1. Institute of Applied Physics University of Bern Sidlerstrasse 5 3012 Bern Switzerland
2. Department of Chemistry, Biochemistry and Pharmaceutical Sciences University of Bern Freiestrasse 3 3012 Bern Switzerland
3. Present address: College of Chemistry Chemical Engineering and Material Science Shandong Normal University Jinan 250014 P. R. China
4. Department of Physical Chemistry University of Geneva 30 Quai Ernest Ansermet 1211 Geneva Switzerland
5. CNRS, MOLTECH-ANJOU UNIV Angers Angers F-49000 France
6. Department of Chemistry Temple University, Pennsylvania Philadelphia Pennsylvania 19122 USA