A dynamical definition of quasi-bound molecular clusters

Molecular configurations which count as snapshots of a quasi-bound cluster are identified through a retrospective dynamical definition. The trajectory of a molecular cluster is followed, and a clear evaporation event is considered to have occurred when a molecule moves a very long distance away from the others. The cluster is judged to have broken before this condition is satisfied, however, at the instant that the energy of the departing molecule in the centre of mass frame becomes positive. The decay of a cluster is therefore defined dynamically as the production of a molecule with positive energy on a separating trajectory. Not all positive energy molecules created by the system follow such a trajectory, hence the need to examine the subsequent behaviour in molecular dynamics. We simulate a sequence of decays by repairing broken clusters as they occur. This approach enables us to calculate mean decay rates of isolated Lennard-Jones clusters in what promises to be a physically realistic fashion.