1. H. C. Brown Laboratory, Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
2. P. Roy and Diana T. Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
3. Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
4. Department of Physics & Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States