1. Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm, Sweden, Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark, and Department of Chemistry, H. C. ⌀rsted Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen ⌀, Denmark