H. Gassert

Goethe University Frankfurt

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T. Jahnke

European X-Ray Free-Electron Laser

R. Dörner

Goethe University Frankfurt

M. S. Schöffler

Goethe University Frankfurt

S. Zeller

Goethe University Frankfurt

M. Waitz

Goethe University Frankfurt

M. Pitzer

Goethe University Frankfurt

Florian Trinter

Fritz Haber Institute of the Max Planck Society

J. Voigtsberger

Goethe University Frankfurt

H. Schmidt‐Böcking

Goethe University Frankfurt

Tobias Bauer

Centre for Human Drug Research

Cooperative Institutions

Goethe University Frankfurt

Lawrence Berkeley National Laboratory

University of Chicago

Auburn University

Kansas State University

Max Planck Institute for Nuclear Physics

GSI Helmholtz Centre for Heavy Ion Research

Goethe Institute

University of Kassel

Donostia International Physics Center

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

Journal of Physics Conference Series (2014)

M. S. Schöffler M. Waitz H-K Kim Florian Trinter Christine H. Müller

It's 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

10.1088/1742-6596/488/10/102003

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Ion-impact-induced interatomic Coulombic decay in neon and argon dimers

Physical Review A (2013)

H.-K. Kim H. Gassert M. S. Schöffler J. Titze M. Waitz

We investigate the contribution of interatomic Coulombic decay induced by ion impact in neon and argon dimers (Ne${}_{2}$ and Ar${}_{2}$) to the production of low-energy electrons. Our experiments cover a broad range of perturbation strengths and reaction channels. We use 11.37 MeV/u S${}^{14+}$, 0.125 MeV/u He${}^{1+}$, 0.1625 MeV/u He${}^{1+}$, and 0.150 MeV/u He${}^{2+}$ as projectiles and study ionization, single and double electron transfer to the projectile, as well as projectile electron loss processes. The application of a COLTRIMS reaction microscope enables us to retrieve the three-dimensional momentum vectors of the ion pairs of the fragmenting dimer into Ne${}^{q+}$-Ne${}^{1+}$ and Ar${}^{q+}$-Ar${}^{1+}$ ($q=$ 1, 2, 3) in coincidence with at least one emitted electron.

10.1103/physreva.88.042707

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Kinematically complete experiments on ion impact

H. Gassert О. Чулуунбаатар J. Gatzke D. Trojanowskaja M. Waitz

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Single ionization of helium by fast proton impact in different kinematical regimes

Physical review. A/Physical review, A (2019)

О. Чулуунбаатар Konstantin Kouzakov S. A. Zaytsev S. A. Zaytsev V. L. Shablov

We present ultrahigh-resolution data on fully differential cross sections for single ionization of helium induced by 1 MeV proton impact. In the present work we explore a different regime of kinematic conditions in terms of momentum transfer and electron energies than previously published data. These data are compared with different theoretical calculations. Reasonable agreement between the first Born approximation and experiment is obtained in the kinematic regime close to the Bethe ridge. Far from this region the calculated binary peak is shifted with respect to experiment. In order to resolve this problem, we analyze several theoretical mechanisms beyond the customary first Born approximation theory. These mechanisms include the 3C model (three Coulomb functions), effective charges, off-shell pair $T$ matrices instead of pair potentials, and semiclassical postcollision interaction. We find that a combination of the 3C model with a semiclassical postcollision interaction effect may explain the observed discrepancy.

Semiclassical physics

Born approximation

Momentum (technical analysis)

10.1103/physreva.99.062711

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

The Journal of Physical Chemistry Letters (2017)

Maurice Tia M. Pitzer Gregor Kastirke J. Gatzke Hong-Keun Kim

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.

Antiparallel (mathematics)

Chirality

10.1021/acs.jpclett.7b01000

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Molecular frame photoelectron angular distributions for core ionization of ethane, carbon tetrafluoride and 1,1-difluoroethylene

Journal of Physics B Atomic Molecular and Optical Physics (2016)

Adrian J. Menssen C. S. Trevisan M. S. Schöffler T. Jahnke I. Bocharova

Molecular frame photoelectron angular distributions (MFPADs) are measured in electron-ion momentum imaging experiments and compared with complex Kohn variational calculations for carbon K-shell ionization of carbon tetrafluoride (CF 4 ), ethane (C 2 H 6 ) and 1,1-difluoroethylene (C 2 H 2 F 2 ).While in ethane the polarization averaged MFPADs show a tendency at low energies for the photoelectron to be emitted in the directions of the bonds, the opposite effect is seen in CF4.A combination of these behaviors is seen in difluoroethylene where ionization from the two carbons can be distinguished experimentally because of their different K-shell ionization potentials.Excellent agreement is found between experiment and simple static-exchange or coupled two-channel theoretical calculations.However, simple electrostatics do not provide an adequate explanation of the suggestively simple angular distributions at low electron ejection energies.

Tetrafluoride

Carbon fibers

10.1088/0953-4075/49/5/055203

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Orientation dependence in multiple ionization ofHe2andNe2induced by fast, highly charged ions: Probing the impact-parameter-dependent ionization probability in 11.37-MeV/uS

Physical Review A (2014)

H.-K. Kim H. Gassert J. Titze M. Waitz J. Voigtsberger

We investigate orientation effects in the fragmentation of He${}_{2}$ and ${\mathrm{Ne}}_{2}$ induced by ${S}^{14+}$ projectiles at an impact energy of 11.37 MeV/u. Multiple ionization shows a strong dependence on the orientation of the dimer axis with respect to the projectile beam axis. We attribute these effects to the impact-parameter-dependent ionization probability $P(b)$ for the atomic scattering process S${}^{14+}+\mathrm{He}$ and S${}^{14+}+\mathrm{Ne}$ and compare our data with a Monte Carlo simulation.

10.1103/physreva.89.022704

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Photo-double-ionization of ethylene and acetylene near threshold

Physical Review A (2014)

B. Gaire Seoho Lee Daniel J. Haxton Philipp Pelz I. Bocharova

We present kinematically complete measurements of the photo-double-ionization of ethylene (double CC bond) and acetylene (triple CC bond) hydrocarbons just above the double-ionization threshold. We discuss the results in terms of the coincident kinetic energy of the photoelectrons and the nuclear kinetic-energy release of the recoiling ions. We have incorporated quantum chemistry calculations to interpret which of the electronic states of the dication have been populated and trace the various subsequent fragmentation channels. We suggest pathways that involve the electronic ground and excited states of the precursor ethylene dication and explore the strong influence of the conical intersections between the different electronic states. The nondissociative ionization yield is small in ethylene and high in acetylene when compared with the dissociative ionization channels. The reason for such a striking difference is explained in part on the basis of a propensity rule that influences the population of states in the photo-double-ionization of a centrosymmetric closed-shell molecule by favoring singlet ungerade and triplet gerade final states. This propensity rule and the calculated potential-energy surfaces clarify a picture of the dynamics leading to the observed dication dissociation products.

Dication

Double ionization

Fragmentation

Acetylene

10.1103/physreva.89.013403

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

Physical Review Letters (2016)

H. Gassert О. Чулуунбаатар M. Waitz Florian Trinter H-K Kim

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

10.1103/physrevlett.116.073201

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

Journal of Physics Conference Series (2015)

H. Gassert О. Чулуунбаатар M. Waitz H-K Kim Tobias Bauer

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.

10.1088/1742-6596/635/2/022053

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