THE ORIENTATION OF FORMATE AND CARBONATE ON ZNO[10(1)OVER-BAR0]

Polarisation dependent CK-edge NEXAFS spectra of carbonate and formate species on ZnO(1010BAR) indicate that both species are aligned by the substrate. The carbonate species, formed by adsorption of CO2, is oriented with its molecular plane close to the [0001] azimuth. This suggests a bond geometry in which one O atom of CO32- is in the substrate, and a second interacts with a surface cation, consistent with the results of previous cluster calculations. In contrast, the formate species, formed by adsorption of formic acid, is not azimuthally ordered, although the molecular rotation axis is aligned close to the surface normal, consistent with bidentate bonding to a single cation.