Quasiclassical 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 complex is investigated for several vibrational levels of I-2, using a quasiclassical trajectory approach. The time evolution of the population of nascent I-2 fragments is calculated. A model is proposed which reproduces the results of the classical trajectories, and allows to obtain the lifetimes associated with the dissociation of the two van der Waals (vdW) bonds. The classical lifetimes are higher in general than the experimental ones of Zewail and co-workers [J. Chem. Phys. 97, 8048 (1992)]. The classical method appears to overestimate mechanisms of energy redistribution between the modes, which slow down the dissociation of the cluster. However, the behavior of the lifetimes with the initial iodine vibrational excitation is in very good agreement with experiment. A sequential path of fragmentation of the two weak bonds via direct predissociation is found to dominate, producing I-2(B,upsilon-2)+2Ne fragments. Although with smaller probability, alternative dissociation paths are observed involving statistical mechanisms of internal energy redistribution. In these paths, the energy initially transferred by the iodine heats the vdW modes without breaking the complex. Further energy transfer produces either simultaneous or sequential dissociation 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.