Effect of cluster size and shape on the 2p324s resonance in free argon clusters

Two types of excitations (surface and bulk) are responsible for the main 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 atom or the Ar atoms at the clusters surface. The comparison of experimental and calculated cross-sections and profiles of the 2p324s resonances has been used to estimate the average cluster sizes. Our studies indicate that 2p324s resonance spectroscopy may be a useful tool to study the (i) density of structural defects in Ar clusters and (ii) mechanism of cluster condensation.