On the precise evaluation of the complete semiclassical spectral line shape for pressure-broadened atomic spectral lines

The problem of computing the shape of an atomic spectral line perturbed by neutral atom collisions is considered and a precise numerical evaluation of the exact semiclassical line shape for a selected variety of potentials, temperatures and gas densities is reported. The need for relatively high numerical accuracy in the evaluation of the correlation function is stressed and the generation of spurious oscillations in the spectral line wing due to numerical error is illustrated. An accurate evaluation shows an absence of rapid oscillations and reveals a satellite very similar but not identical in shape to the satellites predicted with a JWKB approximation for a simple potential well. The general features of the computed line wings agree with available observations. Dynamical smearing of the classical static singularity in the line wing is an important process. Only potentials with constant depth over long range have been found to produce very sharp satellites, while the usual potential wells produce simple shoulders on the spectral line wings. The possible application of this computational technique for the evaluation of excited-atom-neutral-perturber potentials from spectral line data is also considered.