1. GKSS Research Centre, Max-Planck Strasse, 21502 Geesthacht, Germany, Department of Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C, Denmark, Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka 812-8581, Japan, and Department of Physics, University of Fribourg, Perolles, 1700 Fribourg, Switzerland