1. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China, Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, D-14195 Berlin, Germany, and Departments of Chemistry and Physics, University of California, Berkeley, California 94720