Conventional and dynamic actinometry of discharges of hydrocarbon–oxygen–argon mixtures

Abstract

Actinometric optical emission spectroscopy was used in the investigation of discharges of mixtures of C2H2, O2, and Ar to determine relative concentrations of the species CH, OH, H, CO, and O, which all increase with increasing proportions of oxygen in the plasma feed, Rox. The mean electron energy E and the mean electron density ρ were probed using Ar and He as actinometers. Additional measurements of the ratio of the intensities of the Hα to Hβ lines, I(Hα)/I(Hβ), showed that E was not strongly dependent on Rox. In contrast, ρ was found to fall with increasing Rox. A dynamic form of actinometry was also used to determine temporal trends in the relative concentrations of the above-mentioned species following cutting of either the O2 or C2H2 flows. On the basis of these data it is concluded that reactions involving oxygen play a major role in the production of the species CH, H, and CO. Plasma–polymer surface reactions contribute significantly to the production of the species H, CH, CO, and OH.