  Cathodoluminescence spectra of free xenon clusters produced by condensation
of xenon-argon gas mixtures in supersonic jets expanding into vacuum were
studied. By varying initial experimental parameters, including xenon
concentration, we could obtain clusters with a xenon core (300-3500 atoms)
covered by an argon outer shell as well as shell-free xenon clusters (about
1500 atoms). The cluster size and temperature (about 40 K for both cases) were
measured electronographically. Luminescence bands evidencing the existence of
bulk and surface excitons were detected for shell-free xenon clusters. The
emission from bulk excitons in small clusters is supposed to be due to
processes of their multiple elastic reflections from the xenon-vacuum
interface. A presence of an argon shell causes extinction of the excitonic
bands. In addition, some new bands were found which have no analogs for bulk
xenon cryosamples.

Atomic and Molecular Clusters;Optics