The composition, stability, and thermal evolution of nitric oxide on Rh(100) have been characterized by means of synchrotron radiation fast x-ray photoelectron spectroscopy and low-energy-electron diffraction. At 140 K, there is a single NO chemisorbed species (alpha(2)-NO) at saturation, forming a disordered phase which develops in an ordered p(4root2xroot2)R45degrees structure after heating the layer to 373 K. A further annealing induces desorption and a progressive dissociation of the NO molecules, which is completed above 425 K, where a c(2x2) phase consisting of coadsorbed N and O atoms is observed. At low NO coverage, a different NO molecular species (alpha(1)-NO), characterized by approximate to 1.7 eV lower N1s binding energy, is detected on Rh(100). alpha(1)-NO is observed to undergo dissociation under the photon beam. The N1s line shape modifications due to irradiation by 500 eV photons were monitored in real-time by using fast photoemission. The different stability of the alpha(1)-NO and alpha(2)-NO species is discussed.
