Adiabatic potential-energy surface of O-2/Al(111): rare entrance-channel barriers but molecularly chemisorbed state apt for abstraction

Extensive density-functional calculations of the adiabatic potential-energy hypersurface for O-2 adsorption on the Al(111) surface present (i) an entr ance-channel barrier only under some very rare conditions and (ii) a molecu larly chemisorbed intermediate state for a non-parallel molecule. The predi cted metastable molecular state is stabilized by a Hund's rule spin effect on the very inequivalent oxygen atoms of the non-parallel O-2 in the strong Al-surface field. It provides a source for abstraction, i.e. dissociative decay by emission of one oxygen atom. (C) 2001 Published by Elsevier Scienc e Ltd.