Speed-dependent pressure broadening and shift in the soft collision approximation

The influence of speed-changing collisions and the correlation between Doppler and collisional broadening on the spectral line profiles is considered in a unified way using the Anderson-Talman classical phase-shift theory for collisional broadening and the Galatry diffusion model for the motion of radiating particles. A general formula for the correlation function is derived in the impact limit, which yields the well known speed-dependent Voigt profile in the case when the speed-changing collisions are neglected, but the Doppler-collision correlations are taken into account. In the opposite case, when the, Doppler-collision correlations are omitted, but the speed-changing collisions are included this formula becomes identical to that derived by Galatry. This formula is shown to lead to the results close to those calculated from the line profile formula recently derived by Duggan et al [Phys. Rev. A 51, 218 (1995)]. (C) 1997 Elsevier Science Ltd.