Circular polarization of the (1s2p)2→ (1s2)0 line emitted by 205Tl79+ ions after collisional excitation by an unpolarized electron beam

The circular polarization of the (1s2p)J=2→ (1s2)J=0 line emitted by the helium-like ion 205Tl79+ following impact excitation by a nonpolarized electron beam is theoretically studied. The probability for the hyperfine induced E1 transition (1s2p)2F=3/2→1s2 has been determined from the first order perturbation theory. Various collision strengths for excitation of thallium ions to the (1s2p)2MJ=0, 1 and 2 magnetic sublevels have been used. It is found that the interference between M2 and E1 radiation occurring in the line can give rise to a significant degree of circular polarization