Berlin 2005 – scientific programme
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O: Oberflächenphysik
O 54: Adsorption an Oberfl
ächen VI
O 54.1: Talk
Wednesday, March 9, 2005, 10:45–11:00, TU EB202
Dissociation of Oxygen at Al(111): The Role of Spin Selection Rules — •Jörg Behler1, Bernard Delley2, Sönke Lorenz1, Karsten Reuter1, and Matthias Scheffler1 — 1Fritz-Haber-Institut, Faradayweg 4-6, D-14195 Berlin — 2Paul-Scherrer-Institut, CH-5232 Villigen PSI
The description of the dissociative adsorption of molecular oxygen at the Al(111) surface remains a most basic and puzzling enigma in surface science. The very low sticking probability of thermal oxygen molecules found experimentally is in strong conflict with the results of state-of-the-art first-principles calculations. We show that this is caused by hitherto unaccounted spin selection rules, which give rise to a highly non-adiabatic behavior in the oxygen-aluminium interaction. As a consequence, the molecular trajectory does not follow the barrier-free adiabatic potential energy surface (PES), but maintains the diabatic triplet state up to close distances to the surface. Detailed density-functional calculations within an appropriate spin-constrained formulation clearly show that the latter PES exhibits sizeable energy barriers, yielding a sticking curve in agreement with experiment. Problems caused by the insufficient accuracy of present-day exchange-correlation functionals and the effects of electronic transitions are also discussed.