Resonance line transfer and transport of excited atoms  I. Basic relations and limiting cases.
Abstract
The classic problem of non(LTE) spectral line formation by twolevel atoms in a selfexcited gas is reconsidered. In contrast to previous investigations, the authors take the convective transport of the excited atoms into account through the streaming term of the corresponding kinetic equation. They establish the governing equations and show that nonLTE line formation is, in general, characterized by three dimensionless parameters ɛ, ζ, η rather than by just one parameter ɛ. The authors consider some limiting cases that are useful in interpreting physically the numerical solutions of the two coupled kinetic equations of photons and excited atoms, respectively. The main topic of the paper is the investigation of the direct effect of a boundary surface on the distribution function of the excited atoms, as opposed to the indirect effect of the boundary on the distribution function via the radiation field in the spectral line. The authors also study the influence of the corresponding boundary layer on the spectral line emitted by the system. They assume pure Doppler broadening of the spectral line throughout.
 Publication:

Journal of Quantitative Spectroscopy and Radiative Transfer
 Pub Date:
 April 1986
 DOI:
 10.1016/00224073(86)90083X
 Bibcode:
 1986JQSRT..35..303B
 Keywords:

 Atomic Excitations;
 Line Spectra;
 Molecular Gases;
 Nonequilibrium Thermodynamics;
 Radiative Transfer;
 Resonance Lines;
 Boundary Value Problems;
 Emission Spectra;
 Inelastic Collisions;
 Kernel Functions;
 Kinetic Equations;
 Velocity Distribution;
 Atomic and Molecular Physics;
 Line Formation:Radiative Transfer;
 Radiative Transfer:Line Formation