FRAGMENTATION PHASE-TRANSITIONS IN ATOMIC CLUSTERS .3. COULOMB EXPLOSION OF METAL-CLUSTERS

We discuss the role and the treatment of polarization effects in many- body systems of charged conducting clusters and apply this to the stat istical fragmentation of Na-clusters. We see a first order microcanoni cal phase transition in the fragmentation of N alpha(70)(Z+) for Z = 0 to 8. We can distinguish two fragmentation phases, namely evaporation of large particles from a large residue and a complete decay into sma ll fragments only. Charging the cluster shifts the transition to lower excitation energies and forces the transition to disappear for charge s higher than Z = 8. At very high charges the fragmentation phase tran sition no longer occurs because the cluster Coulomb-explodes into smal l fragments even at excitation energy epsilon = 0.