1. Department of Chemical Engineering and Materials Science, University of California, Irvine, California 92697, Department of Chemistry, Korea Advanced Institute of Science and Technology, 373-1 Geseong-dong, Yuseong-gu, Daejeon, 305-701, Korea, and Quantum Science Research Group, Hewlett-Packard Laboratories, MS 1123, 1501 Page Mill Road, Palo Alto, California 94304