Dominance of the Breit interaction in the cross section and circular polarization of x-ray radiation following longitudinally-polarized-electron-impact excitation of highly charged ions

Abstract

Longitudinally-polarized-electron-impact excitation cross sections from the ground state to the individual magnetic sublevels of the excited state $1s2{s}^{2}2{p}_{3/2}$($J = 2$) of highly charged Be-like ions are calculated using a fully relativistic distorted-wave method. The contributions of the Breit interaction to the cross sections and circular polarizations of the $1s2{s}^{2}2{p}_{3/2}$($J = 2$)$\ensuremath{\rightarrow}1{s}^{2}2{s}^{2}$($J = 0$) magnetic quadrupole (M2) line for selected Be-like ${\mathrm{Ag}}^{43+}$, ${\mathrm{Ho}}^{63+}$, and ${\mathrm{Bi}}^{79+}$ ions are investigated systematically. It is found that the Breit interaction has a large effect and makes the cross sections increase, especially to the ${m}_{f}$ = $\ensuremath{-}1$ and $\ensuremath{-}2$ sublevels, the Breit interaction can modify the cross sections by several orders of magnitude. These dramatic influences also lead to a remarkable decrease in the circular polarization of subsequent x-ray radiation, the character of which becomes more and more evident with increasing incident energy and atomic number. And all these characteristics are very different from the conclusions for the linear polarization of radiation following the electron-impact process [S. Fritzsche, A. Surzhykov, and T. St\"ohlker, Phys. Rev. Lett. 103, 113001 (2009); Z. W. Wu, J. Jiang, and C. Z. Dong, Phys. Rev. A 84, 032713 (2011)].