1. Contribution from the School of Chemistry, University of Manchester, Oxford Road, Manchester, U.K. M13 9PL, Chemistry Department, Brookhaven National Laboratory, P.O. Box 5000, Upton, New York 11973-5000, Laboratory of Chemical and Biological Dynamics, Center for Research on Molecular Electronics and Photonics, University of Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium, Departamento de Química Orgánica, ICMA, Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain, and EPSRC National...