LINE-MIXING EFFECTS IN Q BRANCHES OF CO2 II - THE PARTICULAR CASE OF PARALLEL BANDS

A theoretical model based on the energy corrected sudden (ECS) approxi mation is used to account for line-mixing effects in infrared Q branch es of parallel bands of CO2. Measurements have been made using a tunab le difference frequency spectrometer system in a pi-pi transition: spe ctra of the 11(1)1(pi) <-- 01(1)0(1) Q branch near 3580.3 cm(-1) have been recorded at room temperature for C0(2)-He and C0(2)-N-2 mixtures in the 0.1-1 arm total pressure range. Comparisons of experimental and computed spectra prove the quality of the ECS approach. It is shown t hat the influence of line mixing on the shape of parallel Q branches i s very weak and much smaller than in perpendicular transitions. This r esult is analyzed in detail and explained in terms of the effects of t he vibrational angular momenta on the dipole transition moments and ve ctor coupling coefficients involved in the relaxation operator element s. The effects of collisions of CO2 with N-2 and He are compared and d iscussed. (C) 1997 Academic Press.