New detection scheme for highly reactive methyl radicals demonstrated

Methyl radicals (CH₃), which are highly reactive and therefore difficult to quantify, nevertheless play a central role in discharges involving hydrocarbons. In collaboration with Nelson de Oliveira from the SOLEIL synchrotron, the gas-plasma conversion team at LPP, led by Olivier Guaitella, has shown that CH₃ can be measured with enhanced sensitivity using vacuum ultraviolet absorption spectroscopy around 150 nm. Synchrotron radiation generated at this wavelength passes through a cold plasma fed with methane and oxygen, and the absorption of part of this light by CH₃ radicals makes it possible to determine their density. Remarkably, the addition of oxygen does not simply lead to a monotonic decrease in this density due to oxidation, but instead produces a maximum, revealing a non-monotonic behavior.

For more information: In-situ quantitative measurements of methyl radicals in oxygen-containing reactive environments by VUV absorption spectroscopy using synchrotron radiation https://doi.org/10.1016/j.cplett.2025.142388