1. Contribution from the Department of Chemistry, Georgetown University, 37th and O Streets, NW, Washington, DC 20057-1227, Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742-2111, and CEA-Grenoble, DRFMC/SI3M Laboratoire Physico-Chimie Moleculaire 17, Rue des Martyrs 38054 Grenoble cedex 9, France