Modeling the spectral line shapes with speed-dependent broadening and Dicke narrowing

Shapes of pressure- and Doppler-broadened spectral lines are obtained by so lving exactly a three-dimension transport and (or) relaxation equation. The speed dependence of collisional broadening and shifting caused by dephasin g collisions and Dicke narrowing caused by velocity-changing collisions are taken into account within the impact approximation. The Rautian-Sobelman a nd Keilson-Storer models are used to describe velocity-changing collisions. We show in the high density or hydrodynamic limit that both models lead to a profile that is the weighted sum of Lorentz profiles if the collisional broadening is much greater than the frequency of velocity-changing collisio ns and to the ordinary Lorentz profile in the opposite case. This shows tha t the relative size of the optical and kinetic cross section is important i n determining the shape of absorption curves. The analytical solutions may be useful in modeling absorption profiles for remote sensing of the atmosph ere.