The contribution of long-range forces to the observed rates of V 4 V energy transfer processes has been studied. The theoretical model uses the first order perturbation approximation to generate a probability function, with the dipoledipole perturbing potential as given by Margenau: Vir = [( 1/6)1/2pl.p2]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 tbe energy mismatch. A complete analysis of energy transfer between CO(u) and COS(OO0) 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 00 (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.
The present study reports the measurement of the V-V energy transfer rates for the CO*-COS system in the temperature range of 195 to 370OK. The measured rates exhibit a slight inverse temperature dependence. The experimental results are compared to prediction based on a model of long-range dipole-dipole interactions between colliding molecules. The effect of single quantum rotational transitions is compared to that of multiquantum rotational transitions.
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