IONIZATION AND FRAGMENTATION OF C-60 BY HIGHLY-CHARGED, HIGH-ENERGY XENON IONS

C-60 vapor was bombarded by Xe-136(35+) and Xe-136(18+) ions in the en ergy range 420-625 MeV to study the various ionization and fragmentati on processes that occur. Since the center-of-mass energies used in thi s work exceeded those of previous slwdies by several orders of magnitu de, new excitation and dissociation modes were expected and indeed fou nd. Positive ions were extracted from the interaction region and their limes of flight were measured both singly and in coincidence with oth er ionic fragments, A wide range of stable charge states and cluster s izes from monatomic carbon up to C-60 was observed. Even-numbered carb on fragments dominated tile heavier mass range but both even and odd c arbon numbers occurred at lower masses. Evidence was found for three q ualitatively different ionization and fragmentation channels suggestin g different ranges of collision impact parameters: ionization of the p arent C-60 molecule, loss of even numbers of carbon atoms, and ''multi fragmentation'' into many small fragments. This later mode included th e production of singly charged C-n(+) fragments with all values of n b eing observed from n = 1 up to at least n = 19. We interpret our resul ts in terms of a theoretical model that indicates that the total inter action cross section contains comparable contributions from (a) excita tion of the giant dipole plasmon resonance, and (b) large-energy-trans fer processes that lead to multiple fragmentation of the molecule. The distribution of fragment cluster masses for N less than or similar to 20 is reproduced by a ''percolation theory'' description analogous to that used to describe multifragmentation of nuclei by high energy pro tons.