Experimental and simulated study of line-shape models for measuring spectroscopic parameters using the WM-DAS method - part I: Collisional broadening and absorption coefficients of H2O-Ar system

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 nu(1) + nu(3) 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. (C) 2020 Elsevier Ltd. All rights reserved.