ANALYSIS OF DISSOCIATION TIMES AND FRAGMENTATION PATTERNS IN THE DECOMPOSITION OF HIGHLY EXCITED CLUSTERS

In this article, the dynamics of fragmentation of highly excited van der Waals clusters are analyzed. An approach to the characterization of complex cluster fragmentation is described, based on a combination of structural and dynamical analysis of classical trajectories. In this method, the final fragmentation pattern is analyzed by a depth-first search algorithm based on graph theory, which provides a partitioning of the system into intact fragments of various sizes: monomers, dimers, trimers, and higher multimers. With knowledge of the final products, a dynamical analysis is accomplished by tracing back the time dependence of the relevant fragment energies. A transition from oscillatory to constant behavior of these energies indicates that the fragment has become energetically isolated from the parent cluster. This allows an unambiguous definition of the dissociation time of the fragment. The method is applied to the characterization of cluster fragmentation of chemically activated I2Ar12* formed in the association reaction I + I(Ar)12 --> I2 + 12 Ar. It is found that cluster decomposition channels, leading to the formation of at least one multi-atom fragment, play an important role in the evaporative cooling of I2, in addition to monoatomic sequential evaporation.