FROM THE SPARSE TO THE STATISTICAL LIMIT OF INTRAMOLECULAR VIBRATIONAL REDISTRIBUTION IN VIBRATIONAL PREDISSOCIATION - ARCL2 AS AN EXAMPLE

The dynamics of intramolecular vibrational relaxation (IVR) for ArCl2 are examined for a wide range of vibrational and rotational excitation . In order to describe the IVR more efficiently, and characterize it m ore quantitatively, we propose a refinement of the traditional Bixon-J ortner description in which the active states are prediagonalized to s implify the coupling scheme that must be considered. This allows for a n explicit determination of the average density of states and average coupling strength for each initial excitation. We fmd that the IVR dyn amics proceed from the sparse regime for upsilon=11, for which the fir st open dissociation channel corresponds to the loss of two Cl-2 quant a, to the intermediate-dense regime for upsilon=25 which dissociates b y the loss of 4 quanta. We find that over this range the increase in t he density of states is less important than the increase in the coupli ng strength. For upsilon=18 we examine the effect of rotation in consi derable detail. Initial states that couple via a manifold of 6000 chan nels can be considered since the calculation is performed on a paralle l computer. The effect of increasing J, the total angular momentum exc itation, is found to be less than that of increasing K, the degree of rotation about the van der Waals bond, This means that the main effect is not simply an increase of the available density of states due to C oriolis coupling. Understanding the details of IVR in a relatively sim ple system like ArCl2 should help us understand the dynamics of more c omplicated molecules. In particular, the case of ArI(2)is discussed. ( C) 1997 American Institute of Physics.