Oxygen States at Metal Surfaces

Oxygen chemisorption at cryogenic temperatures provided the clue for the presence of metastable reactive oxygen states at metal surfaces, with XPS 

Studies of coadsorption at Cu(110) and Zn(0001) where a coadsorbate, ammonia, acted as a probe of a reactive oxygen transient let to the development of the model where the kinetically hot Os transient [in the case of Cu(110)] and the molecular transient [in the case of Zn(0001)] participated in oxidation catalysis16 (see Chapters 2 and 5). At Zn(0001) dissociation of oxygen is slow and the molecular precursor forms an ammonia-dioxygen complex, the concentration of which increases with decreasing temperature and at a reaction rate which is inversely dependent on temperature. Which transient, atomic or molecular, is significant in chemical reactivity is metal dependent. 

The classical picture, where following the transition state the two oxygen atoms are channelled downwards to the nearest available metal atoms, is 

To probe the early stage of oxygen chemisorption, that is, prior to the onset of surface reconstruction and oxide formation and relevant to our coadsorption reactivity studies, there were obvious advantages for STM observations to be made at cryogenic temperatures. 

In 1999, we reported21 low-temperature studies of oxygen states at Cu(110). At 110K the oxygen state present at high coverage is largely disordered but 

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