The structure of methanol and methoxy on Cu(1 1 1)

The local registry of methoxy and methanol adsorbed on Cu(1 1 1) has been studied using normal incidence X-ray standing wavefield absorption (NIXSW). Methanol adsorbs to the surface with its oxygen atom directly above a Cu atom, with a Cu–O separation of 2.69 ± 0.19 Å. This distance is only slightly shorter than that expected for a purely van der Waals interaction (2.96 Å), which indicates that the molecule is only weakly chemisorbed to the surface. In contrast to methanol, methoxy is strongly chemisorbed on Cu(1 1 1). The NIXSW data can be modelled assuming methoxy adopts threefold hollow adsorption sites, in agreement with other studies. The NIXSW data is consistent with methoxy populating both FCC and HCP hollow sites, this contradicts previous work which suggests that the species only occupies FCC type hollows. The results of our studies have been compared with previous theoretical predictions for the structure of methanol and methoxy on Cu(1 1 1), and differences between experiment and theory have been highlighted.