Kinetics and diagnostics of DC and modulated cold plasmas of air. Investigation of Neutral and Ion Chemistry

摘要

The DC and square wave modulated air plasmas generated in two hollow cathode discharge reactors of very different sizes, at a range of pressures extended between 0.003 and 0.6 mbar, are experimentally studied by quadrupole mass spectrometry for the detection of neutrals and charged species and by a double Langmuir probe. Visible emissions of electronically excited atoms are recorded by means of a grating spectrometer. A model based on a reduced set of kinetic equations, which considers homogeneous and heterogeneous reactions and takes into account electrons, neutrals and ions is developed and compared with the experimental data. It is consistent with energy balance and predicts that heterogeneous processes are the main source of the nitrogen oxides NO and N_2O, and that the contribution of ions to the global chemistry of neutrals is of minor significance, even for the lowest pressures.