1. Department of Chemistry and Physics, Hood College, 401 Rosemont Avenue, Frederick, Maryland 21701-8524, United States
2. Department of Chemistry, The University of Memphis, 213 Smith Chemistry Building, Memphis, Tennessee 38152-3550, United States
3. Radiation and Biomolecular Physics Division, Physical Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899-8443, United States