The adsorption of nitric oxide on Cu(100) has been investigated by high resolution X-ray photoelectron spectroscopy; at 85 K a number of distinct molecular processes have been recognised including dissociation, oxygen chemisorption, and the catalytic formation of nitrous oxide, which desorbs at 110 K leaving at 295 K only chemisorbed oxygen which exhibits a [graphic omitted] R 45° low energy electron diffraction pattern.