1. Institute of Chemistry, University of Tromsø, N-9037 Tromsø, Norway, Institute of Physics, Stockholm University, S-106 91 Stockholm, Sweden, Institute of Radiochemistry, Forschungszentrum Rossendorf e.V., P.O. Box 510119, D-01314 Dresden, Germany, and Inorganic Chemistry, Department of Chemistry, Royal Institute of Technology (KTH), S-100 44 Stockholm, Sweden