De-Excitation of Molecular Vibration by Collision

Abstract

The reaction rate has been calculated for a vibrationally excited diatomic molecule to be de‐excited by collision with another atom or molecule, the second particle carrying away the excess vibrational energy as kinetic energy. The quantum mechanical distorted wave method has been used in the ``modified wave number'' approximation, and the large amplitude of the vibrational motion is taken into account both in the choice of vibrational wave functions (Morse functions) and in the interaction potential. The calculation is performed for the process $${\mathrm{N}}_2{\mathrm{(a}}^1{\Pi }_g\mathrm{;v)+}{\mathrm{N}}_2{\mathrm{(X}}^1{\Sigma }_g^{+}\mathrm{)\Rightarrow }{\mathrm{N}}_2{\mathrm{(a}}^1{\Pi }_g{\mathrm{;v}}^{\prime }\mathrm{<v)+}{\mathrm{N}}_2{\mathrm{(X}}^1{\Sigma }_g^{+}\mathrm{)+}\mathrm{kinetic\; energy}$$ for the vibrational transitions v = 5 to v′ = 4, 3, 2, 1, 0, and for v = 2 to v′ = 0 and v = 1 to v′ = 0, for the temperature range 300–6000°K. The results show clearly that in a situation of this kind the collisional de‐excitation of the molecular vibration proceeds in steps v—v′ = δv = 1, rather than δv>1.