Absorption and emission line profile coefficients of multilevel atoms—II. Velocity-averaged profile coefficients

Abstract

Starting from the atomic profile coefficients of a multilevel atom derived in the previous first part of this paper, we consider the velocity-averaged line profile coefficients appearing in the radiative transfer equation for the important special case that the velocity distribution of atoms in the ground state is Maxwellian and that the streaming of excited atoms is negligible. Elastic velocity-changing collisions of excited atoms with other particles are taken into account in the framework of a strong-collision model. Neglecting stimulated emissions, we obtain explicit, albeit in some cases approximate, expressions for the line profile coefficients of a three-level atom in terms of the specific radiation intensity locally present. The emission and absorption profile coefficients are written in a form that exhibits the various physical effects responsible for deviations of these profiles from complete redistribution. The case of two-level atoms in the presence of elastic collisions with the excited atoms is also treated.