Carbon dioxide is one of the most important trace gases in the terrestrial atmosphere. The spectral data required in remote sensing are the spectral parameter of each absorption line and a line shape model. This paper describes the absorption properties of CO2 near 2400 cm-1; these properties are of interest to those in the atmospheric temperature sounding field. The shape of the far-wing of N2- and O2-broadened CO2 lines was investigated in the 2200–2500 cm-1 spectral region in a temperature range of atmospheric interest (230–318°K). We focused on the higher rotational quantum number of the R-branch in the v3 band, where the effect of the far-wing is enhanced. The effect of the far-wing has been studied extensively by others, since the CO2 v3 band is known to exhibit sub-Lorentzian behavior. Here, we show the observed spectra along with calculated spectra for five temperatures. We used first-order line-mixing and the x-factor, which accounts for the effect of the far-wing, to create the calculated spectra. Our results provide new knowledge of quantum interference of the spectral line in the v3 band of CO2.
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Quantitative absorpance measurements have been made in pure CO2 and mixtures of CO2 with N2 and O2 in a 10 m White Perkin-Elmer cell. With absorbing paths up to 50 m-atm, results have been obtained from the band head at 2397 cm-1 to 2575 cm-1. The continuous absorption, which is due to the extreme tails of the strong lines in the v3 band centered at 2349 cm-1, is much less than calculated with the Lorentz line shape. A good fit with the data is obtained with an empirical line-shape which retains the Lorentz pressure dependence but requires a nearly exponential modification of the frequency dependence.
