Revisiting the emission behavior of the characteristic line 1s2pP11→1s2S01 following electron-impact excitation of heliumlike ions

In light of the work of Reed and Chen [Phys. Rev. A 48, 3644 (1993)], electron-impact excitation from the ground state $1{s}^{2}\phantom{\rule{0.16em}{0ex}}^{1}S_{0}$ to the excited energy level $1s2p\phantom{\rule{0.16em}{0ex}}^{1}P_{1}$ of heliumlike ions and subsequent electric dipole radiative decay $1s2p\phantom{\rule{0.16em}{0ex}}^{1}P_{1}\ensuremath{\rightarrow}1{s}^{2}\phantom{\rule{0.16em}{0ex}}^{1}S_{0}$ are revisited by using the multiconfigurational Dirac-Fock method and relativistic distorted-wave theory. Special attention is paid to the effect of the Breit interaction on the angular and polarization behaviors of the characteristic electric dipole line radiated from heliumlike ions. It is found that the presently obtained linear polarization without inclusion of the Breit interaction agrees very well with the results of Reed and Chen for all the heliumlike ions and impact electron energies considered. In contrast to the results of Reed and Chen, the Breit interaction makes the electric dipole line much less linearly polarized and anisotropic, especially for high-$Z$ ions and high impact energies. This behavior quickly becomes more prominent with increasing atomic number $Z$ and impact energy.