| Abstract
| - The neutral and charged species present in a direct current (dc) hollow cathode, gas flow, air reactor areexperimentally studied by quadrupole mass spectrometry. The degree of ionization of the plasma and theelectron mean temperature with decreasing air pressure, for constant discharge current, are measured with adouble Langmuir probe. The chemical composition of the plasma changes appreciably over the 3 × 10-3 to5 × 10-2 mbar range investigated: at the lowest pressures studied, O2 dissociation is up to 60% and theconcentration of NO is half that of N2; concerning ions, NO+ and N2+ are dominant for the whole pressurerange. A kinetic model of the plasma including electrons, neutrals, and positive ions is developed to accountfor the experimental observations; it is consistent with energy balance and predicts that heterogeneous processesare the main source of NO and that the contribution of ions to the global chemistry of neutrals is of minorsignificance even for the lowest pressures.
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