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Klaus Bartschat - One of the best experts on this subject based on the ideXlab platform.
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electron impact excitation of argon at intermediate energies
Physical Review A, 2014Co-Authors: Oleg Zatsarinny, Klaus Bartschat, Yang WangAbstract:Large-scale $R$-matrix-with-Pseudostates calculations for electron collisions with argon atoms, using a recently developed parallel version of our B-spline $R$-matrix code, are reported. The calculations were carried out in the semirelativistic $\mathit{jK}$-coupling scheme. They are intended to provide converged (with respect to the number of coupled states) results for electron-impact excitation of individual target states with dominant configurations $3{p}^{5}4s$, $3{p}^{5}4p$, $3{p}^{5}3d$, and $3{p}^{5}5s$ for incident electron energies from threshold to 300 eV. The close-coupling expansion includes 500 target states, with the lowest 78 states representing the bound spectrum and the remaining 422 the ionization continuum. The results reveal dramatic reductions of the predicted excitation cross sections at intermediate energies due to a strong influence of coupling to the target continuum and the higher-lying Rydberg states. Comparison with available experimental data for excitation raises questions about the absolute normalization in the measurements.
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electron impact ionization of neon at low projectile energy an internormalized experiment and theory for a complex target
Physical Review Letters, 2013Co-Authors: Oleg Zatsarinny, Klaus Bartschat, Thomas Pfluger, Arne Senftleben, J Ullrich, Alexander DornAbstract:: As a fundamental test for state-of-the-art theoretical approaches, we have studied the single ionization (2p) of neon at a projectile energy of 100 eV. The experimental data were acquired using an advanced reaction microscope that benefits from high efficiency and a large solid-angle acceptance of almost 4π. We put special emphasis on the ability to measure internormalized triple-differential cross sections over a large part of the phase space. The data are compared to predictions from a second-order hybrid distorted-wave plus R-matrix model and a fully nonperturbative B-spline R-matrix (BSR) with Pseudostates approach. For a target of this complexity and the low-energy regime, unprecedented agreement between experiment and the BSR model is found. This represents a significant step forward in the investigation of complex targets.
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nonperturbative treatment of ionization with excitation of helium by electron impact
Physical Review Letters, 2011Co-Authors: Oleg Zatsarinny, Klaus BartschatAbstract:: We present cross sections for electron-impact ionization and simultaneous ionization plus excitation of helium by electron impact. The results are obtained from a fully nonperturbative close-coupling formalism using our B-spline R-matrix approach. A large number of Pseudostates in the expansion of the wave function represent the coupling to the ionization continuum. We obtain excellent agreement with the directly measured experimental cross section ratios (Bellm et al., Phys. Rev. A 75, 042704 (2007)) for ionization leaving the residual He⁺ ion in either the 1s ground state or the n = 2 (2s + 2p) excited states.
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ionization and ionization excitation of helium to the n 1 4 states of he by electron impact
Physical Review A, 2007Co-Authors: Susan Bellm, Klaus Bartschat, Julian Lower, Xiaoxu Guan, Daniel Weflen, Matthew S Foster, Allison L Harris, Don H MadisonAbstract:We present experimental and theoretical results for the electron-impact-induced ionization of ground-state helium atoms. Using a high-sensitivity toroidal electron spectrometer, we measured cross-section ratios for transitions leading to the first three excited states of the residual helium ion relative to the transition leaving the ion in the ground state. Measurements were performed for both symmetric- and asymmetric-energy-sharing kinematics. By presenting results as a ratio, a direct comparison can be made between theoretical and experimental predictions without recourse to normalization. The experimental data are compared to theoretical predictions employing various first-order models and a second-order hybrid distorted-wave $+$ convergent $R$ matrix with Pseudostates (close-coupling) approach. All the first-order models fail in predicting even the approximate size of the cross-section ratios. The second-order calculations are found to describe the experimental data for asymmetric-energy-sharing with reasonable fidelity, although significant disparities are evident for the symmetric-energy-sharing cases. These comparisons demonstrate the need for further theoretical developments, in which all four charged particles are treated on an equal footing.
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electron impact ionization and excitation of helium to the n 1 4 ionic states
Physical Review Letters, 2006Co-Authors: Susan Bellm, Julian Lower, Klaus BartschatAbstract:We present high-precisione; 2emeasurements and calculations for the e-He four-body Coulomb breakup problem. Cross-section ratios for ionization and excitation of the first three excited states of He � relative to the ground state have been measured for incident energies between 112 and 319 eV. Comparing the data with predictions from a state-of-the-art hybrid distorted-waveconvergent R matrix with Pseudostates (close coupling) approach shows that treating the projectile-target interaction at least to second order is crucial to obtain reasonable agreement between theory and experiment. Nevertheless, our benchmark studies reveal significant theoretical problems for the symmetric energy-sharing cases, thus indicating the need for further improvement.
Oleg Zatsarinny - One of the best experts on this subject based on the ideXlab platform.
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b spline r matrix with Pseudostates approach for excitation and ionization of atomic oxygen by electron collisions
Physical Review A, 2016Co-Authors: S S Tayal, Oleg ZatsarinnyAbstract:Electron scattering with atomic oxygen has been studied using the $B$-spline $R$-matrix-with-Pseudostates method. Cross sections for elastic scattering, excitation, emission, and ionization processes are presented. The excitation cross sections have been calculated for transitions between the $2{s}^{2}2{p}^{4}$ and $2{s}^{2}2{p}^{3}3l$ states of oxygen in the energy range from threshold to 200 eV. The present work differs from numerous previous studies due to the inclusion of a large number of Pseudostates in the calculation. We included a total of 1116 spectroscopic bound, core-excited autoionizing, and target continuum states in the close-coupling expansion. The atomic oxygen structure model has been described by combining the multiconfiguration Hartree-Fock and the $B$-spline box-based multichannel methods. The inclusion of a large number of Pseudostates representing the target continuum has a major impact, especially on the theoretical prediction of the excitation cross sections for many transitions at intermediate energies. A large reduction in excitation and emission cross sections has been noted due to the inclusion of coupling to the ionization continuum. The calculated cross sections are now in better agreement with available experimental results. The ionization cross sections for the ground $2{s}^{2}\phantom{\rule{0.16em}{0ex}}2{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{3}P$ and metastable $2{s}^{2}2{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{1}D$ and $^{1}S$ states are also presented. The electron-impact-induced emission cross sections for the $(2{s}^{2}2{p}^{3}3s){\phantom{\rule{0.16em}{0ex}}}^{3}{S}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (130.4 nm), $(2{s}^{2}2{p}^{3}3d){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (102.7 nm), $(2{s}^{2}2{p}^{3}3{s}^{\ensuremath{'}}){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (98.9 nm), and $(2{s}^{2}2{p}^{3}3{s}^{\ensuremath{'}\ensuremath{'}}){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (87.8 nm) transitions have been calculated and compared with the available experimental results.
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electron impact excitation of argon at intermediate energies
Physical Review A, 2014Co-Authors: Oleg Zatsarinny, Klaus Bartschat, Yang WangAbstract:Large-scale $R$-matrix-with-Pseudostates calculations for electron collisions with argon atoms, using a recently developed parallel version of our B-spline $R$-matrix code, are reported. The calculations were carried out in the semirelativistic $\mathit{jK}$-coupling scheme. They are intended to provide converged (with respect to the number of coupled states) results for electron-impact excitation of individual target states with dominant configurations $3{p}^{5}4s$, $3{p}^{5}4p$, $3{p}^{5}3d$, and $3{p}^{5}5s$ for incident electron energies from threshold to 300 eV. The close-coupling expansion includes 500 target states, with the lowest 78 states representing the bound spectrum and the remaining 422 the ionization continuum. The results reveal dramatic reductions of the predicted excitation cross sections at intermediate energies due to a strong influence of coupling to the target continuum and the higher-lying Rydberg states. Comparison with available experimental data for excitation raises questions about the absolute normalization in the measurements.
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electron impact ionization of neon at low projectile energy an internormalized experiment and theory for a complex target
Physical Review Letters, 2013Co-Authors: Oleg Zatsarinny, Klaus Bartschat, Thomas Pfluger, Arne Senftleben, J Ullrich, Alexander DornAbstract:: As a fundamental test for state-of-the-art theoretical approaches, we have studied the single ionization (2p) of neon at a projectile energy of 100 eV. The experimental data were acquired using an advanced reaction microscope that benefits from high efficiency and a large solid-angle acceptance of almost 4π. We put special emphasis on the ability to measure internormalized triple-differential cross sections over a large part of the phase space. The data are compared to predictions from a second-order hybrid distorted-wave plus R-matrix model and a fully nonperturbative B-spline R-matrix (BSR) with Pseudostates approach. For a target of this complexity and the low-energy regime, unprecedented agreement between experiment and the BSR model is found. This represents a significant step forward in the investigation of complex targets.
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nonperturbative treatment of ionization with excitation of helium by electron impact
Physical Review Letters, 2011Co-Authors: Oleg Zatsarinny, Klaus BartschatAbstract:: We present cross sections for electron-impact ionization and simultaneous ionization plus excitation of helium by electron impact. The results are obtained from a fully nonperturbative close-coupling formalism using our B-spline R-matrix approach. A large number of Pseudostates in the expansion of the wave function represent the coupling to the ionization continuum. We obtain excellent agreement with the directly measured experimental cross section ratios (Bellm et al., Phys. Rev. A 75, 042704 (2007)) for ionization leaving the residual He⁺ ion in either the 1s ground state or the n = 2 (2s + 2p) excited states.
Jonathan Tennyson - One of the best experts on this subject based on the ideXlab platform.
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on the use of Pseudostates to calculate molecular polarizabilities
Journal of Physics B, 2010Co-Authors: Marc Jones, Jonathan TennysonAbstract:The polarizability of a molecule is an intrinsic property which is important for a large variety of problems. However, determining reliable values for these polarizabilities is not straightforward: for instance the standard sum over states formulation of the problem does not converge because of the need to include not only many excited states but also to allow for contributions from the continuum. Here a formulation of this technique is given which uses Pseudostates to allow for physical and continuum states otherwise omitted from the expansion. The Pseudostates are represented by even-tempered expansions of Gaussian-type orbitals at the molecular centre-of-mass. The method is tested for LiH, Li2, water and CO molecules. For LiH and CO, calculations for the polarizability of low-lying excited states are presented including that for the A 3Π state of CO, whose polarizability appears not to have been previously determined. It is suggested that the use of Pseudostates provides a straightforward method of calculating static polarizabilities of molecules in both ground and excited electronic states. The extension of the method to the calculation of dynamic polarizabilities is discussed.
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resonances in electron impact electron detachment of c2
Physical Review Letters, 2008Co-Authors: Gabriela Halmova, Jonathan TennysonAbstract:Molecular $R$-matrix with pseudostate calculations are reported for the electron-impact ionization cross section of the carbon dimer anion. A $^{1}\ensuremath{\Sigma}_{g}^{+}$ resonance is found near the detachment threshold and two further resonances, of $^{3}\ensuremath{\Pi}_{g}$ and $^{1}\ensuremath{\Pi}_{g}$ symmetry, are found near 10 eV close to the structures observed experimentally. These unusual shape resonances are a result of the competition between the repulsive Coulomb interaction and the large, attractive polarizability of $\mathrm{C}_{2}{}^{\ensuremath{-}}$. Use of the Born approximation to allow for higher partial waves gives a total cross section close to that observed experimentally.
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Electron impact ionization of small molecules at intermediate energies: the molecular R-matrix with Pseudostates method
Journal of Physics B: Atomic, Molecular and Optical Physics, 2005Co-Authors: Jonathan TennysonAbstract:A procedure for the ab initio study of electron–molecule collisions at intermediate energies is presented in detail. The molecular R-matrix with Pseudostates method is based on the inclusion of discretized continuum states in the close-coupling expansion. This method allows, for the first time, the calculation of totally ab initio cross sections for electron impact ionization of molecules as well as for electronic excitation above the first ionization threshold. The method is general and can be applied to multielectron targets. Results for collisions with H+3 and H2 are presented. Numerical considerations necessary for performing a successful calculation are detailed.
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Electron-molecule collisions at low and intermediate energies using the R-matrix method
European Physical Journal D: Atoms, Molecules and Clusters and Optical Physics, 2005Co-Authors: Jonathan TennysonAbstract:We present the latest developments of the R-matrix method as applied to electron-molecule collisions. A variety of calculations for H2O are presented including the study of rotational excitation and preliminary data for dissociative electron attachment. Results for the application of the recently developed molecular R-matrix with Pseudostates (MRMPS) method to neutral and cationic targets are also included. This method is currently being applied to the study of collisions with anionic targets.
S S Tayal - One of the best experts on this subject based on the ideXlab platform.
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b spline r matrix with Pseudostates approach for excitation and ionization of atomic oxygen by electron collisions
Physical Review A, 2016Co-Authors: S S Tayal, Oleg ZatsarinnyAbstract:Electron scattering with atomic oxygen has been studied using the $B$-spline $R$-matrix-with-Pseudostates method. Cross sections for elastic scattering, excitation, emission, and ionization processes are presented. The excitation cross sections have been calculated for transitions between the $2{s}^{2}2{p}^{4}$ and $2{s}^{2}2{p}^{3}3l$ states of oxygen in the energy range from threshold to 200 eV. The present work differs from numerous previous studies due to the inclusion of a large number of Pseudostates in the calculation. We included a total of 1116 spectroscopic bound, core-excited autoionizing, and target continuum states in the close-coupling expansion. The atomic oxygen structure model has been described by combining the multiconfiguration Hartree-Fock and the $B$-spline box-based multichannel methods. The inclusion of a large number of Pseudostates representing the target continuum has a major impact, especially on the theoretical prediction of the excitation cross sections for many transitions at intermediate energies. A large reduction in excitation and emission cross sections has been noted due to the inclusion of coupling to the ionization continuum. The calculated cross sections are now in better agreement with available experimental results. The ionization cross sections for the ground $2{s}^{2}\phantom{\rule{0.16em}{0ex}}2{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{3}P$ and metastable $2{s}^{2}2{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{1}D$ and $^{1}S$ states are also presented. The electron-impact-induced emission cross sections for the $(2{s}^{2}2{p}^{3}3s){\phantom{\rule{0.16em}{0ex}}}^{3}{S}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (130.4 nm), $(2{s}^{2}2{p}^{3}3d){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (102.7 nm), $(2{s}^{2}2{p}^{3}3{s}^{\ensuremath{'}}){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (98.9 nm), and $(2{s}^{2}2{p}^{3}3{s}^{\ensuremath{'}\ensuremath{'}}){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (87.8 nm) transitions have been calculated and compared with the available experimental results.
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low energy differential and integral electron impact cross sections for the 2s22p4 3p 2p33s 3so excitation in atomic oxygen
Journal of Physics B, 2003Co-Authors: Paul V Johnson, I Kanik, M A Khakoo, J W Mcconkey, S S TayalAbstract:Differential and integral cross sections (ICSs) for excitation in atomic oxygen have been measured at electron-impact energies of 15, 17.5, 20, 22.5 and 27.5 eV. Differential measurements were conducted with a conventional electron energy-loss spectrometer and a microwave discharge source of atomic oxygen. Relative differential cross sections (DCSs) were determined between 15 and 30 eV impact energy. With the help of theoretical predictions of the shape of the DCS at large angles, measured results were extrapolated to 180° scattering angle and relative ICSs were deduced. The relative excitation function was normalized to the 30 eV impact energy ICS given by Kanik et al (2001 J. Phys. B: At. Mol. Opt. Phys. 34 2647). Normalization of the ICS values allowed the measured DCSs to be put on the absolute scale. Theoretical calculations of the DCSs were carried out using the R-matrix with the Pseudostates approach. A total of 22 spectroscopic bound and autoionizing states, together with 19 Pseudostates, were included in the close-coupling expansion. The Pseudostates were chosen to simulate continuum target states. Theoretical results, along with other available experimental data, have been compared with the current experimental results.
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breit pauli r matrix calculation for electron impact collision strengths and rates of o vi
The Astrophysical Journal, 2003Co-Authors: S S TayalAbstract:The Breit-Pauli R-matrix with Pseudostates approach has been used to calculate electron collisional excitation strengths for transitions between the 24 lowest fine-structure levels belonging to 14 LS terms (ns 2S, np 2P0 [n = 2-5], nd 2D [n = 3-5], nf 2F0 [n = 4, 5], and 5g 2G) of O VI. The effects of coupling to the highly excited bound and continuum target states have been simulated by using a set of Pseudostates in the close-coupling expansion. Our 43 state Breit-Pauli calculation includes 24 physical and 19 pseudolevels in the R-matrix expansion. Rydberg series of resonances converging to the excited level thresholds are explicitly included in the calculation. The effective collision strengths are obtained from the total collision strengths by integrating over a Maxwellian velocity distribution of electron energies. These are listed over a wide temperature range from 103 to 6 × 106 K.
Bartschat K. - One of the best experts on this subject based on the ideXlab platform.
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Wave-packet continuum-discretization approach to single ionization of helium by antiprotons and energetic protons
'American Physical Society (APS)', 2017Co-Authors: Abdurakhmanov Ilkhom, Kadyrov Alisher, Bray Igor, Bartschat K.Abstract:© 2017 American Physical Society. The recently developed wave-packet continuum-discretization approach [I. B. Abdurakhmanov, A. S. Kadyrov, and I. Bray, Phys. Rev. A 94, 022703 (2016)2469-992610.1103/PhysRevA.94.022703] is extended to antiproton-helium collisions. The helium target is treated as a three-body Coulomb system using a frozen-core approximation, in which the electron-electron correlation within the target is accounted for through the static interaction. The Schrödinger equation for the helium target is solved numerically to yield bound and continuum states of the active electron. The resulting continuum state is used to construct wave-packet Pseudostates with arbitrary energies. The energies of the Pseudostates are chosen in a way that is ideal for detailed differential ionization studies. Two-electron target wave functions, formed from the bound and continuum wave-packet states of the active electron and the 1s orbital of He+, are then utilized in the single-center semiclassical impact-parameter close-coupling scheme. A comprehensive set of benchmark results, from angle-integrated to fully differential cross sections for antiproton impact single ionization of helium in the energy range from 1 keV to 1 MeV, is provided. Furthermore, we use our single-center convergent close-coupling approach to study fully differential single ionization of helium by 1-MeV proton impact. The calculated results are in good agreement with recent experimental measurements [H. Gassert, O. Chuluunbaatar, M. Waitz, F. Trinter, H.-K. Kim, T. Bauer, A. Laucke, C. Müller, J. Voigtsberger, M. Weller, Phys. Rev. Lett. 116, 073201 (2016)PRLTAO0031-900710.1103/PhysRevLett.116.073201] for all considered geometries
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Differential cross sections for electron impact excitation of then= 2 states of helium at intermediate energies (80, 100 and 120 eV) measured across the complete angular scattering range (0–180°)
'IOP Publishing', 2011Co-Authors: Ward Rupert, Zatsarinny O., Cubric D, Bowring N, King G C, Read F H, Fursa D, Bartschat K.Abstract:Differential cross sections (DCS) for inelastic electron scattering to the n = 2 states in helium have been measured at incident energies of 80, 100 and 120 eV. These DCS have been determined across the complete angular scattering range (0–180◦) using a magnetic angle changer (MAC) with a soft-iron core. The convergent close-coupling (CCC), R-matrix with Pseudostates (RMPS), and B-spline R-matrix (BSR) methods have been used to calculate these DCS. Agreement between the experimental data and the predictions from these highly sophisticated theoretical methods is generally good. The remaining discrepancies mainly occur at small and large angles for the triplet states 23S and 23P, whereas excellent agreement is found between 30◦ and 150◦. The small-angle differences are likely due to contamination of the observed experimental signal from the neighbouring 21S and 21P states. The present results demonstrate the effective use of a soft-iron core MAC for DCS measurements at intermediate energies, extending the operational energy range of such devices by a factor of approximately 25
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Benchmark experiment and theory for near-threshold excitation of helium by electron impact
'AIP Publishing', 2006Co-Authors: Lange M., Matsumoto J., Lower J., Buckman S., Zatsarinny O., Bartschat K., Fursa D.v.Abstract:A new experimental technique has been applied to measure absolute scattering cross sections for electron impact excitation of the n ≤ 2, 3 states of helium at near-threshold energies. The experimental results are compared with predictions from recent state-of-the-art theoretical calculations. The calculations are performed using the R-matrix with Pseudostates, B-spline R-matrix, and the convergent close-coupling methods. Generally, very good agreement is found between the experiment and the three theorie
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Electron-impact ionization and excitation of helium to the n=1-4 ionic states
'American Physical Society (APS)', 2006Co-Authors: Bellm S., Lower J., Bartschat K.Abstract:We present high-precision (e; 2e) measurements and calculations for the e-He four-body Coulomb breakup problem. Cross-section ratios for ionization and excitation of the first three excited states of He+ relative to the ground state have been measured for incident energies between 112 and 319 eV. Comparing the data with predictions from a state-of-the-art hybrid distorted-wave + convergent R matrix with Pseudostates (close coupling) approach shows that treating the projectile-target interaction at least to second order is crucial to obtain reasonable agreement between theory and experiment. Nevertheless, our benchmark studies reveal significant theoretical problems for the symmetric energy-sharing cases, thus indicating the need for further improvement.S. Bellm, J. Lower and K. Bartscha
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Angle-differential cross sections and spin-asymmetry parameters for spin-polarized electron-impact excitation of spin-polarized cesium atoms
The American Physical Society, 2004Co-Authors: Baum G., Förster S., Pavlović N., Roth B., Bartschat K.Abstract:Relative angle-differential cross sections and spin-asymmetry parameters are presented for spin-polarized electron-impact excitation of spin-polarized cesium atoms for incident projectile energies ranging from 5 eV to 25 eV. The experimental data, obtained in the angular range of 40° to 140°, are compared with predictions from a nonrelativistic convergent close-coupling treatment for the differential cross section and the (spin) exchange asymmetry and from a semirelativistic R matrix with Pseudostates approach. The latter also yields nonzero values for two other spin asymmetries that require the presence of explicitly relativistic effects such as the spin-orbit interaction. The overall agreement between the experimental data and the theoretical predictions is satisfactory
