Energy gain in collisions of highly charged ions with C 60

We have extended the recently developed dynamical classical over-barrier model for charge transfer in soft ion-cluster collisions in order to simulate the projectile kinetic energy gain of 3.3$q$-keV Ar${}^{q+}$ ions in large-impact-parameter collisions with neutral C${}_{60}$ targets. Our semiclassical theory allows for the direct calculation of the energy defect $Q$ and of the projectile kinetic-energy gain in two different ways: either as difference of electronic binding energies before and after the collision or by integration of the dynamically varying force between the collision partners along the trajectory. A comparison between the two ways provides an intrinsic test of the model calculations. A comparison with recent experimental data shows good agreement in the main features of the projectile energy gain spectra and facilitates their interpretation in terms of the number of transferred electrons and projectile shells into which electrons are captured.