Experiments reveal that NO molecules react with atomic O on the Au(111) surface at low temperature to form NO2. We studied this process using a density functional method and periodic slab models. Structures and energies of all low-coverage adsorption complexes have been determined. Very small calculated adsorption energy of NO on regular Au(111) surface, -20 U mol-', implies that the NO adsorption detected on Au(111) at -175 K takes place on defects. (NO + 0)/Au(111) species form NO2/Au(111) without an activation barrier, releasing 170 kJ mol(-1). No qualitative difference between the reactivity of two- and four-layer Au(111) films is found. (c) 2006 Elsevier B.V. All rights reserved.