Transition from during- to post-collision multifragmentation in cluster surface impact

Multifragmentation of C-60(-) was studied by measuring the kinetic energies of outgoing C-n(-) (n=2-12) fragments following C-60(-) collisions with a gold surface at sub-keV impact energies. We observe the transition from a multifragmentation with common average energy for all fragments ("during-collision" event) to a one with a common average velocity for all fragments ("post-collision" event). The energy distributions for both multifragmentation modes were successfully modeled by treating the fragmenting cluster as a hot "gas" consisted of various C-n fragments and moving with some center of mass velocity.