Open Access

Gregor Kastirke, Markus S. Schöffler, Miriam Weller, Jonas Rist, Rebecca Boll, Nils Anders, Thomas M. Baumann, Sebastian Eckart, Benjamin Erk, Alberto De Fanis, Kilian Fehre, Averell Gatton, Sven Eric Grundmann, Patrik Grychtol, Alexander Hartung, Max Hofmann, Markus Ilchen, Christian Sören Janke, Max Kircher, Maksim Kunitski, Xiang Li, Tommaso Mazza, Niklas Melzer, Jacobo Montano, Valerija Music, Giammarco Nalin, Yevheniy Ovcharenko, Andreas Pier, Nils Rennhack, Daniel E. Rivas, Reinhard Dörner, Daniel Rolles, Artem Rudenko, Philipp Schmidt, Juliane Siebert, Nico Strenger, Daniel Trabert, Isabel Vela-Perez, Rene Wagner, Thorsten Weber, Joshua B. Williams, Pawel Ziolkowski, Lothar Schmidt, Achim Czasch, Florian Trinter, Michael Meyer, Kiyoshi Ueda, Philipp V. Demekhin, Till Jahnke

• A central motivation for the development of x-ray free-electron lasers has been the prospect of time-resolved single-molecule imaging with atomic resolution. Here, we show that x-ray photoelectron diffraction—where a photoelectron emitted after x-ray absorption illuminates the molecular structure from within—can be used to image the increase of the internuclear distance during the x-ray-induced fragmentation of an O2 molecule. By measuring the molecular-frame photoelectron emission patterns for a two-photon sequential K-shell ionization in coincidence with the fragment ions, and by sorting the data as a function of the measured kinetic energy release, we can resolve the elongation of the molecular bond by approximately 1.2 a.u. within the duration of the x-ray pulse. The experiment paves the road toward time-resolved pump-probe photoelectron diffraction imaging at high-repetition-rate x-ray free-electron lasers.