Theoretical study of [Na(NH3)(n)](-) (n=1-4)

In connection with the recent photoelectron spectroscopy of negatively char ged Na atom in ammonia clusters, the geometries, electronic state, vertical detachment energies, and harmonic frequencies of [Na(NH3)(n)](-)-(n =1-4) have been studied by the ab initio MO method. Structures having as many Na- N bonds as possible becomes more stable than other isomers as it grows. The Na 3 s electrons are widely sp;ead and delocalized in space outside the [N a(NH3)(n)](+) core for n greater than or equal to2. The dramatic redshifts of the photoelectron band for the 3(2)P-type transition with inreasing n re flect the electronic change from an atomic state to one-center Rydberg-type states in the neutrals. The frequencies of the combined vibrations of the NH3 mode are nearly degenerate and are expected to coalesce into only one s trong IR band in the-NH stretch region irrespective of n. (C): 2000 America n Institute of Physics. [S0021-9606(00)0945-X].