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Using a new experimental setup we have measured UV (h ν = 6.4 eV) photoelectron spectra of cold silicon cluster anions Si n - in a very broad size range. For sizes up to n = 46 the spectra exhibit rich structures. For larger sizes only smooth spectra have been obtained. No trace of a bandgap has been found even for clusters with more than 1000 atoms.

Copper cluster anions in the size range of 1-18 atoms are studied by photoelectron spectroscopy. Using photons of 5.0 eV energy the electronic level structure built from the delocalized s-orbitals of the atoms is revealed. An attempt is made to assign the observed bands to the electronic shells predicted by the jellium model. Even though the general behavior resembles the predictions of this model, the spectra are much more complicated reflecting the discrete atomic geometry of these particles.

The competition between electron emission and unimolecular dissociation following the absorption of a single photon is studied for small clusters of various elements. Electron emission results from either direct photoemission, observed as a series of peaks in the spectrum, or thermionic emission, giving rise to a continuous background. Depending on the energetics involved, thermionic emission is in competition with evaporation of atoms. These results are compared to the corresponding events observed for solids, where the dominant decay products are inelastically scattered photoelectrons.

A systematic study of the size dependence of the vibrational modes of carbon clusters with 5-70 atoms is presented. The vibrational frequencies are measured using photoelectron spectroscopy of mass-separated negatively charged clusters. The clusters are carefully annealed. Only the most stable isomers are present in the beam after the annealing. Observed vibrational modes can be assigned to four dominant isomeric structures: linear chains (C5-, C7-, and C9-), monocyclic rings (C10-, C12-, C14-, C16-, and C18-), bicyclic rings (C20-, C24-, and C28-), and fullerenes (even n>C30-).

Photoelectrons from mass-identified jet-cooled tin and lead cluster anions (Sn n , Pb n ) are detached by ultraviolet laser light (hngr=3.68 eV). The photoelectron energy spectra give the detachment energies of ground state cluster anions (electron affinities) as well as excitation energies of neutral clusters in the geometry of the anions. The energy spectra for Sn n are dominated by flat thresholds with ann-dependence similar to that of other group IV clusters. In contrast, for Pb n we find pronounced narrow lines close to threshold, generally followed by a 0.3 1.4 eV gap which indicates closed-shell behaviour of Pb n for nearly alln.

Aluminium cluster anions (Al n ) are produced by laser vaporization without additional ionization and cooled by supersonic expansion. Photoelectrons from mass-identified anion bunches (n=2...25) are detached by laser light (hv=3.68 eV) and undergo energy analysis in a magnetic bottle-type time-of-flight spectrometer. The measurements provide information about the electronic excitation energies from ionic ground states to neutral states of the clusters. In contrast to bulk aluminium these cluster photoelectron spectra partially have well-resolved bands which originate from low-lying excited bands. For small clusters, especially the aluminium dimer and trimer, quantum-chemical calculations will be compared to the measurements. The electron affinity size dependence of larger clusters shows conclusive evidence for "shell" effects.