SELF-RELAXATION OF VIBRATIONALLY EXCITED H2O MOLECULES

This study on the self-relaxation of vibrationally excited H2O molecules is based on a model in which an excited molecule and its collision partner undergo a long-lived collision in the presence of strong molecular attraction. Transition probabilities are obtained by semiclassical procedures using ladder operators. The study shows that large-impact parameter collisions are responsible for the negative temperature dependence of the VV transition probabilities in H2O(001) --> H2O(020), H2O(020) --> H2O(010), and H2O(010) --> H2O(000). These energy transfer processes occur intramolecularly, and the transfer of the vibrational energy mismatch that is released by the VV process to the low frequency oxygen-oxygen motion in the complex is found to be very efficient, whereas energy transfer to the hindered rotational motions of the excited molecule is inefficient. The model predicts VV probabilities to decrease on deuteration.