1. Department of Physics, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany
2. Institute of Physics, Poznan University of Technology, Piotrowo 3, 60-965 Poznan, Poland
3. Department of Chemistry, University of Hamburg, Martin-Luther-King-Platz
6, D-20146 Hamburg, Germany
4. Department of Chemistry, Technical University of Kaiserslautern, Erwin-Schrödinger-Str. 52, D-67663 Kaiserslautern, Germany