Localization of an excess electron in sodium halide clusters

Abstract

Measurements of abundances and electronic properties of neutral sodium halide clusters, ${\mathrm{Na}}_{\mathrm{n}}$ ${\mathrm{X}}_{\mathrm{n}\mathrm{-}1}$ (n<100), demonstrate a remarkable range of excess-electron-dominated behavior. Clusters which can form a cubic lattice containing a single anion vacancy have the electron localized in the vacancy, stabilizing the cluster against fragmentation. For the singular values of n which correspond to a filled cubic lattice, the electron is very weakly bound. A simple quantitative model of electron localization is proposed to account for the observed patterns of abundances and electron binding energies.