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Abstract
Oxide material obtained by Chemical Vapour Deposition is particularly well suited as a model substance for surface studies aiming at the correlation of structure and reactivity. There are two fundamentally different surface effects of UV excitation for MgO in an O2 atmosphere. Polychromatic UV light (λ > 200 nm) initiates two charge transfer processes, one ending up with O− and the other one with O3 −, both of which were identified by electron paramagnetic resonance spectroscopy (EPR). Another important issue of the present study is the fascinating system of parallel and consecutive surface reactions between the subsequent levels of surface states: anion vacancies (reacting with H− and H atoms as reducing agent), colour centres (bleached by N2O), O− species (splitting H2 homolytically and providing H atoms as reducing agent) for other anion vacancies. The discrimination of the products of parallel reactions on each level was possible on the basis of EPR experiments which also provided relevant data contributing to our present knowledge related to the structure-reactivity correlation. In the preliminary surface model developed in this paper the anion-cation divacancy plays a very prominent role. In the course of the characterization of surface colour centres, OH groups interacting with colour centre electrons turn out to be a powerful IR active probe. They react sensitively on physical and chemical changes in their immediate environment.