Inelastic Scattering of H Atoms from Surfaces

Bünermann, Oliver; Kandratsenka, Alexander; Wodtke, Alec M.

doi:10.1021/acs.jpca.1c00361

Cited by 18 publications

(23 citation statements)

References 183 publications

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“…Inelastic H-atom scattering from metal surfaces 24 , 25 , 37 , 38 provides a direct probe of electronically nonadiabatic forces in a system that can be treated classically in full dimensions, including surface atom motion. 39 , 40 Experimental and theoretical energy-loss distributions can be compared to test models of electronic friction.…”

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“…Inelastic H-atom scattering from metal surfaces ,,, provides a direct probe of electronically nonadiabatic forces in a system that can be treated classically in full dimensions, including surface atom motion. , Experimental and theoretical energy-loss distributions can be compared to test models of electronic friction. However, since the Langevin equation describes how a system evolves under the influence of a frictional drag and a random force, the experimental manifestations of a model of electronic friction cannot be realized without the influence of the random force.…”

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Random Force in Molecular Dynamics with Electronic Friction

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Originally conceived to describe thermal diffusion, the Langevin equation includes both a frictional drag and a random force, the latter representing thermal fluctuations first seen as Brownian motion. The random force is crucial for the diffusion problem as it explains why friction does not simply bring the system to a standstill. When using the Langevin equation to describe ballistic motion, the importance of the random force is less obvious and it is often omitted, for example, in theoretical treatments of hot ions and atoms interacting with metals. Here, friction results from electronic nonadiabaticity (electronic friction), and the random force arises from thermal electron–hole pairs. We show the consequences of omitting the random force in the dynamics of H-atom scattering from metals. We compare molecular dynamics simulations based on the Langevin equation to experimentally derived energy loss distributions. Despite the fact that the incidence energy is much larger than the thermal energy and the scattering time is only about 25 fs, the energy loss distribution fails to reproduce the experiment if the random force is neglected. Neglecting the random force is an even more severe approximation than freezing the positions of the metal atoms or modelling the lattice vibrations as a generalized Langevin oscillator. This behavior can be understood by considering analytic solutions to the Ornstein–Uhlenbeck process, where a ballistic particle experiencing friction decelerates under the influence of thermal fluctuations.

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Random Force in Molecular Dynamics with Electronic Friction

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“…The importance of quantum effects in surface chemistry needs much more effort. Recently, H atom beams have been produced at energies as low as 0.2 eV and with such narrow speed distributions, they could not be measured by Rydberg‐atom tagging 486 . These could deliver a great deal of excellent quantitative scattering data capable of testing quantum mechanical theories of reaction dynamics.…”

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Chemical dynamics from the gas‐phase to surfaces

2021

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The field of gas‐phase chemical dynamics has developed superb experimental methods to probe the detailed outcome of gas‐phase chemical reactions. These experiments inspired and benchmarked first principles dynamics simulations giving access to an atomic scale picture of the motions that underlie these reactions. This fruitful interplay of experiment and theory is the essence of a dynamical approach perfected on gas‐phase reactions, the culmination of which is a standard model of chemical reactivity involving classical trajectories or quantum wave packets moving on a Born–Oppenheimer potential energy surface. Extending the dynamical approach to chemical reactions at surfaces presents challenges of complexity not found in gas‐phase study as reactive processes often involve multiple steps, such as inelastic molecule‐surface scattering and dissipation, leading to adsorption and subsequent thermal desorption and or bond breaking and making. This paper reviews progress toward understanding the elementary processes involved in surface chemistry using the dynamical approach. Key points The fruitful interplay between chemistry and physics leads to an atomic scale view of reactions taking places at catalytically active surfaces. Improved observations of chemical reactions taking place in complex environments drive the development of new approaches to theoretical chemistry. Complex reaction networks from real catalysts are boiled down to their elementary steps and examined from first principles.

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“…The H atom scattering apparatus has been described elsewhere, 24 and a review has recently appeared. 25 Briefly, H atoms were generated by photodissociation of a supersonic molecular beam of hydrogen iodide with pulses of laser light at 212.5 nm, producing H atoms with incidence energy E i = 2.76 eV and an energy uncertainty δ E i ∼ 0.005 eV. H atoms traveling normal to the molecular beam scatter from the Xe sample that was condensed on a Au(111) substrate held at 45 K by cold He gas.…”

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Multibounce and Subsurface Scattering of H Atoms Colliding with a van der Waals Solid

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We report the results of inelastic differential scattering experiments and full-dimensional molecular dynamics trajectory simulations for 2.76 eV H atoms colliding at a surface of solid xenon. The interaction potential is based on an effective medium theory (EMT) fit to density functional theory (DFT) energies. The translational energy-loss distributions derived from experiment and theory are in excellent agreement. By analyzing trajectories, we find that only a minority of the scattering results from simple single-bounce dynamics. The majority comes from multibounce collisions including subsurface scattering where the H atoms penetrate below the first layer of Xe atoms and subsequently re-emerge to the gas phase. This behavior leads to observable energy-losses as large as 0.5 eV, much larger than a prediction of the binary collision model (0.082 eV), which is often used to estimate the highest possible energy-loss in direct inelastic surface scattering. The sticking probability computed with the EMT-PES (0.15) is dramatically reduced (5 × 10 –6 ) if we employ a full-dimensional potential energy surface (PES) based on Lennard-Jones (LJ) pairwise interactions. Although the LJ-PES accurately describes the interactions near the H–Xe and Xe–Xe energy minima, it drastically overestimates the effective size of the Xe atom seen by the colliding H atom at incidence energies above about 0.1 eV.

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Inelastic Scattering of H Atoms from Surfaces

Cited by 18 publications

References 183 publications

Random Force in Molecular Dynamics with Electronic Friction

Random Force in Molecular Dynamics with Electronic Friction

Chemical dynamics from the gas‐phase to surfaces

Multibounce and Subsurface Scattering of H Atoms Colliding with a van der Waals Solid

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