1. Department of Chemistry, Institute for Biophysical Dynamics, and James Franck Institute, University of Chicago, Chicago, Illinois 60637, United States
2. Center for Bio/Molecular Science and Engineering, Code 6900, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States
3. National Research Council, Washington, D.C. 20001, United States
4. College of Science, George Mason University, Fairfax, Virginia 22030, United States
5. Electronic Science and Technology Division, Code 6800, U.S. Naval Research Laboratory, Washington, D.C. 20375, United States