DYNAMICS OF PERSISTENT COLLISION COMPLEXES IN MOLECULAR-BEAM REACTIVE SCATTERING

New microcanonical theories for the angular distributions of reactive scattering arising from long-lived collision complexes and their application to a wide range of transition state geometries are reviewed. Transition states formed at the top of centrifugal barriers on potential energy surfaces without a potential energy barrier are well described by symmetric top transition states, provided that the loosening of bending mode vibrations into product rotation is included. A phase space description appropriate for collisions at small impact parameters can be incorporated into a consistent mathematical description. Tight transition states formed at the top of a potential energy barrier and involving H atom displacement are described by an asymmetrical top transition state theory which includes all the symmetric top configurations as limiting cases. However the effects of transition state flexibility rapidly obscure the observable consequences of preferred geometry for directions of dissociation away from the principal axes. These theories are used to explore the effects of structural isomerism of collision complexes in studies of a wide range of F and O atom abstraction and displacement reactions, where the structure and interconversion of highly vibrationally excited complexes is related to the nature of the chemical bonding involved.