Role of Steps and of Terrace Width in Gas-Surface Interaction: $O_2/\mathrm{Ag}\left(410\right)$

We demonstrate by vibrational spectroscopy that open steps are the active site for ${\mathrm{O}}_2$ dissociation on Ag(410), and that the barrier to adsorption at defects can be measured by energy and angle resolved investigation of the dynamics of the gas-surface interaction. We identify a molecular adsorption channel with considerably reduced activation barrier and a nonactivated dissociative pathway. The ${\mathrm{O}}_2$ sticking probability is increased at steps and strongly reduced at terraces with respect to Ag(100), implying that reactivity is influenced by terrace width.