Journal of Electron Spectroscopy and Related Phenomena最新文献

We present a theoretical study for electron and positron-impact ionization of water molecule by using the three-body formalism of distorted-wave approximation. In this approximation, the final state contains one-Coulomb, two-Coulomb, and three-Coulomb distortion due to pairwise Coulombic interactions, respectively. In the entrance channel, the initial state is a product of two wavefunctions: the first one for the incident electron/positron described by a Coulomb wave and the second one for the ten bound electrons. The molecular wavefunction for these bound electrons of $H_{2}O$ are described by the linear combination of atomic orbitals. We investigate the angular distribution of the triple differential cross section (TDCS) for single ionization of the outer orbitals $1b_1,3a_1,1b_2$, and $2a_1$. The structure with two peaks around the binary and recoil region are clearly observed for $1b_1$, $3a_1$, and $1b_2$ orbitals. At the same time, a single peak in the binary region with no recoil peak is found for the $2a_1$ orbital. The present TDCS results are compared with available experimental and theoretical findings. Fair agreement regarding the structure of angular profile of the TDCS is observed for all orbitals except $2a_1$. Finally, an enhanced TDCS have been found for positron impact compared to the electron impact.

We investigate in the present paper the doubly excited ${}^1{P}^o$ states in the C${}^{4+}$ ion. We report highly accurate results of their energy positions in the energy spectrum, their lifetimes and the x-ray photon energies required to populate them and observe their autoionization. The results were obtained by using our B-spline based spectral approach combined with the complex rotation method that has proven its effectiveness in the detection of the doubly excited states in the O${}^{6+}$ [1] and Li${}^{+}$ [2] ions. We also report in the paper the first results on the characterization and identification of the states that share similar angular correlation pattern, which allows their classification into distinct resonance series.

In this paper, we report an extensive theoretical study of the magnetic-field and hyperfine-induced transition parameters for magnesium-like ions from Cr XIII to Zn XIX and chlorine-like ions from Mn IX to Co XI. These ions have a high abundance in the astrophysical plasma. Zeeman splitting level energies, hyperfine- and/or magnetic-field dependent wavelengths, and transition rates of the 3s3p ${}^3{P}_{2,1,0}\to 3s^2$ ${}^1{S}_0$ (for magnesium-like ions) and the 3p⁴3d ${}^4{D}_{7/2}\to$ 3p⁵ ${}^2{P}_{3/2}$ line (for chlorine-like ions), are computed using the multiconfiguration Dirac–Fock method. Some higher-order effects, such as the Breit interaction and quantum electrodynamics corrections, are included in the relativistic configuration interaction method, as this makes the results more accurate. A comparison between the our predictions and other theoretical and experimental values is made. A satisfactory agreement is achieved. Besides providing valuable information for spectral line analysis, the present work will have a variety of implications for fusion and astrophysical plasma sources, for example, in the determination of magnetic fields in solar coronas and other stars.

Absolute generalized oscillator strengths of the valence-shell excitations of krypton have been determined with an incident electron energy of 1500 eV and an energy resolution of about 80 meV. By employing the relative flow technique with a dilute target, the pressure effect is excluded and the accuracy of the measured generalized oscillator strengths is improved. By comparing the present generalized oscillator strengths with the previous experimental and theoretical results, it is found that the first Born approximation is not reached at the squared momentum transfer larger than 1 a.u.. The optical oscillator strengths have been obtained by extrapolating the measured generalized oscillator strengths to zero squared momentum transfer, which cross-checks the previous electron impact and photoabsorption results. With the aid of the BE-scaling method, the integral cross sections of krypton have been determined from the excitation threshold to 5000 eV. The present oscillator strengths and integral cross sections supplement the fundamental database of the electron scattering of krypton and provide a benchmark for the theoretical methods.

In this work, the integral elastic, inelastic, ionization, and momentum transfer scattering cross sections of ${\mathrm{WF}}_6$, ${\mathrm{WCl}}_6$, and ${\mathrm{W(CO)}}_6$ molecules are calculated using a quantum mechanical method. These are considered precursors for tungsten deposition using the focused electron beam-induced deposition (FEBID) technique. The spherical complex optical potential (SCOP) formalism is used to figure out the total elastic, inelastic, and momentum transfer cross sections. The complex scattering potential ionization contribution (CSP-ic) method is used to find the ionization cross sections in the inelastic channel. The calculations are performed on a fine grid in the energy range from the ionization potential to 5 keV. We have also reported comparisons of our data with available theoretical and experimental results. All types of scattering cross sections for ${\mathrm{WCl}}_6$ is reported for the first time.

Recent advances using Density Functional Theory (DFT) to augment Multiplet Ligand Field Theory (MLFT) have led to ab-initio calculations of many formerly empirical parameters. This development makes MLFT more predictive instead of interpretive, thus improving its value for studies of highly correlated $3d$, $4d$, and f-electron systems. Synchrotron time is always at a premium, and tools that provide predictive capabilities have clear value when it comes to planning studies. Here, we develop a DFT + MLFT based approach for core-to-core Kα x-ray emission spectra (XES) and evaluate its performance for a range of transition metal systems. We find good agreement between theory and experiment, as well as the ability to capture key spectral trends related to spin and oxidation state. We also discuss limitations of the model in the context of the remaining free parameters and suggest directions forward.

The structure of 10 Prussian Blue Analogs containing trivalent hexacyanoferrate was investigated by extended X-ray absorption fine structure spectroscopy at the Fe 1 s edge and the transition metal 1 s edges. Despite the changes in physical properties due to differences in the non-iron transition metal and the interatomic distance between Fe and the non-iron transition metal, there was almost no change in the structure of trivalent hexacyanoferrate ions. Although this result agrees with the conclusions of many previous structural analyses, it raises a new question compared to our previous research conducted soft X-ray absorption measurements at the Fe 2p edge, which states that the detailed electronic state of Fe varies in proportion to the interatomic distance between Fe and the non-iron transition metal.

Measuring the momentum and energy distribution of photoemitted correlated electron pairs is a promising approach to directly probe the nature of electron–electron interactions in quantum materials. In this work, we present a two electron angle resolved photoemission spectroscopy (2e-ARPES) setup based on two time-of-flight (TOF) analyzers and a gas fiber high-harmonic generation (HHG) extreme ultraviolet (XUV) source. For each incident XUV pulse, the system is capable of recording six-dimensional coincidence datasets (kinetic energy and two orthogonal momenta for each electron) with an unprecedented double photoemission energy resolution of $<$ 25 meV. The two TOF analyzers permit measurements of correlated electron pairs with momentum separation of $\sim 2{\text{Å}}^{-1}$. The performance of the setup is demonstrated by both single and double photoemission measurements, with an emphasis on the coincidence acquisition electronics and data extraction procedure for isolating correlated pair emission.

Two-dimensional (2D) systems, such as high-temperature superconductors, surface states of topological insulators, and layered materials, have been intensively studied using vacuum-ultraviolet (VUV) angle-resolved photoemission spectroscopy (ARPES). In semiconductor films (heterostructures), quantum well (QW) states arise due to electron/hole accumulations at the surface (interface). The quantized states due to quantum confinement can be observed by VUV-ARPES, while the periodic intensity modulations along the surface normal (k_z) direction of these quantized states are also observable by varying incident photon energy, resembling three-dimensional (3D) band dispersion. We have conducted soft X-ray (SX) ARPES measurements on thick and ultrathin III-V semiconductor InSb(001) films to investigate the electronic dimensionality reduction in semiconductor QWs. In addition to the dissipation of the k_z dispersion, the SX-ARPES observations demonstrate the changes of the symmetry and periodicity of the Brillouin zone in the ultrathin film as 2D QW compared with these of the 3D bulk one, indicating the electronic dimensionality reduction of the 3D bulk band dispersion caused by the quantum confinement. The results provide a critical diagnosis using SX-ARPES for the dimensionality reduction in semiconductor QW structures.