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Borovik A.A.,Institute of Electronic Physics | Ogurtsov G.N.,RAS Ioffe Physical - Technical Institute
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2010

The energy shift of lines arising from the decay of the (np5(n + 1)s2)2P3/2 autoionizing states in Na (n = 2) and Cs (n = 5) atoms has been studied for the first time in ejected-electron spectra measured over the excess energy range -0.1 to 5.4 eV. In Na spectra, the energy dependence of the shift possesses a clear oscillatory-like character. In particular, the shift becomes of negative or positive sign depending on the presence or absence of a negative-ion resonance structure in the excitation function of the (2p53s2)2P3/2 state. Earlier, we reported a similar behaviour of the line shift for the (3p 54s2)2P3/2 autoionizing state in K atoms. Though in Cs atoms the strong negative-ion resonance is also present close to the excitation threshold of the (5p56s2) 2P3/2 state, in contrast to Na and K data, the energy dependence of the line shift possesses a smooth asymptotic behaviour described well by the classical model of the post-collision effect. The comparative analysis of the spectroscopic classification of the resonance structure in the excitation of the (np5(n + 1)s2)2P 3/2 autoionizing states in Na, K and Cs atoms has shown that the observed effect most probably reflects the complication of the compound character of resonances. In whole, the obtained data show that under the condition of the high polarizability of a resonantly excited target the relation between polarization attraction, centrifugal and Coulomb repulsion becomes a crucial factor which determines the final energy distribution of outgoing electrons. © 2010 IOP Publishing Ltd.


Borovik A.,Institute of Electronic Physics | Kupliauskien A.,Vilnius University
Journal of Physics: Conference Series | Year: 2014

The energy-loss spectrum of scattered electrons due to the excitation of the 1sn1l1n2l2 autoionizing states and the ejected-electron spectrum arising from the decay of these states in lithium atoms were measured at scattering angle 54.7° and 80 eV impact energy. A comparative analysis of excitation and decay channels of autoionizing states was performed. © Published under licence by IOP Publishing Ltd.


Borovik A.,Institute of Electronic Physics | Kupliauskien A.,Vilnius University
Journal of Physics: Conference Series | Year: 2014

The excitation-autoionization cross section of sodium atoms was studied as a function of the incident electron energy over the range from the lowest autoionization threshold at 30.77 eV up to 400 eV. The present data are compared with the similar excitation-autoionization cross sections for Li, K, Rb, and Cs atoms. © Published under licence by IOP Publishing Ltd.


Borovik A.,Institute of Electronic Physics | Kupliauskien A.,Vilnius University
Journal of Physics: Conference Series | Year: 2014

The 2p6 autoionization cross section of Na atoms was measured over the incident electron energy range from the lowest autoionization threshold at 30.77 eV to 37.2 eV. The observed structure was assigned to the negative-ion resonances based upon the lowest autoionizing configurations 2p 53s2 and 2p53s3p. © Published under licence by IOP Publishing Ltd.


Borovik A.,Institute of Electronic Physics | Kupliauskien A.,Vilnius University | Zatsarinny O.,Drake University
Journal of Physics: Conference Series | Year: 2012

By comparative analyzing of experimental and calculated data on excitation functions, energies, cross sections and decay rates, the spectroscopic classification for the 4p55d6s, 6s6d, 6s6p lowest autoionizing levels in cesium has been revised. Strong configuration-mixing and relativistic effects which accompany the electron impact excitation of the 5p6 subshell result in the essential different character of the level structure if comparing with other alkali atoms.


Borovik A.,Institute of Electronic Physics | Roman V.,Institute of Electronic Physics | Zatsarinny O.,Drake University | Bartschat K.,Drake University
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2013

Electron impact excitation of the (4p55s2) 2P3/2,1/2 and (4p54d5s)4P 1/2,3/2,5/2 autoionizing states in rubidium atoms was studied experimentally by measuring the ejected-electron excitation functions and theoretically by employing a fully relativistic Dirac B-spline R-matrix (close-coupling) model. The experimental data were collected in an impact energy range from the respective excitation thresholds up to 50 eV with an incident electron energy resolution of 0.2 eV and an observation angle of 54.7°. Absolute values of the excitation cross sections were obtained by normalizing to the theoretical predictions. The observed near-threshold resonance structures were also analysed by comparison with theory. For the 2P 3/2,1/2 doublet states, a detailed analysis of the R-matrix results reveals that the most intense resonances are related to odd-parity negative-ion states with dominant configurations 4p55s5p2 and 4p 54d5s6s. The measured excitation functions for the 2P 1/2 and 4PJ states indicate a noticeable cascade population due to the radiative decay from high-lying autoionizing states. A comparative analysis with similar data for other alkali atoms is also presented. © 2013 IOP Publishing Ltd.


Borovik A.,Institute of Electronic Physics | Kupliauskiene A.,Vilnius University | Zatsarinny O.,Drake University
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2013

The excitation-autoionization (EA) cross section of Na atoms was obtained experimentally in the form of normalized intensities of autoionizing spectra measured in the ejected-electron energy region between 25.5 and 33.7 eV for electron impact energies from the 2p6 excitation threshold at 30.77 up to 400 eV. The cross section exhibits the strong resonance behaviour in the near-threshold region and reaches the maximum value of 1.2 × 10 -17 cm2 at 200 eV. By assigning the lines in ejected-electron spectra, the relative role of the 2p6 and 2s 2 subshells as well as quartet and doublet levels in formation of the EA cross section was estimated. In particular, the autoionizing doublets in 2p53sns(n = 3 - 6), np(n = 3 - 6), nd(n = 3 - 4) configurations provide approximately 80% of the EA cross section at 200 eV impact energy. A comparative analysis of the EA cross sections for whole alkali group Li-Cs indicates that the near-threshold resonance behaviour of all cross sections is caused exclusively by the negative-ion resonances formed on the basis of the levels 1sn1l1n2l2 in Li and np 5n1l1n2l2 in Na-Cs atoms. The relative EA contribution to the total single ionization cross section does not exceed 2% in Li and 5% in Na, and reaches 26% in K, 32% in Rb and 39% in Cs atoms. © 2013 IOP Publishing Ltd.


Borovik A.,Institute of Electronic Physics | Kupliauskiene A.,Vilnius University | Zatsarinny O.,Drake University
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2011

The electron impact excitation of the 5p6 subshell in a caesium atom was studied by measuring the excitation cross sections of lines in ejected-electron spectra arising from the decay of the 5p5n 1l1n2l2 autoionizing doublet and quartet levels. The data were obtained for the incident electron energies ranging from the lowest excitation threshold 12.31 up to 600 eV at an observation angle of 54.7° and with incident-electron energy resolutions of 0.2 and 0.7 eV for the near-threshold and high impact-energy regimes, respectively. Spectroscopic assignment and excitation cross sections of levels in 6s2, 5d6s, 6s6p and 6s6d configurations are considered. © 2011 IOP Publishing Ltd.


Borovik A.,Institute of Electronic Physics | Roman V.,Institute of Electronic Physics | Kupliauskien A.,Vilnius University
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2012

The autoionization cross section of rubidium atoms was obtained by measuring the total normalized intensities of ejected-electron spectra arising from the decay of the 4p 5n 1l 1n 2l 2 autoionizing levels. The electron impact energy range from the 4p 6 excitation threshold at 15.31 up to 50 eV was investigated. The cross section reaches the maximum value of (2.9 ± 0.6) × 10 16cm 2 at 21.8 eV impact energy. The general behaviours of the cross section and the role of particular autoionizing configurations in its formation were considered on the basis of large-scale configuration interaction calculations of energies, cross sections, autoionization probabilities in 5snl(n 7; l 4) and 4d nl(n 5; l 2) configurations as well as the measured excitation functions for the lowest levels in 5s 2 and 4d5s configurations. The resonance behaviour of the cross section between 15.3 and 18.5 eV impact energy is caused exclusively by the negative-ion resonances present close to the excitation thresholds of the (5s 2) 2P and (4d5s) 4P autoionizing levels. At higher impact energies, the autoionization cross section is composed of contributions from the high-lying quartet and doublet levels in 4d5s, 5p and 5s5p, 5d, 6s, 6p configurations. From the comparison of the present data with available experimental and calculated ionization cross sections, the 5s + 4p 6 direct ionization cross section of rubidium atoms was determined with the maximum value of (7.2 ± 2.2) × 10 16cm 2 at 36 eV. It was also found that the 4p 6 excitationautoionization is the dominant indirect ionization process contributing over 30% of the total single ionization of rubidium atoms by electron impact in the 15.350 eV energy range. © 2012 IOP Publishing Ltd.


Borovik A.A.,Institute of Electronic Physics | King G.C.,University of Manchester
Journal of Physics: Conference Series | Year: 2012

Near-threshold excitation of the 3p6nl levels in potassium has been studied by measuring the "conventional" electron energy-loss spectrum and the near-threshold, constant residual energy-loss spectrum. The data were obtained at an incident energy resolution of 0.07 eV and an observation angle of 90°. Drastic changes in relative intensity of peaks when impact energy approaches the excitation threshold may denote the important role of resonance processes in excitation of the lowest np, ns and nd levels.

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