1. Centre for Ultrafast Imaging; University of Hamburg; Luruper Chaussee 149 22761 Hamburg Germany
2. Department of Chemistry; University of Sheffield; Brook Hill Sheffield South Yorkshire S3 7HF UK
3. Department of Chemistry; University at Buffalo; The State University of New York; 359 Natural Sciences Complex; Buffalo NY 14260-3000 USA
4. Institute for Chemical Technology and Polymer Chemistry; Karlsruhe Institute of Technology; Engesserstrasse 18 76131 Karlsruhe Germany