LINE-MIXING EFFECTS IN THE 3-NU(3) BAND OF CO2 PERTURBED BY AR

Measurements of absorption coefficients in the 3v(3) band of CO2 at 1. 44 mu m perturbed by Ar up to 146 bar have been analyzed by using two line-mixing theoretical calculations within the impact approximation. In the first approach, the relaxation operator is treated semi-classic ally with adiabatic corrections. In the second, the relaxation operato r is modelled with the Energy Corrected Sudden (ECS) approximation ass ociated with a power fitting law providing the basic rotational state- to-state rates. Although the line-coupling spectroscopic cross-section s of the two models are significantly different, they both lead to sat isfactory agreement with bandshapes at moderate densities (<100 Amagat ). Significant deviations between experimental and calculated spectra appear at higher densities. They are mainly attributed to the probable breakdown of the impact and binary collision approximations and to a number of reasons including an incorrect ECS calculation of the interb ranch coupling, the nonlinear density dependence due to the finite vol ume of the molecules, and the neglect of the unknown imaginary part of the off-diagonal elements in the calculated relaxation matrix.