Modeling buckminsterfullerene spinning in (C60)n clusters

Temperature-dependent rate constants for the spinning of buckminsterfullerene in (C-60)(n) clusters (n = 3-13) are calculated using unimolecular reaction rate theory with parameters obtained from molecular mechanics simulations. The lowest lying intracluster rotations tend to spread over several cages toward the surface and the edges of the clusters. Coaxial rotations appear also in this regime. A simple argument is put forward to justify the use of harmonic spacing in the study of the dynamics of these degrees of freedom. The increase in the size of the cluster makes the calculated rate constants converge toward the value reported in the solid. The satisfactory result of this simple form of kinetic theory implies that the energy of the internal degrees of freedom is randomized sufficiently fast with respect to the spinning coordinates.