Calculated linewidths for CH4 broadened by N2 and O2

Abstract

The Anderson‐Tsao‐Curnutte theory of collision‐broadened spectral lines, as extended by Tejwani for octopolar interactions, has been used to compute linewidths for methane broadened by molecular nitrogen and oxygen. Widths of vibration‐rotation lines in the infrared‐active fundamental bands ν2, ν3, and ν4; the combination bands ν2 + ν3 and ν3 + ν4; and the overtone bands 2ν3, 2ν4, and 3ν3 have been calculated for the symmetry species A, E, and F separately, and for a large range of the total angular momentum quantum number J. The effect of the dipole moment of CH4 due to vibration‐rotation interactions was considered. The temperature dependence of the linewidths has been obtained for 210°K ≤ T ≤ 300°K. These results were used to compute corresponding air‐broadened linewidths. It has been shown that the calculated linewidths depend significantly on the magnitude of the octopole moment for methane.