Measurements of pure CO(2) absorption in the 2.3-μm region are presented. The 3800-4700-cm(-1) range has been investigated at room temperature for pressures in the 10-50-atm range by using long optical paths. Phenomena that contribute to absorption are listed and analyzed, including the contribution of far line wings as well as those of the central region of both allowed and collision-induced absorption bands. The presence of simultaneous transitions is also discussed. Simple and practical approaches are proposed for the modeling of absorption, which include a line-shape correction factor χ that extends to approximately 600 cm(-1) from line centers.

Line-mixing effects have been studied in the 3 band of CH 4 perturbed by N 2 at room temperature. New measurements have been made and a model is proposed which is not, for the first time, strictly empirical. Three different experimental set ups have been used in order to measure absorption in the 2800-3200 cm Ϫ1 spectral region for total pressures in the 0.25-2 and 25-80 atm ranges. Analysis of the spectra demonstrates the significant influence of line mixing on the shape of the Q branch and of the P and R manifolds. A model is proposed which is based on state-to-state collisional transfer rates calculated from the intermolecular potential surface with a semiclassical approach. The line-coupling relaxation matrix is constructed from these data and two additional parameters which are fitted on measured absorption. Comparisons between measurements and spectra computed accounting for and neglecting line mixing are made. They prove the quality of the approach which satisfactory accounts for the effects of pressure and of rotational quantum numbers on the spectral shape under conditions where modifications introduced by line mixing are important. For high rotational quantum number lines, the main features induced by collisions are predicted but some discrepancies remain; the latter may be due to improper line-coupling elements but there is strong evidence that the use of inaccurate line broadening parameters also contributes to errors in calculated spectra.