1. Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139.
2. Gorlaeus Laboratorium, Rijksuniversiteit te Leiden, NL-2300 RA Leiden, The Netherland.
3. Department of Chemistry, Brandeis University, Waltham, MA 02254.
4. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139.