Relative intensities of the 3d-2p lines emitted by Ar¹³⁺ ions after impact excitation by an electron beam

The intensity ratio R of the dipole-allowed lines 3d²D_{3/2,5/2} → 2p²P_{3/2} and 3d²D_{3/2} → 2p²P_{1/2} emitted from highly charged boron-like Ar¹³⁺ ion collisionally excited by a monoenergetic electron beam has been theoretically studied versus electron densities from 10⁹ to 5× 10¹³ cm^{-3}. The calculations were performed at different angles θ of observation with respect to the electron beam direction and various incident-electron energies e_{ı} from 0.65 to 3 keV. By taking into account all important transitions among 290 magnetic sublevels of the 2s²2p, 2s2p², 2p³, 2s²3l, 2s2p3l, 2p²3l (l = 0-2) configurations, a collisional-radiative model has been used for determining the populations of the upper magnetic sublevels of the lines. All required atomic data were computed with the Flexible Atomic Code. We find that the effect of anisotropy in the photon emission, due to the directionality of the incident electron beam, can lead to very significant differences between R(0°) and R(90°). Our results also indicate that the contribution from the ²D_{3/2}→ ²P_{3/2} line which blends with the ²D_{5/2} → ²P_{3/2} line enhances the effect of anisotropy.