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 correlated level. Water molecules are bound to Na- via Na−H as well as hydrogen-bond interactions. The calculated VDEs are in good agreement with the recent photoelectron spectroscopy, and all observed bands are assignable to the 32S(Na)−31S(Na-) and 32P(Na)−31S(Na-) type transitions perturbed by hydration. They are shifted to higher energy with increasing n by keeping their separation almost unchanged, which reflects the hydration structure of Na-. We also report the calculated IR spectra that are informative about the ionic Na−H bonds and the hydrogen-bond network among water molecules in the clusters.