Abstract
A single spin-rotational state-selected [(J,M)=(2,2)] O2 beam developed recently allows us to define the alignment of an O2 molecule with respect to the defining magnetic field. A fully alignment-resolved O2 sticking experiment on a single domain Si(100) has provided the first experimental evidence that the reactivity of O2 depends on both the polar and azimuthal angles of the molecular axis relative to a surface. The analysis of the observed steric effects has clarified the followings. (1) Side-on collision is much more favorable than end-on collision for O2 dissociation on Si(100). (2) In case of side-on collision, an O2 molecule perpendicular to the dimer on Si(100) is about 40% more reactive than that parallel to the dimer. No steric effect was observed for the precursor-mediated process. O2 dissociation on the double-layer step was found to proceed nearly barrierlessly.
