Theoretical study of the mechanism for spin‐forbidden quenching process O( 1 D) + CO 2 ( 1 Σ + g ) → O( 3 P) + CO 2 ( 1 Σ + g )

The mechanism of the spin‐forbidden quenching process O( 1 D) + CO 2 ( 1 Σ   + g ) → O( 3 P) + CO 2 ( 1 Σ   + g ) was investigated by ab initio quantum chemistry methods. The calculations showed the singlet potential surface [O( 1 D)+CO 2 ] is attractive where a strongly bound intermediate complex CO 3 is formed in the potential basin without a transition state, whereas the complex CO 3 that is formed on the triplet surface [O( 3 P)+CO 3 ] must overcome a barrier. The complex channel was documented by searching minimum energy intersection points in the region of the bound complex CO 3 and calculating spin‐orbit coupling at the point. A direct channel was proposed by a study of cross point of singlet and triplet PESs with different collision angles and calculations of spin‐orbit coupling at those cross points in a nonbound region of the [O( 1 D)+CO 3 ] system. The mechanism of the energy transfer is discussed on the basis of the theoretical results. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005