Calculation of Collision-Broadened Linewidths in the Infrared Bands of Methane

Abstract

Anderson–Tsao–Curnutte theory of collision‐broadened spectral lines has been extended to octopolar molecules, and the results are applied to the rotational lines in the ${\nu }_3$ band of methane. Calculated half‐widths are in excellent agreement with the high‐resolution measurements of Varanasi for self‐broadening and broadening by N₂, O₂, H₂, and He. The theory has also been applied to CO lines broadened by CH₄ and to CH₄ lines broadened by HCl. The excellent agreement with experimental data in both the cases leads to the estimate of ${\text{Ω\hspace{0.17em}=\hspace{0.17em}5.0\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−34}}\mathrm{esu}·{\mathrm{cm}}^3$ for the octopole moment of CH₄.