arXiv subjects

L. V. Chernysheva

Publications and source records attributed to L. V. Chernysheva.

At least 37 records · Page 2Linked to original sources

arXiv2014

Electron elastic scattering off a spin-polarized Cr atom

Electron elastic scattering off a spin-polarized Cr(...$3d^{5}4s^{1}$, $^{7}S$) atom is theoretically studied in the region of electron energies up to $15$ eV using both a one-electron "spin-polarized" Hartree-Fock and multielectron "spin-polarized" random phase approximation with exchange. It is found that scattering phase shifts of oppositely spin-polarized incoming electrons and corresponding cross sections of the scattering reactions significantly differ from each other, in general, even without accounting for spin-orbit interaction. This is shown to be associated with the presence of two semifilled $3d^{5}$ and $4s^{1}$ subshells in the Cr's configuration which induce considerably different exchange in the interaction of oppositely spin-polarized incoming electrons with the atom-target. The importance of electron correlation in $e^{-}+\rm Cr$ elastic scattering process is revealed. Moreover, correlation is shown to induce strong differences between scattering of oppositely spin-polarized electrons off Cr. A physically transparent interpretation for the latter is provided.

physics.atom-ph↗

arXiv2014

Explanation of the recent results on photoionization of endohedral atoms

We suggest an explanation of the recently observed discrepancy between the experimental and theoretical results on ionization of atoms, encapsulated into the fullerenes by photons with the energies of about 80-190eV. On the ground of previous theoretical considerations we conclude that the photoionization of the caged atom without excitation of the fullerene shell has low probability.

physics.atom-ph↗

arXiv2013

Comment on the paper Photoionization of endohedral atoms using R-matrix methods: application to Xe@C60 by T. W. Gorczyca, M. F. Hasoglu and S. T. Manson, Phys. Rev. A86, 033204 (2012) [1]

We demonstrate serious misrepresentation of existing experimental data and important omissions in the List of references in the paper [1]. We demonstrate that what is called in [1] total photoionization cross-section is in fact a partial photoionization cross-section. We demonstrate that long before [1] and presented there experimental data for photoionization of Xe@C60+ were obtained, a theoretical prediction for Xe@C60 have been published that was in a reasonable agreement with experiment. These data are even not mentioned in [1].

physics.atom-ph↗

arXiv2013

Featured trends in e$^{-}+$Mn electron elastic scattering

The impacts of both exchange interaction and electron correlation, as well as their combined impact, on electron elastic scattering off a semifilled shell Mn(...$3d^{5}$$4s^{2}$, $^{6}S$) atom are theoretically studied in the electron energy range of $ε= 0-25$ eV. Corresponding elastic scattering phase shifts $δ_{\ell}(ε)$ as well as partial $σ_{\ell}(ε)$ and total $σ(ε)$ cross sections are found to be subject to a strong correlation impact. The latter is shown to be drastically different for oppositely spin-polarized scattered electrons, in some cases, thereby bringing significant differences in corresponding $δ_{\ell}(ε)$s, $σ_{\ell}(ε)$s, and $σ(ε)$s between said electrons. This is proven to be an inherent features of electron scattering off a semifilled shell atom in general. Electron correlation is accounted for in the framework of the self-energy part $Σ$ of the Green function of a scattered electron concept. The latter is calculated both in the second-order perturbation theory in the Coulomb interelectron interaction as well as beyond it by solving the Dyson equation for $Σ$. The significance of the "Dyson" correlation corrections in e$^{-}+$Mn scattering is unraveled. They are shown to aggravate noticeably the inherent differences between elastic scattering phase shifts and cross sections of spin-up ($\uparrow$) and spin-down ($\downarrow$) polarized electrons scattered off a spin-polarized Mn atom, in some cases. In particular, the existence of a narrow resonant maximum in $σ^{\downarrow}(ε)$ near $ε\approx 8$ eV but the absence of such in $σ^{\uparrow}(ε)$ in e$^{-}+$Mn scattering is predicted.

physics.atom-ph↗

arXiv2012

Generalized oscillator strength of endohedral molecules

We investigate here the fast electron scattering upon endohedral atoms that present a fullerene CN staffed by an atom A, A@CN. We calculate the inelastic scattering cross-section expressing it via generalized oscillator strengths (GOS) density. We take into account two major effects of CN upon ionization of the atom A. Namely, the scattering of the electron by the static potential of the fullerenes shell and modification of the interaction between the fast incoming and atomic electrons due to polarization of the fullerenes shell by the incoming electron beam. To obtain the main features of the effect, we substitute the complex fullerenes shell CN by a static zero thickness potential, express its deformation under incoming electron action via CN polarizabilities. We perform all consideration in the frame of the so-called random phase approximation with exchange (RPAE) that gave reliable results for GOSes of isolated atoms, and expressions for absolute and differential in angle cross-sections. We limit ourselves with dipole and biggest non-dipole contributions to the differential in angle cross-section. We compare fast electron scattering with photoionization as a source of information on the target electronic structure and emphasize some advantages of fast electron scattering. As concrete objects of calculations, we choose noble gas endohedrals Ar@C60 and Xe@C60. The results are presented for two transferred momentum q values: q=0.1 and 1.0. Even for small q=0.1, in the so-called optical limit, the deviation from photoionization case is prominent and instructive. As an interesting and very specific object, we study onion-type endohedrals A@CN1@CN2, in which the all construction A@CN1 is stuffed inside CN2 with N2 >> N1.

physics.atm-clus↗

arXiv2011

On the strong influence of inner shell resonances upon the outer shell photoionization of endohedral atoms

It is demonstrated by the example of the Xe atom stuffed inside the C60 fullerene, that the so-called confinement resonances in 4d subshell strongly affect the photoionization cross-section of outer 5p and subvalent 5s electrons near 4d ionization threshold. It is a surprise that these narrow inner 4d shell resonances are not smeared out in the outer shell photoionization cross-section. On the contrary; the inner shell resonances affect the outer cross-section by enhancing them enormously. Close to its own photoionization thresholds, 5p and 5s photoionization cross-sections of Xe endohedral are dominated by their own confinement resonances greatly affected by the amplification of the incoming radiation intensity due to polarization by it of the C60 electron shell. In between 4d and 5p thresholds, the effect of 4d is becoming stronger while own resonances of 5p and 5s are becoming much less important.

physics.atom-ph↗

arXiv2011

Angular distributions of secondary electrons in fast particle-atom scattering

We present the angular distribution of electrons knocked out from an atom in a fast charge particle collision at small momentum transfer. It is determined not only by dipole but also by quadrupole transitions, the contribution of which can be considerably enhanced as compared to the case of photoionization. There the non-dipole parameters are suppressed as compared to the dipole ones by the parameter ωR/c << 1, where is the photon energy, R is the ionized shell radius and c is the speed of light. This suppression in fast electron-atom collisions can be considerably reduced: the corresponding expansion parameter ωR/ ν<< 1 is much bigger than in photoionization, since the speed of the incoming electron is much smaller than c. In formation of the angular distribution it is decisively important that the ionizing field in collision process is longitudinal, while in photoionization - it is transversal. We illustrate the general formulas by concrete results for outer s-, p-, and some nd-subshells of multi-electron noble gas atoms Ar, Kr and Xe, at several transferred momentum values: q=0.0, 0.1, 1.1, 2.1. Even for very small transferred momentum q, i.e. in the so-called optical limit, the deviations from the photoionization case are prominent.

physics.atom-ph↗

arXiv2011

Confinement and correlation effects in the Xe@C60 generalized oscillator strengths

The impact of both confinement and electron correlation on generalized oscillator strengths (GOS's) of endohedral atoms, A@C60, is theoretically studied choosing the Xe@C60 4d, 5s, and 5p fast electron impact ionization as the case study. Calculations are performed in the transferred to the atom energy region beyond the 4d threshold, omega = 75--175 eV. The calculation methodology combines the plane wave Born approximation, Hartree-Fock approximation, and random phase approximation with exchange in the presence of the C60 confinement. The confinement is modeled by a spherical delta-function-like potential as well as by a square well potential to evaluate the effect of the finite thickness of the C60 cage on the Xe@C60 GOS's. Dramatic distortion of the 4d, 5p, and 5s GOS's by the confinement is demonstrated, compared to the free atom. Considerable contributions of multipolar transitions beyond dipole transitions in the calculated GOS's is revealed, in some instances. The vitality of accounting for electron correlation in calculation of the Xe@C60 5s and 5p GOS's is shown.

physics.atom-ph↗

arXiv2011

Qualitative difference between the angular anisotropy parameters in fast electron scattering and photoionization

It is demonstrated for the first time that in spite of well known big similarities between atomic ionization by photons and fast electrons, a qualitative difference exists in angular anisotropy parameters of electrons knocked out in these processes. The difference is disclosed here and attributed to distinction between normal (transverse) and virtual (longitudinal) photons. Formulas are derived for dipole and non-dipole angular anisotropy parameters in fast electronatom scattering. The ratio of quadrupole-to-dipole matrix elements is determined by the parameter ωR/v << 1 where ωis the transferred in collision energy, R is the ionized shell radius and v is the speed of projectile. This factor can be much bigger than in the case of photoionization, where one has the speed of light c that is much bigger than v . We illustrate general formulas by concrete results for outer s-subshells of noble gas atoms Ar and Xe. Even for very small transferred momentum q, in the so-called optical limit, the deviation from photoionization case is prominent and instructive.

physics.atom-ph↗

arXiv2010

Non-dipole effects in angular distributions of secondary electrons in fast particle-atom scattering

We demonstrate that the angular distribution of electrons knocked out from an atom by a fast charge particle is determined not only by dipole but also by quadrupole transitions, the contribution of which can be considerably enhanced as compared to the case of photoionization. To obtain these matrix elements one has to study the angular distribution of electrons emitted by the atom in its collision with a fast charged particle. The distribution has to be measured relative to the momentum q transferred from the projectile to the target atom. The situation is similar, but not identical to the photoionization studies, where the matrix elements of continuous spectrum atomic quadrupole transitions can be determined by measuring the so-called non-dipole angular anisotropy parameters of photoelectrons. However, they are strongly suppressed as compared to the dipole matrix elements by small ratio of atomic size to the photon wavelength. This suppression is controlled in fast electron-atom collisions, where it can be much less than in photoionization since the respective virtual photon wavelength can be much smaller than in photoionization. We present not only general formulas, but also concrete results of calculations for noble gas atoms He, Ar and Xe. We have investigated their outer and subvalent subshells, as well as strongly collectivized 4d10 subshell in Xe. It appeared that even for the case of very small transferred momentum q, i.e. in the so-called optical limit the deviation from photoionization case is prominent.

physics.atom-ph↗

arXiv2009

Photoionization of atoms stuffed inside a two-shell fullerene

The photoionization of a two-shell endohedral A@CN1@CN2 is considered. Formulas are presented for cross-sections and angular anisotropy parameters, both dipole and non-dipole. The effect of the fullerenes shell upon photoelectron from atom A is taken into account substituting the action of the fullerene by two zero-thickness "bubble potential". The fullerenes shells polarization is included assuming that the radius of the outer shell R2 is much bigger than the inner R1 and both much exceeds the atomic radius r. This permits to express the effect via CN1,N2 polarizabilities, which are connected to their photoionization cross-sections. The interaction between shells CN1 and CN2 is taken into account in the Random Phase Approximation (RPA). The effect of photoelectron scattering by both "bubble potentials" is included in the lowest order and in the RPA frame. As concrete examples, two endohedrals Ar@C60@C240 and Xe@C60@C240 are considered. In the first case we consider 3p and 3s, while in the second 5p, 5s and 4d subshells. A whole variety of new peculiarities are found that deserve experimental verification.

physics.atm-clus↗

arXiv2008

Endohedral resonances: modification of atomic photoionization by the fullerenes shell

We discuss the complicated resonance structure of the endohedral atom photoionization cross section. Very strong enhancement and interference patterns in the photoionization cross-section of the valent and subvalent subshells of noble gas endohedral atoms A@C60 are demonstrated. It is shown also that the atomic Giant resonance can be either completely destroyed or remains almost untouched depending on the velocity of photoelectrons that are emitted in the resonance's decay process. These effects are results of dynamic modification of the incoming beam of radiation due to polarization of the fullerenes electron shell and reflection of photoelectrons be the fullerenes shell static potential. We have considered the outer np- and subvalent ns-subshells for Ne, Ar, Kr and Xe noble gas atoms. The modification of the Giant resonances is considered for a whole sequence of endohedrals with atoms and ions Xe, Ba, La, Ce+, Ce+4, Eu. The polarization of the fullerene shell is expressed via the total photoabsorption cross section. The photoelectron reflection from the static potential is taken into account in the frame of the so-called bubble potential that is a spherical -type potential.

physics.atom-ph↗

arXiv2008

Distortion and preservation of Giant resonances in Endohedral Atoms A@C60

It is demonstrated in this Letter that the effect of the fullerene shell upon atomic Giant resonance decisively depends upon energy of photoelectrons, by which the resonance decay. According to the prediction in [1], the Giant resonance in Xe is strongly modified in the endohedral Xe@C60 being transformed from a single broad and powerful maximum in Xe into four quite narrow but with almost the same total oscillator strength. On the contrary, the 4d Giant resonances in ions Ce3+ (the electronic structure that Ce has, when stuffed into fullerene), in Ce4+, and Eu are considered. In none of them the 4d Giant resonance in endohedrals is affected essentially. This is because the decay of the Giant resonances in these endohedrals proceeds by emission of fast photoelectrons that are almost unaffected by the C60 shell. The results obtained give at least qualitative explanation to the fact that recent observation of 4d Giant resonance in Ce@C82+, where the Giant resonance was observed as a maximum without noticeable structure.

physics.atom-ph↗

arXiv2007

Destruction and Resurrection of Atomic Giant resonances in Endohedral Atoms A@C60

It is demonstrated that in photoabsorption by endohedral atoms some atomic Giant resonances are almost completely destroyed while the others are totally preserved due to different action on it of the fullerenes shell. As the first example we discuss the 4d10 Giant resonance in Xe@C60 whereas as the second serves the Giant autoionization resonance in Eu@C60. The qualitative difference comes from the fact that photoelectrons from the 4d Giant resonance has small energies (tens of eV) and are strongly reflected by the C60 fullerenes shell. As to the Eu@C60, Giant autoionization leads to fast photoelectrons (about hundred eV) that go out almost untouched by the C60 shell. As a result of the outgoing electrons energy difference the atomic Giant resonances will be largely destroyed in A@C60 while the Giant autoionization resonance will be almost completely preserved. Thus, on the way from Xe@C60 Giant resonance to Eu@C60 Giant autoionization resonance the oscillation structure should disappear. Similar will be the decrease of oscillations on the way from pure Giant to pure Giant autoionization resonances for the angular anisotropy parameters. At Giant resonance frequencies the role of polarization of the fullerenes shell by the incoming photon beam is inessential. Quite different is the situation for the outer electrons in Eu@C60, the photoionization of which will be also considered.

physics.atm-clus↗

arXiv2007

On photoionization of the subvalent subshells of noble gas endohedral atoms

We demonstrate strong interference patterns in the photoionization cross-section of the subvalent subshells of noble gas (NG) endohedral atoms NG@F. This interference is a result of common action of three factors: the effect of neighboring atomic subshells, reflection of photoelectron waves by the fullerene F shell and resonance modification of the incoming photon beam by the complex effect under the action of the F electrons. We have considered the outer ns-subshells for Ne, Ar, Kr and Xe noble gas atoms. The polarization of the fullerene shell is expressed via the F total photoabsorption cross section. The photoelectron reflection from the static F potential is taken into account in the frame of the so-called bubble potential that is a spherical zero--thickness type potential. It is assumed in the derivations that NG is centrally located in the fullerene. It is assumed also, in accordance with the available experimental data, that the fullerene radius is much bigger than the atomic radius and the thickness of the fullerene shell. These assumptions permit, as demonstrated recently, the NG@F photoionization cross section to be presented as a product of the NG subvalent cross section and two calculated factors that account for polarization of the F electron shell and reflection of photoelectrons by the fullerene static potential.

physics.atm-clus↗

arXiv2007

On the photoionization of the outer electrons in noble gas endohedral atoms

We demonstrate the prominent modification of the outer shell photoionization cross-section in noble gas (NG) endohedral atoms NG@F under the action of the fullerene F electron shell. This shell leads to two important effects, namely to strong enhancement of the cross-section due to fullerenes shell polarization under the action of the incoming electromagnetic wave and to prominent oscillation of this cross-section due to the reflection of the photoelectron from NG by the F shell. All but He noble gas atoms are considered. The polarization of the fullerene shell is expressed via the total photoabsorption cross-section of F. The reflection of the photoelectron is taken into account in the frame of the so-called bubble potential that is a spherical zero --thickness potential. It is assumed in the derivations that NG is centrally located in the fullerene. It is assumed also, in accord with the existing experimental data, that the fullerenes radius R is much bigger than the atomic radius and the thickness of the fullerenes shell . These assumptions permit, as it was demonstrated recently, to present the NG@F photoionization cross-section as a product of the NG cross-section and two well defined calculated factors.

physics.atm-clus↗

arXiv2007

Giant resonances of endohedral atoms

We demonstrate for the first time that the effect of fullerene shell upon photoionization of the "caged" atom in an endohedral can result in formation of Giant Endohedral Resonances or GER. This is illustrated by the concrete case of Xe@C60 photoionization cross-section that exhibits at 17 eV a powerful resonance with total oscillator strengths of about 25. The prominent modification of the 5p6 electron photoionization cross-section of Xe@C60 takes place due to strong fullerene shell polarization under the action of the incoming electromagnetic wave and oscillation of this cross-section due to the reflection of the photoelectron from Xe by the C60. These two factors transform the smoothly decreasing 5p6 cross-section of Xe into a rather complex curve with a powerful maximum for Xe@C60, with the oscillator strength being equal to 25! We present also the results for the dipole angular anisotropy parameter that is strongly affected by the reflection of the photoelectron waves but not modified by C60 polarization. The polarization of C60 is expressed via its total photoabsorption cross-section. The reflection of the photoelectron is taken into account in the frame of the so-called bubble potential that is a spherical delta-type potential.

physics.chem-ph↗

arXiv2007

Photoionization of 3d electrons of Xe, Cs and Ba endohedral atoms: comparative analyses

We demonstrate rather interesting manifestations of co-existence of resonance features in characteristics of the photoionization of 3d-electrons in Xe, Cs and Ba endohedral atoms. It is shown that for all of the considered atoms the reflection by the fullerene shell of photoelectrons produced by the 3d subshell photoionization affects greatly partial photoionization cross-sections of 3d5/2 and 3d3/2 levels and respective angular anisotropy parameters, both dipole and non-dipole adding to all of them additional maximums and minimums. The results obtained demonstrate distinctive differences between the three atoms. The calculations are performed treating the 3/2 and 5/2 electrons as electrons of different kinds with their spins "up" and "down". The effect of C60 shell is accounted for in the frame of the "orange" skin potential model. It is essential that in the considered photon frequency region presented resonance features are not affected by the C60 polarization.

physics.atom-ph↗