ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
We report detailed molecular beam studies of the effects of K adsorption on the dissociative chemisorption probabilities S0 for D2 on Pt(111). In contrast to conventional wisdom for many other molecular systems, we find that K is a very strong poison rather than promoter for H2 dissociation. S0 decreases roughly exponentially with K coverage aitch-thetaK. The effective cross section for poisoning per adsorbed K varies between 70 and 430 A(ring)2, depending upon incident energy Ei. This suggests that an extremely long-range electronic perturbation is responsible for the poisoning. A theoretical model is developed to describe these sticking measurements. It is based on the fact that the adsorbed K lowers the work function of the surface. This enhances Pauli repulsion for the molecule-surface interaction which, in turn, increases the barrier to dissociation. When the model is generalized to include inhomogeneous effects through a local work function, excellent agreement is obtained between the model and experiments. This model also naturally accounts for the increased associative desorption temperatures for H2 when coadsorbed K is present.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.460827
Permalink