1. Department of Physics, Washington State University, 2710 University Drive, Richland, Washington 99352, W. R. Wiley Environmental Molecular Sciences Laboratory, Chemical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, MS-K88, Richland, Washington 99352, and Chemistry Department, The University of Alabama, Shelby Hall, Box 870336, Tuscaloosa, Alabama 35487-0336