N2-collisional shift coefficients of lines in the ν3 band of methane from low to high temperatures

Abstract

This paper reports collisional N2-shift coefficients of 12 lines in the ν3 band of methane measured from low to high temperature (from 123 to 598 K). The measurements were done with an improved two beams tunable diode-laser spectrometer coupled with specific absorption cells that allow to make measurements at low and high temperatures. The collisional line shifts were determined by individual fits of the experimental line shapes using the Voigt profile, as well as the Rautian-Sobel’man and the Galatry models that take into account the Dicke narrowing. The measurement procedure records simultaneously an unperturbed line of pure CH4 and the same N2-shifted transition to determine the line shift coefficient for each temperature. The temperature dependence of the line shift coefficient were determined using the linear law, the power law and the new physics based model (Double Power Law - DPL) developed by Gamache and Vispoel [Gamache and Vispoel, JQSRT, 217, 440–452, 2018]. The DPL fit of the line shift coefficient evolution with the temperature were compared to the power law and the linear law. The results show a better agreement with the DPL model.