Low energy electron diffraction determination of the surface structures formed by the carbon monoxide chemisorption on the nickel(110) surface

Low Energy Electron Diffraction is used to determine the different structures formed by the CO adsorption on the Ni(110) surface at two coverages. At full coverage the superlattice is Ni(110)-(2 x 1)2CO. For this superlattice, the CO molecules adsorb at the short bridge sites with a 20 degrees common tilt in the +-[001] directions. The Ni-C and the C-O bond lengths are 1.85 A and 1.15 A, respectively. In the Ni(110)-c(2 x 4)3CO superlattice structure, which is formed at an intermediate coverage, the CO molecules adsorb at the top sites with two types of configurations on alternate (110) rows. Half the rows are filled with CO molecules having a 9 degrees zig-zag common tilt in the $\pm$ (001) directions, and half the rows are half filled with untilted CO molecules. The Ni-C and the C-O bond lengths are 1.67 A and 1.15 A, respectively. The possible role of hydrogen in the formation of the surface structure is discussed.