1. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Department of Chemistry, University of Athens, Panepistimiopolis, 157 71 Zougrafou, Athens, Greece, National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973, and Corporate Research Science Lab, Exxon Research and Engineering Company, Clinton Township, Annandale, New Jersey 08801