1. Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551, Department of Chemistry, Bielefeld University, D-33615 Bielefeld, Germany, Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts 01003, and School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853