Transient trapping-desorption

Figure 6 Schematic potential energy diagrams for the interaction between O2 and Ag(l 11). Four panels are shown. In (a), the three states into which O2 can adsorb at the surfaces are depicted as a function of a reaction coordinate. In (b), the two potentials leading to direct inelastic scattering are shown. In (c), a trajectory representing a one dimensional representation of transient trapping-desorption in the O2 state is shown. In (d), two path ways leading to dissociative chemisorption are shown. From Kleyn et al. [45],...

Figure 19 Normal energy dependence of the probabilities for physisorption trapping (closed symbols) and transient trapping-desorption (open symbols) for three different values of Oj. The full lines through the data points serve to guide the eye only. The molecular chemisorption probability is shown by the dashed and the dash-dotted line. Note the different Y-axes. From Raukema and Kleyn [152].

A variety of processes can occur in the interaction of 02 molecules and Ag(l 11). At first scattering from and trapping in the physisorption potential can occur. Secondly, scattering from the chemisorption (02 ) potential occurs, together with transient trapping-desorption. The chemisorption potential well is very shallow. From being transiently trapped the molecule can be captured in the molecular chemisorption well presumably surface imperfections are necessary to stabilize the molecular adsorbate in this case. From the molecular chemisorption well the molecule can proceed to dissociation. In this step ad atoms may be involved on Ag(l 11). Finally, there is a small probability for direct dissociative chemisorption of 02 at Ag(l 11). The formation of added Ag-O rows (fences) at the surface inhibit further sticking at the surface. 

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