1. Contribution from the Department of Chemical and Nuclear Engineering and Center for Micro-Engineered Materials, University of New Mexico, Albuquerque, New Mexico 87131; Sandia National Laboratories, Albuquerque, New Mexico 87106; Chimie de la Matière Condensée, Université Pierre et Marie Curie, 75005 Paris, France; and Department of Physics, Brookhaven National Laboratory, Upton, New York 11973