VIBRATIONAL-RELAXATION OF WATER-MOLECULES IN H2O+AR COLLISIONS BETWEEN 200-K AND 1000-K - 001-]020, 020-]010, AND 010-]000 TRANSITIONS

The vibrational relaxation of the stretching levels of H2O in the H2O+Ar collision is studied using a model of vibration-to- rotation (VR) energy transfer in the temperature range of 200-1000 K. The dominant relaxation pathway from the rapidly equilibrating ν1 and ν3 levels is deexcitation to the 2ν2 level followed by the 020→010 and 010→000 relaxation processes. At 300 K, the probabilities of 001→020, 020→010, and 010→000 are 2.2×10-3, 2.6×10-3, and 1.4×10 -3, respectively. In the model the energy release △E of each deexcitation process is preferentially removed by rotation. Transition probabilities calculated by a semiclassical procedure indicate that when △E is large, the VR mechanism is of major importance at lower temperatures. The VR model correctly predicts both the temperature dependence and magnitude of the 020→010 probability over the temperature range of 200-1000 K. A model which assumes the removal of the energy release by translation seriously underestimates the probability of this process, especially at lower temperatures, and predicts a temperature dependence which is too steep. The contribution of translational motion to the relaxation process becomes important at higher collision energies, especially for 001→020, where ΔE is small. Calculations are extended to the D2O+Ar collision in order to study isotope effects. © 1990 American Institute of Physics.