We describe a new experimental setup for photoluminescence spectroscopy on van der Waals clusters. It consists of a molecular beam apparatus with a cluster beam installed behind a high intensity vacuum ultraviolet synchrotron radiation beamline. Special emphasis was given to the design of a very intense cluster source which can also be used for the preparation of quantum clusters (He,H2). For the determination of the cluster size a time-of-flight mass spectrometer can be attached to the setup. In addition, an atomic cross jet is installed in the experimental chamber which can be used for mass separation or for doping of the clusters. The luminescence light can be recorded with several different detectors or spectrally analyzed with a secondary monochromator which is equipped with a position sensitive detector. The pulsed nature of synchrotron radiation provides the basis for time-resolved measurements in the regime 100 ps–3 μs.

No abstract

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.

We deduce the evolution of electronic excitations in Kr clusters (TV = 2-3000) from fluorescence excitation spectroscopy with synchrotron radiation. In small clusters (7V< 30), a broad absorption band appears, slightly red shifted compared with the atomic 5s(3/2)\ resonance line. Intermediate-size clusters (50200). Absorption processes at the surface and inside the cluster correlate well to the surface-to-volume ratio of the clusters.

No abstract