The Energy Corrected Sudden approach is used in order to deduce collisional parameters and to model infrared quantities in Sigma-Sigma 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 fine-broadening data as well as absorption in both the wing and central part of the nu(3) and 3 nu(3) 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.