Electronic versus vibrational excitation in Heq+ collisions with fullerenes

Collisions of Heq+ ions with neutral fullerenes have been studied as a func tion of projectile velocity (v approximate to 0.1-1.0 a.u.) and charge stat e (q = 1, 2). With increasing velocity, two trends are observed for both ch arge states: The yield of C-60-2m(r+) clusters decreases with 1/v, as expec ted for quantities related to direct vibrational excitation. The relative c ross section for multifragmentation increases linearly with v and can be as sociated with electronic excitations. The additional potential energy of He 2+ with respect to He+ manifests in increased direct ionization cross secti ons thigh v) and multifragmentation cross sections (low v), respectively, r evealing information about coupling times between electronic and vibrationa l excitation. (C) 1999 Elsevier Science B.V.