COLLECTIVE RESONANCES AND RESPONSE PROPERTIES OF ELECTRONS IN METAL-CLUSTERS

The delocalized valence electron cloud in metal clusters displays strong collective behavior. This fact is reflected in a variety of cluster properties, including photoabsorption resonances and electric polarizability. Experiments have demonstrated that the response properties of cluster electrons possess a number of features unique to the microscopic size regime. In this paper the experimental picture is considered, and a theoretical discussion of the size-dependent behavior of electrons in finite systems is presented. Topics discussed include collective resonance frequencies and oscillator strengths in spherical and deformed clusters, electron distribution, and static polarizability. The theoretical analysis presents a consistent picture of cluster spectra which reflects the unique properties of these systems and is successful in explaining the experimental data for a wide variety of metal clusters. Suggestions for further measurements are made, including the prediction of a new photoabsorption mode unique to small metallic clusters.