Influence of the Breit interaction on linear polarization of radiation lines following electron-impact excitation of the boron isoelectronic sequence

Electron-impact excitation cross sections from the ground state $1s^{2}2s^{2}2p_{1/2}$ to the excited states ${\left[{\left(1s^{2}2s2p_{1/2}\right)}_{0}2p_{3/2}\right]}_{3/2}$, ${\left[{\left(1s^{2}2s2p_{3/2}\right)}_{1}2p_{3/2}\right]}_{5/2}$, ${\left[{\left(1s2s^{2}2p_{1/2}\right)}_{0}2p_{3/2}\right]}_{3/2}$, and ${\left[{\left(1s2s^{2}2p_{3/2}\right)}_{1}2p_{3/2}\right]}_{5/2}$ of highly charged boronlike ${\mathrm{Ca}}^{15+}$, ${\mathrm{Xe}}^{49+}$, and ${\mathrm{W}}^{69+}$ ions have been calculated with the fully relativistic distorted-wave method. The degrees of linear polarization of the corresponding radiation lines are further obtained. It is found that the Breit interaction makes the lines corresponding to the $2p\to 2s$ transition depolarized, and it makes the ones corresponding to the $2p\to 1s$ transition more polarized. These characteristics are very different from the results obtained for the linear polarization of the same radiation lines but formed via the dielectronic recombination process [Phys. Rev. A 91, 042705 (2015)], in which the Breit interaction has no effect on the linear polarization.

Figure 1

Total EIE cross sections (${\mathrm{cm}}^2$) from the ground state $1s^{2}2s^{2}2p_{1/2}$ to the excited state ${\left[{\left(1s^{2}2s2p_{1/2}\right)}_{0}2p_{3/2}\right]}_{3/2}$ of highly charged boronlike ${\mathrm{Ca}}^{15+}$, ${\mathrm{Xe}}^{49+}$, and ${\mathrm{W}}^{69+}$ ions as functions of incident electron energy in threshold units. N+N denotes that both the target wave functions and impact matrix elements are calculated without the Breit interaction included; B+N denotes the former are calculated with an inclusion of the Breit interaction but the latter without the Breit interaction included; B+B represents both of them are calculated with the Breit interaction included.

Figure 2

The same as Fig. 1 but for the excitation to the excited state ${\left[{\left(1s^{2}2s2p_{1/2}\right)}_{1}2p_{3/2}\right]}_{5/2}$.

Figure 3

The same as Fig. 1 but for the excitation to the excited state ${\left[{\left(1s2s^{2}2p_{1/2}\right)}_{0}2p_{3/2}\right]}_{3/2}$.

Figure 4

The same as Fig. 1 but for the excitation to the excited state ${\left[{\left(1s2s^{2}2p_{1/2}\right)}_{1}2p_{3/2}\right]}_{5/2}$.

Figure 5

Degrees of linear polarization of the emission line radiated from the ${\left[{\left(1s^{2}2s2p_{1/2}\right)}_{0}2p_{3/2}\right]}_{3/2}\to 1s^{2}2s^{2}2p_{1/2}$ transition of highly charged boronlike ${\mathrm{Ca}}^{15+}$, ${\mathrm{Xe}}^{49+}$, and ${\mathrm{W}}^{69+}$ ions as functions of incident electron energy in threshold units.

Figure 6

The same as Fig. 5 but the emission line radiated from the ${\left[{\left(1s^{2}2s2p_{1/2}\right)}_{1}2p_{3/2}\right]}_{5/2}\to 1s^{2}2s^{2}2p_{3/2}$ transition.

Figure 7

The same as Fig. 5 but for the excitation to the excited state ${\left[{\left(1s2s^{2}2p_{1/2}\right)}_{0}2p_{3/2}\right]}_{3/2}$.

Figure 8

The same as Fig. 5 but the emission line radiated from the ${\left[{\left(1s2s^{2}2p_{1/2}\right)}_{1}2p_{3/2}\right]}_{5/2}\to 1s^{2}2s^{2}2p_{3/2}$ transition.