A. Sarfati

Collective Optical Excitation in Free Metal Clusters

Metal cluster provides an ideal object to study a many body system. In particular it consists of many electrons which strongly interact each other. Two kinds of electrons may be distinguished i.e.: the valence electrons which become more delocalized as the cluster size increases, and the core electrons which may remain localized around each nucleus whatever the cluster size is. The correlations between the electrons, within each variety, induce collective effects revealed by the observation of giant resonances.

Photofragmentation of Hot Clusters: Evaporation, Fission, Photofragmentation Spectroscopy

Fragmentation is an ubiquitous phenomenon which occurs in microscopic systems such as nucleons, and in macroscopic objects as well. Despite its destructive nature, the fragmentation gives insight into the intrinsic stability and the binding forces of the fragmented object.

Excitation and Fission in Alkali-Atom Clusters

The study of the electronic structure of clusters is subjected to various experimental and theoretical approches. Currently used are the evolution with size of ionization potentials, static polarizabilities, collective excitation and stability against an excess of charge or internal energy. Results are interpreted in terms of simple models as the classical metallic drop, successefully applied to alkali-atom clusters, or with quantum mechanical models which reproduce in more details the variations with size. Here we present new results obtained for alkali-atom clusters in two different domains. First we have analyzed in details the fission of doubly charged potassium clusters around the critical size of stability. Second we have studied the response of singly ionized potassium clusters K n + to an external electromagnetic field, in an extended domain of size.