1. Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
2. Stanford Synchrotron Radiation Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
3. Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
4. Department of Chemistry and Loker Hydrocarbon Research Institute, University of Southern California, Los Angeles, California 90089-1661, United States