ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The kinetics of adsorption and abstraction for the system H(D) on Al(111) and Ni(111) has been investigated using an efficient atomic beam source, thermal desorption spectroscopy, and multiplexed mass spectrometry. The initial sticking coefficient of atomic hydrogen on Ni(111) is 1.0 and independent of the angle of incidence. For H on Al(111) the initial sticking coefficient is 0.6 and increases with increasing angle of incidence (S(cursive-phi)∼cos−0.4 cursive-phi). On Al(111) preadsorbed oxygen leads to a decrease of the initial sticking coefficient for H down to 0.1; potassium on the other hand has no significant influence on the initial sticking probability. On both surfaces, Ni(111) and Al(111), abstraction of deuterium proceeds at a surface temperature of 150 K due to impinging H atoms (H+D→HD), with an initial abstraction coefficient of 0.20 on Al(111) and 0.12 on Ni(111). In the case of Al(111) this coefficient is nearly independent of the initial D coverage and therefore the abstraction reaction cannot be described by a simple Eley–Rideal process, but rather by a hot-precursor mechanism. In addition to abstraction there is also a small probability for the removal of an adsorbed species by a collision induced desorption process. Abstraction of deuterium by impinging H-atoms is strongly affected by modification of the Al(111) surface, either by oxygen or by potassium. Oxygen decreases the HD abstraction coefficient, probably by inhibiting the hot-precursor state of H on the surface. Potassium increases the HD abstraction rate, most likely by increasing the lifetime of atomic hydrogen in the precursor state. © 1999 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.478157
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