Plasma induced vibrational excitation of CH4-a window to its mode selective processing

TitlePlasma induced vibrational excitation of CH4-a window to its mode selective processing
Publication TypeJournal Article
Year of Publication2020
AuthorsT.D Butterworth, A.W van de Steeg, D.CM van den Bekerom, S A. da Silva, M.CM van de Sanden, G.J van Rooij
JournalPlasma Sources Science and Technology
Volume29
Issue9
Pagination095007
Abstract

Vibrational excitation of methane is believed to promote chemistry and improve product selectivity, compared to thermal conversion methods. We report on unique direct measurements of vibrational–rotational non-equilibrium in methane plasma. The non-equilibrium is sustained for 50 μs, after which the gas temperature equilibrates with the vibrational temperature at around 900 K. The plasma is generated by applying 200 μs, 30 Hz pulses of microwave radiation to methane at 25 mBar. We demonstrate that in microwave discharges, power transfer to vibrational modes of CH4 is the dominant power transfer mechanism, which leads to creation of a vibrational–translational (VT) non-equilibrium. VT relaxation is determined to be the dominant translational heating mechanism in the discharge. However, the high electron temperature at breakdown also leads to strong electronic excitation which may be responsible for some of the heating. Furthermore, we find that the CH4 vibrational levels are in equilibrium with each other due to fast intra-polyad relaxation (VV), and therefore bending vibrational modes population density is greatly in excess of stretching vibrational modes. The window of opportunity to exploit this non-equilibrium is limited by the VT relaxation timescale, which is approximately 50 μs in our experiment.

DOI10.1088/1361-6595/aba1c9
Division

MaSF

Department

PSFD

PID

3131d4bbcd428dee6c906bec2737ad9e

Alternate TitlePlasma Sources Sci. Technol.

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