1. Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551, Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts 01003, and Physikalische Chemie I, Universität Bielefeld, D-33501 Bielefeld, Germany