1. Departament de Química Física, Universitat de València, Dr. Moliner 50, E-46100 Burjassot, Spain, Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, and Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 18200 Prague 8, Czech Republic