Capture dynamics in collisions between fullerene ions and rare gas atoms

The collision energy dependence of capture in collisions between C₆₀⁺ ions and small rare gas atoms (He, Ne) is studied in detail and compared with the results of classical molecular dynamics simulations. Additional insight is obtained on the dynamics of the collisions by also studying the kinetic energy loss of the projectile ions. Two capture mechanisms are found for He collisions: penetration of a six-membered ring with no significant cage distortion and scattering from a C₂ unit followed by deflection inside the cage. Good agreement is found with the simulations. Ne capture appears to be mainly the product of collisions with ring-structures on the cage followed by bond-breaking and insertion via a window mechanism. The very low threshold energy for Ne capture by fullerene ions (10 eV), reported previously, is attributed to the presence of highly excited, deformed fullerene ions in the beam. A second, higher threshold is found which is in better agreement with other experiments reported in the literature. The simulations of the Ne collisions do not give such good agreement as the He simulations. We attribute this to a too low value of the screening parameter used in the Ne-C potential.