Effect of collisions on the rotational recurrences in an ensemble of photofragments

Abstract

The aim of the present work is to study the dynamics of the decay of rotational coherences for ensembles of photofragments in collision environments. To simplify the presentation, we consider linear fragments produced through an impulsive dissociation of planar asymmetric top parent molecules. Adopting the formalism of quantum kinetic equations in the impact approximation, we derive general analytical expressions for the time development of rotational recurrences (RRs). To perform explicit calculations, the Gordon's J- and M- collision models are generalized to describe orientational relaxation under non-equilibrium conditions and implemented for treating different types of encounters. It is demonstrated that (i) collisions and dissociation do not affect the RR period; (ii) the widths and shapes of rotational transients are both dissociation and collision specific; (iii) the rate of decay of RRs is very sensitive to the collision dynamics but is almost independent of the photofragmentation dynamics. It is concluded that monitoring of RRs in collisional ensembles of photoproducts supplies one not only with structural information on the fragments, but also allows one to know about the photofragmentation dynamics and the efficiency of the angular momentum scrambling.