Catalytic decomposition of O2, NO, N2O and NO2 on a heated Ir filament to produce atomic oxygen

Production of O atoms was confirmed in the catalytic decomposition of O2, NO, N2O and NO2 on a heated Ir filament. No change in electric resistivity was observed when the filament was kept at 2350 K in the presence of 0.8 Pa of these species, showing that oxidation is not taking place under such conditions. The O-atom densities were evaluated by a vacuum-ultraviolet (vuv) laser-induced fluorescence technique at 130.2 nm as well as a vuv laser absorption technique, by which the absolute values can be evaluated. Arrhenius-type filament temperature dependences were observed for the O-atom densities in all systems. The activation energies for nitrogen oxides were similar, but that for O2 was smaller. The O-atom density was the highest when O2 was used as a source gas and the density could be increased up to 2 x 1012 cm-3. The O-atom density increased with the oxidant pressures, but showed saturation. The possible causes of such behaviours are discussed on the basis of the changes in the coverage conditions of the catalyst surfaces.