Eley−Rideal Surface Chemistry:  Direct Reactivity of Gas Phase Atomic Hydrogen with Adsorbed Species

Weinberg, W. H.

doi:10.1021/ar9500980

Cited by 111 publications

(61 citation statements)

References 73 publications

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“…1(a). Two characteristic maxima around 320 and 380 K are in accordance with previous reports [6,9] and are practically identical for both H 2 and D 2 . This indicates that there is no noticeable isotope effect in the thermal desorption kinetics, presumably because the zero-point energy differences are very similar in the initial and final states.…”

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confidence: 92%

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Electronic Excitation and Dynamic Promotion of a Surface Reaction

et al. 2003

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The mechanism of recombinative desorption of hydrogen from a Ru(0001) surface induced by femtosecond-laser excitation has been investigated and compared to thermally initiated desorption. For the laser-driven process, it is shown that hot substrate electrons mediate the reaction within a few hundred femtoseconds resulting in a huge isotope effect between H 2 and D 2 in the desorption yield. In mixed saturation coverages, this ratio crucially depends on the proportions of H and D. Deviations from second order desorption kinetics demonstrate that the recombination is dynamically promoted by excitation of neighboring, but nonreacting adatoms. A concentration dependent rate constant which accounts for the faster excitation of H versus D is proposed. DOI: 10.1103/PhysRevLett.91.226102 PACS numbers: 82.65.+r, 68.43.Mn, 78.90.+t, 82.53.-k Chemical reactions involving species adsorbed on a metal surface are mediated through excitation of electrons and/or phonons of the substrate. Since thermal equilibration between these excitations occurs on a femtosecond (fs) to picosecond (ps) time scale, the rate normally may be described to a very good approximation within the framework of transition state theory [1] in terms of the temperature dependent rate constant and as a function of the surface concentrations. Rapid absorption of a fs-laser pulse by the conduction electrons of the substrate may, however, trigger the onset of a surface reaction before equilibration between the heat baths of electrons and phonons is reached, as has been exemplified in the reaction between O and CO adsorbed on a Ru(0001) surface yielding the release of CO 2 into the gas phase [2]. For adsorption on thin metal films with Schottky contact, it was recently demonstrated that nonadiabatic coupling to electron-hole pairs plays an important role in surface reactions and is not negligible even in low-energy processes in which phononic excitations are thought to dominate [3]. Hot electrons were proposed to routinely participate in substrate-mediated reactions contrary to the traditional picture of a thermal surface reaction, in which phonons solely drive the system over the reaction barrier in the electronic ground state.Coadsorbed species on a metal substrate can modify the electronic structure and hence influence the surface reactivity. Altering the height of the reaction barrier in the electronic ground state and/or energetic shifts of the potential energy surface in electronically excited states are typical consequences. In the case of catalytic promotion (e.g., by alkali atoms), these static changes in the electronic potential energy landscape result in an enhanced reaction rate [4]. In this Letter, we report on dynamic promotion of a prototype surface reaction, H ad H ad ! H 2;gas on Ru(0001). Hydrogen recombination may be initiated thermally (i.e., under conditions of thermal equilibrium between all degrees of freedom), but if induced by fs-laser excitation characteristic differences are observed: (i) The hydrogen molecules coming off the surf...

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supporting

confidence: 92%

“…1(a). Two characteristic maxima around 320 and 380 K are in accordance with previous reports [6,9] and are practically identical P H Y S I C A L …”

supporting

confidence: 92%

Electronic Excitation and Dynamic Promotion of a Surface Reaction

et al. 2003

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“…A low activation barrier would be consistent with both mechanisms. 10,16 Experimental and theoretical literature on the abstraction of H͑D͒ by atomic D͑H͒ from c-Si surfaces is extensive and has been recently summarized by Dinger et al 17 Briefly, Koleske et al 11,13 measured an activation energy barrier of 0.022-0.043 eV for the abstraction of H by D and H on both Si͑100͒ and Si͑111͒ surfaces independent of the isotope. Srinivasan et al 18 used ab initio configuration interaction ͑CI͒ theory in a collinear interaction geometry to calculate the activation energy barrier for the abstraction of hydrogen from silicon mono-hydride and silicon di-hydride in Si 4 H 10 and Si 3 H 8 clusters, respectively.…”

Section: Introductionmentioning

confidence: 99%

Abstraction of atomic hydrogen by atomic deuterium from an amorphous hydrogenated silicon surface

Agarwal

Takano

Sanden

et al. 2002

The Journal of Chemical Physics

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We have studied the interactions of atomic deuterium with hydrogenated amorphous silicon (a-Si:H) surfaces using surface-sensitive infrared spectroscopy. We deconvoluted the effects of the abstraction reaction from insertion and etching reactions and determined the activation energy barrier for abstraction of H by D from a-Si:H surfaces. Both abstraction and insertion are observed in our experiments conducted over times ranging from a few seconds to hundreds of seconds and sequential insertion of D eventually results in the formation of deuterated silane and etching of the film. The abstraction rate is found to be independent of temperature with an essentially zero activation energy barrier (0.011±0.013 eV), consistent with an Eley–Rideal mechanism and in agreement with recent atomistic calculations.

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“…Gas-surface reactions are often thought to proceed between two extremes: the Langmuir-Hinshelwood (LH) mechanism, which requires all reactants to be adsorbed onto and in thermal equilibrium with the surface, and the Eley-Rideal (ER) mechanism, where an energetic reactant (the "projectile") impinges onto a surface adsorbate and bonds with it directly [1]. The LH mechanism applies to most surface chemical reactions and is well understood [2].…”

Section: Direct or Eley-rideal Reactions Between Energetic Nmentioning

confidence: 99%

Kinematics of Eley-Rideal Reactions at Hyperthermal Energies

Yao

Giapis

2016

Phys. Rev. Lett.

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Direct or Eley-Rideal reactions between energetic N þ and O þ projectiles and O atoms, adsorbed onto Pt and Pd surfaces, are studied experimentally at incidence energies between 20 and 200 eV. The exit energies of the diatomic molecular products NO and O 2 depend linearly on the incidence energy of the corresponding projectiles. A reaction mechanism is proposed, where the incident projectile collides with a single metal atom on the surface, linked to an adsorbed O atom. At the apsis point, a high-energy transient state is formed between the projectile, substrate, and adsorbate atoms. As the projectile begins to rebound, the transient state decomposes into a diatomic molecule, consisting of the original projectile and the adsorbed O atom, which exits the surface with memory of the incidence energy. Energy and momentum conservation during this single-bounce event (atom in, molecule out) accurately predict the exit energy of the molecular product, thus capturing the kinematics of the direct reaction. DOI: 10.1103/PhysRevLett.116.253202 Gas-surface reactions are often thought to proceed between two extremes: the Langmuir-Hinshelwood (LH) mechanism, which requires all reactants to be adsorbed onto and in thermal equilibrium with the surface, and the Eley-Rideal (ER) mechanism, where an energetic reactant (the "projectile") impinges onto a surface adsorbate and bonds with it directly [1]. The LH mechanism applies to most surface chemical reactions and is well understood [2]. The ER mechanism is still being debated: the rarity of chemical environments where hyperthermal reactive species bombard surfaces, combined with experimental difficulties in detecting energetic reaction products, has impeded progress in understanding such reactions. In fact, even the definition of an ER reaction is outright crude: the notion of a bond forming between an energetic projectile and a surface adsorbate in a head-on collision, followed up by ejection from the surface of an energetic reaction product, violates momentum conservation. This problem does not arise if the projectile collides first with the surface. Hot atom reactions represent an intermediate mechanism, where the projectile undergoes few bounces before reacting with an adsorbate [3]. Owing to multiple collisions, which lead to variable energy losses, these do not qualify as prompt ER reactions.What comprises an ER reaction? The literature consensus suggests that ER reactions should have at least the following attributes: (i) they require a gas-phase projectile with high kinetic or potential energy, impinging onto an adsorbate-covered surface; (ii) they yield a fast-moving molecular product, consisting of the projectile-adsorbate combination, which leaves the surface (no trapping); and (iii) the product translational energy must be directly correlated to the energy of the incident projectile. Secondary attributes include that (iv) the product molecule may be internally excited; and (v) the product angular flux distribution deviates from the cosine law, with subspecular pref...

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Eley−Rideal Surface Chemistry: Direct Reactivity of Gas Phase Atomic Hydrogen with Adsorbed Species

Cited by 111 publications

References 73 publications

Electronic Excitation and Dynamic Promotion of a Surface Reaction

Electronic Excitation and Dynamic Promotion of a Surface Reaction

Abstraction of atomic hydrogen by atomic deuterium from an amorphous hydrogenated silicon surface

Kinematics of Eley-Rideal Reactions at Hyperthermal Energies

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