Endothermic dissociative chemisorption of molecular D2 on Ag(111)

Healey, Frank; Carter, R.N.; Worthy, G.; Hodgson, A.

doi:10.1016/0009-2614(95)00815-l

Cited by 34 publications

(35 citation statements)

References 30 publications

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“…[36] For Ag(100) we have also obtained an activation barrier of about 1 eV. These high values for he dissociation reaction explain why on both silver surfaces the second step is electrochemical desorption according to Equation (3).…”

Section: Chemical Versus Electrochemical Recombinationmentioning

confidence: 83%

Hydrogen Evolution on Single‐Crystal Copper and Silver: A Theoretical Study

et al. 2010

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Hydrogen evolution on single-crystal copper and silver is investigated by a combination of density functional theory and a theory developed in our own group. At short times, the reaction rate is determined by the transfer of the first proton to the electrode surface. In accord with experiment, we find for both metals that this reaction proceeds faster on the (111) surfaces than on the (100) ones. The main cause is the lower, that is, more favourable, adsorption energy on the former surfaces. On both silver surfaces, the second step is electrochemical desorption. The same mechanism is likely to operate on copper.

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Section: Chemical Versus Electrochemical Recombinationmentioning

confidence: 83%

Hydrogen Evolution on Single‐Crystal Copper and Silver: A Theoretical Study

et al. 2010

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“…7 Very recently it has been proposed that D 2 dissociatively adsorbs in a metastable state at Ag͑111͒. 8 The adsorbed D-atoms are energetically unstable with respect to recombination and desorption. However, the recombining D-atoms are separated by an energetic barrier from the vacuum.…”

Section: Introductionmentioning

confidence: 99%

O2 transient trapping-desorption at the Ag(111) surface

Raukema

Butler

Kleyn

1997

The Journal of Chemical Physics

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Molecular beam scattering experiments of O2 from Ag(111) carried out at a surface temperature of 150 K, which is below the desorption temperature for the molecular chemisorption state, show three different scattering paths: physisorption followed by desorption, direct-inelastic scattering and transient trapping-desorption. The transient trapping-desorption process is attributed to transient adsorption of the molecule in a metastable O2δ− state at the surface. The translational desorption energy of the transiently trapped molecules is far above thermal, strongly dependent on the surface temperature and independent of the translational energy and angle of the incident oxygen molecule. A strongly peaked intensity distribution around the surface normal is observed for the desorption. The transient trapping probability shows a sharp increase above a threshold energy and a subsequent decrease with increasing incidence energy. It is accompanied by a strong broadening in the angular direct-inelastically scattered flux distribution. The possible origin of the metastable O2δ− state will be discussed.

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“…Similar distributions were obtained following D dosing at 100 K and flash desorption of D 2 near 200 K, although with a reduced signal to noise. It is immediately obvious that the energy release into D 2 product translation is relatively small, much lower than the median barrier to dissociation of the ground state which is expected to lie above 800 meV [4,5]. This contrasts with the result of desorption from a hot Cu(111) permeation source [7] where the mean desorption energy is similar to the barrier inferred from sticking, E 0 ͑y͒.…”

mentioning

confidence: 95%

“…Dissociative chemisorption of D 2 on a 100 K Ag(111) surface is highly activated and has been observed only for gas temperatures above 1000 K and translational energies E . 200 meV [4]. Sticking has been modeled using "S " shaped vibrational state dependent sticking functions of the form S͑y͒ A͑y͒͞2͕1 2 tanh͓E i 2 E 0 ͑y͔͒͞w͑y͖͒, where the dissociation probability S͑y͒ is determined by three parameters, A͑y͒ the limiting sticking probability at high energy, E 0 ͑y͒ the median barrier height, and w͑y͒ the effective width of the barrier distribution.…”

mentioning

confidence: 99%

Role of Surface Thermal Motion in the Dissociative Chemisorption and Recombinative Desorption ofD2on Ag(111)

Murphy

Hodgson

1997

Phys. Rev. Lett.

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Although D 2 dissociation exhibits a large barrier on Ag(111), recombinative desorption occurs with minimal translational energy release. A strong surface temperature dependence is seen with a bimodal energy release at high temperatures. We propose that desorption occurs through two channels: by recombination at thermally activated sites, with a high steric constraint but low activation barrier, and directly via a large barrier at high surface temperatures. Surface thermal motion determines the distribution of dissociation barriers, a model which will be important in other activated systems. [S0031-9007 (97)03280-8] PACS numbers: 68.35.JaHydrogen dissociative chemisorption on metal surfaces has become a test bed for models of gas-surface reaction dynamics principally because of the simplifications that can be made when comparing experimental results with scattering calculations. These simplifications arise from the low mass of the molecule relative to the substrate and the different time scales associated with the motion of H͞D atoms and the metal atoms of the surface [1]. As a result, phonon excitation is far weaker than for other molecules and energy dissipation can generally be ignored without losing the central features of the problem. Similarly, the short time scale for H 2 dissociation ensures that relaxation of the metal lattice occurs only after dissociation is complete, while surface reconstruction of close packed metal faces is minimal compared to that shown by heavier adsorbates such as N, C, and O. Models of the dissociation dynamics generally consider the metal as a rigid lattice and ignore both relaxation and thermal motion, an approach justified by the insensitivity of H 2 dissociative chemisorption on metals to surface temperature.We have measured the energy release into translational motion for D 2 recombinative desorption from Ag(111) as a function of internal state and surface temperature T s . We find that the form of the translational energy distributions, P͑E͒, is sensitive to surface temperature, with desorption occurring by different mechanisms to give products with low or high translational energies. At high surface temperatures D atoms can directly overcome a large activation barrier to recombination, resulting in products with considerable translational energy, whereas at lower temperatures desorption gives rise only to products with a low translational energy release. The system therefore has two different paths to desorption, one which relies on thermal activation to overcome a large energy barrier and a second which has a lower energy requirement, but a large entropic constraint, and dominates desorption. The shape of the P͑E͒ distributions can be related to the sticking probability S͑E͒ by detailed balance and implies a strong surface temperature dependence. This is in contrast to the usual insensitivity of S to T s for H 2 ͞D 2 dissociation on metals, and we attribute this to a broadening of the barrier distribution caused by thermal activation of the surface.Although D 2 dissociat...

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Endothermic dissociative chemisorption of molecular D2 on Ag(111)

Cited by 34 publications

References 30 publications

Hydrogen Evolution on Single‐Crystal Copper and Silver: A Theoretical Study

Hydrogen Evolution on Single‐Crystal Copper and Silver: A Theoretical Study

O2 transient trapping-desorption at the Ag(111) surface

Role of Surface Thermal Motion in the Dissociative Chemisorption and Recombinative Desorption ofD2on Ag(111)

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