Streamer-induced kinetics of excited states in pure N₂: I. Propagation velocity, E/N and vibrational distributions of N₂(C 3Πu ) and N 2+ (B 2Σu+ ) states

Abstract

Abstract The emission spectra of a streamer discharge in pure nitrogen provide an important tool for investigating the fundamental kinetics of excited electronic states of N 2 and benchmark data for validating advanced kinetic schemes for numerical models. In this work, we characterize a streamer monofilament developed in a dielectric barrier discharge configuration, including electrical characteristics, time-resolved images and N 2 /N <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi/> <mml:mn>2</mml:mn> <mml:mo>+</mml:mo> </mml:msubsup> </mml:math> emission spectra, all acquired with nanosecond temporal resolution. Time-resolved images and emission characteristics provide clear evidence of the formation of a cathode-directed streamer and allow determining the streamer propagation velocity and the typical <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>E</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>N</mml:mi> </mml:math> values using the intensity ratio of nitrogen spectral bands in the center of the discharge gap. We also measure the vibrational distributions of the N 2 (C <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi> </mml:mi> <mml:mn>3</mml:mn> </mml:msup> <mml:msub> <mml:mi mathvariant="normal">Π</mml:mi> <mml:mrow> <mml:mtext>u</mml:mtext> </mml:mrow> </mml:msub> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mo>=</mml:mo> </mml:math> 0–4) and N <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi> </mml:mi> <mml:mn>2</mml:mn> <mml:mo>+</mml:mo> </mml:msubsup> </mml:math> (B <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi> </mml:mi> <mml:mn>2</mml:mn> </mml:msup> <mml:msubsup> <mml:mi mathvariant="normal">Σ</mml:mi> <mml:mrow> <mml:mtext>u</mml:mtext> </mml:mrow> <mml:mo>+</mml:mo> </mml:msubsup> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mo>=</mml:mo> </mml:math> 0–2) states. The population of N 2 (C <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi> </mml:mi> <mml:mn>3</mml:mn> </mml:msup> <mml:msub> <mml:mi mathvariant="normal">Π</mml:mi> <mml:mrow> <mml:mtext>u</mml:mtext> </mml:mrow> </mml:msub> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mo>=</mml:mo> </mml:math> 0–4) state, initially formed by energetic electrons in the streamer head, changes later significantly due to the decrease in the mean energy and concentration of the streamer channel electrons. After a few tens of nanoseconds, the electron-impact excitation rate of N 2 (C <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mi> </mml:mi> <mml:mn>3</mml:mn> </mml:msup> <mml:msub> <mml:mi mathvariant="normal">Π</mml:mi> <mml:mrow> <mml:mtext>u</mml:mtext> </mml:mrow> </mml:msub> </mml:math> ) becomes negligible compared to its population by the N 2 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">A</mml:mi> </mml:mrow> </mml:mrow> <mml:mn>3</mml:mn> </mml:msup> <mml:msubsup> <mml:mi mathvariant="normal">Σ</mml:mi> <mml:mrow> <mml:mtext>u</mml:mtext> </mml:mrow> <mml:mo>+</mml:mo> </mml:msubsup> </mml:math> ) + N 2 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">A</mml:mi> </mml:mrow> </mml:mrow> <mml:mn>3</mml:mn> </mml:msup> <mml:msubsup> <mml:mi mathvariant="normal">Σ</mml:mi> <mml:mrow> <mml:mtext>u</mml:mtext> </mml:mrow> <mml:mo>+</mml:mo> </mml:msubsup> </mml:math> ) pooling. The experimental findings are supported and consistent with the 0D state-to-state kinetic mode

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