We calculate the rotationally equilibrated vibrational excitation rate for parahydrogen in argon from 1620 to 4500°K. We use the most accurate available potential energy surface and the well tested classical-trajectory forced quantum oscillator method. We find the temperature dependence is not well fit by the popular Landau-Teller functional form. We find a large effect of initial rotational excitation which is not necessarily associated with rotational to vibrational energy transfer. To the extent that our rates can be used to predict experimentally measured relaxation rates they are about a factor of 3 too large. We also studied two other (less accurate) potential energy surfaces to show the sensitivity of the calculated results to the assumed interaction potential.
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