1. Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada, Snowbird Software, Inc., 71A Leland Street, Hamilton, Ontario, L8S 3A1, Canada, and William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 906 Battelle Boulevard, P.O. Box 999, KI-83, Richland, Washington 99352