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 d er 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 s earch algorithm based on graph theory, which provides a partitioning o f 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 dependen ce of the relevant fragment energies. A transition from oscillatory to constant behavior of these energies indicates that the fragment has b ecome energetically isolated from the parent cluster. This allows an u nambiguous definition of the dissociation time of the fragment. The me thod is applied to the characterization of cluster fragmentation of ch emically activated I2Ar12 formed in the association reaction I + I(Ar )12 --> I2 + 12 Ar. It is found that cluster decomposition channels, l eading to the formation of at least one multi-atom fragment, play an i mportant role in the evaporative cooling of I2, in addition to monoato mic sequential evaporation.