SIMPLE-MODEL FOR LAMBDA-DOUBLET PROPENSITIES IN BIMOLECULAR REACTIONS

A simple geometric model is presented to account for Λ-doublet propensities in bimolecular reactions A+BC → AB+C. It applies to reactions in which AB is formed in a Π state, and in which the unpaired molecular orbital responsible for Λ-doubling arises from breaking the B-C bond. The Λ-doublet population ratio Π(A′):Π(A″) is predicted to be 2:1 provided that: (1) the motion of A in the transition state [ABC] determines the plane of rotation of AB; (2) the unpaired π orbital lying initially along the BC bond may be resolved into a projection onto the AB plane of rotation, which correlates with Π(A′), and a projection perpendicular to this plane, correlating with Π(A″); (3) there is no preferred geometry for dissociation of [ABC]. The 2:1 Λ-doublet ratio is the "unconstrained dynamics prior" Λ-doublet distribution for such reactions. © 1990.