Comparison of electron width models for fast line profile calculations

The first non-vanishing term in the perturbation expansion of the electron contribution to the line width, commonly used in spectral line broadening by plasmas, was previously expressed in terms of the thermally averaged bremsstrahlung Gaunt factor. The approximations in the derivation, however, suggest that the result is uncertain. The electron width formula is tested with the hydrogen Balmer series and found suspect. Calculations for the He II Lyman series also display similar difficulties. The limitation of this electron width formulation is traced to the absence of an explicit strong collision cutoff beyond which the second-order theory is invalid.