1. Contribution from the Department of Chemistry, Stanford University, Stanford, California 94305, Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Stanford University, Stanford, California 94309, Institut de Ciència de Materials de Barcelona, Campus de la Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain, and Departamento de Química, Instituto Tecnológico e Nuclear, CFMC-UL, P-2686-953 Sacavém, Portugal