Electron collision shift of the Lyman-alpha line in H and He+

The interaction of plasma microfields with radiating atoms and ions causes a line broadening that governs both the half-width and shift of the spectral line, i.e., the intensity distribution in frequency is altered to reflect the presence of the plasma. The line shifts are of particular interest both for their intrinsic value in terms of providing insight into the fundamental nature of the underlying physical processes affecting the emission of radiation as well as its diagnostic value in the study of high density plasmas. In addition, exact wavelengths of spectral lines of highly charged ions are required in the determination of line opacities and level positions for X-ray laser transitions. The sensitivity of spectral line shift is investigated in the impact approximation for a variety of assumptions using the distorted-wave with exchange approach. The formalism is applied to the Lyman-alpha line of hydrogen and ionized helium to determine the influence of various assumptions on the line shift as well as identifying the differences between a neutral and ionized radiator. The results are compared and contrasted with a number of other calculations and experimental measurements.