High-temperature line strengths with He- and Ar-broadening coefficients of the P(20) line in the 1 ← 0 band of carbon monoxide.

A tunable quantum cascade laser was scanned over the P(20) line in the 1 ← 0 transition band of CO at 2059.91 cm−1. Line strengths were measured in mixtures with helium and argon at room temperature (296 K) and broadening parameters at high temperatures between 1100 and 2800 K, and for pressures from 4.7 kPa up to 147.4 kPa behind reflected shock waves. Two mixtures were used to study the broadening coefficients: 0.006 CO/He and 0.006 CO/0.01 H2/Ar, for which CO vibrational equilibrium is ensured by He in the former mixture and by 1% H2 in the latter one. Direct measurements of γ CO - He T 0 and γ CO - Ar T 0 at room temperature were obtained, and the broadening coefficients, defined as γ T = γ T 0 T 0 / T n , were fully investigated by extrapolating the temperature-dependent coefficients n CO - He and n CO - Ar from the new, high-temperature scanning data. For validation purposes, two calibrations from the literature that characterize the P(20) line absorption coefficient (k υ) with a temperature-dependent equation using mixtures of CO perturbated in 0.2 He/Ar bath are compared with our computed k υ obtained via the linestrength taken from the HITRAN database and the line-shape function modeling with a pseudo-Voigt profile that depends on the new collisional broadening coefficients. Good agreement is observed. The CO–He broadening was found to not be identical to CO–Ar broadening, and when He is assumed to be Ar in the broadening effect analyses, large discrepancies can appear in the k υ quantifications, therefore in the CO time histories measured in a shock tube. The simulated CO absorption coefficients that account for He-related broadening are necessary for accurate CO measurements to validate modern detailed kinetics mechanisms. [ABSTRACT FROM AUTHOR]