Valence- and inner-shell spectroscopy on rare-gas clusters

An overview of the present status of valence- and inner-shell spectroscopy on rare-gas clusters is given. Fluorescence excitation, time-of-flight ion and photoelectron spectroscopy with synchrotron excitation was used to study the electronic level structure of rare-gas clusters. Ne and Ar clusters covering the size range from the monomer up to a few thousand atoms/cluster are used as examples. Specific advantages and limitations of different methods of the study of electronic level structure as well as geometrical structure are discussed. A wealth of information on the evolution of electronic level structure has already been obtained. Nevertheless, several interesting questions concerning the evolution of energy-level shifts remain unresolved. Prospects for future work and experimental developments are given.