Temperature, pressure, and perturber dependencies of line-mixing effects in CO₂ infrared spectra. II. Rotational angular momentum relaxation and spectral shift in Σ←Σ bands

The Energy Corrected Sudden approach is used in order to deduce collisional parameters and to model infrared quantities in Σ-Σ bands of CO₂-He and CO₂-Ar mixtures at room temperature. Measurements are first used for the determination (from a fit) of the rotational angular momentum relaxation time and of some parameters representative of the imaginary part of the relaxation operator. It is shown that line-broadening data as well as absorption in both the wing and central part of the ν₃ and 3ν₃ bands lead to consistent determinations. The model is then used for detailed analysis of line-mixing effects. The influences of pressure, of the band spectral structure, and of the collision partner are studied. Differences between the effects of collisions with He and Ar are pointed out and explained.