Surface-Catlyzed Formation of Electronically Excited Nitrogen Dioxide and Oxygen

Article abstract of DOI:10.1021/j100275a023

The surface-catalyzed recombination of NO and O atoms to produce excited NO2 molecules has been studied.By using the reaction of N atoms with NO (N+NO-> N2+O), the O atoms were produced in the absence of molecular oxygen.The resultant orange glow attributed to the electronically excited NO2 molecule was observed directly over a nickel metal catalyst in a flow system operated in the 20 mtorr range.Measurements of the attenuation of the intensity as a function of distance from the catalyst yielded an observed effective lifetime of approximately 79 μs, which is in the range of radiative lifetimes of NO2*.Using molecular oxygen partially dssociated to O atoms in a discharge and reacting with NO produced an orange glow directly over the nickel catalyst.The observed effective lifetime was 960 μs and this much longer lifetime is attributed to a precursor of an excited oxygen molecule.It is concluded that more than one reaction mechanism is needed to account for emissions of the orange glow of NO2*.The Herzberg emission from O2(A³Σ_u⁺) state was observed as a function of distance from the catalyst surface.With increasing O-atom concentration the observed effective lifetime appears to increase.However, since the O2(A³Σ_u⁺) state is known to be quenched strongly by O atoms the mechanism for emission must include another excited state as a precursor.When the reaction of NO with N atoms was used to produce O atoms at the equivalence point, i. e. with no excess NO and N atoms, no Herzberg emission was observed.