1. Institute of Physical Chemistry “Rocasolano”, CSIC, Serrano 119, 28006 Madrid, Spain
2. Perkin-Elmer España S.L., Ronda de Poniente 19, 28760 Tres Cantos, Madrid, Spain
3. Department of Chemistry and Biochemistry, University of Missouri-St. Louis, One University Boulevard, St. Louis, Missouri 63121-4499, United States