Spectral Profiles for Atmospheric Absorption by Isolated Lines: A Comparison of Model Spectra with P- and R-Branch Lines of CO in N2and Ar

There is a need in atmospheric research to accurately model absorption profiles over a wide range of pressures and temperatures. Here we explore the suitability of four profiles to describe absorption by an isolated line. Three of the profiles, a Lorentzian, a Voigt profile, and a hard-collision model, are speed independent. The fourth profile is an empirical speed-dependent hard-collision model. We test the quality of the profile and the pressure dependence of the broadening by fitting to precise experimental absorption curves for CO broadened by N2and Ar. Of the four profiles, we find that only the empirical model is satisfactory. This profile also meets the need of atmospheric modeling in that it is easily evaluated.