Stark broadening of the H-alpha line of hydrogen at low densities - Quantal and semiclassical results

Stark profiles of the H-alpha lines of hydrogen are computed at densities from (1 to 1000) x 10 to the 10th/cu cm in the 'impact' theory. By a comparison with quantal results it is shown that a simple semiclassical perturbational approach with appropriate cutoffs is sufficient to give accurate profiles in the line center. Neglecting the natural broadening and the fine-structure effects, it is proved that the electronic broadening is negligible and that the profile has a Lorentzian shape; and an analytical expression of the half width is obtained.