SIZE-DEPENDENT K-EDGE EXAFS STUDY OF THE STRUCTURE OF FREE AR CLUSTERS

Extended x-ray absorption fine structure (EXAFS) spectroscopy is used to study the size-dependent structural evolution of free clusters. K-e dge EXAFS data are obtained for Ar clusters in beams having mean clust er size ranging from 17 to 2900 atoms per cluster. EXAFS analysis yiel ds size-dependent features which indicate the presence of an fee struc ture at (N) greater than or equal to 200. It has been proposed in the literature that small rare-gas clusters have an icosahedral structure. The transition of this structure to the experimentally observed fee l attice of rare-gas solids has been of long-standing interest and debat e. The implications of our results are discussed in this light.