1. Laboratoire F. Perrin, URA 2453 CEA-CNRS, Centre d'Etudes de Saclay, Bâtiment 522, 91191 Gif-sur-Yvette Cedex, France, and Computational Center for Molecular Structure and Interactions, Department of Chemistry, Jackson State University, P. O. Box 17910, 1325 Lynch Street, Jackson, Mississippi 39217