1. Institute for Physical Chemistry, University of Göttingen, Tammannstr. 6, 37077 Göttingen, Germany.
2. Department of Dynamics at Surfaces, Max-Planck Institute for Biophysical Chemistry, Am Faßberg 11, 37077 Göttingen, Germany.
3. National Institute of Standards and Technology, Boulder, CO 80305, USA.
4. International Center for Advanced Studies of Energy Conversion, Georg-August University of Göttingen, Tammannstraße 6, 37077 Göttingen, Germany.