Vibrational energy transfer in near resonance due to dipole–dipole interactions

The contribution of long-range forces to the observed rates of V → V energy transfer processes has been studied. The theoretical model uses the first order perturbation approximation to generate a probability function, with the dipole–dipole perturbing potential as given by Margenau: V_if = (1/6)^1/2_{μ1 · μ2}]R^?3. The probability function derived is shown to be a strong function of the energy mismatch between the IR bands of the colliding molecules. The calculation emphasizes the importance of rotational state population effects, the most important J states being those which minimize the energy mismatch. A complete analysis of energy transfer between CO(v) and COS(000) where v = 1,2, ? 13 is presented. The calculation reveals the importance of combination bands in the energy transfer mechanism of polyatomics. The temperature dependence for near-resonant processes is also studied and the importance of the V → R energy transfer leads to the classification of ω₀ (band-center energy mismatch) into three categories small, medium, and large, according to the temperature dependence that the corresponding processes exhibit. The predictions of the theoretical model are compared to experimental data for the same system.