Structure Determination of an Alkali Metal–CO Coadsorption Phase: Ni(111)-K $/$CO

The structure of a Ni(111)- $(2\times 2)$–K $/n$CO $\left(n\approx 2\right)$ coadsorption phase has been determined using K $2p$, C $1s$, and O $1s$ scanned energy mode photoelectron diffraction, and compared with results from pure CO and K adsorption phases having similar coverages. Coadsorbed K has little influence on the local hollow site geometry of the adsorbed CO molecules; the K remains in the atop site of the pure K layer, but the K-Ni bond length increases substantially (by $0.15\pm 0.05$ Å), as does the Ni-Ni outer layer spacing. The results conflict with aspects of current interpretations of spectroscopic data from such systems.