T. Kammler et al., INTERACTION OF H-ATOMS WITH OXYGEN ADSORBED ON NI(100) SURFACES - DIRECT REACTIONS TOWARDS OH AND H2O, Surface science, 382(1-3), 1997, pp. 116-126
The reactions of oxygen adlayers on Ni(100) surfaces with gaseous ther
mal H and D atoms were studied with AES, TDS and reaction-product moni
toring methods in the temperature range 120-400 K. Independent of temp
erature and coverage, adsorbed O atoms are hydrogenated to adsorbed OH
(OD) by impinging H(D) atoms. A cross-section of sigma=0.3 Angstrom(2
) suggests that this reaction proceeds via an Eley-Rideal (ER)-type di
rect mechanism. Independent of temperature, in a second ER step with a
cross-section of sigma=4.5 Angstrom(2), adsorbed OH (OD) groups are h
ydrogenated to water. Well above the water desorption temperature (180
K) the product molecules desorb either through a thermally activated
or an energetically mediated step. Below the water desorption temperat
ure (at 120 K), 90% of the product molecules remain adsorbed on the su
rface and 10% desorb through the energy set free at reaction. an isoto
pe effect (H/D) on the cross-sections was not observed. The processes
were observed independent of the oxygen coverage and also at oxidized
Ni surfaces, which could be reduced completely at sufficiently high H
or D atom fluences. (C) 1997 Elsevier Science B.V.