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SUMMARY:H Atom Scattering\, Adsorption\, and Absorption in Collisions with
  Metal Surfaces: the crucial role of electron-hole-pair excitation
DTSTART:20170329T110000
DTEND:20170329T120000
DTSTAMP:20260415T081425Z
UID:af4c456aa6dfb342d35d367fa774347e2a35bf16958f3805038c02f6
CATEGORIES:Conferences - Seminars
DESCRIPTION:Daniel J. AUERBACH\nMax Planck Institute for Biophysical Chemi
 stry\, Göttingen\, Germany\nAbstract:\nWhen an H atom collides with a sol
 id surface\, it can transfer some of its kinetic energy into elementary ex
 citations of the solid like phonons and electron-hole pairs. If the atom l
 oses enough kinetic energy\, it can become bound to the solid\, either on 
 the surface or in the bulk. For a metal\, the availability of a continuum 
 of low lying electronic excitations can lead to the breakdown of the adiab
 atic Born Oppenheimer approximation and the facile nonadiabatic excitation
  of electron-hole pairs (ehp). If the H atom loses sufficient energy\, it 
 can enter a bound state with the solid\, either on the surface or in the b
 ulk. We have used a combined theoretical and experimental approach to eluc
 idate the relative roles of adiabatic processes (phonon excitation) and no
 nadiabatic processes (ehp excitation) in collisions of H atoms with metals
 \, insulators\, and graphene. The experiments use photolysis to produce ne
 arly mono-energetic beams of H atoms with energies of 1 - 3.3 eV and high 
 resolution energy loss measurements using Rydberg atom tagging time-of-fli
 ght analysis. The theory involves calculations of classical trajectories f
 or H atom collisions with two techniques. In the first\, we calculate ener
 gies and forces on-the-fly during the course of a trajectory using density
  functional theory (DFT) and ab initio molecular dynamics (AIMD). In the s
 econd\, we construct a full dimensional potential energy surface (PES) usi
 ng a flexible functional form fit to DFT energies and bulk properties of t
 he solid. The measured mean energy loss for H atoms scattering from metals
  is large\, approximately 30% of the initial energy and there is a tail in
  the energy loss distribution (ELD) extending to the full energy of incide
 nce. The measured ELD is in reasonable agreement with theory only if nonad
 iabatic effects are included\; adiabatic theory drastically underestimates
  the energy loss. Scattering from insulators (where ehp excitation can be 
 excluded) shows much smaller energy loss and results consistent with adiab
 atic theory. For metals\, nonadiabatic effects not only dominate the energ
 y loss process\, but also change both the magnitude and mechanism for adso
 rption on metals. With nonadiabatic effects\, the most probable pathway to
  adsorption is for H atoms to penetrate the surface\, lose energy in the s
 ubsurface region\, and then reemerge to adsorb on the surface.
LOCATION:Zeuzier
STATUS:CONFIRMED
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