PNNL

Abstract

The existence of a transitional size regime where preferential stabilization alternates between “all-surface” (all atoms on the surface of a cluster) and “internally solvated” (one water molecule at the center of the cluster, fully solvated) configurations with the addition or the removal of a single water molecule, predicted earlier with the TTM2-F interaction potential, has been confirmed from electronic structure calculations for (H2O)n, n=17-21. The onset of the appearance of the first “interior” configuration in water clusters occurs for n=17. This trend was previously predicted by the TTM2-F interaction potential and it is confirmed from electronic structure calculations. The observed structural alternation between “interior” and “all-surface” global minima between n=17-21 is accompanied by a corresponding spectroscopic signature, namely the undulation in the position of the most red-shifted OH stretching vibrations according to the trend: “interior” configurations exhibit more red-shifted OH stretching vibrations than “all-surface” ones. These most red-shifted OH stretching vibrations form distinct groups in the intramolecular region of the spectra and correspond to localized vibrations of donor OH stretches that are connected to neighbors via “strong” (water dimer-like) hydrogen bonds and belong to a water molecule with a “free” OH stretch.