Importance of rotational motion in the vibrational relaxation of H 2O molecules. Relaxation of the bending level in H 2O+Ar collisions

Abstract

A model of vibration-to-rotation energy transfer is developed for the relaxation of the bending mode of H 2O in the H 2O+Ar collision. In the model the energy release Δ E of the ν 2=2→1 transition is efficiently removed by rotation. Transition probabilities are calculated by a semiclassical procedure. The model correctly predicts both the temperature dependence and magnitude of the (020→010) probability over the temperature range of 200–1000 K. The importance of the coupling of rotation with bending is discussed. A model which assumes the removal of the energy release by translation seriously underestimates the probability especially at lower temperatures and predicts a temperature dependence which is too steep.