Rotational energy dispersions for van der Waals molecular clusters: Analytic descriptions for Rg3, Rg4, and Rg6

Rotationally induced transitions in small clusters

The dynamics of an Ar6 cluster held together by Lennard-Jones forces is studied classically. The development of chaotic dynamics is mainly followed by a calculation of the maximum Lyapunov exponent (MLE). Initial momentum vectors are chosen from the eigenvectors of the Hessian of the potential energy so that rotating and nonrotating clusters can be studied systematically. It is found that the dependence of MLE on the total energy is considerably different for rotational and vibrational excitations. As the magnitude of the angular momentum increases, sharp transitions in MLE are observed. These transitions are explained in terms of the changes of the topology of the effective rovibrational potential energy surface and the dynamic equilibration between the global and local minima.