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. [ABSTRACT FROM AUTHOR]