Multifragmentation in cluster-surface impact: A shattering event with a common velocity for all outgoing fragments

C60 is used in this work as a model system for studying the multifragmentation dynamics of a large molecule/cluster impacting a solid surface. We are addressing the issue of a shattering event that occurs away from the surface (post-collision) as compared with a direct shattering event which is completed while the collider is still in close contact with the surface (during collision). We have carried out detailed measurements of kinetic energy and angle distributions of Cn- (n = 2-12) fragment anions resulting from the impact induced disintegration (shattering) of C60- projectiles at a gold surface following near grazing incidence at impact energies of 80-900 eV. The Cn- fragments abundance distribution (odd and even) and the sharp fragmentation threshold observed (around Eo = 150 eV) point at a prompt shattering event. However, it is also found that for each given impact energy (300, 600 and 900 eV) all the Cn- fragments are scattered at the same velocity and with nearly identical angle distributions. These combined observations provide clear evidence for a multifragmentation event of the C60- collider, which does not occur at the surface (during collision) but at some distance away from the surface after scattering as a superhot C60- (precursor for post-collision fragmentation). Further support for this conclusion is provided by the observation of thermionically ionized C60+ ions (undergoing sequential unimolecular decay) whose kinetic energies are in agreement with the C60- precursor concept.