The solvation of two electrons in the gaseous clusters of Na-(NH3)n and Li-(NH3)n

Alkali metal ammonia clusters, in their cationic, neutral, and anionic form, are molecular models for the alkali-ammonia solutions, which have rich variation of phases with the solvated electrons playing an important role. With two s electrons, the Na-(NH3)(n) and Li-(NH3)(n) clusters are unique in that they capture the important aspect of the coupling between two solvated electrons. By first principles calculations, we demonstrate that the two electrons are detached from the metal by n = 10, which produces a cluster with a solvated electron pair in the vicinity of a solvated alkali cation. The coupling of the two electrons leads to either the singlet or triplet state, both of which are stable. They are also quite distinct from the hydrated anionic clusters Na-(H2O)(n) and Li-(H2O)(n), in that the solvated electrons are delocalized and widely distributed among the solvent ammonia molecules. The Na-(NH3)(n) and Li-(NH3)(n) series, therefore, provide another interesting type of molecular model for the investigation of solvated electron pairs. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3697968]