Oxidation of NO Into NO₂ by Surface Adsorbed O Atoms

Plasma‐surface interactions are increasingly recognised as a key factor in explaining molecule production and conversion processes. In order to scrutinise such effects well‐defined surface and gas phase conditions are required. Hence, the inner surface of a Pyrex tube was treated by a capacitively coupled RF plasma at low pressure. The post‐plasma oxidation of gas mixtures containing 1 % NO into NO 2 has been studied by means of quantum cascade laser absorption spectroscopy in the mid‐infrared spectral range. The plasma pre‐treatment experiments with oxygen containing precursors suggest O atom adsorption on the Pyrex tube with a surface density of 2.7 x 10 14 cm –2 . A simple kinetic model was developed and shows good agreement with the measured NO and NO 2 gas phase concentrations. In the model a fraction of the surface is considered to be covered with chemisorption sites where atoms and molecules can be adsorbed, whereas they can be removed only by recombination (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)