A5019965015- Atomic and Molecular Physics
- Advanced Chemical Physics Studies
- Laser-Matter Interactions and Applications
- Mass Spectrometry Techniques and Applications
- Nuclear physics research studies
- Ion-surface interactions and analysis
- Advanced X-ray Imaging Techniques
- Spectroscopy and Quantum Chemical Studies
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum, superfluid, helium dynamics
- Laser-Plasma Interactions and Diagnostics
- Molecular spectroscopy and chirality
- Photochemistry and Electron Transfer Studies
- Atomic and Subatomic Physics Research
- X-ray Spectroscopy and Fluorescence Analysis
- Astro and Planetary Science
- Quantum optics and atomic interactions
- Strong Light-Matter Interactions
- Electron and X-Ray Spectroscopy Techniques
- Nuclear Physics and Applications
- Advanced Electron Microscopy Techniques and Applications
- Molecular Spectroscopy and Structure
- Photocathodes and Microchannel Plates
- Plasma Diagnostics and Applications
- Spectroscopy and Laser Applications
Goethe University Frankfurt
2014-2023
Lawrence Berkeley National Laboratory
2015-2021
Goethe Institute
2018
Max Planck Institute for Nuclear Physics
2018
Abstract Following structural dynamics in real time is a fundamental goal towards better understanding of chemical reactions. Recording snapshots individual molecules with ultrashort exposure times key ingredient this goal, as atoms move on femtosecond (10 −15 s) timescales. For condensed-phase samples, ultrafast, atomically resolved structure determination has been demonstrated using X-ray and electron diffraction. Pioneering experiments have also started addressing gaseous samples....
We report on coulomb explosion imaging of the wavefunction quantum halo system He$_2$. Each atom this is ionized by tunnelionization in a femto second laser pulse and experiment single photon ionization employing free electron laser. visualize exponential decay probability density tunneling particle over distance for two orders magnitude up to an internuclear 250 {\AA}. By fitting slope regime we obtain binding energy 151.9 $\pm$ 13.3 neV, which agreement with most recent calculations.
During the past 15 years a novel decay mechanism of excited atoms has been discovered and investigated. This so-called interatomic Coulombic (ICD) involves chemical environment electronically atom: excitation energy is transferred (in many cases over long distances) to neighbor initially particle usually ionizing that neighbor. It turned out ICD very common route in nature as it occurs across van der Waals hydrogen bonds. The time evolution predicted be highly complex, its efficiency...
Most large molecules are chiral in their structure: they exist as two enantiomers, which mirror images of each other. Whereas the rovibronic sublevels enantiomers almost identical (neglecting a minuscular effect weak interaction), it turns out that photoelectric is sensitive to absolute configuration ionized enantiomer. Indeed, photoionization randomly oriented by left or right circularly polarized light results slightly different electron flux parallel antiparallel with respect photon...
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 helium induced by 1\,MeV protons compare these to different calculations. The overall agreement strikingly good already the first Born approximation yields theory experiment. This has been expected since several decades, but so far not accomplished....
Ultrashort x-ray pulses from free-electron lasers can efficiently charge up and trigger the full fragmentation of molecules. By coincident detection to five ions resulting rapid Coulomb explosion highly charged iodomethane, we show that three-dimensional equilibrium geometry this prototypical polyatomic system be determined measured ion momenta with help a buildup model. Supported by simulations how would reflect specific changes in molecular bond lengths angles, demonstrate...
We investigate the ionization of HeNe from below He $1s3p$ excitation to threshold. observe ${\mathrm{HeNe}}^{+}$ ions with an enhancement by more than a factor 60 when side couples resonantly radiation field. These are experimental proof two-center resonant photoionization mechanism predicted Najjari et al. [Phys. Rev. Lett. 105, 153002 (2010)]. Furthermore, our data provide electronic and vibrational state resolved decay widths interatomic Coulombic in dimers. find that lifetime strongly...
A central motivation for the development of x-ray free-electron lasers has been prospect time-resolved single-molecule imaging with atomic resolution. Here, we show that photoelectron diffraction—where a emitted after absorption illuminates molecular structure from within—can be used to image increase internuclear distance during x-ray-induced fragmentation an O2 molecule. By measuring molecular-frame emission patterns two-photon sequential K-shell ionization in coincidence fragment ions,...
We report on a joint experimental and theoretical study of photoelectron circular dichroism (PECD) in methyloxirane. By detecting O 1s-photoelectrons coincidence with fragment ions, we deduce the molecule's orientation emission direction laboratory frame. Thereby, retrieve fourfold differential PECD clearly beyond 50%. This strong chiral asymmetry is reproduced by ab initio electronic structure calculations. Providing such pronounced contrast makes fixed-in-space molecules an even more...
Chirality is omnipresent in living nature. On the single molecule level, response of a chiral species to probe depends on their respective handedness. A prominent example difference interaction with left or right circularly polarized light. In present study, we show by Coulomb explosion imaging that light can also induce fragmentation planar and thus achiral molecule. The observed enantiomer strongly orientation respect propagation direction helicity ionizing This finding might trigger new...
The ultrafast structural dynamics of water following inner-shell ionization is a crucial issue in high-energy radiation chemistry. We have exposed isolated molecules to short x-ray pulse from free-electron laser and detected momenta all produced ions coincidence. By combining experimental results theoretical modeling, we can image dissociation individual unprecedented detail. reveal significant molecular H2O2+, such as asymmetric deformation bond-angle opening, leading two-body or three-body...
We demonstrate the use of cold target recoil ion momentum spectroscopy to perform state-selective measurements dissociative channels following single-photon double-ionization ${\mathrm{H}}_{2}\mathrm{O}$. The two dominant dissociation observed lead two-body (${\mathrm{OH}}^{+}+{\mathrm{H}}^{+}+2{e}^{\ensuremath{-}}$) and three-body ($2{\mathrm{H}}^{+}+\mathrm{O}+2{e}^{\ensuremath{-}}$) ionic fragmentation channels. In case we observe presence an autoionization process with a...
Photoionization is one of the fundamental light-matter interaction processes in which absorption a photon launches escape an electron. The time scale this process poses many open questions. Experiments have found delays attosecond (10-18 seconds) domain between electron ejection from different orbitals, electronic bands, or directions. Here, we demonstrate that, across molecular orbital, not launched at same time. Rather, birth depends on travel molecule, 247 zeptoseconds (1 zeptosecond =...
We report on a multiparticle coincidence experiment performed at the European X-ray Free-Electron Laser Small Quantum Systems instrument using COLTRIMS reaction microscope. By measuring two ions and electrons in coincidence, we investigate double core-hole generation O_{2} molecules gas phase. Single-site two-site core holes have been identified their molecular-frame electron angular distributions obtained for breakup of oxygen molecule into doubly charged ions. The measured are compared to...
We investigate the differential ionization probability of chiral molecules in strong field regime as a function helicity incident light. To this end, we analyze fourfold bromochlorofluoromethane (CHBrClF) with subsequent fragmentation into four charged fragments and different dissociation channels singly ionized methyloxirane. observe variation range several percent. Accordingly, conclude that light is quantity should be considered for theoretical description rate molecules.
We investigate the temporal evolution of molecular frame angular distributions Auger electrons emitted during ultrafast dissociation HCl following a resonant single-photon excitation. The electron emission pattern changes its shape from that σ orbital to an atomic p state as system evolves molecule into two separated atoms.
Resonant interatomic Coulombic decay (RICD) has been studied with HeNe dimers, where two channels are identified by bound HeNe${}^{+}$ states and low-energetic He+Ne${}^{+}$ fragments, the state-resolved angular emission distributions of respective RICD electrons examined in detail.
We present ultrahigh-resolution data on fully differential cross sections for single ionization of helium induced by 1 MeV proton impact. In the work we explore a different regime kinematic conditions in terms momentum transfer and electron energies than previously published data. These are compared with theoretical calculations. Reasonable agreement between first Born approximation experiment is obtained close to Bethe ridge. Far from this region calculated binary peak shifted respect...
The investigation of the photoelectron circular dichroism (PECD) in strong field regime (800 nm, 6.9 × 1013 W/cm2) on methyloxirane (MOX) reveals a flip sign PECD between different fragmentation channels. This finding is great importance for future experiments and applications chemistry or pharmacy using as analysis method. We suggest that observed change not caused by ionization from orbitals but effectively selecting differently oriented nonisotropic subsamples molecules via channel.
We present the momentum distributions of nucleus and electrons from double ionization helium atom by Compton scattering photons with hν=40 keV. find that doubly charged ion distribution is very close to profile in ground state atom, singly give a precise image electron profile. To reproduce these results, nonrelativistic calculations require use highly correlated initial- final-state wave functions.
We investigate the dissociation of H_{2}^{+} into a proton and H^{0} after single ionization with photons an energy close to threshold. find that p^{+} do not emerge symmetrically in case dissociating along 1sσ_{g} ground state. Instead, preference for ejection direction escaping photoelectron can be observed. This symmetry breaking is strongest very small electron energies. Our experiment consistent recent prediction by Serov Kheifets [Phys. Rev. A 89, 031402 (2014)]. In their model, which...
X-ray single-photon ionization and fragmentation of the chiral molecule halothane from a racemic mixture have been investigated using cold target recoil ion momentum spectroscopy technique. Two important facets related to core this species are examined: Firstly, distinction enantiomers (mirror isomers) determination absolute configuration on single-molecule level by four-body Coulomb explosion; secondly, interplay site-selective excitation patterns. These results easily transferable other...
This paper shows a forward/backward asymmetric and enantiosensitive rotation of the photoelectron momentum distribution as new chiral signal becoming accessible for elliptically polarized light upon strong field ionization. is aspect circular dichroism in elliptical light.
Almost ten years ago, energetic neutral hydrogen atoms were detected after a strong-field double ionization of H$_2$. This process, called 'frustrated tunneling ionization', occurs when an ionized electron is recaptured being driven back to its parent ion by the electric field femtosecond laser. In present study we demonstrate that related process naturally in clusters without need external field: observe charge hopping during Coulomb explosion small helium cluster, which leads atom. claim...
We suggest that low energy electrons, released by resonant decay processes, experience substantial scattering on the electron density of excited which remain a spectator during decay. As result, angular emission distribution is altered significantly. This effect expected to be common feature secondary emission. In this letter, we exemplify our idea examining interatomic Coulombic (sRICD) Ne dimers. Our theoretical predictions are confirmed corresponding coincidence experiment.