Mode resolved heating dynamics in pulsed microwave CO2 plasma from laser Raman scattering

D.C.M. van den Bekerom, A. van de Steeg, M.C.M. van de Sanden, G.J. van Rooij (Corresponding author)

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Efficient CO2 reduction is predicted for CO2 microwave plasma by virtue of predominant excitation of the asymmetric stretch vibration. Although interpretation of ongoing research is generally based on this mechanism, direct measurement of the power partitioning to support the assumed preferential vibrational excitation in CO2 microwave plasma is currently lacking. Here, such measurements are performed on a 100 μs pulsed microwave CO2 discharge. The <1% duty cycle ensures low gas temperature conditions at the discharge onset. Raman and Rayleigh scattering are employed to reveal vibrational, rotational, and gas temperatures in a spatially and temporally resolved manner. A novelty in the approach is that asymmetric stretch excitation is determined from the bending - symmetric stretch Raman spectrum. During the first 40 μs a significant inter-vibrational non-equilibrium is observed with the symmetric stretch and bending temperature reaching 750 K and the asymmetric stretch temperature reaching 1150 K. A maximum rotational-vibrational non-equilibrium occurs after 60 μs when the rotational temperature is half of the 1150 K vibrational temperature. Rotational and translational modes are measured to be in equilibrium at all times. The power partitioning is analyzed to estimate the power consumed by vibrational excitation, which is used to estimate the reduced electric field in the discharge. This work confirms strong vibrational excitation in CO2 microwave plasma albeit less predominant than often assumed.

Original languageEnglish
Article number054002
Number of pages11
JournalJournal of Physics D: Applied Physics
Issue number5
Publication statusPublished - 30 Jan 2020


  • CO2 reuse
  • microsecond pulsing
  • microwave plasma
  • Raman scattering
  • vibrational excitation


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