ARE MODELS OF ANION HYDRATION OVERBOUND? THE SOLVATION OF THE ELECTRON AND CHLORIDE ANION COMPARED

Abstract. By means of a fully polarizable model for the chloride ion-water interaction we show that the modelling of anion solvation suffers from a similar inconsistency as the current electron-solvent potent~als. Either the.bujk h dration enthalpies are correct with the first hydration shell overbound, or the potential 1s adpted t o describe the local environment of the solute at the expense o f a major loss of solvation enthal. I t is argued that boundary effects in the simulation are at least partl responsible for this a m m a. A further parallel between a polarizable aqueous halide ion and the solvated electron is the anisotropy in the surrounding solvent, which is reflected in an asymmetry in the electronic excitation spectrum. 1 The excess electron in water The solvated electron is o f fundamental importance in many chemical processes in solution. In particular the excess electron in polar solvents has been the subject o f intensive experimental and theoretical investigation (for a review of the computer simulation work see Refs. [1,2]). The picture that emerged from these studies is that the excess electron in the solvated state resembles in may respects an anion of moderate size such as C1-. Computer simulation allows us to compare the structure of the solvent around the electron and anion in detail. I t was found that the electron is localized in a cavity wit