Thermal infrared lines of methane broadened by nitrogen at low temperatures

Abstract Measurements of spectral transmittance in the v 4 -fundamental band of 12 CH 4 have been performed at low temperatures using a Fourier transform spectrometer with apodized spectral resolution of 0.06 cm -1 . With applications to lines formed in the atmospheres of Titan and Earth in mind, N 2 has been used as the broadening gas. Comparisons of observed and computed spectral transmittances on a line-by-line basis have yielded line strengths, N 2 -broadened half-widths and their variation with temperature. Best agreement between measured and computed spectra was obtained when the absolute intensity of the band was taken as 128 cm -2 -atm -1 at 296 K. Line widths were found to vary as T n with n = -1.0 for lines of the F -species and 0.63 for the A -species. Our measured line widths are considerably larger than those used in the AFGL compilation.