1. Contribution from the Melvin Calvin Laboratory, Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Department of Chemistry, University of California, Berkeley, California 94720-5230, Department of Applied Science, University of California, Davis, California 95616, and Laboratoire de Chimie Inorganique, UMR CNRS 8613, Université de Paris-Sud, 91405 Orsay, France