The 4p⁶autoionization cross section of Rb atoms excited by low-energy electron impact

Abstract

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 5 n 1 l 1 n 2 l 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 −16 cm 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 ) 2 P and (4d5s) 4 P 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 −16 cm 2 at 36 eV. It was also found that the 4p 6 excitation-autoionization is the dominant indirect ionization process contributing over 30% of the total single ionization of rubidium atoms by electron impact in the 15.3-50 eV energy range.

The post-collision interaction effect in autoionizing spectra of alkali atoms excited by electron impact

“…The obtained width of the 2 P 3/2 state agrees well with the value of 5 meV determined earlier from spectroscopic studies [18]. In view of these data and the calculated ratio of the autoionizing probabilities A a ( 2 P 3/2 )/A a ( 2 P 1/2 ) = 0.765 [19], the autoionization width of the 2 autoionizing states in rubidium atoms. Solid lines represent the fitting results obtained using the Barker-Berry formula [17] (see text).…”

Classification of the 5p5nln'l' LSJ energy levels of Cs excited by 30 eV electrons

“…The change was made based on the three criteria, the first and the second being the absolute value and position of the expansion coefficient of an assigned state. For the third criterion, we have assumed that the states originating from the 5p 5 6s 3 P and 5p 5 5d 3 L (L = P, D, F) in the assignment should be lower than the 5p 5 6s 1 P and 5p 5 5d 1 L ones if the expansion coefficients are approximately equal, as it was in the case of K [5] and Rb [6]. Differences among the absolute values of expansion coefficients are small, therefore a condition for the unambiguous classification was used, i. e. not to attribute the same LSJ state to two levels in all calculated spectrum.…”

“…Theoretical investigation of the 5p-core-excited autoionizing states of Cs is a complex task as the relativistic effects play a more important role compared with Na [1,2,3,4], K [5] or Rb [6]. The first attempt to perform the classification of Cs spectrum registered in an ultraviolet absorption experiment was made by Connerade [7] in jK notations.…”

The 5p autoionization spectra of Ba atoms excited by electron impact: identification of lines

“…However, the authors emphasized that there is little or no agreement between their experimental and calculated ejected-electron spectra that correspond to process (1). Meanwhile, as was shown in our recent studies of ejected-electron spectra of heavy alkalis Rb [17,18] and Cs [19], an accurate identification of the complex line structure may be feasible only if a certain minimum of data on processes (1) and (2) is available. These data are (i) experimental excitation thresholds and excitation dynamics of lines; (ii) calculated excitation energies, cross sections and decay rates of the states under study.…”