Photoelectron spectra of Ag n Ϫ clusters with nϭ1-21 recorded at different photon energies ͑hϭ4.025, 4.66, 5.0, and 6.424 eV͒ are presented. Various features in the spectra of Ag 2 Ϫ-Ag 9 Ϫ can be assigned to electronic transitions predicted from quantum chemical ab initio calculations. While this comparison with the quantum chemical calculations yields a detailed and quantitative understanding of the electronic structure of each individual cluster, a discussion in terms of the shell model is able to explain trends and dominant patterns in the entire series of spectra up to Ag 21 Ϫ .

Photoelectron spectra of Al; and Ga; clusters in the size range n = l-l 5 are presented. Using 5.0 and 3.68 eV W light (KrF excimer and nitrogen laser, respectively), electrons from molecular orbitals corresponding to the 3p and 4p orbitals of the atoms are detached. The spectra reveal a rich fine structure not observed in earlier experiments. The data are compared with the results of quantum chemical calculations. A change in the pattern of the spectra near n = 6 can be interpreted as a transition from planar to compact 3D structures. The spectrum of Al, agrees with the icosahedral structure predicted for this particle. The data do not agree with jellium model predictions. Differences between Al and Ga data can be correlated with the larger binding energy of the Ga 4s band.

We describe a new experimental setup for photoelectron spectroscopy on mass selected clusters. The recently developed pulsed arc cluster ion source (PACIS) for metal and semiconductor clusters is used as an anion source. The design of the PACIS is optimized for maximum intensity of cluster ion production and a minimum internal temperature of the particles. A simple modification allows vaporization of liquid and low melting point metals. The produced anions are mass selected via an inline time-of-flight setup with the option of using a reflectron for increased mass resolution. Photoelectron spectra of the mass selected cluster anions are collected in a "magnetic bottle" type electron spectrometer. First results on copper clusters are presented.

We present a comparison of the electronic level structure of Cu; clusters with the jellium model using photoelectron spectroscopy of metal cluster anions. The spectra are recorded at an energy resolution of 30 meV using photon energies of up to 6.4 eV. We obtain a well resolved picture of the electronic structure of the 4s derived electronic states in the energy region between the localized 3d derived states and the highest occupied molecular orbital. The observed features can be assigned to the Is, lp, and Id shells predicted by the jellium model if ellipsoidal distortions and effects like shake-up processes, multiplet splittings and the s-d hybridization are taken into consideration.

Photoelectron spectra of Na; , Cu; , Ag; , and Au; clusters reveal the electronic structure of these particles. The experimental results are compared to the predictions of quantum chemical calculations and of the shell model. The spectra of Ag; allow for a stringent test of both approaches, because most of the observed features are assigned to s-derived orbitals and they also display much sharper features than the alkali data. A qualitative equivalence of the electronic shell model with high-level quantum chemical calculations in terms of the symmetries of the involved single particle orbitals is found for the delocalized states derived from the atomic s-electrons.