Intramolecular energy flow and the mechanisms for dissociation of atomic clusters

This paper explores the mechanisms for dissociation of atomic clusters in terms of internal energy flow and driving forces. We employ the hyperspherical coordinates to investigate internal dynamics of atomic clusters. The hyperspherical coordinates consist of three gyration radii and 3n - 9 hyperangular degrees of freedom that parameterize the shape of an n-atom system in the three-dimensional physical space. The latter 3n - 9 hyperangular degrees of freedom are further classified into three twisting modes and 3n-12 shearing modes. We numerically characterize the patterns of energy flow among the internal degrees of freedom leading to dissociations. It is shown that a large amount of kinetic energy tends to accumulate in the largest gyration radius upon dissociations of the cluster. We also identify some of the twisting and shearing modes that are active right at the instant of dissociation. These modes may be regarded as the triggers that drive dissociation of the cluster by pumping energy into the largest gyration radius. Physically, this pumping of energy is mediated by the internal centrifugal forces that originate from twisting and shearing motions of the system. These results are consistent with theoretical expectations from the equations of motion for gyration radii, and could be an initial step towards the control of large-amplitude collective motions of complex molecular systems.