1. Institut für Physikalische und Theoretische Chemie, Technische Universität München, Lichtenbergstrasse 4, 85747 Garching, Germany, CQFB, Department of Chemistry, Faculty of Sciences and Technology, Universidade Nova de Lisboa, P-2829-516 Caparica, Portugal, and CEFITEC, Department of Physics, Faculty of Sciences and Technology, Universidade Nova de Lisboa, P-2829-516 Caparica, Portugal