CO$_2$ collision-induced line parameters for the $\nu_3$ band of $^{12}$CH$_4$ measured using a hard-collision speed-dependent line shape and the relaxation matrix formalism

Abstract

Ten high resolution Fourier transform spectra of the pentad region near 3.3 {\mu}m of methane diluted in carbon dioxide at total pressures up to 800 hPa have been recorded at 296.5(5) K. Including a high resolution spectrum of pure methane at low pressure, these spectra have been analyzed using multi-spectrum fitting techniques. The methane lines were modeled using hard-collision speed-dependent line profiles and line mixing was included in the strongest absorption regions, considering the first order Rosenkranz approximation and the relaxation matrix formalism. CO$_2$ broadening and shift coefficients have been measured, together with the speed dependence of broadening. Results obtained using the two line mixing models are intercompared and compared with previous work.