Radiative Transfer in a Gas of Uniform Properties in Local Thermodynamic Equilibrium. Part I. Absorption Coefficients in Nonhydrogenic Gases

摘要

The report discusses the data needed to perform radiative transfer calculations in nonhydrogenic gases in local thermodynamic equilibrium and presents some approximate methods for computing the radiative energy transferred by spectral lines where the properties of the gas are uniform. The methods currently available for calculating the cross sections of radiative processes are described and compared. An accurate method for calculating the species composition of nitrogen is described and the results of such a calculation are presented. The important line broadening mechanisms are discussed and the potentially accurate, modern theories of line broadening are outlined. The results of these theories are used to justify approximate line profiles which are simple enough for use in radiative transfer calculations. Simple approximations to the exact curves of growth of intensity are described for lines with Doppler profiles and for lines with profiles of a class which includes the dispersion and quasi-static forms. The concept of the effective width of a line intensity profile is introduced and techniques are developed for dealing with the overlapping of the intensity profiles of small groups of closely spaced lines (as, for example, in a multiplet). (Author)