INTERACTIONS OF GASEOUS H-ATOMS WITH ADSORBATE COVERED SURFACES VIA ELEY-RIDEAL REACTIONS

Reactions of gaseous H atoms with adsorbates at surfaces of solids hav e found a growing interest. From the reaction cross sections measured in many studies, only in the Angstrom(2) range, it is apparent that El ey-Rideal type mechanisms, in which the H atom is not accommodated at the surface but reacts on impact close to the adsorbed reaction partne r, is the appropriate description of these processes. The phenomology of H atom impact induced reactions with adsorbates is rather simple an d can be separated into abstraction and hydrogenation routes. Several examples of Eley-Rideal reactions are discussed here: abstraction of H and O adsorbed at Ni(100) surfaces, hydrogenation of and abstraction from physisorbed hydrocarbon molecules, benzene, dimethyl-cyclohexane, p-xylene, and i-propanol. It is shown that in addition to the reactio n energy the existence of favorable intermediates determine the probab ilities or cross sections of reaction routes.