On the nature of bulk and surface excitations in Argon clusters

Absorption spectra of Ar clusters containing between 10 and 10$^6$ atoms are dominated by strong transitions into bulk and surface states. The intensity variation of bulk and surface excitations is analyzed within a model, which divides the cluster into a surface layer and into an interior part. The thickness of the surface layer is determined by the intensity ratio of bulk and surface excitations. For then=2, 2′ excitons a reasonable value ranging between the radius of then=2 exciton and the nearest neighbour distance is obtained. In case of then=1 excitons the thickness of the surface layer is much smaller than the nearest-neighbour distance indicating that then=1 surface excitons might be interpreted as excitations of atoms on the cluster surface