J. Rist

Agreement of Experiment and Theory on the Single Ionization of Helium by Fast Proton Impact

Even though the study of ion-atom collisions is a mature field of atomic physics, large discrepancies between experiment and theoretical calculations are still common. Here we present experimental results with high momentum resolution on the single ionization of helium induced by 1-MeV protons, and we compare these to theoretical calculations. The overall agreement is strikingly good, and even the first Born approximation yields good agreement between theory and experiment. This has been expected for several decades, but so far has not been accomplished. The influence of projectile coherence effects on the measured data is briefly discussed in terms of an ongoing dispute on the existence of nodal structures in the electron angular emission distributions.

Observation of Enhanced Chiral Asymmetries in the Inner-Shell Photoionization of Uniaxially Oriented Methyloxirane Enantiomers

Most large molecules are chiral in their structure: they exist as two enantiomers, which are mirror images of each other. Whereas the rovibronic sublevels of two enantiomers are almost identical (neglecting a minuscular effect of the weak interaction), it turns out that the photoelectric effect is sensitive to the absolute configuration of the ionized enantiomer. Indeed, photoionization of randomly oriented enantiomers by left or right circularly polarized light results in a slightly different electron flux parallel or antiparallel with respect to the photon propagation direction-an effect termed photoelectron circular dichroism (PECD). Our comprehensive study demonstrates that the origin of PECD can be found in the molecular frame electron emission pattern connecting PECD to other fundamental photophysical effects such as the circular dichroism in angular distributions (CDAD). Accordingly, distinct spatial orientations of a chiral molecule enhance the PECD by a factor of about 10.

Ultrafast preparation and detection of ring currents in single atoms

Quantum particles can penetrate potential barriers by tunnelling1. If that barrier is rotating, the tunnelling process is modified2,3. This is typical for electrons in atoms, molecules or solids exposed to strong circularly polarized laser pulses4–6. Here we measure how the transmission probability through a rotating tunnel depends on the sign of the magnetic quantum number m of the electron and thus on the initial direction of rotation of its quantum phase. We further show that our findings agree with a semiclassical picture, in which the electron keeps part of that rotary motion on its way through the tunnel by measuring m-dependent modification of the electron emission pattern. These findings are relevant for attosecond metrology as well as for interpretation of strong-field electron emission from atoms and molecules7–14 and directly demonstrate the creation of ring currents in bound states of ions with attosecond precision. In solids, this could open a way to inducing and controlling ring-current-related topological phenomena15.When an electron with specific orbit — either clockwise or anticlockwise — in a rare gas atom is selectively ionized, the remaining ion will possess a stationary ring current, which can be probed in a time-delayed second ionization step.

Electron Localization in Dissociating H2+ by Retroaction of a Photoelectron onto Its Source

We investigate the dissociation of H_{2}^{+} into a proton and a H^{0} after single ionization with photons of an energy close to the threshold. We find that the p^{+} and the H^{0} do not emerge symmetrically in the case of the H_{2}^{+} dissociating along the 1sσ_{g} ground state. Instead, a preference for the ejection of the p^{+} in the direction of the escaping photoelectron can be observed. This symmetry breaking is strongest for very small electron energies. Our experiment is consistent with a recent prediction by Serov and Kheifets [Phys. Rev. A 89, 031402 (2014)]. In their model, which treats the photoelectron classically, the symmetry breaking is induced by the retroaction of the long-range Coulomb potential onto the dissociating H_{2}^{+}.

Single ionization of Helium at 0.5-2 MeV proton impact: On the quest for projectile coherence effects

J. Gatzke, F. Navarrete, M. Ciappina, H. Gatzke, O. Chuluunbaatar, S. A. Zaytsev, A. A. Bulychev, K. A. Kouzakov, A. Galstyan, M. Waitz, H.-K. Kim, T. Bauer, A. Laucke, S. Eckart, G. Kastirke, J. Müller, M. Ritzer, E. Bloch, M. Richter, K. Fehre, M. Kunitski, Ch. Müller, J. Voigtsberger, J. Rist, K. Pahl, M. Honig, M. Pitzer, M. Weller, I. Vela Pérez, J. Hoehl, G. Nalin, S. Grundmann, H. Maschkiwitz, C. Janke, S. Zeller, C. Goihl, Y. Herrman, D. Trabert, T. Jahnke, L. Ph. H. Schmidt, Yu. V. Popov, R. Dörner R. O. Barrachina, and M. S. Schöffler 1

Erratum: Electron Localization in Dissociating H2+ by Retroaction of a Photoelectron onto Its Source [Phys. Rev. Lett. 116 , 043001 (2016)]

This corrects the article DOI: 10.1103/PhysRevLett.116.043001.

Single ionization of helium by fast proton impact: Searching for projectile coherence

The fully differential cross section (FDCS) for single ionization p + He → p + e + He+ at proton energy of 1 MeV is studied both experimentally and theoretically. The 3D angular electron distribution is presented. The role of electron-electron correlations both in a trial helium ground-state wave function and in the final helium state is inspected.

Transfer ionization of D+ and He+ projectiles with H2-molecules – electron emission dependency on the internuclear axis

Its well known for atomic targets that the ionization in transfer ionization originates from electron knock-off or initial state correlated shake-off. For H2 molecules we have observed a similar behavior and additionally a dependency of the electron emission from the internuclear axis