1. Paul Scherrer Institute and ETH Zürich, CH-5232 Villigen PSI, Switzerland
2. Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
3. Lehrstuhl für Theoretische Chemie, Universität Bonn, Wegelerstrasse 12, D-53115 Bonn, Germany
4. Institute Laue Langevin, Avenue des Martyrs, BP 156, F-38042 Grenoble Cedex 9, France
5. Institute of Chemistry, Universitetsparken 5, DK-2100 Copenhagen, Denmark