We report results of our studies on the dissociative adsorption of hydrogen on An thin films grown epitaxially on Ir{111} surface, using nuclear reaction analysis. We found that H-2 dissociatively adsorbs on these Au {111} films. This feature can be contrasted to the well-known noble bulk Au surfaces, which do not dissociate hydrogen molecules. We attribute this to the local surface properties, e.g., electron localization (the narrowing of the s-band, the s-band center model), which can explain the unexpected high reactivity of a thin An {111} film. (c) 2004 Elsevier B.V. All rights reserved.