Initiation of Vacancy-Mediated, Surface Explosion Reactions:Tartaric and Aspartic Acid on Cu Surfaces

Surface explosion reactions have highly non-linear reaction kinetics that exhibit auto-acceleration under isothermal conditions. These can lead to phenomena such as oscillatory reaction rates and on chiral surfaces to extremely enantiospecific reactions of chiral adsorbates. Tartaric acid (TA) decomposes on Cu surfaces by an explosion mechanism that is propagated by vacancies, empty adsorption sites that self-replicate autocatalytically during TA decomposition. Surface explosion kinetics result from chain-branching steps in which one vacancy decomposes an adsorbate to yield two new vacancies. In the absence of vacancies, surface explosions cannot occur; they require some initiation step that creates vacancies. By comparison with the chain-branching explosion step, little is known about the processes that initiate or nucleate surface explosion reactions. Time-resolved XPS measurements during the early stages of explosion initiation of TA/Cu(hkl) reveal a process that involves direct TA loss from the surfac...