Line parameters for hot methane ν3 band broadened by H2 from 296 to 1100 K

Methane (CH4) spectra in the nu(3) band near 3.3 m were measured for 0, 50, 150, 240, 320, and 400 Torr pressure of added hydrogen. The spectra were recorded using a high resolution Fourier transform spectrometer. The CH4 spectra were measured at 5 different tem peratures from room temperature up to similar to 1100 K. A multi-spectrum non-linear least squares fit method was used to determine the line parameters at each temperature. Voigt lineshape functions were used to determine the broadening and shifting of methane lines in the P and R branches. The temperature dependence of exponent parameters for the line width and the linear frequency shift coefficients were determined from a fit for temperatures ranging from 296 to 1098 K. The temperature dependence of the retrieved line broadening parameters was observed to follow the Double Power Law (DPL) proposed by Gamache and Vispoel. The temperature dependence of the pressure shift coefficients follows a linear trend for the first three temperatures. The pressure broadening parameters decrease with increasing temperature, and the pressure shift parameters increase with increasing temperature, especially for the first three temperatures. Finally, the dependence of pressure broadening (gamma(0)) and shift (delta(0)) parameters on the rotational quantum number (J) was studied. The pressure broadening coefficients decrease about 20-30% for temperatures up to 894 K and about 40% for 1098 K, with increasing J quantum number. A complete set of fitted parameters including line position (sigma), line intensity (S), pressure broadening (gamma(0) ), shifting (delta(0)), and their corresponding fitting errors are provided in supplementary tables. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The study investigated the spectral characteristics of methane molecules by measuring the spectra under different hydrogen pressures and temperatures, and studying the changes in parameters such as line width and frequency shift. Experimental data showed that the line width and frequency shift parameters exhibit different patterns with variations in temperature and pressure, influenced by the rotational quantum number. These research findings provide a theoretical basis for further understanding the spectral behavior of methane molecules.