Connecting Cluster Anion Properties to Bulk: Ion Solvation Free Energy Trends with Cluster Size and the Surface vs Internal Nature of Iodide in Water Clusters

Abstract

There is disagreement in the literature on whether small water clusters (up to ∼60 waters) accommodate an excess iodide anion at the surface, in the interior, or in states intermediate between the two extremes. Small cluster solvation data, the results of ion simulations in model polar solvent clusters of intermediate size, and limiting continuum dielectric trends at large cluster size have been combined to illustrate the progression of the free energy of ion solvation from the smallest cluster size to bulk, establishing a set of general expectations for cluster ion solvation properties vs cluster size. The surface vs internal state issue for iodide in water clusters is examined in the context of the cluster ion properties of solvation thermochemistry, electron vertical detachment thresholds, and vertical detachment energies with specific regard to variation with cluster size and extrapolation to bulk. In aqueous systems, the anionic cluster property of vertical detachment threshold is shown to bear a bet...