A single spin-rotational state-selected [(J, M)＝(2, 2)] O₂ beam allows us to investigate how the molecular alignment and electron spin affect oxygen chemisorption. Recent experiments of O₂ chemisorption on magnetized Ni(111) have indicated that O₂ sticking probability is higher when its spin is oriented anti-parallel to the majority spin direction of the Ni substrate. The spin dependence becomes more significant at lower translational energy, and amounts to over 40% at thermal energy. This clear spin effect suggests that incident O₂ molecules keep high spin polarizations even at the position of the dissociation barrier. In this article, the observed spin effect is reviewed after introducing the spinrotational state of O₂ (³Σ_g^-).