A unified theory of Stark broadening for hydrogenic ions—II: Line wings

Abstract

The consequences of the attractive Coulomb force between positively charged hydrogenic radiators and electrons on line broadening in the quasistatic wings are examined. Due to the speeding up of the electrons by the Coulomb attraction, static results are not obtained until further out into the wings for (e.g.) He II lines, as compared to the analogous hydrogen lines. In fact, for low principal quantum numbers the region of validity is outside of, or close to, the limit ħΔω ⪅ kT imposed by the weak coupling approximation. The effects of doubly-excited bound states are discussed in detail and we conclude that within the validity range of the Unified Theory all except possibly the most tightly bound doubly-excited states (which can give rise to “satellites” to the ionic lines) are relatively unimportant. In the near line wings the profile goes approximately as Δω - 5 2 . But in the far line wings (ħΔω ⪅ kT) the wings lie somewhat above the Δω - 5 2 wing of neutral species and a Δω - 9 4 dependence is more appropriate. No exponential divergence of the spectrum is obtained for large Δω when bound states (for which a classical distribution of states is inappropriate) are excluded. Unfortunately, no conclusive experimental comparisons are possible with presently available data.