1. Department of Physical Chemistry, Chalmers University of Technology, SE-412 96 Göteborg, Sweden; Laboratories for Molecular Dynamics and Spectroscopy, Chemistry Department, K. U. Leuven, Celestijnenlaan 200 F 3001, Leuven, Belgium; and Institute of Materials Chemistry, Tampere University of Technology, P.O. Box 541, FIN-33101 Tampere, Finland