SiF4 anomalous behaviour reassessed

The Si 1s−1, Si 2s−1, and Si 2p−1 photoelectron spectra of the SiX4 molecules with X = F, Cl, Br, CH3 were measured. From these spectra the Si 1s−1 and Si 2s−1 lifetime broadenings were determined, revealing a significantly larger value for the Si 2s−1 core hole of SiF4 than for the same core hole of the other molecules of the sequence. This finding is in line with the results of the Si 2p−1 core holes of a number of SiX4 molecules, with an exceptionally large broadening for SiF4. For the Si 2s−1 core hole of SiF4 the difference to the other SiX4 molecules can be explained in terms of Interatomic Coulomb Decay (ICD)-like processes. For the Si 2p−1 core hole of SiF4 the estimated values for the sum of the Intraatomic Auger Electron Decay (IAED) and ICD-like processes are too small to explain the observed linewidth. However, the results of the given discussion render for SiF4 significant contributions from Electron Transfer Mediated Decay (ETMD)-like processes at least plausible. On the grounds of our results, some more molecular systems in which similar processes can be observed are identified

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

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 organic thiophene-based polymers at the sulfur K-edge. A combination of core-hole clock spectroscopy with real-time propagation time-dependent density functional theory simulations gives an insight into the electron dynamics underlying the CT process. Our method provides control over CT by a selective excitation of a specific resonance in the sulfur atom with monochromatic X-ray radiation. Our combined experimental and theoretical investigation establishes that the dominant mechanism of CT in polymer powders and films consists of electron delocalisation along the polymer chain occurring on the low-femtosecond time scale

a tool to disentangle overlapping core-excited states

We have measured resonant-Auger decay following Cl 1s−1 excitations in HCl and CH3Cl molecules, and extracted the pseudo-cross sections of different Cl 2p−2 final states. These cross sections show clear evidence of shake processes as well as contributions of electronic state-lifetime interference (ELI). To describe the spectra we developed a fit approach that takes into account ELI contributions and ultrafast nuclear dynamics in dissociative core-excited states. Using this approach we utilized the ELI contributions to obtain the intensity ratios of the overlapping states Cl 1s−14pπ/1s−14pσ in HCl and Cl 1s−14pe/1s−14pa1 in CH3Cl. The experimental value for HCl is compared with theoretical results showing satisfactory agreement

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

Hard-X-Ray-Induced Multistep Ultrafast Dissociation

Creation of deep core holes with very short (τ≤1  fs) lifetimes triggers a chain of relaxation events leading to extensive nuclear dynamics on a few- femtosecond time scale. Here we demonstrate a general multistep ultrafast dissociation on an example of HCl following Cl 1s→σ∗ excitation. Intermediate states with one or multiple holes in the shallower core electron shells are generated in the course of the decay cascades. The repulsive character and large gradients of the potential energy surfaces of these intermediates enable ultrafast fragmentation after the absorption of a hard x-ray photon

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

Time and position sensitive photon detector for coincidence measurements in the keV energy range

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