Double Core-Hole Generation in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> Molecules Using an X-Ray Free-Electron Laser: Molecular-Frame Photoelectron Angular Distributions
Gregor Kastirke, M. S. Schöffler, M. Weller, J. Rist, Rebecca Boll, N. Anders, T. Baumann, S. Eckart, Benjamin Erk, A. De Fanis, K. Fehre, Averell Gatton, Sven Grundmann, Patrik Grychtol, Alexander Hartung, M. Hofmann, Markus Ilchen, Christian Jänke, M. Kircher, M. Kunitski, Xiang Li, Tommaso Mazza, N. Melzer, J. Montaño, Valerija Music, G. Nalin, Yevheniy Ovcharenko, A. Pier, Nils Rennhack, Daniel E. Rivas, R. Dörner, Daniel Rolles, Artem Rudenko, Philipp Schmidt, J. Siebert, N. Strenger, D. Trabert, Isabel Vela-Pérez, R. Wagner, Th. Weber, Joshua Williams, Pawel Ziółkowski, Lothar Schmidt, A. Czasch, Kiyoshi Ueda, Florian Trinter, Michael Meyer, Philipp V. Demekhin, T. Jahnke
Abstract
We report on a multiparticle coincidence experiment performed at the European X-ray Free-Electron Laser at the Small Quantum Systems instrument using a COLTRIMS reaction microscope. By measuring two ions and two electrons in coincidence, we investigate double core-hole generation in O_{2} molecules in the gas phase. Single-site and two-site double core holes have been identified and their molecular-frame electron angular distributions have been obtained for a breakup of the oxygen molecule into two doubly charged ions. The measured distributions are compared to results of calculations performed within the frozen- and relaxed-core Hartree-Fock approximations.