PHOTOELECTRON-SPECTRA OF THE HYDRATED IODINE ANION FROM MOLECULAR-DYNAMICS SIMULATIONS

In this paper, we present the first calculations, based on molecular dynamics techniques, of vertical electron binding energies for the ionic clusters I- (H2O)n, (n=1-15). In these studies, we employ the polarizable water model developed recently by Dang [J. Chem. Phys. 97, 2659 (1992)]. We construct the ion-water potential so that the successive binding energies for the ionic clusters, the hydration enthalpy, and the structural properties of the aqueous ionic solution agree with the results obtained from experiments. The simulated vertical electron binding energies compare well with recent data from photoelectron spectroscopy experiments by Markovich, Giniger, Levin, and Cheshnovsky [J. Chem. Phys. 95, 9416 (1991)]. Interestingly, we obtain coordination numbers of 4 to 5 for the ionic clusters, I- (H2O)n, for n greater-than-or-equal-to 6. This result is smaller than the coordination number, based on the energetic properties predicted by Markovich et al Possible reasons for this discrepancy are discussed in the paper. Furthermore, our simulations place the iodine anion on the surface of the water clusters. This study demonstrates the usefulness of the molecular dynamics technique and provides a detailed picture of the ion solvation in clusters.