TENSOR LEED ANALYSIS OF THE NI(111)-P(2X2)-CH3CN STRUCTURE

The adsorption of acetonitrile on Ni(111) leads to an ordered (2 x 2) overlayer. In the first detailed surface structure determination of or ganic molecules containing both C and N, LEED intensity versus energy (I-V) curves for this structure have been measured and analyzed using an automated search method based on the tensor LEED approximation. The adsorbed acetonitrile is bound to the surface by both carbon and nitr ogen with its C-N axis almost parallel to the metal surface. The adsor bed acetonitrile rehybridizes on the surface, becoming non-linear with a C-C-N angle estimated at 123-degrees. This structure is in accordan ce with models which were proposed from HREELS and XPS studies for ace tonitrile adsorbed on platinum and nickel surfaces. It is also somewha t similar to the structure of nitriles in tri-iron and tri-osmium clus ters. A slight adsorbate induced relaxation of the surface nickel atom s is also observed.