A note on Δ n ≠ 0 Stark transitions in hydrogenlike atoms

In a gaseous helium or hydrogen target slow muons or antiprotons are captured into orbits with a high principal quantum number ( n = 15 to 50) to form (μ − α) + ions, ( p α) + ions, or ( p p ) atoms respectively. In the subsequent deexcitation process Stark mixing of the intermediary states plays an important role. The successful Mainz Cascade Model assumed Δ n = 0 for the Stark transitions, although formally no such selection rule exists. This note examines the reasons why Δ n ≠ 0 Stark transitions play only a negligible role in the deexcitation cascade.