  We discuss lower-than-predicted collisional-excitation cross-sections for
helium-like xenon measured at an Electron Beam Ion Trap facility. In a review
paper (H. Chen and P. Beiersdorfer, Can. J. Phys. 86, 55 (2008)), the authors
find a significant effect due to the Breit interaction between the free and the
bound electrons in the excitation process of He-like xenon. The authors state
that the agreement between the measured and calculated cross-section values can
only be found when the generalized Breit interaction is included in the
calculations. We have performed new calculations with a Multi-Configuration
Dirac-Fock code, as well as with the Penn State University suite of codes, and
our conclusions are that the contribution of the Breit interaction is much
lower than found in the calculations presented in the abovementioned article.
In fact, our predictions are subsequently almost twice as large as the
experimental values. We present these considerations in hopes of motivating new
experimental investigations.
