Trajectory calculations of intermolecular energy transfer in H2O+Ar collisions

The collisional deactivation of H2O by Ar has been studied by using classic al trajectory calculations, with an initial vibrational energy of 50, 75, a nd 100 kcal/mol, rotational temperatures in the range 0-10 000 K, and trans lational energies corresponding to the Boltzmann distribution at 298 K. Som e results at 1000 K are also presented. The effect of internal energy on th e first and second moments is examined. Increasing the initial vibrational energy enhances the intermolecular relaxation. However, the rotational temp erature has a complex effect. The results are analyzed using a cumulative p robability distribution of the amount of energy transferred in deactivating collisions, Q(Delta E), obtained by direct count of the number of trajecto ries that transfer an amount of energy equal to or greater than a certain a mount, Delta E. The transition probability for energy transfer, P(E',E), is then obtained by differentiation of the cumulative function. Scaling of Q( Delta E) in terms of the mean down energy lost in deactivating collisions, [Delta E](d), for each group of trajectories, results in a unique distribut ion. This function then allows us to obtain a global P(E',E) which depends on [Delta E](d) as a single parameter.