Quenching of CH(a4Σ-) by CO(XΣ+): Surfaces of Intersection, Spin−Orbit Interactions, and the Incorporation of Kramers' Degeneracy

It has been suggested ( J. Am. Chem. Soc . 1993, 115, 6904) that CH(a 4 Σ - ) is collisionally quenched to CH(X 2 Π) by CO(X 1 Σ + ) via an intermediate complex involving the 4 A‘‘ state of the ketenyl (HCCO) radical. To shed further light on this proposition, points of the surface of intersection of the 4 A‘‘ potential energy surface with the 2 A‘ and 2 A‘‘ potential energy surfaces, surfaces correlating with CH(X 2 Π) + CO(X 1 Σ + ), were determined. The 4 A‘‘−( 2 A‘, 2 A‘‘) spin−orbit interactions were determined and analyzed in a basis that simplifies the incorporation of Kramers' degeneracy. The noncrossing rule for odd electron states in the presence of the spin−orbit interaction is discussed. The computational results support a generalization of the proposed mechanism of CH(a 4 Σ - ) quenching.