Argon 1s(-2) Auger hypersatellites

The 1s(-2) Auger hypersatellite spectrum of argon is studied experimentally and theoretically. In total, three transitions to the final states 1s(-1)2p(-2)(S-2(e),D-2(e)) and 1s(-1)2s(-1)(S-1)2p(-1)(P-2(o)) are experimentally observed. The lifetime broadening of the 1s(-2) -> 1s(-1)2p(-2)(S-2(e),D-2(e)) states is determined to be 2.1(4) eV. For the used photon energy of h nu = 7500 eV a KK/K ionisation ratio of 2.5(3) x 10(-4) is derived. Generally, a good agreement between the experimental and present theoretical energy positions, linewidths, and intensities is obtained

Electron spectroscopy and dynamics of HBr around the Br 1s-1 threshold

A comprehensive electron spectroscopic study combined with partial electron yield measurements around the Br 1s ionization threshold of HBr at approximately equal to 13.482 keV is reported. In detail, the Br 1s(-1) X-ray absorption spectrum, the 1s(-1) photoelectron spectrum as well as the normal and resonant KLL Auger spectra are presented. Moreover, the L-shell Auger spectra measured with photon energies below and above the Br 1s(-1) ionization energy as well as on top of the Br 1s(-1)sigma* resonance are shown. The latter two Auger spectra represent the second step of the decay cascade subsequent to producing a Br 1s(-1) core hole. The measurements provide information on the electron and nuclear dynamics of deep core-excited states of HBr on the femtosecond timescale. From the different spectra the lifetime broadening of the Br 1s(-1) single core-hole state as well as of the Br(2s(-2),2s(-1)2p(-1),2p(-2)) double core-hole states are extracted and discussed. The slope of the strongly dissociative HBr 2p(-2)sigma* potential energy curve is found to be about -13.60 eV angstrom(-1). The interpretation of the experimental data, and in particular the assignment of the spectral features in the KLL and L-shell Auger spectra, is supported by relativistic calculations for HBr molecule and atomic Br

Generalization of the post-collision interaction effect from gas-phase to solid-state systems demonstrated in thiophene and its polymers

We demonstrate experimentally and theoretically the presence of the post-collision interaction (PCI) effect in sulfur KL2,3L2,3 Auger electron spectra measured in the gas-phase thiophene and in solid-state organic polymers: polythiophene (PT) and poly(3-hexylthiophene-2,5-diyl), commonly known as P3HT. PCI manifests itself through a distortion and a blueshift of the normal Auger S KL2,3L2,3 spectrum when S 1s ionization occurs close to the ionization threshold. Our investigation shows that the PCI-induced shift of the Auger spectra is stronger in the solid-state polymers than in the gas-phase organic molecule. Theoretical modeling within the framework of the eikonal approximation provides good agreement with the experimental observations. In a solid medium, two effects influence the interaction between the photoelectron and the Auger electron. In detail, stronger PCI in the polymers is attributed to the photoelectron scattering in the solid, which overcompensates the polarization screening of electron charges which causes a reduction of the interaction. Our paper demonstrates the general nature of the PCI effect occurring in different media

A von Hamos spectrometer based on highly annealed pyrolytic graphite crystal in tender x-ray domain

We have built an x-ray spectrometer in a von Hamos configuration based on a highly annealed pyrolytic graphite crystal. The spectrometer is designed to measure x-ray emission in the range of 2–5 keV. A spectral resolution E/ΔE of 4000 was achieved by recording the elastic peak of photons issued from the GALAXIES beamline at the SOLEIL synchrotron radiation facility

Argon KLL Auger spectrum: Initial states, core-hole lifetimes, shake, and knock-down processes

State-of-the-art argon KLL Auger spectra measured using photon energies of hν=3216 and 3400 eV are presented along with an Ar [1s] photoelectron spectrum (square brackets indicate holes in the respective orbital). The two different photon energies used for measuring the Auger spectra allow distinguishing between the shake transitions during the Auger decay and the Auger transitions of the photoelectron satellites. A complete assignment of satellite transitions is provided, partially based on configuration-interaction calculations. In addition, Ar [1s3(s,p)]n′l′→[2p2(1D2)] transitions are observed, which can be explained by knock-down transitions leading to a direct exchange of angular momentum between the excited electron and the Auger electron. The lifetime broadenings of the Ar [2s] single-core-hole state and the [2s2] and [2s2p] double-core-hole states are also determined, confirming previously observed trends for double-core-hole states

X-ray induced ultrafast charge transfer in thiophene-based conjugated polymers controlled by core-hole clock spectroscopy

We explore ultrafast charge transfer (CT) resonantly induced by hard X-ray radiation in organicthiophene-based polymers at the sulfur K-edge. A combination of core-hole clock spectroscopy withreal-time propagation time-dependent density functional theory simulations gives an insight into theelectron dynamics underlying the CT process. Our method provides control over CT by a selectiveexcitation of a specific resonance in the sulfur atom with monochromatic X-ray radiation. Our combinedexperimental and theoretical investigation establishes that the dominant mechanism of CT in polymerpowders and films consists of electron delocalisation along the polymer chain occurring on the low-femtosecond time scale

Ultrafast Nuclear Dynamics in Double-Core Ionized Water Molecules

Double-core-hole (DCH) states in isolated water and heavy water molecules, resulting from the sequential absorption of two x-ray photons, have been investigated. A comparison of the subsequent Auger emission spectra from the two isotopes provides direct evidence of ultrafast nuclear motion during the 1.5 fs lifetime of these DCH states. Our numerical results align well with the experimental data, providing for various DCH states an in-depth study of the dynamics responsible of the observed isotope effect

Double Inner-Shell Vacancies in Molecules

Molecular electronic states possessing a double core-vacancy, referred to as double-core-hole (DCH) states, were predicted more than thirty years ago, to have interesting properties, which would allow one to probe matter in a much more detailed way compared to conventional single core-vacancy techniques. Though DCH states are characterized by low cross-sections compared to the dominant single-core-hole (SCH) states, which implies experimental challenges, the development of third generation synchrotron radiation (SR) facilities and X-ray free electron lasers (XFEL), in combination with advanced spectroscopy techniques, resulted recently in a significant number of scientific works reporting on the observation of different types of DCH states. Within the framework of this thesis, experimental work in terms of high resolution single channel electron spectroscopy was carried out, detecting DCH states of the form K-1L-1V, where one core electron has been ionized and the second has been excited to an unoccupied orbital V. One example concerns the case of HCl, where the experimental spectrum has been reproduced by a fit model taking into account Rydberg series within different spin-orbit multiplicities. From this analysis, the thresholds for the double ionization continua and the quantum defects for different Rydberg electrons have been extrapolated. Furthermore, electron spectra reflecting the formation of K-2V DCH states, which involve the K shells of the N and C atoms in CH3CN, have also been recorded and interpreted based on a theoretical model considering the direct (dipolar ionization - monopolar excitation) or the conjugate (dipolar excitation - monopolar ionization) nature of each observed transition. In addition, the initial and final state effects contributing to the chemical shift between the two non-equivalent C atoms have been discussed and visualized by employing a Wagner plot. Related results are reported on the formation of K-2V DCH states in SF6 and CS2. The influence of the slope of the potential energy curve on the broadening of the spectral features is discussed along with the appearance of a pronounced background. Fingerprints of nuclear dynamics upon the decay of several types of DCH states in H2O have been identified by recording the related hyper-satellite Auger spectrum. Complementary, the technique of multi-electron coincidence spectroscopy was used for the study of the formation of K-2V and K-2 DCH states in C4H10, where the latter type of DCHs with both core electrons being ejected to the continuum, has been measured directly and in the same experiment as the K-2V states

Nonstatistical behavior of the photoionization of spin–orbit doublets

The photoionization branching ratios of spin–orbit doublets are studied both experimentally and theoretically at energies several keV above threshold. The results show significant relativistic effects for Ar 2p in the autoionizing region below the 1s threshold, and large many-body effects for Xe 3d and 4d in the vicinity of the L-shell thresholds. The branching ratios in Xe are also found to vary significantly over very broad multi-keV energy regions both above and below the inner-shell thresholds. In addition, the Ar 2p study confirms experimentally the decades-old theoretical prediction that the nonresonant branching ratio does not approach the statistical (nonrelativistic) value, and, in fact, progressively diverges from statistical with increasing photon energy

Ghost-imaging-enhanced noninvasive spectral characterization of stochastic x-ray free-electron-laser pulses

High-intensity ultrashort X-ray free-electron laser (XFEL) pulses are revolutionizing the study of fundamental nonlinear x-ray matter interactions and coupled electronic and nuclear dynamics. To fully exploit the potential of this powerful tool for advanced x-ray spectroscopies, a noninvasive spectral characterization of incident stochastic XFEL pulses with high resolution is a key requirement. Here we present a methodology that combines high-acceptance angle-resolved photoelectron time-of-flight spectroscopy and ghost imaging to enhance the quality of spectral characterization of x-ray free-electron laser pulses. Implementation of this noninvasive high-resolution x-ray diagnostic can greatly benefit the ultrafast x-ray spectroscopy community by functioning as a transparent beamsplitter for applications such as transient absorption spectroscopy in averaging mode as well as covariance-based x-ray nonlinear spectroscopies in single-shot mode where the shot-to-shot fluctuations inherent to a self-amplified spontaneous emission (SASE) XFEL pulse are a powerful asset