LINE-MIXING, FINITE DURATION OF COLLISION, VIBRATIONAL SHIFT, AND NONLINEAR DENSITY EFFECTS IN THE NU(3) AND 3-NU(3) BANDS OF CO2 PERTURBEDBY AR UP TO 1000 BAR

We present high-density experimental and theoretical results on CO2-Ar gas-phase absorption in the nu(3) and 3 nu(3) infrared bands. Measure ments 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 pertur ber density dependence of the absorption, clearly shown in the far win g, is attributed to the finite volume of the molecules. Furthermore, e xperiments show vibrational dephasing and narrowing effects. We have p erformed line-mixing computations based on the Energy Corrected Sudden approximation (ECS impact model). Significant discrepancies between e xperimental 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 mix ing effects. Finally, an effective width is used in order to take othe r effects into account. (C) 1997 Elsevier Science Ltd.