The intensity ratio R of the dipole-allowed lines 3d 2 D 3/2,5/2 → 2p 2 P 3/2 and 3d 2 D 3/2 → 2p 2 P 1/2 emitted from highly charged boron-like Ar 13+ ion collisionally excited by a monoenergetic electron beam has been theoretically studied versus electron densities from 10 9 to 5 × 10 13 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 i from 0.65 to 3 keV. By taking into account

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... l important transitions among 290 magnetic sublevels of the 2s 2 2p, 2s2p 2 , 2p 3 , 2s 2 3l, 2s2p3l, 2p 2 3l (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 2 D 3/2 → 2 P 3/2 line which blends with the 2 D 5/2 → 2 P 3/2 line enhances the effect of anisotropy.