Interaction between vibrationally excited diatomic and triatomic molecules

A theoretical analysis is made of the vibrational interaction of diatomic molecules with combination levels of triatomic molecules. Allowance is made for the V–V and V–T processes, and for the intramolecular exchange. Simple expressions are obtained for the relationship between the vibrational temperature of the ν₃ mode of a triatomic molecule and the vibrational temperature of a diatomic molecule under quasiequilibrium conditions. It is shown that in some cases the ν₃ mode may be heated by the energy stored in the diatomic molecule vibrations. Estimates of this effect are obtained for the HF–CO₂, DF–CO₂, D₂–CO₂, and CO–CS₂ systems. Experimental measurements are reported of the gain in a supersonic D₂–CO₂ stream for the 00⁰1–10⁰0 transition. The experimental values of the gain show that the ν₃ mode of CO₂ is heated in the D₂–CO₂ system by the energy stored in the vibrations of D₂.