Electron binding and stability of excess-electron alkali halide clusters: Localization and surface states

Metal-excess alkali halide clusters have been investigated experimentally using a cluster-beam source comprised of laser ablation of alkali metal and reaction of helium-seeded halogen gas. Metal-excess neutrals and charged clusters, ${\mathit{M}}_{\mathit{n}}$ ${\mathit{X}}_{\mathit{m}}^{\mathrm{}(+)\mathrm{}}$ where M=Na or Li and X=F, Cl, or Br, have been produced, with the neutral series, ${\mathit{M}}_{\mathit{n}}$ ${\mathit{X}}_{\mathit{n}\mathrm{-}1}$, displaying a wide range of excess-electron-dominated behavior. An extensive investigation of the abundances and electronic properties of ${\mathrm{Na}}_{\mathit{n}}$ ${\mathrm{F}}_{\mathit{n}\mathrm{-}1}$ (nn that correspond to a filled cubic lattice, the excess electron is very weakly bound, and that (ii) clusters that can form a cubic lattice with a single anion vacancy have the electron localized in the vacancy, stabilizing the neutral cluster against atom loss.