1. Kitt Peak National Observatory, National Optical Astronomy Observatories, Tucson, AZ 85726, USA.
2. Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1, and Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA.
3. National Solar Observatory, National Optical Astronomy Observatories, Post Office Box 26732, Tucson, AZ 85726, USA.
4. Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.