1. Contribution from the Department of Chemistry, University of California, Berkeley, Berkeley, California 94720-1460, Chemical Sciences Division, Lawrence Berkeley Laboratory, 1 Cyclotron Road, Berkeley, California 94720, Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310, and Department of Chemistry, Florida State University, Tallahassee, Florida 32306-3006