Mechanism and speed of initial step of oxygen chemisorption-O2 on W

A direct first step in the mechanism for the initial oxidation of a polycrystalline tungsten surface, the catalyzed dissociation of O₂ on it, or the formation of WO _X by O₂ at intermediate temperatures is shown to occur in ∼10⁻¹³ s. Molecular beam experiments demonstrated that the reactivity was greater than 90%, the unreacted O₂ was substantially unaccommodated in translational energy to the surface temperature, and the reaction probability was nearly independent of surface temperature from 2800 to 415 K although there was a small increase at 415 K. The general conditions when no molecular surface precursor state contributes to the surface reactivity are discussed.