1. Physical Chemistry 1, Lund University, P.O. Box 124, SE- 221 00, Lund, Sweden, Department of Physical Chemistry, Åbo Akademi University, Porthansgatan 3-5, FI-20 500 Turku, Finland, Department of Heterogeneous Catalysis, Max-Planck-Institute for Coal Research, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim/Ruhr, Germany, and Institute of Biophysics and X-Ray Structure Research, Austrian Academy of Sciences, Schmiedelstrasse 6, A-8042 Graz, Austria