1. Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada, Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, Stuttgart D-70569, Germany, and William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 906 Batelle Boulevard, P.O. Box 999, KI-83, Richland, Washington 99352