Optical emission characteristics of glow discharges in Ar-O2 and He-O2 gas mixtures

We have investigated optical emissions from low-pressure DC glow discharges in Ar-O-2 and He-O-2 gas mixtures in the 300 to 850 nm spectral range. The ionic species present in these discharges reveal interesting energy transfer pathways between different constituents of the gas mixtures. In the case of Ar-O-2 mixture, we observed the presence of highly excited Ar and O atoms as well as Ar+, Ar-2(+) and O-2(+) ions. Apparently, charge-exchange collisions between Ar-2(+) and O-2 yield O-2(+) ions. The path ways of energy transfer are different for He-O-2 gas mixture where O-2(+) ions are formed directly through collisions with excited He atoms. The O-2(+) ions subsequently capture free electrons and dissociate into excited O atoms.