Stark broadening of the Hα line of hydrogen at low densities: quantal and semiclassical results

Stark profiles of the H alpha lines of hydrogen are computed at low densities (from 10 10 to 10 13 cm -3 ) in the 'impact' theory. By a comparison with quantal results the authors show that a simple semiclassical perturbational approach with appropriate cutoffs is sufficient to give accurate profiles in the line centre. Neglecting the natural broadening and the fine-structure effects, they prove that the electronic broadening is negligible and that the profile has a Lorentzian shape, and they give an analytical expression of the half width.