1. Center
for Free-Electron Laser Science, DESY, Notkestrasse 85, 22607 Hamburg, Germany
2. Department
of Chemistry, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany
3. Department
of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
4. The Hamburg Centre for Ultrafast Imaging, Luruper Chausee 149, 22761 Hamburg, Germany
5. Department
of Physics, University of Hamburg, Jungiusstrasse 9, 20355 Hamburg, Germany