Excitation and ionization of outer shells in Rb by electron impact

Abstract

The relativistic distorted-wave and binary-encounter-dipole approximations were employed for calculating the electron-impact single ionization cross sections of the 5s, 4p6, 4s2, 3d10 shells and 4p6 excitation cross section for Rb atom taking into account both configuration interaction and relativistic effects. The capabilities of the most used theoretical approaches in describing the single ionization of Rb atom were considered by comparing the present and other available calculated data with the experimental total ionization and total direct single ionization cross sections over the electron-impact energy range from the 5s threshold to 600 eV. The best agreement within experimental uncertainty was obtained by using the non-relativistic binary-encounter-dipole approximation included in the LANL Atomic Physics Codes package. At present none of the used approximations (plane-wave Born or relativistic distorted wave) can satisfactorily describe the experimental excitation-autoionization cross section in rubidium because the efficient formation of the 4p6 core-excited negative-ion rubidium states at near-threshold impact energies is ignored in calculations.

Excitation-autoionization contribution to single ionization of Sr by electron impact

“…Given the shape and absolute value of the calculated cross-sections as well as taking into account the possible contribution from doubly-excited states, one may say that the ionization crosssection BED-MC provides the best agreement with the experimental data [13,14]. This conclusion is also supported by our earlier analysis of the single ionization cross-section of Rb atoms [40].…”

“…In Sr atoms, the total single ionization cross-section s + tot can be represented by the sum of partial cross-sections s + nl tot ( ), nl=5s 2 , 4p 6 , 4s 2 , 3d 10 and other deeper subshells. Theoretical estimates made in this work and those in [14], as well as a comparison with ionization data for Rb atoms [40] show that the maximum contribution from ionization and excitation-autoionization of the 4s 2 and 3d 10 subshells can be no more than 3%-4%.…”

“…In both approximations, the radial wave functions were obtained as numerical solutions of the Dirac-Fock-Slater equations [39]. Excitation cross-sections were obtained in the RDW approximation using a calculation procedure similar to that described in detail elsewhere [25,40].…”