Models of Energy Transfer and Adsorption

The existence of a precursor state, where the incident atom or molecule is temporarily trapped in a shallow attractive potential, has been proposed by Kisliuk [34, 35]. In this precursor state, the molecule may visit several surface sites, one of which permits chemisorption. This model provides enough variables to explain the decrease of the sticking probability with increasing coverage and its complex temperature dependence, as found during the chemisorption of N2 on W(IOO), and O2 on W(llO) and Pt(lll). 

For noninteracting adsorbates [36], the rate of adsorption of gas-phase species, r, can be written as 

The form of depends on whether adsorption occurs directly from the gas 

When adsorption is assumed to proceed via a precursor state, the mechanism of 

If the intrinsic and extrinsic precursors are energetically equivalent and each occupies only a single adsorption site, then the rates of non-dissociative and dissociative adsorption can be written as [37] 

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