Line-mixing, finite duration of collision, vibrational shift, and non-linear density effects in the V3 and 3V3 bands of CO2 perturbed by AR up to 1000 bar

We present high-density experimental and theoretical results on CO2-Ar gas-phase absorption in the v3 and 3v3 infrared bands. Measurements have been made at room temperature for pressures up to 1000 bar in both the central and wing regions of the bands. A non-linear perturber density dependence of the absorption, clearly shown in the far wing, is attributed to the finite volume of the molecules. Furthermore, experiments show vibrational dephasing and narrowing effects. We have performed line-mixing computations based on the Energy Corrected Sudden approximation (ECS impact model). Significant discrepancies between experimental and calculated spectra appear when pressure increases. We then tested the influence of the finite duration of collision by using interpolations between ECS and quasi-static calculations, and we have evaluated the sensitivity of the band profiles to the interbranch mixing effects. Finally, an effective width is used in order to take other effects into account. © 1997 Elsevier Science Ltd.