1. Caudill Laboratories, Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
2. U.S. Army Research Office, P.O. Box 12211, Research Triangle Park, North Carolina 27709, United States
3. Ames Laboratory, Ames, Iowa 50011, United States
4. Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States