QUASI-CLASSICAL DYNAMICS OF THE I-2-NE-2 VIBRATIONAL PREDISSOCIATION - A COMPARISON WITH EXPERIMENT

The vibrational predissociation dynamics of the I-2(B,upsilon)-Ne-2 co mplex is investigated for several vibrational levels of I-2, using a q uasiclassical trajectory approach. The time evolution of the populatio n of nascent I-2 fragments is calculated. A model is proposed which re produces the results of the classical trajectories, and allows to obta in the lifetimes associated with the dissociation of the two van der W aals (vdW) bonds. The classical lifetimes are higher in general than t he experimental ones of Zewail and co-workers [J. Chem. Phys. 97, 8048 (1992)]. The classical method appears to overestimate mechanisms of e nergy redistribution between the modes, which slow down the dissociati on of the cluster. However, the behavior of the lifetimes with the ini tial iodine vibrational excitation is in very good agreement with expe riment. A sequential path of fragmentation of the two weak bonds via d irect predissociation is found to dominate, producing I-2(B,upsilon-2) +2Ne fragments. Although with smaller probability, alternative dissoci ation paths are observed involving statistical mechanisms of internal energy redistribution. In these paths, the energy initially transferre d by the iodine heats the vdW modes without breaking the complex. Furt her energy transfer produces either simultaneous or sequential dissoci ation of the two weak bonds in a rather evaporative way,populating the upsilon-2 and upsilon-3 exit channels. (C) 1996 American Institute of Physics.