1. Department of Chemistry and Biochemistry, University of California Santa Barbara, California 93106-9510, FOM-Institute for Plasmaphysics Rijnhuizen, Edisonbaan 14, NL-3439 MN Nieuwegein, The Netherlands, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry and Center for Complex Molecular Systems and Biomolecules, Academy of Sciences of the Czech Republic, 166 10 Prague 6, Czech Republic