Experimental and simulated study of line-shape models for measuring spectroscopic parameters using the WM-DAS method — Part II: Broadening and narrowing of select near-infrared [formula omitted] and CO lines perturbed by Ar, [formula omitted] and He

Abstract

Wavelength modulation-direct absorption spectroscopy (WM-DAS) has been used to measure the absorption line shapes of the H2O transition at 7299.431 cm−1 and the CO transition at 4297.705 cm−1 perturbed by Ar, N2 and He. The foreign-gas broadening, narrowing and pressure-shift parameters were determined from various lineshape models at pressures from 1 to 100 kPa. The measured N2-broadening coefficients are the largest among the three perturbers and the measured N2- and Ar-pressure-shift coefficients are both negative while that for He is positive. The nonlinear pressure dependence of the velocity-changing rates for the Galatry and Rautian profiles and the speed-dependent coefficients for Speed-dependent Voigt profile were all observed for the 6 binary systems. The measured velocity-changing rates were all larger than the corresponding dynamic friction coefficients in H2O-Ar/N2/He while smaller than those in CO-Ar/N2/He. The narrowing parameters were also retrieved and compared by taking both the Dicke narrowing and speed dependent effects into account. The partially Correlated quadratic Speed-dependent Hard-Collision profile was simulated and fit by the other simplified profiles to further validate the nonlinear behaviour of the narrowing parameters, which is consistent with the measured results.