Desorption of vibrationally excited adsorbates in competition with relaxation: A quantal picture

The competition between desorption and relaxation of vibrationally excited CO adsorbed on a series of model surfaces is examined theoretically using a quantum mechanical description of the dynamics. This study complements that reported in the preceding paper which studied the classical mechanics of these processes. Quantitative differences between the quantal and classical results are seen in the rate constants for the various energy transfer processes. Moreover, qualitative differences are seen in the trend in the dynamics as the Debye frequency of the model surface is increased. The differences in the various rate constants in the quantal and classical calculations lead to an unusual "quantum effect" in which the trend in the energy flow with increasing Debye frequency is in different directions. Relaxation of the excited adsorbate is the dominant trend in the classical mechanics; thermal desorption of the excited adsorbate is the dominant trend in the quantal calculations.