The shapes of the extreme wings of self-broadened CO2(lines have been investigated)in three spectral regions near 7000, 3800, and 2400 cm-1. Absorption measurements have been made on the high-wavenumber sides of band heads where much of the absorption by samples at a few atm is due to the extreme wings of strong lines whose centers occur below the band heads. New information has been obtained about the shapes of self-broadened CO2 lines as well as CO2 lines broadened by N2, O2, Ar, He, and H2. Beyond a few cm-1 from the line centers, all of the lines absorb less than Lorentz-shaped lines having the same half-widths. The deviation from the Lorentz shape decreases with increasing wavenumber, from one of the three spectral regions to the next. The absorption by the wings of H2- and He-broadened lines is particularly low, and the absorption decreases with increasing temperature at a rate faster than predicted by existing theories.
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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.
