1. Institut für Physikalische und Theoretische Chemie Universität Bonn Römerstraße 164 53117 Bonn Germany
2. Current address: Accumulator Materials Research (ECM) Zentrum für Sonnenenergie-und Wasserstoff-Forschung Baden-Württemberg (ZSW) Lise-Meitner-Str. 24 89081 Ulm
3. Permanent address: National Research Centre Physical Chemistry Dept. El-Bohouth St. Dokki 12311 Cairo Egypt
4. Current address: Key Laboratory of Chemical reaction engineering of Shaanxi Province College of Chemistry & Chemical engineering Yan'an University Yan'an 716000 P.R. China