ADSORPTION OF OXYGEN ON CU(110)

This paper describes molecular beam measurements of the initial sticking coefficient for dissociative chemisorption of O2 on Cu(110). The sticking coefficient has been measured as a function of translational energy (E(i)), angle of incidence (theta(i)) and surface temperature (T(s)). Two sticking channels are identified, an activated, 'direct' dissociation at high E(i) and T(s) and a precursor-mediated trapping mechanism at low E(i) and T(s). The activated channel (E(i) > 50 meV, T(s) = 300 K) shows a sharp increase in S0 from 0.2 at 50 meV and saturates with S0 = 0.48 for energies above 100 meV. The initial sticking coefficient scales with the normal component of the translational energy and this channel is attributed to direct, translational activation via a barrier (almost-equal-to meV) located early in the surface O2 coordinate. Below 50 meV the sticking coefficient is independent of both translational energy and angle, and increases steadily as T(s) is reduced. The precursor state is tentatively identified as a weakly bound physisorbed state by analogy with the O2/Ag and Pt systems.