Journal of Electron Spectroscopy and Related Phenomena最新文献

In the present work, the Hf target was irradiated by tuning the energy (E_p) of synchrotron radiation across the L_i (i = 1–3) edge-energies ranging from 9.6 keV to 14.0 keV in order to measure the cross sections for production of the fluorescent L_k X-rays (k = l, α, η, β_1,6, β₃, β₄, β_2,15, β_5,7, β_9,10, γ_1,5, γ_2,3,6,8, γ₄). These measurements were performed with the aim to check the validity of independent particle approximation (IPA) models at incident photon energies in proximity to the L_i absorption edges of a heavy transition element. The measured cross sections were compared with three sets of values calculated using the X-ray emission rates based on the Dirac-Fock model, the L_i (i = 1–3) sub-shell photoionization cross-sections based on the non-relativistic Hartree-Fock-Slater model and three sets of the fluorescence (ω_i) and Coster-Kronig (f_ji) yields.

The calculated asymmetry parameter ($\beta$) and photoionisation cross sections for eight outermost orbitals ($1e_{1g}$, $3e_{2g}$, $1a_{2u}$, $3e_{1u}$, $1b_{2u}$, $2b_{1u}$, $3a_{1g}$, and $2e_{2g}$) of benzene, in the gas phase, are presented in the range from threshold to 35 eV. The Schwinger Variational Method with Padé approximants was employed to generate the continuum wavefunction of photoelectrons and the dipole matrix transition was computed in the velocity ($V$) and length ($L$) approach of the dipole operator. This operator in $V$ or $L$ form does not affect significantly $\beta$ values in the energy range studied. The cross sections in $V$ form produce lower magnitudes than $L$ and are closer to the measurements. The resonance peaks were observed in the cross sections for some orbitals and their positions were not affected by the dipole approach. Finally, symmetry analysis is done on the partial cross sections to assign the main contributing final state to the resonance feature and also link this to the minimum in the asymmetry parameter. The comparison of our results with other theories has, in general, good qualitative and some quantitative agreement. For some orbitals ($1a_{2u}$, $2b_{1u}$), severe disagreements between theory and experiment are highlighted. Some possible causes for these differences are pointed out. Because of this, we conclude that some asymmetry parameters and PICS for benzene, in ionisation studies, cannot yet be considered as a benchmark and will be necessary further investigation to clarify such discrepancies.

Circular dichroism angle-resolved photoemission spectroscopy (CD-ARPES) receives much attention due to a resolving power of topological and quantum geometrical nature of two-dimensional systems. We propose the Lippmann-Schwinger photoelectron final state, a scattering solution of the lattice model comprising screened short-range potentials at periodically arranged atomic sites, which characterizes the time-reversed low energy electron diffraction (LEED) state well enough to describe the final state effect entailed in CD-ARPES. We find that, through the final state effect, the electron screening length identifies CD-ARPES not only in the qualitative dichroic polarity but also in the quantitative dichroic strength in various graphene systems like the monolayer graphene, the AA-stacking bilayer graphene, and the twisted bilayer graphene especially in a unified fashion. This finding reveals an interplay between electron screening and circular dichroism and enables to extend the spectroscopic expertise of CD-ARPES to a direct probe of the electron screening.

The vertical, valence ionization energies of some [12]circulenes (C₄₈H₂₄) topoisomers have been calculated as free molecules in the gas phase using high-level ab initio coupled-cluster method: EOM-DLPNO-CCSD. Their valence electronic structures depend on molecular topology. We have used calculated vertical, valence ionization energies to simulate their UV photoelectron spectra (UPS). HOMO-LUMO bandgaps and the influence of molecular topology on the spectra were also studied. Our results indicate the presence and importance of stabilizing intramolecular π-π stacking interactions and molecular distortion (via strain energy) on electronic structures and UPS spectra. For example, the HOMO ionization energy increases along the sequence: infinitene<Möbius<Kekulene. The results presented may help in identification and analysis of photoelectron spectra of circulenes which can not be obtained in the gas phase, but rather as adsorbed molecules on metal surface.

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.

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.

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.

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.

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.