1. Institute for Physical Chemistry, Bulgarian Academy of Science, 1113 Sofia, Bulgaria
2. Institut für Physik, Johannes Gutenberg Universität Mainz, Staudinger Weg 7, 55099 Mainz, Germany
3. Department of Physics, American University of Beirut, Beirut, Lebanon
4. Chemical-Pharmaceutical Academy, Prof. Popova 14, 197022 St. Petersburg, Russia