M. H. Prior

Ultrafast Probing of Core Hole Localization in N2

Although valence electrons are clearly delocalized in molecular bonding frameworks, chemists and physicists have long debated the question of whether the core vacancy created in a homonuclear diatomic molecule by absorption of a single x-ray photon is localized on one atom or delocalized over both. We have been able to clarify this question with an experiment that uses Auger electron angular emission patterns from molecular nitrogen after inner-shell ionization as an ultrafast probe of hole localization. The experiment, along with the accompanying theory, shows that observation of symmetry breaking (localization) or preservation (delocalization) depends on how the quantum entangled Bell state created by Auger decay is detected by the measurement.

Complete photo-fragmentation of the deuterium molecule

All properties of molecules—from binding and excitation energies to their geometry—are determined by the highly correlated initial-state wavefunction of the electrons and nuclei. Details of these correlations can be revealed by studying the break-up of these systems into their constituents. The fragmentation might be initiated by the absorption of a single photon, by collision with a charged particle or by exposure to a strong laser pulse: if the interaction causing the excitation is sufficiently understood, the fragmentation process can then be used as a tool to investigate the bound initial state. The interaction and resulting fragment motions therefore pose formidable challenges to quantum theory. Here we report the coincident measurement of the momenta of both nuclei and both electrons from the single-photon-induced fragmentation of the deuterium molecule. The results reveal that the correlated motion of the electrons is strongly dependent on the inter-nuclear separation in the molecular ground state at the instant of photon absorption.

Matter wave optics perspective at molecular photoionization: K-shell photoionization and Auger decay of N2

In this paper, we shed new light on the molecular photoionization of a diatomic molecule. We will elaborate the differences and analogy between a quantum optical and light?matter interaction approach in a study of K-shell photoionization of N2 in which the photoelectron and the subsequently emitted Auger electron are both measured in coincidence in the body fixed frame of the molecule. The two electrons form an entangled state inside a double slit. By changing the photon energy we create different types of interference in the photoelectron and the Auger electron wave.

The hollow atoms

Abstract This talk briefly reviews the atomic properties of the hollow atoms and presents recent results on the interaction of highly charged ions with surfaces.

Auger decay of 1 σ g and 1 σ u hole states of the N 2 molecule: Disentangling decay routes from coincidence measurements

Results of the most sophisticated measurements in coincidence with the angular-resolved K-shell photoelectrons and Auger electrons and with two atomic ions produced by dissociation of N{sub 2} molecule are analyzed. Detection of photoelectrons at certain angles makes it possible to separate the Auger decay processes of the 1{sigma}{sub g} and 1{sigma}{sub u} core-hole states. The Auger electron angular distributions for each of these hole states are measured as a function of the kinetic-energy release of two atomic ions and are compared with the corresponding theoretical angular distributions. From that comparison one can disentangle the contributions of different repulsive doubly charged molecular ion states to the Auger decay. Different kinetic-energy-release values are directly related to the different internuclear distances. In this way one can trace experimentally the behavior of the potential energy curves of dicationic final states inside the Frank-Condon region. Presentation of the Auger-electron angular distributions as a function of kinetic-energy release of two atomic ions opens a new dimension in the study of Auger decay.

Cold Target Recoil Ion Momentum Spectroscopy

The experimental technique of Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) is described. It allows a three dimensional imaging of momentum space of the recoiling ion for all ionizing atomic reaction with 4π solid angle for momentum measurement. The resolution presently achieved is ±0.035 a.u.. Depending on the collision system this corresponds to a resolution in projectile energy loss of down to ΔE/E=10−9 and a scattering angle resolution of down to 10−9 rad for fast heavy ion collisions. We discuss the experimental technique and some recent results on dynamics of recoil ion production for electron capture, target ionization and projectile electron loss.

Photo double ionization of helium 100 eV and 450 eV above threshold: III. Gerade and ungerade amplitudes and their relative phases

We present a joint experimental and theoretical study of the gerade and ungerade amplitudes of the photo double ionization of helium at excess energies of 100 eV and 450 eV above the threshold. We describe a method of extracting the amplitudes from a COLTRIMS data set. The experimental results are well reproduced by convergent close-coupling (CCC) calculations. The fully differential cross section data underlying this study can be found in our companion papers immediately preceding this one.

Photo double ionization of helium 100 eV and 450 eV above threshold: I. Linearly polarized light

We present a joint experimental and theoretical study for the fully differential cross section of the photo double ionization (PDI) of helium with linearly polarized light at the excess energies Eexc = 100 eV and 450 eV above the threshold. The fully differential cross section is obtained by measuring the three-dimensional momentum vectors of one electron and the He 2+ ion in coincidence using the COLTRIMS method. We give an overview of the momentum distribution of the three-body continuum 100 eV above the threshold. We show angular distributions for both electrons for various energy sharings at Eexc = 100 eV and 450 eV. The experimental results are well reproduced by a set of convergent close-coupling (CCC) calculations.

Production of low-energy continuum electrons at 0° by 4.4 keV/u O8+ ions

Abstract Low-energy continuum-electron emission along the beam direction (i.e., at 0°) has been investigated for collisions of 4.4 keV u O8+ with H2, He, and Ar targets. At this energy, forward-ejected, low-energy continuum electrons were found to be associated only with outgoing projectiles that underwent bound-state capture; that is, no coincidences were observed between continuum electrons and outgoing projectiles remaining in the initial charge state. These results are consistent with previous results for O6++He and suggest that the electron-electron interaction is important in giving rise to low-energy continuum electrons at 0°.

Nondipole effects in the angular distribution of photoelectrons from the C K shell of the CO molecule

Measurements and calculations of a contribution of the nondipole terms in the angular distribution of photoelectrons from the C K shell of randomly oriented CO molecules are reported. In two sets of measurements, the angular distribution in the plane containing the photon polarization and the photon momentum vectors of linearly polarized radiation and the full three-dimensional photoelectron momentum distribution after absorption of circularly polarized light have been measured. Calculations have been performed in the relaxed core Hartree-Fock approximation with a fractional charge. Both theory and experiment show that the nondipole terms are very small in the photon energy region from the ionization threshold of the K shell up to about 70 eV above it.