1. Chemistry Department, Rensselaer Polytechnic Institute, Troy, New York 12180-3590; Rexam Graphics, R&D Center, 87 Alvord St., South Hadley, Massachusetts 01075; and Chimie de la Matière Condensée, Université Pierre et Marie Curie/CNRS, 4 place Jussieu, 75005 Paris, France