A reaction mechanism for oxygen plasmas

Abstract

Abstract This work presents a reaction mechanism for oxygen plasmas, i.e. a set of reactions and corresponding rate coefficients that are validated against benchmark experiments. The kinetic scheme is validated in a DC glow discharge for gas pressures of 0.2–10 Torr and currents of 10–40 mA, using the 0D LisbOn KInetics simulation tool and available experimental data. The comparison comprises not only the densities of the main species in the discharge— <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">X</mml:mi> </mml:mrow> <mml:mn>3</mml:mn> </mml:msup> <mml:msubsup> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">g</mml:mi> </mml:mrow> <mml:mo>−</mml:mo> </mml:msubsup> <mml:mo stretchy="false">)</mml:mo> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:msup> <mml:mi mathvariant="normal">a</mml:mi> <mml:mn>1</mml:mn> </mml:msup> </mml:mrow> <mml:msub> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">g</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:msup> <mml:mi mathvariant="normal">b</mml:mi> <mml:mn>1</mml:mn> </mml:msup> </mml:mrow> <mml:msub> <mml:mi mathvariant="normal">Σ</mml:mi> <mml:mrow> <mml:msup> <mml:mi mathvariant="normal">g</mml:mi> <mml:mo>+</mml:mo> </mml:msup> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">O</mml:mi> <mml:mrow> <mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mn>3</mml:mn> </mml:msup> </mml:mrow> <mml:mi mathvariant="normal">P</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> —but also the self-consistent calculation of the reduced electric field and the gas temperature. The main processes involved in the creation and destruction of these species are identified. Moreover, the results show that the oxygen atoms play a dominant role in gas heating, via recombination at the wall and quenching of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">X</mml:mi> </mml:mrow> <mml:mn>3</mml:mn> </mml:msup> <mml:msub> <mml:mi mathvariant="normal">Σ</mml:mi> <mml:mrow> <mml:msup> <mml:mi mathvariant="normal">g</mml:mi> <mml:mo>−</mml:mo> </mml:msup> <mml:mo>,</mml:mo> <mml:mi mathvariant="normal">v</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> vibrations and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> electronically-excited states. It is argued that the development and validation of kinetic schemes for plasma chemistry should adopt a paradigm based on the comparison against standard validation tests , as it is done in electron swarm validation of cross sections.

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