Asymmetric fission and evaporation of Cr+60 (r = 2–4) fullerene ions in ion–C60 collisions: III. Universal behaviour of fission

Abstract

The behaviour of the asymmetrical fission (AF) scheme (correlated ion distributions) against the collision conditions is investigated using H+x (x = 1–3) and He+ projectiles in the 1–130 keV collision energy range. The present work is an extension of our recent publications on this topic using 11 keV protons (Rentenier et al 2004 J. Phys. B: At. Mol. Opt. Phys. 37 2429 and 2455). The threshold for AF is observed at 2 keV proton energy corresponding to a maximum deposited energy equal to about 41 eV. The main result concerns the fragment distributions resulting from AF of Cr+60 ions, and secondary dissociation of even-n C+n fragments, which are both found to remain independent of the projectile species and collision velocity. These findings indicate that they are insensitive to the internal energy distributions of the parent ions. In addition, a contribution of binary collisions between the projectile and individual carbon atoms of the C60 molecule to AF is identified in the C+1 production at the lowest collision velocities, the so-called impulsive fragmentation.