Absolute CH concentration measurements by cavity ring-down spectroscopy in an atmospheric diffusion flame

Absolute concentrations of CH radical are reported for the first time in an atmospheric diffusion flame. Measurements are performed by cavity ring-down (CRD) spectroscopy by probing the C–X system of CH around 315 nm. We used standard 308 nm coated mirrors also suitable for OH CRD measurements. Absolute concentrations are obtained from integrated absorption measurements after a deconvolution procedure. Peak mole fractions are found to be around 0.6 ppm in satisfying agreement with previously reported predictions issued from flame modelling. The ability of CRD technique to describe very narrow species profiles is demonstrated by comparison with laser-induced fluorescence measurements.