ELECTRONIC AND GEOMETRIC STRUCTURE OF SMALL MASS-SELECTED CLUSTERS

An experimental setup for photoelectron spectroscopy on mass selected cluster anions is described. The photoelectron spectra reveal the elec tronic structure of the particles as function of their size (mass). Fo r clusters consisting of elements which are counted among the simple m etals, i.e., the alkali's as well as Cu, Ag, and Au, the electronic st ructure is indicative of extended, delocalized states formed by tile a tomic s-electrons. This is the first indication of metallic behavior e ven though the particles containing up to 20 atoms clearly exhibit a ' bandgap' in the electronic structure. Additionally, in cases where vib rational finestructure is observed in the photoelectron spectra, the m easured vibrational quanta allow to deduce the particle geometry. This is especially helpful in studies of chemisorption phenomena on the cl usters. Moreover, electron phonon coupling constants can be extracted from a high resolution spectrum of C-60(-), which confirm the alkali d oped fullerenes to be conventional BCS type superconductors.