Molecular-dynamics simulations of collisions of Ne with La@C₈₂

Collisions of Ne with endohedral La@C₈₂ at a center-of-mass energy of 1.44 keV have been investigated using molecular dynamics. The interactions among the C atoms are modeled using the empirical potential of Takai et al., which includes two- and three-body terms. All other interactions are treated using two-body potentials. A total of about 7200 trajectories are calculated, using randomly selected initial orientations of the fullerene and impact parameters in the range 0.5 Å to 6.0 Å. The trajectories are analyzed to determine the energy transferred to the fullerene target and the pattern of fragmentation of the target following the impact. The average energy transferred at a given impact parameter is well correlated with the density of C atoms in the path of the incident projectile. The fragmentation data can be compared with recent experiments of Lorents et al. on the similar system Ne-(La@C₈₂)⁺. We find a narrower distribution of fragment sizes than these experiments. We also see no preference for the production of fullerene fragments with even numbers of C atoms. However, we analyze the fragments only about 80 fs after impact, and at that time they have sufficient internal energy to split even further. Since the experimental mass analysis takes place about a microsecond after the collision, our results suggest that further fragmentation and equilibration into the more stable fragments with an even number of C atoms takes place well after the collision.