# Regensburg 2004 – wissenschaftliches Programm

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# O: Oberflächenphysik

## O 26: Adsorption an Oberflächen II

### O 26.3: Vortrag

### Dienstag, 9. März 2004, 16:15–16:30, H45

**Non-adiabatic spin effects in O**_{2}** dissociation at Al(111)** — •Jörg Behler^{1}, Sönke Lorenz^{1}, Bernard Delley^{2}, Karsten Reuter^{1}, and Matthias Scheffler^{1} — ^{1}Fritz-Haber-Institut, Faradayweg 4-6, D-14195 Berlin — ^{2}Paul Scherrer Institut, CH-5232 Villigen PSI

The experimentally well established low initial sticking coefficient of
thermal oxygen molecules impinging on an Al(111) surface is still lacking a
physical explanation. The calculation of the six-dimensional potential
energy surface using density functional theory (DFT) followed by extensive
molecular dynamics (MD) simulations results in a far too high sticking
probability due to the absence of energy barriers in this adiabatic
description. By including a constrained DFT method we extend this standard
approach to describe the spin triplet state of the oxygen molecule and the
singlet state of the metal surface. This is a generalization of the fixed
spin moment approach, and it enables us to investigate the effect of
non-adiabatic processes in the dissociative adsorption.
For the total energy surface of the spin triplet O_{2} we find energy
barriers up to 0.5 eV for most molecular orientations agreeing well with
the experimental data. MD simulations on this surface yield a significantly
lower sticking probability than obtained in the adiabatic case.