Collisional energy transfer to methane by octupole coupliing

A linear molecule or one electron atom interacting with a tetrahedral molecule is considered. Formulae are presented for various rotationally averaged E → R and V → R first order transition probabilities arising from dipole-octupole (R^?5) and quadrupole-octupole (R^?6) coupling. Relatively large amounts of rotational energy can be transferred in first order (ΔJ ? 3). With CH₄ as the octupolar partner, energy transfer upto 350 cm^?1 at room temperature is shown to proceed very efficiently. For the 5²P_{$\text{3}\text{2}$} → 5²P_{$\text{1}\text{2}$} transition in Rb, σ_qu is calculated to be ? 28 A² in quite good agreement with experiment and using an independent value of the octupole moment of CH₄. Energy transfer above 350 cm^?1 becomes rapidly less efficient. Among V → R transfer processes in the 500–700 cm^?1 range, the long range mechanism is almost certainly not the dominant one in the relaxation of CO₂⁺ (010) by CH₄ (σ_calc ≈ 10^?3 σ_obs) but will be important in the relaxation of SO₂.