Distribution Of Auger Electrons Research Articles

Effect of the Breit interaction on the angular distribution of Auger electrons following electron-impact excitation of highly charged Be-like ions

The electron-impact excitation from the ground state to the autoionizing level $1s2{s}^{2}2{p}_{1/2}\phantom{\rule{0.16em}{0ex}}J=1$ and the subsequent nonradiative Auger decay $1s2{s}^{2}2{p}_{1/2}\phantom{\rule{0.16em}{0ex}}J=1\ensuremath{\rightarrow}1{s}^{2}2s\phantom{\rule{0.16em}{0ex}}J=1/2$ of Be-like ions have been studied by using the multiconfigurational Dirac-Fock method and the relativistic distorted-wave theory. Special attention has been paid to the effect of the Breit interaction on the angular distribution of the Auger electrons emitted. To do so, the partial cross sections, alignment parameters of the autoionizing level, and intrinsic anisotropy parameters of the Auger decay are evaluated for Be-like ${\mathrm{Mg}}^{8+}, {\mathrm{Fe}}^{22+}, {\mathrm{Mo}}^{38+}, {\mathrm{Nd}}^{56+}, {\mathrm{Au}}^{75+}$, and ${\mathrm{U}}^{88+}$ ions, from which the angular distribution of the Auger electrons is further obtained. It is found that the Breit interaction hardly contributes to the angular distribution for low-$Z$ ions such as ${\mathrm{Mg}}^{8+}$, especially at low impact energies, while for medium- and high-$Z$ ions the situation becomes fairly different. To be specific, the Breit interaction contributes to lowering the anisotropy of the angular distribution, which first becomes quickly more prominent with increasing atomic number up to certain high-$Z$ ions and then behaves very slowly less prominently for higher-$Z$ ions. Moreover, for high-$Z$ ions the effect of the Breit interaction on the angular distribution is found to be nearly independent of the atomic number $Z$. Owing to opposite effects of the Breit interaction on the alignment parameters and the intrinsic anisotropy parameters, such an ``abnormal behavior'' is speculated to be caused very likely by a ``competition'' between the opposite effects of the Breit interaction on both of them.

Angular distribution of Auger electron following photoionization in Xe atom

The angular distribution of Auger electron following photoionization in Xe atom is investigated using the multiconfiguration Dirac-Fock (MCDF) method and the density matrix theory. The alignment parameters of residual ions produced by the np3/2(n=2−5) and md3/2,5/2(m=3,4) sub-shell photoionization and the anisotropic angular parameters of Auger electron for different transition channels are calculated using our modified relativistic program, based on the RATIP package. The relationships of the angular distribution of Auger electron and the alignments of the core-ionized atomic states are given. The influences of the multipole radiation field, the Breit interaction, and the electron exchanged interaction on the photoionization and subsequent Auger decay processes are discussed. Our results show that the alignment parameters of the residual ions and the angular distribution of Auger electrons are strongly related to the atomic shell, yet they show a low sensitivity to the Breit interaction and the electron exchange effect. This work is of significance to the experimental study of photoionization induced Auger electrons.

Ion-induced Auger electrons contrast on cross-beam systems

The article deals with the basic aspects of ion-stimulated Auger process. The authors suggested using the standard Everhart–Thornley detector to obtain a contrast of ion-induced Auger electrons on cross-beam systems using mathematical processing of the image which is based on spectroscopic information. As a result, this work consisted of obtaining images that showed the contrast distribution of Auger electrons and the sputtering yield on aluminum thin films samples.

Kinetic Energy Distribution of Auger Electrons of MgO, CaO, SrO and BaO Induced by Auger Neutralization of He$^+$, Ne$^+$, Ar$^+$ and Xe$^+$ Ions

Kinetic Energy Distribution of Auger Electrons of MgO, CaO, SrO and BaO Induced by Auger Neutralization of He$^+$, Ne$^+$, Ar$^+$ and Xe$^+$ Ions

Imaging the Temporal Evolution of Molecular Orbitals during Ultrafast Dissociation

We investigate the temporal evolution of molecular frame angular distributions of Auger electrons emitted during ultrafast dissociation of HCl following a resonant single-photon excitation. The electron emission pattern changes its shape from that of a molecular σ orbital to that of an atomic p state as the system evolves from a molecule into two separated atoms.

Classification of the 5p5n1l1n2l2 LSJ autoionizing states of Cs excited by 30 eV electron-impact

SynopsisClassification of the 5p5n1l1 (L'S')n2l2 LSJ autoionizing states of Cs excited by 30 eV electron-impact was performed by using more accurate calculations of energy levels, excitation cross sections and autoionization probabilities obtained in the Dirac-Fock-Slater approximation. Calculated parameters were used for simulation of the ejected Auger electron intensity spectrum and identification of the experimental ejected-electron spectrum of Cs excited by 30 eV electrons taking into account the asymmetry of the angular distribution of Auger electrons.

Spatial distribution of Auger electrons emitted from internalised radionuclides in cancer cells: the photoresist autoradiography (PAR) method.

Microdosimetric evaluation of Auger electron-emitting radionuclides involves a detailed evaluation of energy deposition at a nanometre scale. To perform Monte Carlo modelling of such energy deposition, accurate information regarding the spatial distribution of the radionuclide is required. A recent addition to the methods for determining the spatial distribution of cellular internalised radionuclides is based on detection in a polymer photoresist (e.g. polymethyl methacralate), followed by atomic force microscopy analysis of the resultant 3D pattern. In comparison with present practice, the method offers greater spatial resolution and improved quantification. The volume of the pattern is proportional to the total dose, thereby permitting assessment of variability of accumulated activity, while the variation in depth across the pattern reflects the lateral spatial distribution in the local fluence per unit area. An added advantage is the similarity in response to ionising radiation of an organic polymer compared to that of biological material. A pattern in the resist from radiation emitted by a radionuclide treated cell gives additional spatial information about the energy deposited in the resist.

Theoretical analysis of Young-type electron interference inHe2++H2collisions using a semiclassical model

A four-body semiclassical model is developed to describe interferences observed in the angular distribution of Auger electrons emitted after double capture in 30-keV $\mathrm{H}{\mathrm{e}}^{2+}+{\mathrm{H}}_{2}$ collisions. The present model is based on both the corpuscular and wave behaviors of the emitted electron. The corpuscular aspect is used to determine the trajectories of the collision partners, while the wave behavior occurs only in the determination of the phase shift. The results of the calculation are found to reproduce the experiment remarkably well. Series of maxima and minima are found in the angular distribution, with periods that are close to the experimental values. In addition, at a fixed angle, oscillations in the energy distribution are clearly evidenced in both the experiment and calculation.

Strong asymmetry of the angular distribution of Auger electrons from electron-impact excited autoionizing states of Rb

The asymmetry parameters of the angular distribution of Auger electrons for a number of electron-impact excited states were calculated in single configuration intermediate coupling approximation. Strong dependence on the energy of exciting electrons was obtained for the angular distribution of the emitted Auger electrons from the states with J > 1/2.

Theoretical study of the 4p5nln′l′ autoionizing states of Rb excited by electron impact

Large scale configuration interaction calculations of energy levels, autoionization probabilities and electron-impact excitation cross sections of the autoionizing states 4p5nln′l′ (nl = 5s,4d,5p,4f; n′l′ = 4d,5s,5p,5d,5f,5g,6s,6p,6d,7s,7p) of Rb up to 19.6 eV were performed for the first time. The relativistic effects were taken into account in the Dirac–Fock–Slater approximation. The asymmetry parameters of the angular distribution of Auger electrons for a number of electron-impact excited states were calculated in a single configuration intermediate coupling approximation. Strong dependence on the energy of exciting electrons was found for the angular distribution of the emitted Auger electrons from the states with J > 3/2 at the polar ‘magic angle’ of 54.73°. The calculated data were used for the novel classification of lines in an experimental ejected-electron spectrum.

Strong interference effects in the angularly resolved Auger decay and fluorescence emission spectra of the core-excited NO molecule

Angular distributions of Auger electrons and subsequent fluorescence photons are studied theoretically and experimentally in the vicinity of the core excitations of NO. In the calculations, lifetime vibrational interference and electronic state interference were taken into account ab initio. The interference between excitation and deexcitation amplitudes for transitions via symmetry-different intermediate resonances 1s−12π2(2Δ, 2Σ±), which is forbidden in the solid-angle-averaged or magic-angle-recorded decay spectra, plays a crucial role in the formation of the angularly resolved decay spectra. Experimentally, angular distribution parameters for the NO+(A1Π → X1Σ+) fluorescence induced by linearly polarized synchrotron radiation are determined in the vicinity of the N*O resonance in the Raman regime for core excitation. Theoretical results are in good agreement with the present experimental fluorescence spectra and with the available vibrationally and angularly resolved resonant Auger electron spectra.

Angular distribution of resonant Auger electrons from atoms with multiple overlapping resonances

We study the angular distribution of resonant Auger electrons from atoms in the presence of many overlapping metastable states. We work within the one-step model of the resonant Auger process and develop a general form for the asymmetry parameters which takes into account the interactions between the bound and continuum states more completely than in previous works. We simulate the theoretical angular distributions of Auger electrons following the electronic decay of a resonantly excited system with two energetically closely spaced resonances, where the energy splitting of the states is varied. We show that when the energy splitting becomes small, the angular distributions can be affected considerably.

Angular distribution of Auger electrons from fixed-in-space and rotating C 1s→2π photoexcited CO: Theory

The one-center approach for molecular Auger decay is applied to predict the angular distribution of Auger electrons from rotating and fixed-in-space molecules. For that purpose, phase shifts between the Auger decay amplitudes have been incorporated in the atomic model. The approach is applied to the resonant Auger decay of the photoexcited C 1s-->2pi resonance in carbon monoxide. It is discussed how the symmetry of the final ionic state is related to features in the angular distributions and a parametrization for the molecular frame Auger electron angular distribution is suggested. The angular distribution of Auger electrons after partial orientation of the molecule by the sigma-->pi-excitation process is also calculated and compared to available experimental and theoretical data. The results of the one-center approach are at least of the same quality as the available theoretical data even though the latter stem from a much more sophisticated method. As the one-center approximation can be applied with low computational demand even to extended systems, the present approach opens a way to describe the angular distribution of Auger electrons in a wide variety of applications.

Measurements of molecular-frame Auger electron angular distributions at the CO C 1s−1 2π* resonance with high energy resolution

The molecular-frame Auger electron angular distributions (MFAEADs) of resonantly excited CO 1s → π molecules in the gas phase were determined with high energy resolution using a novel experimental approach. We investigated the process of excitation, Auger decay and fragmentation in unprecedented detail. We confirmed theoretical predictions for the different MFAEADs of close lying Auger final states. By examining the dependence of the MFAEADs on the vibrational state of the excitation and on the fragmentation energy we found that the measured MFAEADs can be considered independent of the vibrational excitation and the fragmentation process. The method used to obtain molecular-frame angular distributions of Auger electrons is based on electron–ion coincidence measurements using two high-resolution electron spectrometers with limited acceptance angles mounted at fixed positions.

Study of second-step Auger transitions in Auger cascades following 1s → 3p photoexcitation in Ne

We present the results of high-resolution measurements of the low-energy part of the Auger electron spectrum generated by photoexcitation of the 1s−13p resonance in Ne. The spectrum was measured in the energy range of 10–33 eV where mainly the electrons from the second-step Auger transitions of the cascades 1s−13p → 2s2p5np → 2s22p4 and 1s−13p → 2s02p6np → 2s2p5(n = 3, 4) are detected. High resolution allows us to study the multiplet structure of the transitions and to determine the widths of the intermediate states of the Ne+ ion. Anisotropy of the angular distribution of Auger electrons is determined for all of the lines observed. The results are in reasonably good agreement with MCDF calculations.

Spin polarization and angular distribution of Auger electrons formed as a result of decay of the 3d −15p state in the Kr atom

The results of numerical calculations of the energies of Auger transitions, as well as the angular distribution (α2) and spin polarization (β2) anisotropy parameters, are presented for transitions in a photoexcited Kr* atom with two open shells. Matrix elements are calculated by the multiconfigurational Fock-Dirac relativistic method using an intermediate type of coupling. The wavefunctions of the initial and final states of the Auger transition are calculated with allowance for relaxation effects. The one-electron wavefunction of the continuous spectrum for an Auger electron is obtained using the single-configuration Fock-Dirac method. The results are compared with experiment and a new experiment is proposed for identifying the Auger state not only from the energy, but also from the total angular momentum of the Auger state.

Calculation of the asymmetry parameters of the angular distribution and of the spin polarization of Auger electrons for open-shell atoms

By means of the multichannel Hartree-Fock-Dirac method, the parameters β and α2 of the angular distribution of Auger electrons and the parameter β2 of their spin polarization are calculated for sodium, krypton, xenon, barium, mercury, and excited argon. Relevant Coulomb matrix elements are determined by using orthogonal multielectron initial-and final-state wave functions for intermediate-type coupling in a relativistic approximation. Exchange interaction is taken into account in all calculations. A comparison of the results of calculations performed in the frozen-core approximation and those obtained with orthogonal initial-and final-state wave functions reveals that the relaxation of core orbital processes has only a slight effect on the anisotropy parameters of the angular distribution. The resulting values of the parameters β, α2, and β2 are compared with the results of different calculations.

Study of the angular distribution of Auger electrons for the N 3 O 1O4, 5 and L 3 M 1 M 4, 5 transitions in the Hg atom

The angular distribution of Auger electrons is considered. The results of numerical calculations of the anisotropy parameter of the angular distribution α2 for the N 3 O 1 O 4, 5 and L 3 M 1 M 4, 5 transitions in the Hg atom are reported. The matrix elements were calculated by the Dirac-Fock method in the relativistic approximation using the intermediate-coupling scheme.

Experimental study of coherence and correlation in the anisotropy of NeKL-LLLsatellite Auger decay

The coherent excitation of overlapping atomic states by ion projectiles has a strong effect on the angular distribution of Auger electrons. Therefore, the measurement of the angular anisotropy of outgoing Auger electrons is suitable for the quantitative studies of the influence of the coherence. In our experiment the Ne target was bombarded with $700--2000\phantom{\rule{0.3em}{0ex}}\text{keV}$ ${\mathrm{H}}^{+}$ and $2000\phantom{\rule{0.3em}{0ex}}\text{keV}$ ${\mathrm{He}}^{+}$ projectiles. The angular distributions of ${KL}_{2,3}{\text{\ensuremath{-}}LLL}_{2,3}$ Auger electrons emitted from the decay of the coherently excited $1s2p$ doubly vacancy states of Ne were measured. The anisotropy parameter of the Auger decay was deduced from the measurements and compared with theoretical results calculated using the multiconfiguration Dirac-Fock method. The results indicate that one should go beyond the $LS$ coupling scheme even at this relatively low atomic number element, but also suggest that only partially overlapping states need to be taken into account.

Angular distribution of auger electrons for (M 3 → N 2, 3 N 2, 3), (M 4 → N 4, 5 N 4, 5), (M 4 → N 1 N 3), and (M 4, 5 → O 2, 3 O 2, 3) in a xenon atom

The angular distribution of Auger electrons is considered, and the angular distribution anisotropy parameter α2 for (M3 → N2, 3N2, 3), (M3 → N3N3), (M4 → N4N5), (M4 → N5N5), and (M4, 5 → O2, 3O2, 3) transitions in a xenon atom is calculated. The matrix elements are evaluated by the nonrelativistic Hartree-Fock method with LS coupling, as well as by the relativistic Hartree-Fock method with jj coupling (single-configuration approximation) and intermediate coupling (multiconfiguration approximation).