Vibrational relaxation in CD4 and CD4-rare gas mixtures

Using the optic-acoustic effect, measurements of the relaxation time were made after exciting the v₄ mode of CD₄. This was done for pure CD₄ and for mixtures of CD₄ with He, Ne, Ar and Kr, the results being 3.9±0.2, 1.8±0.2, 18±2, 70±15 and ? 100 μs at 1 atm, respectively. From the relaxation time dependence on mass as well as from a comparison between results for CH₄ and CD₄ it is concluded that energy transfer takes place via a vibration-rotation-translation (V-R-T) mechanism.Experiments were also conducted to study the most probable deexcitation path from the higher energy mode, v₃, to translation. This was done for CD₄-CD₄ as well as for CD₄-atom collisions. For pure CD₄ deexcitation occurs via the lower energy group (v₂, v₄), while for CD₄ mixtures it may also occur via the higher energy group (v₁, 2v₂, v₂ + v₄, 2v₄).