1. Institute of Physics, Stockholm University, P.O. Box 6730, S-11385 Stockholm, Sweden, Theoretical Chemistry, Department of Chemistry, Royal Institute of Technology (KTH), S-10044 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