A simple model for thermal associative desorption
1984; Elsevier BV; Volume: 144; Issue: 2-3 Linguagem: Inglês
10.1016/0039-6028(84)90105-5
ISSN1879-2758
Autores Tópico(s)Quantum, superfluid, helium dynamics
ResumoA simple microscopic model is presented in order to give a possible explanation to the double peak structure observed in several thermal desorption spectra, e.g. for hydrogen on transition metals. We focus on situations when adsorbed atoms associate and form diatomic molecules, which desorb from the surface. The model is characterized by the following features: (i) the vibrationally excited atoms, for which it is energetically favourable to desorb, are treated as a quasi localized overlayer, (ii) the adsorbed atoms experience a repulsive nearest neighbour interaction which also shifts their vibrational frequency, (iii) the desorption rate is expressed as a collision frequency within the adsorbed overlayer. We find that, in order to reproduce the two-peak structure in experimental data, the repulsive nearest neighbour interaction has to be combined with a negative shift in the vibrational frequency for increasing coverage. For the system H/Ni(100) a frequency shift of −8% between zero and full surface coverage is predicted.
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