For those in German-speaking church communities, "Sonntag 23" refers to the (Sonntag im Jahreskreis).
If you want the medical paper, search for "Sonntag C1-C2 wiring PDF." If you want the gas data, search for "Crain and Sonntag Argon PDF." Download Sonntag23 pdf
In chemistry and physics, "Sonntag23" is a frequent citation for research on the (often citing Crain & Sonntag). For those in German-speaking church communities
