1. Contribution from the Department of Chemistry, Stanford University, Stanford, California 94305, Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford, California 94309, Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, and Departamento de Química, CQFB, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2825-114 Caparica, Portugal