CO-Ar collisions: ab initio model matches experimental spectra at a sub percent level over a wide pressure range

•The R(0) line of CO perturbed by Ar is studied experimentally in a wide pressure range.•Line shape parameters are calculated ab initio using two potential energy surfaces for a wide temperature range.•Theoretical model reproduces experimental spectra at a sub percent level of uncertainty.•Significance of the line-mixing effect for accurate modeling of spectra is demonstrated.