Dissociative sticking ofO2on Al(111)

The dissociative sticking probability, ${\mathrm{S}}_0$, of ${\mathrm{O}}_2$ on Al(111) has been measured as a function of incident translational and vibrational energy. ${\mathrm{S}}_0$ rises from ≈${10}^{\mathrm{-}2}$ for energies ≈30 meV to near unity in the range 0.6–2.0 eV, demonstrating an activated dissociation event. Vibrational excitation enhances the sticking. Surface temperature has no effect on ${\mathrm{S}}_0$. A peculiar dependence on polar angle is observed. The results are used to discuss possible mechanisms for the recent observation [H. Brune et al. Phys. Rev. Lett. 68, 624 (1992)] of widely separated O atoms after ${\mathrm{O}}_2$ dissociation on Al(111).