1. Biomolecular Optics and Center for Integrated Protein ScienceLudwig-Maximilians-University Munich Oettingenstr. 67 80538 Munich Germany
2. present affiliation: Harvard-Smithsonian Center for Astrophysics Department of AstronomyHarvard University 60 Garden Street Cambridge MA 02138 USA
3. present affiliation: Department of ChemistryTechnical University of Munich Lichtenbergstr. 4 85748 Munich Germany