Angular distributions of reactive scattering arising from persistent complexes with prolate symmetric top transition states

Microcanonical transition state theory has been employed to predict the angular distribution of reactive scattering arising from a long-lived collision complex dissociating via a transition state which approximates to a prolate symmetric top. Forward and backward peaked angular distributions arise only when the orientation of the product angular momentum becomes unconstrained with respect to the direction of the final relative velocity vector as the transition state dissociates to products. If, as assumed in previous models, the orientation of the product angular momentum is constrained to that prevailing at the transition state so that the final relative velocity vector is coincident with the symmetry axis of the transition state, then a conical angular distribution ensues. Explicit formulae for each of these limiting cases are presented. The physical basis for the ubiquity of forward and backward peaking of reactive scattering compared with the rarity of conical angular distributions is examined in the light of the theory.