Photoionization of Na(NH3)nand Na(H2O)nclusters: A step towards the liquid phase?

Abstract

Ionization potentials (IP's) for Na(${\mathrm{H}}_{2}$O${)}_{\mathit{n}}$ and Na(${\mathrm{NH}}_{3}$${)}_{\mathit{n}}$ are reported for the first time up to n=20. As expected, for Na(${\mathrm{NH}}_{3}$${)}_{\mathit{n}}$ the IP decreases more or less monotonically with decreasing (n+1${)}^{\mathrm{\ensuremath{-}}1/3}$ to a limit consistent with the bulk value of 1.45 eV. In contrast, for Na(${\mathrm{H}}_{2}$O${)}_{\mathit{n}}$ we find the IP to be constant at 3.17 eV for n\ensuremath{\ge}4, close to the bulk value. For comparison we solve a one-electron Schr\"odinger equation in a dielectrically screened Coulomb potential. While agreement with the experiment is reasonable for small n, this one-center model fails for larger clusters, thus giving some first indication for the existence of two-center localized states in these microclusters.