1. Contribution from the Department of Applied Science, University of California, Davis, California 95616, Department of Inorganic Chemistry and Catalysis, Debye Institute, Utrecht University, 3584 CA Utrecht, The Netherlands, Department of Chemistry, University of Florida, Gainesville, Florida 32611, Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, and Melvin Calvin Laboratory, Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720