AB-INITIO MO STUDY OF NA(NH3)(N) (N=1-6) CLUSTERS AND THEIR IONS - A SYSTEMATIC COMPARISON WITH HYDRATED NA CLUSTERS

Stability and structure of Na(NH3)(n) (n = 1-6) clusters as well as th eir ions have been investigated by the ab initio MO method and systema tically compared with those of Na(H2O)(n) clusters. Both neutral and i on ammonia complexes with n greater than or equal to 4 have an interio r structure where Na is surrounded by NH3 molecules rather than a surf ace structure preferred by Na(H2O)(n) clusters. Both neutral and ion c lusters are stabilized by the Na-N bonds; the interior structure allow s formation of a maximum number of such bonds in the first solvation s hell. The calculated ionization potential as a function of the number of solvent molecules is in good quantitative agreement with experiment and behaves differently from that of the surface structures of Na(H2O )(n) clusters. In the interior structure the SOMO (singly occupied mol ecular orbital) electron is distributed on and between Na and solvent molecules inside the cluster; interior ionization is expected to take place.