Electronic and geometric properties of doped rare gas clusters with a shell-like structure

Some important but currently unanswered questions concerning the electronic structure and energy dissipation processes in pure rare gas clusters were investigated by embedding small rare gas clusters inside large rare gas clusters. Fluorescence spectroscopy with synchrotron radiation was used as the experimental method. Here, the energetic splitting and the intensity ratios of the first excited states of the clusters as well as desorption processes of excited atoms or molecules were of special interest. In the first part fluorescence excitation spectra of ArMNe7500-clusters (M < 100) in the vacuum-ultraviolet (VUV) as well as in the visible and near-infrared spectral range (VIS/IR) are presented. The embedded clusters were prepared in a ''pick-up'' process, by doping large Ne-clusters with a defined number of Ar-atoms from a cross-jet. With this technique it is possible to build up small clusters of the doped material on the inside of large clusters. Electronic excitation of Ne-clusters (17,3-18 eV) leads to VIS/IR-emission of the embedded Ar-clusters, which indicates an energy transfer to the embedded clusters. Since no energy-transfer is observed for Ne-clusters upon surface excitation, the Ar-atoms condense mainly on the inside. In the energy range of the characteristic absorption of Ar-clusters (11,5 - 13 eV), surface excitons of Ar-clusters embedded in Ne disappear, while new absorption bands appear. They are assigned to excitons at the interface between the Ar-cluster and the Ne host cluster. The observed energy shift of the absorption bands is proportional to the logarithm of the cluster size, which is in agreement with the Frenkel-exciton model. (orig.)