Intracavity laser absorption spectroscopy detection of singlet CH2 radicals in hydrocarbon flames

The spectrum of methylene, the CH2 radical, in the singlet electronic state was detected with a high signal/noise ratio in methane-oxygen-nitrogen flames using intracavity laser absorption spectroscopy. The spectra were recorded at different pressures including first measurements at atmospheric pressure. The maximum concentration of the singlet CH2 radical in a 30 Torr flat flame was estimated based on literature data from laser photolysis experiments done at room temperature. The value of 2 × 1013 cm−3 seems to be higher than that predicted by the model calculations. The dependence of the calculated maximum concentration of singlet CH2 on the equivalence ratio is in qualitative agreement with measured values.