arXiv subjects

Sebastian Hartweg

Publications and source records attributed to Sebastian Hartweg.

9 recordsLinked to original sources

arXiv2026

Dissociative Single and Double Ionization of Pyridine

Dissociative ionization processes of simple heterocyclic molecules like pyridine are relevant for an understanding of radiation damage processes in biological material that occur naturally in complex condensed environments. Pyridine can thereby be considered a simple analogue of nucleobases and related ring structures are included in many important biomolecules. We present here a detailed study of dissociative single-photon single and double ionization processes using double imaging photoelectron photoion coincidence spectroscopy, supported by quantum chemical calculations. In the case of single ionization we correlate previously described cationic states to their corresponding ionic dissociation products observed at a photon energy of 23 eV, providing additional information beyond previously reported ion appearance energies. For the case of double ionization by 36 eV photons the analysis of electron-ion-ion triple coincidences provides detailed information on the onsets of various dissociative double ionization pathways, often only different by the locations of single hydrogen atoms. The detailed understanding of dissociative single and double ionization of pyridine is a prerequisite for future studies addressing radiation damage processes of such molecules in complex environments.

physics.chem-ph↗

arXiv2025

Large circular dichroism in the total photoemission yield of free chiral nanoparticles created by a pure electric dipole effect

Spectroscopic techniques that are sensitive to molecular chirality are important analytical tools to quantitatively determine enantiomeric excess and purity of chiral molecular samples. Many chiroptical processes however produce weak enantio-specific asymmetries due to their origin relying on weak magnetic dipole or electric quadrupole effects. Photoelectron circular dichroism (PECD) in contrast, is an intense effect, that is fully contained in the electric dipole description of light matter interaction and creates a chiral asymmetry in the photoelectron angular distribution. Here, we demonstrate that this chiral signature in the angular distribution of emitted electrons can be translated into the total photoionization yield for submicron-sized condensed samples. The resulting chiral asymmetry of the photoionization yield (CAPY), mediated by the attenuation of light within the particles, can be detected experimentally without requiring high vacuum systems and electron spectrometers. This effect can be exploited as an analytical tool with high sensitivity to chirality and enantiopurity for studies of chiral organic and hybrid submicron particles in environmental, biomedical or catalytic applications.

physics.chem-ph↗

arXiv2025

H2-roaming dynamics in the formation of H3+ following two-photon double ionization of ethanol and aminoethanol

Roaming reactions involving a neutral fragment of a molecule that transiently wanders around another fragment before forming a new bond are intriguing and peculiar pathways for molecular rearrangement. Such reactions can occur for example upon double ionization of small organic molecules, and have recently sparked much scientific interest. We have studied the dynamics of the H$_2$-roaming reaction leading to the formation of H$_3^+$ after two-photon double ionization of ethanol and 2-aminoethanol, using an XUV-UV pump-probe scheme. For ethanol, we find dynamics similar to previous studies employing different pump-probe schemes, indicating the independence of the observed dynamics from the method of ionization and the photon energy of the disruptive probe pulse. Surprisingly, we do not observe a kinetic isotope effect in ethanol-D$_6$, in contrast to previous experiments on methanol where such an effect was observed. This distinction indicates fundamental differences in the energetics of the reaction pathways as compared to the methanol molecule. The larger number of possible roaming pathways compared to methanol complicates the analysis considerably. In contrast to previous studies, we additionally analyze a broad range of dissociative ionization products, which feature distinct dynamics from that of H$_{3}^{+}$ and allow initial insight into the action of the disruptive UV-probe pulse.

physics.chem-ph↗

arXiv2024

Method of Kinetic Energy Reconstruction from Time-of-Flight Mass Spectra

We present a method for the reconstruction of ion kinetic energy distributions from ion time-of-flight mass spectra through ion trajectory simulations. In particular, this method is applicable to complicated spectrometer geometries with largely anisotropic ion collection efficiencies. A calibration procedure using a single ion mass peak allows the accurate determination of parameters related to the spectrometer calibration, experimental alignment and instrument response function, which improves the agreement between simulations and experiment. The calibrated simulation is used to generate a set of basis functions for the time-of-flight spectra, which are then used to transform from time-of-flight to kinetic-energy spectra. We demonstrate this reconstruction method on a recent pump-probe experiment by Asmussen et al. (J. D. Asmussen et al., Phys. Chem. Chem. Phys., 23, 15138, (2021)) on helium nanodroplets and retrieve time-resolved kinetic-energy-release spectra for the ions from ion time-of-flight spectra.

physics.atm-clus↗

arXiv2024

Non-adiabatic electronic relaxation of tetracene from its brightest singlet excited state

The ultrafast relaxation dynamics of tetracene following UV excitation to a bright singlet state S6 has been studied with time-resolved photoelectron spectroscopy. With the help of high-level ab-initio multireference perturbation theory calculations, we assign photoelectron signals to intermediate dark electronic states S3, S4 and S5 as well as a to a low-lying electronic state S2. The energetic structure of these dark states has not been determined experimentally previously. The time-dependent photoelectron yields assigned to the states S6, S5 and S4 have been analyzed and reveal the depopulation of S6 within 50 fs, while S5 and S4 are populated with delays of about 50 and 80 fs. The dynamics of the lower-lying states S3 and S2 seem to agree with a delayed population coinciding with the depopulation of the higher-lying states S4-S6, but could not be elucidated in full detail due to the low signal levels of the corresponding two-photon ionization probe processes.

physics.chem-ph↗

arXiv2024

Strong-field quantum control in the extreme ultraviolet using pulse shaping

Tailored light-matter interactions in the strong coupling regime enable the manipulation and control of quantum systems with up to unit efficiency, with applications ranging from quantum information to photochemistry. While strong light-matter interactions are readily induced at the valence electron level using long-wavelength radiation, comparable phenomena have been only recently observed with short wavelengths, accessing highly-excited multi-electron and inner-shell electron states. However, the quantum control of strong-field processes at short wavelengths has not been possible, so far, due to the lack of pulse shaping technologies in the extreme ultraviolet (XUV) and X-ray domain. Here, exploiting pulse shaping of the seeded free-electron laser (FEL) FERMI, we demonstrate the strong-field quantum control of ultrafast Rabi dynamics in helium atoms with high fidelity. Our approach unravels a strong dressing of the ionization continuum, otherwise elusive to experimental observables. The latter is exploited to achieve control of the total ionization rate, with prospective applications in many XUV and soft X-ray experiments. Leveraging recent advances in intense few-femtosecond to attosecond XUV to soft X-ray light sources, our results open an avenue to the efficient manipulation and selective control of core electron processes and electron correlation phenomena in real time.

physics.atom-ph↗

arXiv2021

Low-energy constraints on photoelectron spectra measured from liquid water and aqueous solutions

We report on the effects of electron collision and indirect ionization processes, occurring at photoexcitation and electron kinetic energies well below 30 eV on the photoemission spectra of liquid water. We show that the nascent photoelectron spectrum and, hence, the inferred electron binding energy can only be accurately determined if electron energies are large enough that cross sections for quasi-elastic scattering processes, such as vibrational excitation, are negligible. Otherwise, quasi-elastic scattering leads to strong, down-to-few-meV kinetic energy scattering losses from the direct photoelectron features, which manifest in severely distorted intrinsic photoelectron peak shapes. The associated cross-over point from predominant (known) electronically inelastic to quasi-elastic scattering seems to arise at surprisingly large electron kinetic energies, of approximately 10-14 eV. Concomitantly, we present evidence for the onset of indirect, autoionization phenomena (occurring via superexcited states) within a few eV of the primary and secondary ionization thresholds. These processes are inferred to compete with the direct ionization channels and primarily produce low-energy photoelectrons at photon and electron impact excitation energies below ~15 eV. Our results highlight that vibrational inelastic electron scattering processes and neutral photoexcitation and autoionization channels become increasingly important when photon and electron kinetic energies are decreased towards the ionization threshold. Correspondingly, we show that for neat water and aqueous solutions, great care must be taken when quantitatively analyzing photoelectron spectra measured too close to the ionization threshold. Such care is essential for both the accurate determination of solvent and solute ionization energies as well as photoelectron branching ratios and peak magnitudes.

physics.chem-ph↗

arXiv2019

Relaxation dynamics and genuine properties of the solvated electron in neutral water clusters

We have investigated the solvation dynamics and the genuine binding energy and photoemission anisotropy of the solvated electron in neutral water clusters with a combination of time-resolved photoelectron velocity map imaging and electron scattering simulations. The dynamics was probed with a UV probe pulse following above-band-gap excitation with a EUV pump pulse. The solvation dynamics is completed within about 2 ps. Only a single band is observed in the spectra, with no indication for isomers with distinct binding energies. Data analysis with an electron scattering model reveals a genuine binding energy in the range of 3.55-3.85 eV and a genuine anisotropy parameter in the range of 0.51-0.66 for the ground-state hydrated electron. All these observations coincide with those for liquid bulk, which is rather unexpected for an average cluster size of 300 molecules.

physics.atm-clus↗

arXiv2016

Size-Resolved Photoelectron Anisotropy of Gas Phase Water Clusters and Predictions for Liquid Water

We report the first measurement of size-resolved photoelectron angular distributions for the valence orbitals of water clusters with up to 20 molecules. A systematic decrease of the photoelectron anisotropy is found for clusters with up to 5-6 molecules, and most remarkably, convergence of the anisotropy for larger clusters. We suggest the latter to be the result of a local short-range scattering potential that is fully described by a unit of 5-6 molecules. The cluster data and a detailed electron scattering model are used to predict liquid water anisotropies. Reasonable agreement with experimental liquid jet data is found.

physics.chem-ph↗