1. Adolphe Merkle Institute, University of Fribourg, Rte de l'Ancienne Papeterie, P.O. Box 209, 1723 Marly 1, Switzerland
2. Swiss Light Source, Paul Scherer Institute, 5232 Villigen, Switzerland
3. Division of Physical Chemistry, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, SE-22100 Lund, Sweden