OBSERVATION OF CLUSTER-SPECIFIC EXCITATIONS IN XE(N) CLUSTERS

The absorption spectra of Xe(N) clusters (N = 50-500) exhibit extra ab sorption bands not seen in condensed Xe gas. They show up if the clust er radius is comparable to the radius of the electronic excitation. Fr om the sharpness of the bands and from the energy-level positions it i s concluded that these excitations have a character which combines fea tures seen in molecular Rydberg states and excitons of the solid. This interpretation is supported by simple model calculations. For small c lusters (N less-than-or-equal-to 150) the number of extra absorption b ands reflects the shell structure of the clusters.