the reaction of oxygen at oms with carbonyl sulphide occurred by a direct stripping mechanism to form the products CO(1SIGMA+) and SO(3SIGMA-). This reaction may proc eed on the singlet potential energy surface through an OCSO intermedia te. This singlet surface lies approximately 60 kcal mol-1 below the tr iplet and the barrier heights leading to the OCSO singlet minima are l ess than 30 kcal mol-1. Multiple intersystem crossings are required to connect ground state reactants to products as both have triplet multi plicity 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 spec ies. Another series of low-lying singlet structures was found and thes e include the lowest energy intermediate on either surface, an asymmet ric ring isomer with sulphur, oxygen and carbon forming a three-member ed ring and a carbonyl group.