1. Department of Pure Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G3, Canada
2. Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G3, Canada
3. Department of Chemistry, Duke University, Durham, North Carolina 27708, USA
4. Department of Physics, Duke University, Durham, North Carolina 27708, USA
5. Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA