1. Department of Physical Chemistry, Institute of Chemical Technology, CZ-166 28 Prague 6, Czech Republic, Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10, CZ-162 53 Prague 6, Czech Republic, and Department of Chemistry, Faculty of Science, University of Porto, Centro de Investigação em Química, Rua do Campo Alegre 687, 4169-007 Porto, Portugal