Measurements of He-collision-induced line-shape parameters of CO2 lines in the ν3 band

Abstract

He-collision-induced line-shape parameters of CO₂ lines were measured in the ν₃ band using Fourier transform spectra recorded at room temperature and with pressures ranging from 263 mbar to 1106 mbar. The measured transmission spectra were analyzed with the Voigt profile combined with the first-order line-mixing approximation, accounting for the instrument line-shape function. The He-broadening coefficients, pressure shifts, and first-order line-mixing parameters were determined for 51 lines, from the P(50) to the R(51). The obtained He-broadening coefficients are in excellent agreement with various literature values. These broadening coefficients, together with data for higher J lines, extrapolated from available high-temperature measurements, allowed us to propose an improved dataset for He-broadening coefficients of CO₂ lines. We demonstrated that accounting for line-mixing effects is essential to accurately determine the pressure shifts. The latter, measured for the first time for the ν₃ band, exhibited a weak rotational dependence, in contrast to the strong dependence observed for air- and self-pressure shifts for CO₂. The obtained line-mixing coefficients agree well with those calculated using the Energy Corrected Sudden model. The results of this study significantly enhance the line-shape parameters dataset for CO₂ perturbed by He, providing improved data for spectroscopic databases and for studies of planetary and exoplanetary atmospheres.