The effect of Breit interaction on alignment parameter and linear polarization after electron-impact excitation.

[WYP020625]

Dear Dr. Gu
We have some questions about using FAC-1.1.5 and FAC-1.1.4 to calculate the alignment parameter by electron-impact excitation.
Question 1:
We have calculated the alignment parameter of Be-like ions (Z=60, 67, 75, 82, 87, 92) resonant level [1s2s22p1/2]J = 1 populated by electron impact from ground state [1s22s2]J=0 with and without the Breit interaction, respectively. We find that the SetBreit( ) function can not consider the Breit interaction well. It seems that SetBreit( ) does not play a role, while in the existing paper (Physical Review A, 109, 032817 (2024)), this effect should be very significant (as shown in Fig.1).

Fig. 1 The figure 1 of Physical Review A, 109, 032817 (2024).

Fig. 2 The alignment results of [1s22s2]J=0→[1s2s22p1/2]J=1 obtained by using FAC-1.1.4 and FAC-1.1.5.
Note: The program script with and without Breit interaction we used are shown in Appendix 1 and 2, respectively.
Question 2:
When calculating the linear polarization of lyman line 2p3/2→1s1/2 of Ti21+ after the electron-impact excitation, we find that the results calculated by the FAC (the earlier version of 1.1.5) considering the Breit interaction at low energy are in good agreement with the results of the paper (Physical Review A, 105, 062813 (2022)). However, when the electron energy arrived at 3 times the threshold or higher, the results of FAC seemed to be overestimated (As shown in the red circle in the figure below).

Fig. 3 The linear polarization of lyman line 2p3/2→1s1/2 of Ti21+ after the electron-impact excitation of our calculation (black open squares) and figure 3 of Physical Review A, 105, 062813 (2022) .
Note : The program script we used are shown in Appendix 3.
We are looking forward to your reply.

Appendix 1.txt
Appendix 2.txt
Appendix 3.txt

[mfgu]

when Breit term is included in collisional excitation, the quasi-relativistic option for computing collision strengths needs to be disabled,
use the following before CETable.
SetCELQR(-1)

[WYP020625]

when Breit term is included in collisional excitation, the quasi-relativistic option for computing collision strengths needs to be disabled, use the following before CETable. SetCELQR(-1)

Thank you for your reminder, after we add the SetCELQR(-1) function, we calculate the results from ground state [1s22s2]J=0 to [1s2s22p1/2]J = 1 after collision excitation are in good agreement with the paper (Physical Review A, 109, 032817 (2024)). However, we attempt to calculate the population of magnetic sublevels from metastable state to the double-excited state after collision excitation has no results. For example, We have calculated the population of the magnetic sublevels from the metastable state 1s2s to the double-excited states [2s1/22p1/2]1, [2p1/22p3/2]1 and [2s1/22p3/2]1 after electron-impact excitation, the PopulationTable function does not output any result. (see Appendix 1 for the script).
Appendix 1.txt

[mfgu]

pol module requires collisional and radiative rates connecting levels included in the model. if you don't have excitation from ground state to the lower level/upper levels of the transition you are studying, they will have 0 population. if you want to look at that particular transition, without effects from other levels, the calculation should include only the lower and upper levels of that transition.