The original version of this Article contained an error in the fifth sentence of the first paragraph of the ‘Application on H2’ section of the Results, which incorrectly read ‘The role of electron correlation is quite apparent in this presentation: Fig. 1a is empty for the uncorrelated Hartree–Fock wave function, since projection of the latter wave function onto the 2pσu orbital is exactly zero, while this is not the case for the fully correlated wave function (Fig. 1d); also, Fig. 1b, c for the uncorrelated description are identical, while Fig. 1e, f for the correlated case are significantly different.’ The correct version replaces ‘Fig. 1e, f’ with ‘Fig. 2e and f’.

The toolbox for imaging molecules is well-equipped today. Some techniques visualize the geometrical structure, others the electron density or electron orbitals. Molecules are many-body systems for which the correlation between the constituents is decisive and the spatial and the momentum distribution of one electron depends on those of the other electrons and the nuclei. Such correlations have escaped direct observation by imaging techniques so far. Here, we implement an imaging scheme which visualizes correlations between electrons by coincident detection of the reaction fragments after high energy photofragmentation. With this technique, we examine the H2 two-electron wave function in which electron-electron correlation beyond the mean-field level is prominent. We visualize the dependence of the wave function on the internuclear distance. High energy photoelectrons are shown to be a powerful tool for molecular imaging. Our study paves the way for future time resolved correlation imaging at FELs and laser based X-ray sources.

In this work we present a comprehensive and detailed study of Interatomic Coulombic Decay (ICD) occurring after irradiating argon dimers with XUV-synchrotron radiation. A manifold of different decay channels is observed and the corresponding initial and final states are assigned. Additionally, the effect of nuclear dynamics on the ICD electron spectrum is examined for one specific decay channel. The internuclear distance-dependent width Γ(R) of the decay is obtained from the measured kinetic energy release distribution of the ions employing a classical nuclear dynamics model.

We investigate the photodouble ionization of H_{2} molecules with 400 eV photons. We find that the emitted electrons do not show any sign of two-center interference fringes in their angular emission distributions if considered separately. In contrast, the quasiparticle consisting of both electrons (i.e., the "dielectron") does. The work highlights the fact that nonlocal effects are embedded everywhere in nature where many-particle processes are involved.

APS/123-QED Hydrogen and fluorine migration in photo-double-ionization of 1,1-difluoroethylene (1,1-C 2 H 2 F 2 ) near and above threshold B. Gaire, 1 I. Bocharova, 1 F. P. Sturm, 1, 2 N. Gehrken, 1, 2 J. Rist, 1, 2 H. Sann, 2 M. Kunitski, 2 J. Williams, 2 M. S. Sch¨ offler, 2 T. Jahnke, 2 B. Berry, 3 M. Zohrabi, 3 M. Keiling, 2, 4 A. Moradmand, A. L. Landers, 4 A. Belkacem, 1 R. D¨orner, 2 I. Ben-Itzhak, 3 and Th. Weber 1 Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA Institut f¨ ur Kernphysik, Goethe-Universit¨ at, Max-von-Laue-Str.1, 60438 Frankfurt am Main, Germany J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS 66506, USA Department of Physics, Auburn University, AL 36849, USA (Dated: February 26, 2014) We have studied the nondissociative and dissociative photo-double-ionization of 1,1- difluoroethylene using single photons of energies ranging from 40 to 70 eV. Applying a coincident electron-ion three-dimensional-momentum imaging technique, kinematically complete measurements have been achieved. We present the branching ratios of the six reaction channels identified in the experiment. Electron-ion energy maps and relative electron emission angles are used to distinguish between direct and indirect photo-double-ionization mechanisms at a few different photon energies. The influence of selection and propensity rules is discussed. Threshold energies of double-ionization are extracted from the sum of the kinetic energies of the electrons, which hint to the involvement of different manifolds of states. The dissociative ionization channels with two ionic fragments are explored in detail by measuring the kinetic energy release of the fragment ions, sum of the kinetic energies as well as the energy sharing of the two emitted electrons. We investigate the migration of hydrogen and fluorine atoms and compare the experimental results to the photo-double-ionization of centro-symmetric linear and planar hydrocarbons (C 2 H 2 and C 2 H 4 ) whenever possible. PACS numbers: 33.80.Eh, 33.90.+h I. INTRODUCTION Photo-double-ionization (PDI) is a process in which two electrons are removed from an atom or a molecular target with a single photon. Studies of PDI lead to a better understanding of the correlation between the elec- trons, the ionization mechanisms leading to the ejection of the two electrons, selection and propensity rules pro- hibiting transitions, and the molecular dynamics during the transition from the neutral ground state to the re- spective dication or the ionic fragments. The ionization to the dication states can occur either through a direct or an indirect process. In the direct process (sometimes also referred to as two-step-one, TS1) the two electrons are ejected simultaneously. In the indirect process (some- times also referred to as a sequential process) photoe- jection of one electron leads to an intermediate cation state, which later decays by autoionization or other pro- cesses (e.g. Auger decay, fluorescence etc.). After a cou- ple of decades of studying the PDI of simple atoms and diatomic molecules (e.g. He, H 2 , N 2 , CO) in great de- tail [1–9], the investigation has been extended to poly- atomic molecules in order to gain a general understand- ing of the double ionization process in more complex sys- tems. Simple hydrocarbon molecules are an ideal test bed for a series of studies with increasing complexity. Here we choose the 1,1-difluoroethylene (1,1-C 2 H 2 F 2 , H H >C= C C= H F C C= C< 2 2 2 F F H We expect differences in the PDI of the valance elec- trons of 1,1-C 2 H 2 F 2 as compared to C 2 H 4 . For exam- ple, the propensity rule proposed for the PDI of centro- symmetric molecules [9, 11, 12], which states that the triplet gerade and singlet ungerade electronic states of the dications are likely to be populated, is no longer valid for 1,1-C 2 H 2 F 2 . Hence, the nondissociative ionization (NDI) of these two species can be very different. In ad- dition, a variety of reaction channels can be expected in the dissociative ionization (DI) of 1,1-C 2 H 2 F 2 . For in- stance, in C 2 H 4 the migration of H atoms from one side of the C=C double bond to the other simply cannot be distinguished (at least in our experiments). In contrast, a migration of atoms from the opposite sides of the double bond in 1,1-C 2 H 2 F 2 leads to distinguishable conforma- tions of the molecule. The symmetric breakup channel of 1,1-C 2 H 2 F 2 leading to two CHF + fragment ions, on the other hand, is very complex since it would require multiple bond breaking and a subsequent rearrangement of the constituent atoms, which is obviously not the case for C 2 H 4 and C 2 H 2 due to their mirror symmetry. In the past Ibuki and coworkers explored the PDI of 1,1-C 2 H 2 F 2 and 1,1-C 2 H 2 D 2 in the photon energy range of 37-85 eV using a photoion-photoion coincidence (PIPICO) technique [13]. They measured the branching