EFFECT OF CLUSTER-SIZE AND SHAPE ON THE 2P(3 2)4S RESONANCE IN FREE ARGON CLUSTERS/

Two types of excitations (surface and bulk) are responsible for the ma in features of photoabsorption in free Ar clusters between the 244 and 246 eV. Both the oscillator strength for the 2p --> 4s transition and its energy in the bulk are higher for the solid than for a free Ar at om or the Ar atoms at the cluster surface. The comparison of experimen tal and calculated cross-sections and profiles of the 2p(3/2)4s resona nces has been used to estimate the average cluster sizes. Our studies indicate that 2p(3/2)4s resonance spectroscopy may be a useful tool to study the (i) density of structural defects in Ar clusters and (ii) m echanisms of cluster condensation.