Investigation of CO Adsorption on an Oxygen-Precovered Cu(111) Surface Using Infrared Spectroscopy.

The adsorption of CO on oxygen-precovered Cu(111) surfaces exhibits distinct structural and spectroscopic behaviors depending on the oxygen distribution. Using reflection absorption infrared spectroscopy (RAIRS), we systematically investigate CO overlayer formation on O/Cu(111). We observe that the kinetic energy of dosed oxygen influences the CO RAIRS spectra. When dosing oxygen from the background (kinetic energy ∼ 38.5 meV), we observe from the RAIRS bands for atop (2075 cm-1) and bridge-site (1835 and 1814 cm-1) adsorption, the formation of all known high-coverage CO structures on Cu(111) 3 × 3 , (1.5 × 1.5), and (1.4 × 1.4)as indicated from their comparison to the low-energy electron diffraction patterns obtained in our earlier work (Zhang et al., J. Phys. Chem. C 2025, 129, 3493). In contrast, oxygen deposition via a supersonic molecular beam (kinetic energy ∼ 396 meV) suppresses the adsorption of CO on bridge sites, indicating that the (1.4 × 1.4) phase, which needs a 7 × 7 Cu(111) substrate unit, cannot be formed. When annealing this surface to 473 K, CO adsorption on bridge sites is restored. We tentatively assign these observations to oxygen aggregation resulting in clean Cu(111) patches that are large enough to accommodate the (1.4 × 1.4) phase. Summarizing, we are observing various local CO adsorption fingerprints in the RAIRS spectra that are consistent with different oxygen distributions on the Cu(111) surface.