Chemisorption of aligned O₂ on Ag(110)

A fully alignment-resolved O₂ chemisorption experiment on Ag(110) conducted with a single rotational state selected O₂ beam is presented. Initial sticking probabilities (S₀) of O₂ impinging with its axis aligned along the [11¯0], [001], and [110] directions of the surface have been derived. The results indicate that, in the case of normal incidence, O₂ molecules perpendicular to the [11¯0] azimuth are more reactive than those parallel to it at translational energies (E₀) <0.3 eV while the alignment preference reverses at higher E₀. The S₀(E₀) curve measured at off-normal incidence does not scale with normal translational energy in case that O₂ impinges along the [001] azimuth with its axis parallel to the [11¯0] direction. These observations have been discussed based on the alignment dependence of the chemisorption barrier and the surface corrugation felt by O₂.