Fine coupling induced by collisions leads to drastic modifications of the absorption profile in the microwindows of the self- and N₂-broadened v₃ CO₂ fundamental vibration-rotation band. Calculations of these modifications have been performed by using the energy-corrected sudden (ECS) scaling law. Linewidths have been inverted to obtain effective rotation-translation basis rate constants and to deduce R-R, P-P and R-P line couplings. The characteristics of these couplings are presented and discussed. Calculated ECS profiles in the microwindows are compared with experimental data and also with previous results based on a statistical fitting law. The ECS approach is particularly suitable for practical infrared spectroscopic applications including line-coupling effects.