ABSOLUTE HCO CONCENTRATION MEASUREMENTS IN METHANE/AIR FLAME USING INTRACAVITY LASER SPECTROSCOPY

Intracavity laser absorption spectroscopy was used to measure the absorption spectra of a premixed, flat methane/air flame at a total pressure of 30 Torr. The spectra were measured in the spectral range of 16 000–16 300 cm−1. A flat flame burner was placed inside the cavity of a broadband dye laser pumped by a cw argon-ion laser. The spectrum of the laser output was measured by a high resolution spectrograph (with a spectral resolution of 0.003 nm). The spectrum of HCO radicals (A 2A′′←X 2A transition) was measured with a high signal-to-noise ratio at different positions above the burner, providing the first quantitative measurement of the absolute concentrations of the HCO radical in flames. The linewidths of the individual rotational lines in the spectrum can be closely fitted by the equation Γ=X+ZN2(N+1)2, where X=0.37±0.03 cm−1 and Z=(8±0.5)10−6. The rotational temperature of the HCO radicals was evaluated from the spectra, but the error and the data scatter are relatively high since the lines with a...