Fragment size distribution in cluster impact: Shattering versus evaporation by a statistical approach

The transition from intact clusters to shattered small fragments is discussed for high velocity impact of cold atomic clusters at hard surfaces. The distribution of fragment sizes is computed as one of maximal entropy subject to conservation of matter and energy. The entropy is computed using a graph-theoretical approach for counting the number of possible isomers for a cluster of given size. As the impact velocity is increased, there is an onset of fragmentation into small fragments and the heat capacity is found to be discontinuous at that point. The results are compared with molecular dynamics simulations for rare gas clusters. Throughout the emphasis is on the special conditions that prevail during the ultrafast compression stage of the high energy cluster.