Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Broadband Time-Resolved Absorption and Dispersion Spectroscopy of Methane and Ethane in A Plasma Using a Mid-Infrared Dual-Comb Spectrometer

Version 1 : Received: 16 September 2020 / Approved: 17 September 2020 / Online: 17 September 2020 (11:03:42 CEST)

How to cite: Abbas, M.A.; Dijk, L.V.; Jahromi, K.E.; Nematollahi, M.; Harren, F.J.; Khodabakhsh, A. Broadband Time-Resolved Absorption and Dispersion Spectroscopy of Methane and Ethane in A Plasma Using a Mid-Infrared Dual-Comb Spectrometer. Preprints 2020, 2020090397 (doi: 10.20944/preprints202009.0397.v1). Abbas, M.A.; Dijk, L.V.; Jahromi, K.E.; Nematollahi, M.; Harren, F.J.; Khodabakhsh, A. Broadband Time-Resolved Absorption and Dispersion Spectroscopy of Methane and Ethane in A Plasma Using a Mid-Infrared Dual-Comb Spectrometer. Preprints 2020, 2020090397 (doi: 10.20944/preprints202009.0397.v1).

Abstract

Conventional mechanical Fourier Transform Spectrometers (FTS) are able to simultaneously measure absorption and dispersion spectra of gas-phase samples. However, they usually need very long measurement times to achieve time-resolved spectra with a good spectral and temporal resolution. Here, we present a mid-infrared dual-comb-based FTS in an asymmetric configuration, providing broadband absorption and dispersion spectra with a spectral resolution of 5 GHz, a temporal resolution of 20 μs, and a total measurement time of a few minutes. We used the dual-comb spectrometer to monitor the reaction dynamics of methane and ethane in an electrical plasma discharge. We observed ethane/methane formation as a recombination reaction of hydrocarbon radicals in the discharge in various static and dynamic conditions. The results demonstrate a new analytical approach for measuring fast molecular absorption and dispersion changes and monitoring fast dynamics of chemical reactions, which can be interesting for chemical kinetic research and particularly for the combustion and plasma analysis community.

Subject Areas

dual frequency comb spectroscopy; mid-infrared absorption and dispersion spectroscopy; electrical discharge plasma; time-resolved plasma kinetics

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