1. Department of Physics, Institute for Energy Technology, NO-2027 Kjeller, Norway
2. Departamento de Química, Universidade de Coimbra, PT-3004-535 Coimbra, Portugal
3. Departamento de Física, CICECO, Universidade de Aveiro, PT-3810-193 Aveiro, Portugal
4. Fachbereich Chemie, Bergische Universität Wuppertal, DE-42097 Wuppertal, Germany
5. GKSS Research Centre, DE-21502 Geesthacht, Germany
6. Department of Physics, POB 64, FI-00014 University of Helsinki, Finland