Quantitative determination of the local adsorption structure of carbonate on Ag(110)

The local geometry of carbonate (CO3) on Ag(1 1 0), formed by the reaction of CO2 with preadsorbed oxygen, has been investigated using C Is scanned-energy mode photoelectron diffraction. The carbonate species is essentially planar and adsorbs almost parallel to the surface in an off-atop site relative to an outermost layer Ag atom, at a C-Ag layer spacing of 2.64 +/- 0.09 Angstrom, with a well-defined azimuthal orientation. This geometry is best understood in terms of the added-row model proposed by Guo and Madix in which additional Ag atoms lie adjacent to the carbonate, such that bonding can occur through at least one of the oxygen atoms. The distance between this oxygen and its nearest neighbour Ag adatom is 1.90 +/- 0.42 Angstrom. The C-O distances are in the range 1.26-1.30 Angstrom. While the symmetry of the carbonate in the optimum structure is reduced, the D-3h symmetry of the isolated species lies within the limits of Precision