Line mixing effects in the Q branch of the 10 00 ← 01 10 transition of CO 2

Abstract

Line mixing effects have been investigated in the Q branch of CO 2 near 720 cm −1, by means of a tunable diode laser. Spectra were obtained at room temperature, in the 100–1000 torr pressure range. In the high-frequency wing of the Q branch, below the Q(2) line, the observed absorption is nearly 50% less than that calculated on the assumption of purely additive Lorentz lines, whereas the Q branch itself is nearly insensitive to line coupling in the pressure range investigated. From the line broadening coefficients alone, a simple scaling law allows an estimate of the state-to-state rotationally inelastic transfer rates. Calculation of line mixing coefficients using these rates yields corrected absorption coefficients, in very good agreement with the observed ones, all over the analyzed spectral range. The results appear to be of importance for modeling outgoing radiances in temperature sounding channels near 14 μm.