Optical properties of argon clusters in the VUV

Optical properties of argon clusters and microcrystals containing between 2 and 500000 atoms have been studied in the VUV using fluorescence excitation spectroscopy with Synchrotron Radiation. Below the ionisation limit the fluorescence yield roughly corresponds to the absorption cross section. Surface and bulk excitations as well as Rydberg states have been observed. The evolution with cluster size shows strong variations of the band intensities whereas the energetic positions are only slightly shifted compared to the solid. It turns out that the Wannier excitons appear only in clusters if the radius of the cluster is approximately four times larger than the radius of the exciton. (orig.)