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

Abstract

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.

Electronically Nonadiabatic H Atom Scattering from Low Miller Index Surfaces of Silver

“…Because the experiment can only detect the final energy of the scattered particles, we now analyze the role of surface penetration which has recently been identified to result in higher energy losses. , The upper panels of Figure show contour plots which provide the number of specular scattering events as a function of energy loss and depth of penetration. A clear correlation between the energy loss and the depth of penetration can be inferred.…”

“…A series of scattering experiments have been performed in which high-energy H atoms were shot onto fcc(111) metal surfaces. In combination with electronically nonadiabatic molecular dynamics (MD) simulations, it was demonstrated that the energy transfer from the projectile to the metallic surface is dominated by electronic excitations. − When the metal surface is exchanged with a noble-gas surface, however, the excess energy is completely taken up by the lattice, and surface penetration was identified to be the first step in adsorption . Regardless of the recent advance on H atom scattering studies, the role of the surface structure has not been the subject of investigation yet.…”

Effective medium theory for bcc metals: electronically non-adiabatic H atom scattering in full dimensions

“…The Effective Medium Theory (EMT) has proven useful to describe gas-surface interactions for fcc metals. 2,14,[22][23][24][26][27][28][29][30] Here, we extend the previously formulated EMT formalism to the case of bcc metals.…”

“…We emphasize that neglecting the random force, as has sometimes been done, 44 can lead to spurious results. 14 The EMT-PES and the Langevin propagator integrating eqn (30) are implemented in our homemade program md_tian2 available at a public repository. 45 The MD trajectories simulating H scattering from a metal surface were started with a H atom placed at 6 Å above the surface with a lateral position chosen randomly.…”

H atom scattering from W(110): A benchmark for molecular dynamics with electronic friction.

“…The first, effective medium theory (EMT) 29,30 is a full dimensional PES approach previously used for H atom scattering from fcc(111) surfaces. 3,4,31 It models excitation of phonons by full dimensional classical MD and the frictional force is computed from EMT-background electron densities associated with the moving lattice. The second is a corrugation reduction procedure (CRP), [32][33][34] which has also been applied to H atom scattering from metal surfaces 7 as well as hydrogen recombination.…”