Hydrogen-graphite interaction: Experimental evidences of an adsorption barrier

Aréou, E.; Cartry, Gilles; Layet, J. M.; Angot, Thierry

doi:10.1063/1.3518981

Cited by 47 publications

(39 citation statements)

References 37 publications

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“…Despite this, para DF shows a dynamical threshold of about 2 kJ·mol −1 (corresponding to a gas-phase temperature T g ∼ 300 K), below which only H 2 recombination is expected. This is in agreement with recent experiments, in which highly oriented pyrolitic graphite (HOPG) samples precovered with D atoms were found to form dimers and clusters only when irradiated with highly energetic H atoms (23); at E coll = 2.4 kJ·mol −1 , only ER recombination was found to occur (24). More generally, as is evident in Fig.…”

Section: Resultssupporting

confidence: 80%

Insights into H ₂ formation in space from ab initio molecular dynamics

Casolo

Tantardini

Martinazzo

2013

Proc. Natl. Acad. Sci. U.S.A.

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Hydrogen formation is a key process for the physics and the chemistry of interstellar clouds. Molecular hydrogen is believed to form on the carbonaceous surface of dust grains, and several mechanisms have been invoked to explain its abundance in different regions of space, from cold interstellar clouds to warm photondominated regions. Here, we investigate direct (Eley-Rideal) recombination including lattice dynamics, surface corrugation, and competing H-dimers formation by means of ab initio molecular dynamics. We find that Eley-Rideal reaction dominates at energies relevant for the interstellar medium and alone may explain observations if the possibility of facile sticking at special sites (edges, point defects, etc.) on the surface of the dust grains is taken into account.graphite-graphene | interstellar chemistry | hydrogen recombination | density functional theory T he complicated interaction between hydrogen atoms and graphite has been widely studied in the last decade because of its relevance in various fields, from hydrogen storage (1) to nuclear fusion (2), from graphene technology (3-6) to interstellar chemistry (7).In the chemistry of the interstellar medium (ISM), H 2 is a precursor for more complex molecules through its protonated form H þ 3 , shields the clouds from the radiation field, and acts as primary cooling agent during the gravitational collapse, which ultimately leads to star formation (7). Its appearance in the early universe steered the development of the first stars and triggered galaxy formation (8).In the harsh ISM conditions, molecular hydrogen is continuously dissociated by stellar UV radiation and cosmic rays; hence efficient synthetic pathways are needed to explain the observed abundances (7). These are known to involve the carbonaceous surface of interstellar dust grains (9), but the detailed mechanisms behind H 2 formation on graphitic surfaces have yet to be fully uncovered.Physisorbed H atoms can only be invoked in cold molecular clouds, where the surface temperature is low enough to prevent desorption (T s ≤ 40 K) from the shallow physisorption well (E ∼ 4 kJ·mol −1 ) (10, 11). In this case, hydrogen molecules may follow from either an Eley-Rideal (ER)/hot-atom (HA) or a LangmuirHinshelwood (LH) pathway, because H atoms are very mobile even at extremely low temperatures (11). Stable (chemisorbed) species on the basal graphitic plane, however, require energetic projectile atoms to overcome an activation barrier to sticking (E ∼ 20 kJ·mol −1 ) (12, 13), which is due to the carbon sp 2 -sp 3 rehybridization needed by the bond formation process, although tunneling might help in this context (14). Chemically bound H atoms are immobile on the surface [they desorb rather than diffusing (15)]; hence LH pathway is ruled out in sufficiently warm environments where only chemisorbed species can be found. No matter how a first chemisorbed species is formed, secondary H atoms undergo facile sticking and preferentially form ortho and para (16, 17) dimers because of the aromatic nature of the...

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Section: Resultssupporting

confidence: 80%

Insights into H ₂ formation in space from ab initio molecular dynamics

Casolo

Tantardini

Martinazzo

2013

Proc. Natl. Acad. Sci. U.S.A.

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“…It has now been well established that sticking is an activated process, with a barrier related to the surface reconstruction accompanying the sp 2 → sp 3 re-hybridization of the carbon atom involved in the bond formation process. 3 As a consequence, carefully conducted scattering experiments which used low energy hydrogen atom beams -as opposed to high energy beams obtained by thermal cracking of H 2 -found that the competing, non-activated hydrogen abstraction process dominates under these conditions, 19 a result which was later confirmed by ab initio molecular dynamics simulations. 25 For all but the smallest coverage, hydrogenation is driven by electronic and substrate-softening effects which lead to dimer formation and clustering; 15,18,26,27 hence, current experimental results leave the question open of how large is the initial hydrogen sticking coefficient on the carbon sheet.…”

Section: Introductionmentioning

confidence: 82%

“…Though experimental studies have shown adsorption-induced metal-insulator transitions, 7,8 reversible opening of a band-gap 9,10 and even ferromagnetic hysteresis, 11 the necessary precise control on the hydrogenation process has yet to be achieved. Hydrogenation of graphite has been studied in a number of experimental works, 3,[12][13][14][15][16][17][18][19][20][21][22][23][24] with a variety of surface-science techniques including thermal desorption, high-resolution electron-energy-loss spectroscopy, scanning tunneling microscopy, low-energy electron diffraction, angle a) Electronic mail: matteo.bonfanti@unimi.it b) Electronic mail: rocco.martinazzo@unimi.it resolved photo-emission spectroscopy, and X-ray photoemission spectroscopy. It has now been well established that sticking is an activated process, with a barrier related to the surface reconstruction accompanying the sp 2 → sp 3 re-hybridization of the carbon atom involved in the bond formation process.…”

Section: Introductionmentioning

confidence: 99%

Quantum dynamics of hydrogen atoms on graphene. II. Sticking

Bonfanti

Jackson

Hughes

et al. 2015

The Journal of Chemical Physics

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Study of the sticking of a hydrogen atom on a graphite surface using a mixed classical-quantum dynamics method J. Chem. Phys. 133, 044508 (2010); 10.1063/1.3463001Reuse of AIP Publishing content is subject to the terms: https://publishing.aip.org/authors/rights-and-permissions. (2015)], we present the results of converged quantum scattering calculations on the activated sticking dynamics. The focus of this study is the collinear scattering on a surface at zero temperature, which is treated with high-dimensional wavepacket propagations with the multi-configuration time-dependent Hartree method. At low collision energies, barrier-crossing dominates the sticking and any projectile that overcomes the barrier gets trapped in the chemisorption well. However, at high collision energies, energy transfer to the surface is a limiting factor, and fast H atoms hardly dissipate their excess energy and stick on the surface. As a consequence, the sticking coefficient is maximum (∼0.65) at an energy which is about one and half larger than the barrier height. Comparison of the results with classical and quasi-classical calculations shows that quantum fluctuations of the lattice play a primary role in the dynamics. A simple impulsive model describing the collision of a classical projectile with a quantum surface is developed which reproduces the quantum results remarkably well for all but the lowest energies, thereby capturing the essential physics of the activated sticking dynamics investigated. C 2015 AIP Publishing LLC.[http://dx

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“…The most well-defined experiment performed to date placed the barrier for H atom adsorption on graphite somewhere within the rather broad range of 25 to 250 meV. 31 Previous theoretical work on extended carbonaceous surfaces (graphite, and more commonly a single graphene layer) have been at the upper end of the experimental range (ca. 200 meV 16,19,[32][33][34][35] ).…”

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confidence: 99%

Cooperative Interplay of van der Waals Forces and Quantum Nuclear Effects on Adsorption: H at Graphene and at Coronene

et al. 2014

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The energetic barriers that atoms and molecules often experience when binding to surfaces are incredibly important to a myriad of chemical and physical processes. However these barriers are difficult to describe accurately with current computer simulation approaches. Two prominent contemporary challenges faced by simulation are the role of van der Waals forces and nuclear quantum effects. Here we examine the widely studied model systems of hydrogen

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Hydrogen-graphite interaction: Experimental evidences of an adsorption barrier

Cited by 47 publications

References 37 publications

Insights into H ₂ formation in space from ab initio molecular dynamics

Insights into H ₂ formation in space from ab initio molecular dynamics

Quantum dynamics of hydrogen atoms on graphene. II. Sticking

Cooperative Interplay of van der Waals Forces and Quantum Nuclear Effects on Adsorption: H at Graphene and at Coronene

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Hydrogen-graphite interaction: Experimental evidences of an adsorption barrier

Cited by 47 publications

References 37 publications

Insights into H 2 formation in space from ab initio molecular dynamics

Insights into H 2 formation in space from ab initio molecular dynamics

Quantum dynamics of hydrogen atoms on graphene. II. Sticking

Cooperative Interplay of van der Waals Forces and Quantum Nuclear Effects on Adsorption: H at Graphene and at Coronene

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Insights into H ₂ formation in space from ab initio molecular dynamics

Insights into H ₂ formation in space from ab initio molecular dynamics