We report theoretical close-coupling calculations for electron-impact excitation cross sections of He-like Ti XXI ions using the R-matrix method, including relativistic and radiation damping effects. The cross sections are in good agreement with experimental measurements from the electron-beam ion trap [Chantrenne et al., Phys. Rev. Lett. 69, 265 (1992)] for the four prominent x-ray transitions: 1${\mathit{s}}^2$${(}^1$${\mathit{S}}_0$)→1s2s${(}^3$${\mathit{S}}_1$), 1s2p${(}^3$${\mathit{P}}_{1,2}^{\mathit{o}}$), 1s2p${(}^1$${\mathit{P}}_1^{\mathit{o}}$), indicating that both the relativistic and the resonance effects, with radiative damping, may affect the electron-impact excitation process significantly in highly charged ions.

• Received 5 May 1995

DOI:https://doi.org/10.1103/PhysRevA.52.3366