In-situ analysis of methane plasmas with mid-infrared supercontinuum-based Fourier-transform spectroscopy

The conversion of methane (CH4) into the hydrocarbons ethane (C2H6) and acetylene (C2H2) in plasma is investigated in the first in-situ study using a mid-infrared supercontinuum source and a Fourier transform spectrometer. Due to the spatial coherence of the supercontinuum source, it is possible to probe the plasma over a path length of 3.5 m and observe CH4, C2H6, and C2H2 with concentrations below percent level at a few mbar pressure. The broad spectral range of the supercontinuum source (1.4–4.1 μm) covers entire rovibrational bands of molecules, allowing simultaneous detection of the rotational and vibrational temperature of CH4 and C2H2. The ability to study these experimental parameters in situ opens new possibilities for understanding and optimizing plasma-based chemical conversions.