Journal of Electron Spectroscopy and Related Phenomena最新文献

State-selective total and angular differential cross sections for positronium formation are presented in the collision of positron with helium atoms in their ground state by using the four-body formalism of the boundary-corrected continuum-intermediate-states approximation. The main purpose of the present study is to investigate the relative importance of intermediate ionization continuum states that has been incorporated with a suitable choice of distorting potential. In addition, the nine-dimensional integrals of the transition amplitude are analytically reduced to a one-dimensional real integral, which can be easily calculated numerically. The influence of the target static electron correlations on the capture probability is investigated using the different bound-state wave functions of He. The theoretical model for the calculation is fairly accurate and predicts a number of interesting features of the state-selective total and differential cross sections in the range of positron impact energy varies from 20 to $250\mathrm{eV}$. The total cross sections are highly peaked at an impact energy of 50 eV. The results are compared with those of other theories and the available experimental data. The present theoretical results and other measurements show satisfactory agreement in the wide energy range. Moreover, surface plots for the state-selective differential cross sections are also presented to illustrate the interesting feature of the positronium formation in this collision process.

The significance of theoretical, experimental, and analytical methods in calculating the intensity ratios of L-shell transitions for diverse elements lies in their widespread applications across various domains, including physical chemistry and medical research. In the present paper, empirical values for intensity ratios were computed through polynomial interpolations using experimental databases within the scope of atomic number 39 ≤ Z ≤ 92 for $\frac{I_{L\beta }}{I_{L\alpha }}$ and $\frac{I_{L\gamma }}{I_{L\alpha }}$, and extending to the range of 39 ≤ Z ≤ 94 for $\frac{I_{\mathrm{Ll}}}{I_{L\alpha }}$. Additionally, new theoretical calculations were conducted using the Multiconfiguration Dirac–Fock Method for specific elements. The obtained results were compared with standard theoretical, experimental, and empirical values, showing a reasonable agreement with them.

The crystal structure of the ternary phosphide Ce₂Ni₁₂P₅ (La₂Ni₁₂P₅-type structure) has been determined from X-ray powder diffraction data: full profile refinement, monoclinic symmetry, space group P2₁/m, a = 10.7809(2) Å, b = 3.6869(1) Å, c = 13.1490(3) Å, β = 107.776(4)º, R_I = 0.068, R_P = 0.044, R_wP = 0.060. Ce₂Ni₁₂P₅ is a ferromagnet with a Curie temperature of 5.8(5) K. A significant deviation from the linearity of the temperature dependence of the electrical resistance for Ce₂Ni₁₂P₅ has been found. The low-temperature part of the electrical resistance indicates the presence of magnetic interactions in Ce₂Ni₁₂P₅. The influence of a magnetic field on the electrical resistance of Ce₂Ni₁₂P₅ has been studied. The X-ray absorption spectrum at the Ce L_III edge and X-ray emission spectra of Ni and P at the K and L_III edges have been studied experimentally and theoretically using DFT+U calculations. The calculations show good agreement with the experimental measurements. The effective valence of Ce in Ce₂Ni₁₂P₅ determined based on the Ce L_III absorption spectrum is ϑ_eff ∼ 3.05.

A method of straightforward construction and analysis of the cascade decay trees is applied to study the cascade energy reemission by silver atoms upon photoionization in the incident photon energy range of 0.01–100 keV. Cascade electrons and photons emitted during the cascade relaxation of an inner-shell vacancy carry away a significant part of the energy initially acquired by the silver atom in a photoionization act. The energies redistributed through following channels were calculated as functions of incident photon energy: energy absorbed by the silver atom itself (a), and energies carried away by the cascade electrons (b) and photons (c). Channel (a) is dominant only at small incident photon energies up to the M₅ ionization threshold. Channel (b) dominates between M and K thresholds making 57–85 % of the acquired energy. Above the K threshold, the weight of channel (b) is still significant, 24 %, however, dominant is channel (c).

Photoelectron spectroscopy (PES) investigation of two widely used herbicide compounds MCPA and 2,4-D is reported. The GW calculations are shown to offer a good description of their electronic structure. There is excellent agreement between the experimental and theoretical energies of the HOMO states of 2,4-D and MCPA, which are at 8.7 eV and 8.5 eV binding energy, respectively. The low energy tail of the HOMO state extends to about 8 eV. The good agreement between the UPS (ultraviolet photoelectron spectroscopy) spectra and the simulation validates the proposed conformer. The presented gas phase data will help researchers to analyze data from liquid and diluted samples of these herbicide molecules and perform additional theoretical modelling.

We have investigated the laser induced ultrafast dynamics of Gd 4f spins at the surface of Co_xGd_100-x alloys by means of surface-sensitive and time-resolved dichroic resonant Auger spectroscopy. We have observed that the laser induced quenching of Gd 4f magnetic order at the surface of the Co_xGd_100-x alloys occur on a much longer time scale than that previously reported in “bulk sensitive” time-resolved experiments. In parallel, we have characterized the static structural and magnetic properties at the surface and in the bulk of these alloys by combining Physical Property Measurement System (PPMS) magnetometry with X-ray Magnetic Circular Dichroism in absorption spectroscopy (XMCD) and X-Ray Photoelectron spectroscopy (XPS). The PPMS and XMCD measurements give information regarding the composition in the bulk of the alloys. The XPS measurements show non-homogeneous composition at the surface of the alloys with a strongly increased Gd content within the first layers compared to the nominal bulk values. Such larger Gd concentration results in a reduced indirect Gd 4f spin-lattice coupling. It explains the “slower” Gd 4f demagnetization we have observed in our surface-sensitive and time-resolved measurements compared to that previously reported by “bulk-sensitive” measurements.

Model exchange potentials are particularly interesting to account for the indistinguishability between the projectile and target electrons in electron-atom scattering in vacuo and plasma environments. It is well known that their performance is pretty satisfactory in the high energies but also that discrepancies from the results obtained with exact exchange are found toward the zero energy limit. In this article, we examine how well established model exchange potentials based on the free electron gas approach compare to phase shifts calculated considering exchange in exact form. In particular, we show that the Hara and the semiclassical exchange potentials are able to reproduce reference low energy phase shifts through a simple scale transformation, in opposition to the previous approaches where energy dependent corrections to the local momentum were adopted. We provide the scale factors and phase shifts for electron scattering by He, Ne and Ar atoms for $k<$ 1,0 a${}_0^{-1}$. Such scaling factors can be determined reproducing the scattering length and the number of s-wave bound states from exact exchange calculations. We also show that the scaling procedure works for electronic densities that present the physically correct asymptotic behavior. The present results are important to the research field, since they form the basis to construction of scattering models based on optical potential approaches.

Earlier study of exchange-correlation functionals for the calculations of outer-valence ionization potentials of 31 molecules shows that our Density Functional Theory (DFT) method called ∆PBE0(SAOP) performs very well except for the three perhalogenated molecules included in the study. The present work expands the study to 85 molecules including 40 containing halogens. Analysis of a total of 500 vertical ionization potentials (VIPs) confirms that ∆PBE0(SAOP) continues to excel for nonhalogenated molecules with an average absolute deviations (AAD) of 0.19 eV and reveals that the best method for halogenated molecules is ∆mPW1K(SAOP) with an AAD of 0.21 eV.

The analysis of X-ray photoelectron spectra often faces challenges due to the lack of standardization in modeling approaches, background subtraction methods, and computational algorithms within the field of computer science. The interpretation of XPS data significantly relies on the unique expertise and judgment of individual researchers. Therefore, the objective of this study is to highlight the difficulties associated with analytical methods that depend heavily on the discretion of individual scientists, to elucidate the prevailing models and background subtraction techniques, and to suggest improvements to these methodologies. This endeavor aims to enhance the reliability and reproducibility of XPS analysis, thereby contributing to the advancement of research in this area. By utilizing the information criterion as part of a thorough search methodology in Bayesian inference, we show that our sophisticated analytical techniques significantly outperform others in the analysis of actual X-ray photoelectron spectroscopy (XPS) spectra. This improvement is evidenced through enhanced accuracy and reliability in spectral interpretation, underscoring the efficacy of our methods in practical applications of XPS.

Manganese oxides (MnOx) are used as electrode materials in many different energy storage applications such as batteries and supercapacitors. X-ray spectromicroscopy, using near edge X-ray absorption spectra (NEXAFS) for chemical speciation, is a powerful tool to study reduction and oxidation processes in such systems. High quality reference spectra are required for both qualitative identification and quantitative mapping of MnOx species. Here we present accurate, quantitative Mn 2p and O 1s NEXAFS spectra of MnO, MnSO₄, Mn₃O₄, Mn₂O₃, α-MnO₂, β-MnO₂, and KMnO₄, measured using both transmission and total electron yield X-ray absorption techniques. An example of the use of these reference spectra in a study of Zn/MnO₂ batteries is given.