Far infrared collision-induced absorption in gaseous methane. II. Determination of the octupole and hexadecapole moments

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Abstract
The octupole and hexadecapole moments of methane are obtained by comparing the experimental and theoretical zeroth spectral moment and the integrated absorption coefficient of the collision‐induced far infrared rotation–translation spectrum. The data presented in Part I of this series and the theory summarized in this paper give the values Ω2/σ7 = 4.67×10−16 erg and Φ2/σ9 = 1.56×10−16 erg, from which we obtain the octupole and hexadecapole moments, respectively, ‖Ω‖ = (2.22±0.12) ×10−34 esu⋅cm3 and ‖Φ‖ = (4.8±0.5) ×10−42 esu⋅cm4 for σ=3.758 Å. An argument is advanced as to why it is preferable to report these results in the form Ω2/σ7 and Φ2/σ9, where σ is the molecular diameter parameter appearing in the potential function.