In this work we discuss and compare the properties of empirical rotational relaxation matrices, which are responsible for the line-mixing effects in IR absorption in the gas phase. The energy-corrected sudden approximation, the strong collision model, the adjusted branch coupling (ABC) model, and the varied collision efficiency (VCE) model are considered. The ABC and VCE models are applied to the band shape calculations for CO2 and CF4 spectra in rare gas mixtures. The VCE model proved to be better for this purpose.