STATISTICAL FRAGMENTATION OF HOT ATOMIC METAL-CLUSTERS

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