Scattering of rare gas cations from C-60 has been studied in a guided-beam tandem mass spectrometer. Charge transfer (CT) is observed to be the dominant channel over the collision energy range from 0 to 100 eV, but dissociative CT and endohedral complex formation are significant at high collision energies. The threshold energies for endohedral penetration are found to be proportional to rare gas atom size. Our CT and dissociative CT data allow us to make several conclusions about the nature of energy transfer in rare gas-fullerene collisions. Surprisingly, the conclusion is that the energy transfer distribution must be sharply bimodal, with similar to 85% of collisions resulting in little collision-to-internal energy transfer, and similar to 15% of collisions being essentially 100% inelastic. The results indicate that the dissociative CT and endocomplex formation channels are closely related. (C) 1997 American Institute of Physics. [S0021-9606(97)02744-X].