1. Contribution from the Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, University Park, Los Angeles, California 90089-1661, the Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, and the Department of Chemistry, Texas A&M University, P.O. Box 300012, College Station, Texas 77842-3012