Noncrystalline structure of argon clusters. I. Polyicosahedral structure of Ar N clusters, 20<N<50

Abstract

Small argon clusters are produced in a free jet expansion and studied by electron diffraction. Due to their very low proportion in the beam sample in comparison to the monomers, the smallest detectable clusters contain about 20 atoms. When they grow up to some 50 atoms, they present the same noncrystalline structure. This structure is identical to that of solid models constructed during a molecular dynamics calculation by cooling a liquid drop of atoms interacting through a Lennard-Jones potential. Because it is composed of icosahedra of 13 atoms, either joined one to the other either interpenetrating each other, this structure may be called polyicosahedral. The comparison between theoretical and experimental diffraction functions leads to an estimate of the cluster temperature 27±3 K and of the proportion of monomers in the beam. We discuss the similarity in the radial distribution functions of both PIC models and bulk amorphous materials, and give arguments for the stability of the clusters.