1. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
2. Physics Department, Universität Hamburg, 22607 Hamburg, Germany
3. Institute of Experimental Physics, TU Bergakademie Freiberg, 09599 Freiberg, Germany
4. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
5. Center for Free-Electron Laser Science DESY, 22607 Hamburg, Germany