Shattering of clusters upon surface impact: An experimental and theoretical study

The shattering transition expected upon ultrafast heating has been observed in size selected (NH3)n-1NH4+ clusters, n=4 to 40, upon impact at supersonic velocities on a graphite surface. As a function of the impact velocity, the transition is between the recoil of the intact parent cluster and the appearance of small, n=1,2,... charged fragments. As the cluster size increases, the transition becomes a sharper function of the impact velocity. The experimental fragmentation pattern is well accounted for by a distribution of maximum entropy subject to conservation of energy, atoms, and charge.