Oxygen adsorption on surfaces studied by a spin- and alignment-controlled O2 beam

Molecular oxygen (O₂) is a paramagnetic linear molecule, yet the effect of its molecular alignment and electron spin on the dynamics of O₂ adsorption has remained unclear. Recently, it has been however shown that the use of magnetic hexapolar field allows us to prepare a single spin-rotational state [($J\text{,}M$) = (2, 2)] selected O₂ beam for which both the molecular alignment and the spin state of O₂ are well defined. State-resolved studies of O₂ sticking on Si(1 0 0), Al(1 1 1), Ni(1 1 1) surfaces conducted with this beam have clarified that the O₂ sticking probability depends strongly on the molecular alignment and the spin orientation of O₂ relative to the surface. The mechanism of O₂ adsorption on Al(1 1 1) has been disputed in the past few decades, but the observed steric effect has provided a reasonable picture for it. The preparation method of the state-selected O₂ beam and its application to the alignment- and spin-resolved O₂ sticking studies are reviewed.