1. a Center for Free–Electron Laser Science , Notkestrasse 85, 22607 , Hamburg , Germany
2. b Max–Planck–Institut für Kernphysik , Saupfercheckweg 1, 69117 , Heidelberg , Germany
3. c Fritz–Haber–Institut der Max–Planck–Gesellschaft , Faradayweg 4–6, 14195 , Berlin , Germany
4. d Laboratoire Aimé Cotton, CNRS, Bâtiment 505 , Université Paris–Sud , 91405 , Orsay , France
5. e Radboud University Nijmegen , Institute for Molecules and Materials , Heyendaalseweg 135, 6525 AJ , Nijmegen , the Netherlands