Line mixing and broadening of carbon dioxide by argon in the v3 bandhead near 4.2 µm at high temperatures and high pressures

•CO2 Ar broadening parameters empirically determined for transitions J” = 99–145.•A modified exponential gap law implement ed to model collisional line mixing.•Thermodynamic scaling of collisional effects examined up to 3000 K and 58 atm. Temperature-dependent line mixing and line broadening parameters were empirically-determined for rovibrational transitions (J = 99–145) in the (0000 → 0001) and (0110 → 0111) bandheads of carbon dioxide near 4.2 µm. Collisional effects by argon on the high rotational energy lines (E″ = 3920–8090 cm−1) in the R-branch were studied over a range of temperatures from 1200–3000 K in a shock tube. Measured absorption spectra comprising the target lines in an argon bath gas at near-atmospheric pressures were fit with Voigt profiles to determine line-broadening coefficients, with temperature dependence accounted by a power law. With line broadening established, line-mixing effects were examined at elevated pressures up to 58 atm and similar temperatures, reflecting conditions in high-pressure combustion environments. A modified exponential gap model for line mixing was developed to capture the pressure and temperature dependence of collisional transfer rates for the bandhead region using the relaxation matrix formalism.