Inclusion of the generalized Breit interaction in excitation of highly charged ions by electron impact

The generalized Breit interaction is included in the scattering matrix elements when determining collision strengths for electron-impact excitation of highly charged ions. We use a relativistic distorted-wave approach that employs a Dirac-Fock-Slater potential to calculate the free-electron wave functions. This same potential is used to calculate the atomic-structure data. Collision strengths are presented for H-like, He-like, and Li-like ions for a range of Z values and impact-electron energies. Good agreement is obtained when comparing to the few existing calculations for hydrogenic ions. The effect of including the interaction is found to be small for ions with Z{}26, but increases steadily with Z. Changes of nearly 70% are observed for Z=92. Effects for the more complex He-like and Li-like ions are greater than for the hydrogenic analogs for the entire range of Z values considered. The accuracy of some simpler forms of the Breit interaction is also discussed.