Photoabsorption of small metal clusters: Surface and volume modes

Abstract

The size-dependent dynamic polarizability of small clusters of simple metals is calculated analytically. It is predicted that the photoabsorption spectrum should consist of two peaks, one corresponding to surface, and the other to volume collective excitations. Unlike the case of bulk matter, the volume mode in small clusters can be excited by photons; its oscillator strength decreases with increasing cluster size. The derived oscillator-strength distribution is shown to satisfy exact energy-weighted sum rules. The results are used to explain experimental photoabsorption data. DOI: http://dx.doi.org/10.1103/PhysRevB.42.3247 © 1990 The American Physical Society