Stark Broadening by Electron and Ion Impacts of NA Hydrogen Lines of Large Principal Quantum Number

The impact approximation is shown to be a valid description of the Stark broadening of atomic hydrogen n n + 1 radio frequency transitions in H ii regions. Most of the Stark broadening is through inelastic electron collisions, because broadening by ion and elastic electron-collisions is much reduced by a near-cancellation of upper- and lower-state perturbations. The ratio of collision and Doppler widths obtained here is easily generalized to the corresponding transitions in neutral and ionized helium and to hydrogen n lines. Upper limits for electron densities in H u regions obtained from measured profiles and the present calculations are consistent with other observations.