Temperature dependence of the vibration–vibration de-excitation rates of HF(v=n)+HF(v=0) →HF(v=n−1)+HF(v=1) for n=2−5

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Abstract
Temperature dependence of the de‐excitation rates of HF(v=n)+ HF(v=0) →HF(v=n−1)+HF(v=1)+ΔE for n=2−5 has been studied for the range of 200 to 2000 °K based on both the energy transfer mechanism through the formation of nonrigid dimers at lower temperatures and through the rotational motion of the colliding molecules at higher temperatures. In the nonrigid dimer model, the energy mismatch is transferred to the restricted translational motion of individual molecules of the dimer, and in the rotational model, it is transferred to the rapid rotational motion of the colliding molecules. Below 300 °K, the de‐excitation rate coefficient decreases with increasing n, while it increases with n above 300 °K. This variation has been explained in terms of the magnitudes of ΔE and the vibrational matrix element. A strong negative temperature dependence of the rate coefficient is found for n=2 at low temperatures but no such variation is seen for n=5. For intermediate values of n, a negative but weak temperature dependence is found.