Theory for the electron affinity of small clusters of polar molecules (NH3)n

Abstract

A simple theory is presented for the electron affinity of a small cluster of polar molecules (${\mathrm{NH}}_3$ ${)}_{\mathrm{n}}$. We obtain that the excess electron is bound inside the cluster essentially by the electric field resulting from the polarization of the molecular dipole moments. In agreement with experiment we obtain a sharp transition from unstable (${\mathrm{NH}}_3$ ${)}_{\mathrm{n}}$ ${\mathrm{}}^{\mathrm{-}}$ to stable (${\mathrm{NH}}_3$ ${)}_{\mathrm{n}+1\mathrm{}}$ ${\mathrm{}}^{\mathrm{-}}$ with a large barrier against dissociation for a critical cluster size n of about 30.