Theoretical study of [Na(H2O)n](-) (n=1-4) clusters: Geometries, vertical detachment energies, and IR spectra

Geometries, vertical detachment energies (VDEs), and IR spectra of [Na(H2O) (n)](-) (n = 1-4) have been investigated by an ab initio MO method at the c orrelated level. Water molecules are bound to Na- via Na-H as well as hydro gen-bond interactions. The calculated VDEs are in good agreement with the r ecent photoelectron spectroscopy, and all observed bands are assignable to the 3(2)S(Na)-3(1)S(Na-) and 3(2)P(Na)-3(1)S(Na-) type transitions perturbe d by hydration. They are shifted to higher energy with increasing n by keep ing their separation almost unchanged, which reflects the hydration structu re of Na-. We also report the calculated IR spectra that are informative ab out the ionic Na-H bonds and the hydrogen-bond network among water molecule s in the clusters.