High-resolution investigation of temperature and pressure-induced spectroscopic parameters of 13C-isotopomer of CH4 in the ν4 band using cavity ring-down spectroscopy

Abstract

Measurements of high-resolution spectroscopic line parameters in the ν4 fundamental band of 13CH4 isotopomer of methane (CH4) occurring at 7.5 µm mid-IR spectral region are important for the studies of remote sensing of the Earth and planetary atmospheres at different conditions. Here, a continuous wave (cw) external-cavity quantum cascade laser (EC-QCL) coupled with cavity ring-down spectroscopy (CRDS) technique has been employed to probe the ν4 (F2) fundamental band of 13CH4 isotopomer. We recorded the high-resolution CRD spectra of 22 interference-free transition lines in the P, Q and R-branches of 13CH4 and subsequently determined the symmetry-specific line parameters such as line-intensity, pressure broadening coefficients along with temperature dependence of broadening coefficients of the transition lines. Our study thus provides more accurate experimental evidences of the high-resolution spectral features of 13CH4 isotopomer with rotational symmetry (A, E, F) for the ν4 (F2) band at wavelengths near 7.5 µm for a range of temperatures.