1. Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0240, Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, and Department of Cell Biology and Environmental Sciences, University of Texas Health Center at Tyler, P.O. Box 2003, Tyler, Texas 75710