FRAGMENT SIZE DISTRIBUTION IN CLUSTER-IMPACT - SHATTERING VERSUS EVAPORATION BY A STATISTICAL APPROACH

The transition from intact clusters to shattered small fragments is di scussed for high velocity impact of cold atomic clusters at hard surfa ces. The distribution of fragment sizes is computed as one of maximal entropy subject to conservation of matter and energy. The entropy is c omputed using a graph-theoretical approach for counting the number of possible isomers for a cluster of given size. As the impact velocity i s increased, there is an onset of fragmentation into small fragments a nd the heat capacity is found to be discontinuous at that point. The r esults are compared with molecular dynamics simulations for rare gas c lusters. Throughout the emphasis is on the special conditions that pre vail during the ultrafast compression stage of the high energy cluster . (C) 1995 American Institute of Physics.