An optic-acoustic study of thermal vibrational relaxation in CO2 and in mixtures of CO2 with monoatomic gases

In order to study the thermal vibrational relaxation of CO₂, the gas is given a perturbation such that the bending mode, b, and the symmetric-stretching mode, s, remain in equilibrium with each other while the asymmetric stretching mode, a, undergoes a different evolution. Two relaxation times, τ_VT and τ_VV, occur in the collisional exchanges of energy: respectively, that of vibration-translation (V-T) between the set bs and the degrees of translation-rotation; and that of vibration-vibration (V-V) between a and bs. A third parameter, $\text{G}$, characterizes the ratio of energies, gained by bs and lost by a, during the V-V exchange. τ_VT can be obtained from thermodynamic experiments and τ_VV by a fluorescence technique. The spectrophone method used here allows the simultaneous determination of τ_VT, τ_VV and $\text{G}$; one can therefore determine the quantum levels concerned in the exchanges and compute the corresponding transition probabilities.