Chemisorption and the vibrational excitation of the adlayer

It is shown that a vibrational non-equilibrium model of the chemisorption process can be employed for interpreting experimental data on adsorption-stimulated desorption. Further analysis of chemisorption rates, on a variety of substrates, also leads to the conclusion that desorption can be stimulated by the adsorption process, which determines an enhancement of the population of the upper bound vibrational level of the adspecies. The presence of this stimulation is revealed by a significant modification of the adsorption kinetics with respect to those expected under Boltzmann equilibrium conditions, An inverse correlation between rates of desorption and rates of vibrational relaxation of the adspecies stems from this analysis. A decrease of the relaxation rates with increasing surface coverage is also obtained for all the systems investigated. (C) 2004 Elsevier B.V. All rights reserved.