Absorption of radiation by gases from low to high pressures. I. Empirical line-by-line and narrow-band statistical models

Abstract

We present new models which provide satisfactory and low cost modeling of infrared absorption spectra of gases from low to high pressures. The first is a line-by-line approach based on simple and empirical corrections of the lorentzian shape which account for the effects of line-mixing and finite duration of collisions. It leads to satisfactory agreement with experimental infrared spectra in a wide density range. It is degraded for the deduction of a Generalized Narrow-Band Statistical Model (GNBSM) which enables very rapid computation of medium resolution radiative properties. The latter is an extension of the low density (i.e., when lines are much narrower than the considered spectral resolution) approach developed by Goody [1] ; it is based on a random representation of line-positions and statistical description of line integrated-intensities and leads to a very simple expression of spectrally averaged absorption properties of gases. It is consistent with previous low density models and requires computer times several orders of magnitude shorter than line-by-line calculations. Comparisons between degraded approaches, line-by-line models, and experimental results demonstrate the accuracy of the present models in cases where previously proposed approaches are very inaccurate.