Abstract

Conventional mechanical Fourier Transform Spectrometers (FTS) can 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 (0.18 nm at a wavelength of 3333 nm), a temporal resolution of 20 μs, a total wavelength coverage over 300 cm−1 and a total measurement time of ~70 s. 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 the fast dynamics of chemical reactions over a broad wavelength range, which can be interesting for chemical kinetic research, particularly for the combustion and plasma analysis community.

Highlights

  • The conversion of ethane and methane to other hydrocarbons in plasmas has been extensively studied, both theoretically and experimentally

  • The water spectrum is modeled for an interaction length of 275 cm at atmospheric pressure; i.e., the distance from the output of the optical parametric oscillation (OPO) cavity till the photodetector (PD1 )

  • The modeled spectra are calculated from the HITRAN 2016 database [59], using a Voigt profile and convolving a Blackman instrument line-shape function corresponding to the applied apodization function to the interferogram (Equation (6))

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Summary

Introduction

The conversion of ethane and methane to other hydrocarbons in plasmas has been extensively studied, both theoretically and experimentally. Different non-thermal plasma techniques, such as direct current (DC), MW or RF discharge, dielectric barrier discharge (DBD), and corona or spark discharge, have been demonstrated for this purpose under various conditions [1,2,3,4,5,6,7,8]. The aim of these studies is to develop an efficient process, for converting small hydrocarbons, such as methane, to other valuable hydrocarbons. The main advantage of optical-based detection is their fast response time, in-situ measurement, and species specificity

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