STATISTICAL FRAGMENTATION OF HOT ATOMIC METAL-CLUSTERS

Fragmentation processes of highly excited neutral and charged atomic m etal clusters are studied in the framework of an equilibrium statistic al model. In the particular case of hot (near and above melting) neutr al and charged sodium clusters of 100 and 200 atoms, a microcanonical Metropolis sampling is used to compute mass (or charge) correlation fu nctions as a function of the excitation energy. This method allows to take the strong anharmonicities in the internal phonon spectrum realis tically into account which are linked to the internal structural chang es like melting. It is found that, at high enough excitation energy, t he system exhibits a phase transition. This phase transition is specif ic for fragmenting finite systems. From the shape of the caloric curve one sees that the two phases involved are connected by a van der Waal s loop characterizing a first order phase transition. Here we observe an enhanced fission and multifragmentation into two or more charged cl usters with more than 10 atoms each. Various fragment correlations are studied.