Abstract
Relative abundances of metal clusters containing up to 100 alkali atoms show magic numbers for clusters of special stability, in agreement with a shell model analogous to the nuclear shell model. Observed ionization energies and photo-emission spectra also reflect the single particle features of the electronic shell structure. The long range Coulomb screening among the delocalized metallic electrons determines the static and dynamic electric polarizability, from which the plasma resonance absorption is derived. The photoabsorption cross sections show peaks in the visible, depending on the shapes of the clusters, and on the oscillator strengths. Experimental values of the peak cross sections are ~1 Å2 per electron, consistent with free electron calculations.
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