1. Contribution from the Department of Chemistry, Organic and Inorganic Chemistry, The Royal Institute of Technology, S-10044 Stockholm, Sweden, Institute of Physics, The AlbaNova University Center, S-10691 Stockholm, Sweden, and Institut für Nukleare Entsorgung, Forschungszentrum Karlsruhe, D-76344 Eggestein-Leopoldshafen, Germany