The air afterglow and its use in the study of some reactions of atomic oxygen

The air afterglow has been studied in a flow system by mixing the products of a microwave discharge in oxygen with NO or mixtures of gases and by measuring the intensity of the glow immediately past the point of mixing and farther downstream in a long glass tube at known pressure, composition, and linear velocity of flow. The intensity of the greenish yellow chemiluminescence is shown to be proportional to the concentrations of atomic oxygen and nitric oxide, and independent of the nature or amount of added inert gases. An average quantum (5500 angstrom) is emitted for every 10$^{7}$ collisions of O with NO. The concentration of atomic oxygen is determined by a 'titration' with NO$_{2}$ in which the end-point is indicated by complete extinction of the glow all along the tube, and which is made possible by the great speed of the reaction O + NO$_{2}\rightarrow $ O$_{2}$ + NO. (1) Observation of the spatial decay of the glow under steady-state conditions is well suited to the study of reactions of atomic oxygen. The concentration of NO remains constant along the tube because reaction (1) quickly regenerates NO from NO$_{2}$, and the light intensity directly measures the concentration of atomic oxygen. The method is applied to give information on the rates of the reactions O + NO + M $\rightarrow $ NO$_{2}$ + M, O + O$_{2}$ + M $\rightarrow $ O$_{3}$ + M, O + SO$_{2}$ + M $\rightarrow $ SO$_{3}$ + M, etc. Some results are also presented for the effect on the disappearance of O of the following added gases: N$_{2}$, A, CO$_{2}$, H$_{2}$, CO, N$_{2}$O, C$_{6}$H$_{6}$, SO$_{3}$, Fe(CO)$_{5}$, H$_{2}$O, O$_{3}$, C$_{2}$H$_{4}$, Cl$_{2}$ and Br$_{2}$. The rapid catalytic recombination of O by added Cl$_{2}$ is discussed in some detail.