Strong velocity effects in collisions of He+ with fullerenes

We have studied fragmentation and ionization of C-60 by He+ impact over a velocity range from 0.1 to 1 a.u. where a transition from vibrational to electronic excitation is predicted. With increasing velocity we observe a strong decrease of evaporative processes (C-60-2m(r+) peaks) and a linearly increasing yield of small fragments (C-n(+), n <15). Apparently direct vibrational excitation leads preferentially to evaporation, whereas electronic excitation is responsible for multifragmentation. In the intermediate range we find indications for a "transparency window" similar to that predicted recently in simulations of Na-9(+)-He collisions. [S0031-9007(98)08105-8].