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

There is disagreement in the literature on whether small water cluster s (up to similar to 60 waters) accommodate an excess iodide anion at t he surface, in the interior, or in states intermediate between the two extremes. Small cluster solvation data, the results of ion simulation s in model polar solvent clusters of intermediate size, and limiting c ontinuum dielectric trends at large cluster size have been combined to illustrate the progression of the free energy of ion solvation from t he smallest cluster size to bulk, establishing a set of general expect ations for cluster ion solvation properties vs cluster size. The surfa ce vs internal state issue for iodide in water clusters is examined in the context of the cluster ion properties of solvation thermochemistr y, electron vertical detachment thresholds, and vertical detachment en ergies with specific regard to variation with cluster size and extrapo lation to bulk. In aqueous systems, the anionic cluster property of ve rtical detachment threshold is shown to bear a better correspondence t han the cluster vertical detachment energy (peak center) to the bulk p roperty of the anionic defect photoemission threshold. It is concluded that in aqueous iodide clusters there is a gradual progression from s urface states at small cluster size to internal states at large cluste r size with the intervening region exhibiting an intermediate degree o f surface character. Small I-(H2O)(n) clusters are unlike bulk I-(ag) in this regard, yet meaningful extrapolations of the photodetachment d ata to the bulk behavior can be made.