1. Institute of Applied Physics, Academy of Sciences of Moldova, Academy Str. 5, MD-2028 Kishinev, Moldova
2. Department of Chemistry, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel
3. Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012 Bern, Switzerland