Angular momentum dependence of first- and second-order singlet-triplet interactions in polyatomic molecules

Abstract

Formulas for the angular momentum dependence of the interaction matrix elements between rotating, nearly degenerate singlet and triplet electronic states are derived for the following conditions: (i) the interaction is first order, involving direct spin‐orbit coupling of the states; (ii) the interaction is second order, occurring by a vibronic spin‐orbit mechanism with vibronic coupling in the singlet or triplet manifold; and (iii) the interaction is second order, occurring by a spin‐rotation mechanism in which the interacting singlet and triplet states are coupled to the manifold of intermediate states by spin‐orbit and orbital‐rotation coupling. Possible applications of these formulas are discussed.