1. Department of Physical Chemistry II Ruhr University Bochum Bochum Germany
2. Current affiliation: Department of Chemistry “U. Schiff” University of Florence I-50019 Sesto Fiorentino FI Italy
3. Current affiliation: Dipartimento di Scienze Matematiche e Informatiche Scienze Fisiche e Scienze della Terra (MIFT) Università di Messina 98166 Messina Italy
4. Department of Physics Technische Universität Dortmund 44227 Dortmund Germany