Femtosecond Real-Time Probing of Reactions. 17. Centrifugal Effects in Direct Dissociation Reactions

The influence of centrifugal repulsion on the real-time photofragmentation dynamics of (quasi)diatomic molecules is investigated. A previously presented classical model (Bersohn, R.; Zewail, A. H. Ber. Bunsenges. Phys. Chem. 1988, 92, 373) for direct dissociation in one (translatory) dimension is invoked to mimic the transient behavior that can be monitored experimentally by femtosecond transition-state spectroscopy. The time-dependent absorption of the probing laser pulse is calculated at transition-state and final product configurations for dissociation with varying amounts of relative rotational angular momentum between separating fragments. In this way, the centrifugal contribution to the potential governing fragmentation is examined in terms of its effect on the characteristic dissociation times for product separation and the lifetimes of transition-state intermediates. Application is made to the photodissociation of ICN via the A continuum, for which it is shown that centrifugal repulsion is not the principal cause of the observed product rotation.