O-Atom Yields from Microwave Discharges in N2O/Ar Mixtures

Article abstract of DOI:10.1021/j100274a024

We have studied the products of Ar/N2O microwave discharges to determine their fitness as sources of atomic oxygen in discharge-flow reactors.For N2O feed rates below 10 to 20 μmol s^-1, the discharge converts about 75percent of the N2O to atomic oxygen and, in addition, prduces small quantities of atomic nitrogen, generally less than 10percent of the O-atom product.At higher N2O feed rates the O-atom production efficiency decreases, and some nitric oxide accompanies the O atoms out of the discharge.At intermediate N2O feed rates, only atomic oxygen is observed, and neither N nor NO leaves the discharge.The exact point at which this occurs is a function of the discharge power and the Ar/N2O mixing ratio.Adding molecular nitrogen to the discharge eliminates any NO product, but at the penalty of a slightly reduced O-atom production efficiency.Atomic oxygen flows in excess of 20 μmol s^-1 are produced at pressures near 1 torr and dicharge powers of only 30 W.In kinetic modeling of the discharge chemistry, we can account for the experimental observations only if the electron-impact dissociation of the N2O in the discharge proceeds through a spin-forbidden channel to produce O(3P).In addition, the model indicates that about 10-20percent of the N2O dissociations resuts from collisions between metastable argon atoms in the discharge and N2O.