TEMPERATURE-DEPENDENCE OF THE SINGLE-PARTICLE SPECTRUM IN SODIUM CLUSTERS

We show that the electronic density of states of small sodium clusters is strongly affected by both thermal fluctuations about the ground st ate ionic configuration and transitions between different shape isomer s as the temperature of the cluster is increased. Contrary to common e xpectations, the clusters undergo a sharp transition in the temperatur e range of 100K to 150K, after which the single-particle level distrib utions become bimodal. At even higher temperatures the signature of th e ground state configuration disappears, and the density of states is dominated by higher energy isomers. We also discuss the implications o f these findings for the interpretation of the photoelectron spectra o f these systems.