Theoretical study of the mechanism for spin-forbidden quenching process O(¹D) + CO₂(¹Σ_g⁺) → O(³P) + CO₂(¹Σ_g ⁺)

The mechanism of the spin-forbidden quenching process O(¹D) + CO₂(¹Σ_g⁺) → O( ³P) + CO₂(¹Σ_g⁺) was investigated by ab initio quantum chemistry methods. The calculations showed the singlet potential surface [O(¹D)+CO₂] is attractive where a strongly bound intermediate complex CO₃ is formed in the potential basin without a transition state, whereas the complex CO₃ that is formed on the triplet surface [O(³P)+CO₃] must overcome a barrier. The complex channel was documented by searching minimum energy intersection points in the region of the bound complex CO₃ 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(¹D)+CO₃] system. The mechanism of the energy transfer is discussed on the basis of the theoretical results.