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Linestrengths, self-broadening and narrowing coefficients for 8 absorption transitions of CO2 near 1.43 µm were measured using the wavelength modulation direct absorption spectroscopy (WM-DAS) at 300–1000 K and 5–20 kPa. The SNR was enhanced to 1500 for the peak absorbance around 5% at room temperature and remains at 550 for the peak absorbance around 1% at high temperatures by use of the WM-DAS method. The Voigt, Rautian, Galatry and quadratic speed-dependent Voigt profiles were used to recover the absorbance and retrieve the best-fit spectroscopic parameters and their temperature dependence. The quadratic speed-dependent Voigt profile was found to give the best combination of accuracy and robust lineshape parameters. The measured linestrengths and self-broadening coefficients compare well with the available values listed in the HITRAN/HITEMP database. The self-narrowing coefficients were also determined for GP, RP and qSDVP with analyses of the uncertainties in these spectroscopic parameters.

Absorption lineshapes for 10 CH4 transitions in the v2 and v4 band were measured at high-resolution in a thermodynamically-controlled optical cell using a quantum cascade laser near 7.16 µm. Linestrength, self-broadening, -narrowing, pressure-shift coefficients and their temperature dependence were recorded over a temperature and pressure range of 290–1050 K and 3–80 kPa, respectively. Voigt, Rautian, speed-dependent Voigt profiles were least-squares fit to the measured absorption spectra to determine the best-fit lineshape parameters. Significant collisional-narrowing and speed-dependent effects were observed but no line mixing behaviour was found in pure CH4 at the experimental conditions. The self-pressure-shift coefficients were found to change signs from negative to positive with increasing temperature and the Frost's formula fit well their temperature dependence for the studied transitions. The measured spectra provided tests of the CH4 line lists near 1397 cm−1 released in HITEMP 2020 and the recorded spectroscopic parameters compared well with the values in the database. Several weak transitions excluded from the HITEMP database were observed at elevated temperatures with the line positions given here. The analyses of uncertainties in all the measured spectroscopic parameters were also demonstrated in this work.

Wavelength modulation-direct absorption spectroscopy (WM-DAS) has been used to measure the absorption line shapes of the H 2 O transition at 7299.431 cm − 1 and the CO transition at 4297.705 cm − 1 perturbed by Ar, N 2 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 N 2 -broadening coefficients are the largest among the three perturbers and the measured N 2 - 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 H 2 O -Ar/ N 2 /He while smaller than those in CO-Ar/ N 2 /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.

Wavelength modulation-direct absorption spectroscopy (WM-DAS) was used to investigate absorption line-shape models by measuring the H2O transition at 7299.431 cm−1 in the ν1+ν3 vibrational band perturbed by Ar. The partially Correlated quadratic Speed-dependent Hard-Collision profile (pCqSDHCP) was found to give the best fit with the smallest residuals. The Ar-induced broadening, narrowing coefficients and the absorption coefficients were measured using various profile models with comparisons to pCqSDHCP. The room-temperature pressure dependence of the measured parameters and their differences over the range from 0.3 kPa to 80 kPa (Lorentzian-to-Doppler broadening ratios from 0.06 to 3.5) were studied. The pCqSDHCP was also simulated and fit by the other simplified profiles to further explore the pressure dependence, which compares well with the experimental results. The pressure dependence of the broadening and absorption coefficients for Voigt profile (VP) were analyzed to provide the optimal pressure range when using VP to measure the spectroscopic parameters. The experimental and simulated results allow us to quantify the systematic errors in the pressure broadening and line intensity associated with simplified line shape models.