Analysis of fragment size distributions in collisions of monocharged ions with the C60 molecule

Fragmentation of the C-60 molecule is investigated using a multicorrelation technique. We first focus on the transition from asymmetrical dissociation (AD) to multifragmentation (MF). These processes are studied in collisions between H-x(+) (x = 1-3) hydrogenic projectiles and C-60 fullerene in the gas phase, in the 2-130 keV collisional energy range. A rather sharp transition from pure AD to predominant MF is observed when plotting the AD/(AD + MF) ratio against the average deposited energy E-dep; it occurs in the 80-240 eV Edep range; this ratio is also found to be independent of the projectile species (scaling law). The evolution of the size distribution shape is also discussed and compared with other data available in the literature. A pure power law is never reached in the present experimental conditions. Finally, an event-by-event analysis of the. fragmentation data is developed for the first time in the study of the C-60 molecule fragmentation and discussed in terms of the predictions of the percolation model near a critical behaviour. Moments of order 2, 3 and 5 are determined for each correlation event. Moments of order 3 and 5 follow a linear behaviour when plotted against the moment of order 2, as predicted, and the exponent tau that is extracted takes a value near 2. The Campi scatter plot is also determined and discussed for total and multiplicity-selected events. Both slopes of the two branches in the Campi plots and tau value are near those that are expected in the percolation of a 2D lattice.