Collision-broadened linewidths of tetrahedral molecules—II. Computations for CH4 lines broadened by N2, O2, He,Ne and Ar

Pressure-broadened widths of CH₄ lines have been calculated, using the recent formulation for tetrahedral molecules by Varanasi in the framework of the Anderson-Tsao-Curnutte theory. The present work deals mainly with lines of the R-branch of the ν₃-fundamental at 300°K, for the range 1≤J≤30 and 0≤K≤18, and for the F species. In the case of CH₄-N₂ and CH₄-O₂ collisions, octopole-quadrupole, octopole-hexadecapole, hexadecapole-quadrupole, hexadecapole-hexadecapole, dispersion and overlap interactions have been included. Broadening by noble gases was treated in terms of dispersion and overlap interactions. The value obtained in the present work by comparing theoretical and experimental results for γ⁰_CH4?N2 is not far from the magnitude deduced in studies of the far-i.r. collision-induced absorption spectra of methane. A magnitude for the hexadecapole moment of |Φ_CH4|=3·0×10^?42 esu cm⁴ was also determined. The calculated and measured linewidths are in good agreement, except in CH₄-Ar collisions. In the latter case, the theoretical values are appreciably lower than the experimental ones, which suggests that induced interactions may have to be included.