Comment on electron-impact excitation cross-section measurements for He-like Xenon

TL;DR

This paper critiques previous measurements of electron-impact excitation cross-sections for helium-like xenon, presenting new calculations that suggest the Breit interaction's contribution is overestimated, and calls for further experimental validation.

Contribution

It provides revised theoretical calculations indicating a lower Breit interaction effect, challenging prior experimental and theoretical results, and encourages new experimental studies.

Findings

Previous measurements showed lower cross-sections than predicted.

New calculations suggest the Breit interaction's contribution is overestimated.

Predicted cross-sections are nearly twice the experimental values.

Abstract

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.