1. Center for Free-Electron Laser Science/DESY, Notkestraße 85, D-22607 Hamburg, Germany
2. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
3. ALS, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
4. Institute of Optics and Atomic Physics, TU Berlin, Straße des 17. Juni 135, D-10623 Berlin, Germany