Following the changes in local geometry associated with a surface reaction: the dehydrogenation of adsorbed ethylene

Abstract
Using scanned-energy-mode photoelectron diffraction we have determined the local adsorption geometry of the reactant and product molecules in a model heterogeneous reaction on a Ni(111) surface in which ethylene (C2H4) is dehydrogenated to acetylene (C2H2). Although the C-C axis remains essentially parallel to the surface, a change in adsorption site occurs, indicating that for the case of a concerted reaction mechanism only two distinct pathways are possible. Precise structural information on a model system of this kind has hitherto been unavailable.