Measurement of CH and CN concentration in flames by laser-induced saturated fluorescence

Laser-excited molecular fluorescence measurements of CH and CN were made in atmospheric-pressure, acetylene flames. The fluorescence intensity dependence on laser intensity was observed to depart from linearity as laser spectral intensities increased, indicating near saturation. This occurred at laser spectral intensities of 10 5–10 6 W/cm 2 cm −1 for both CH and CN. These are the first observations of near saturated fluorescence from these important flame radicals. Radical species concentrations were determined from the fluorescence data. Absorption measurements were made to test the validity of the saturated fluorescence results. Absorption indicated a CH concentration of about 60 ppm in an oxyacetylene flame and approximately 150 ppm of CN in a nitrous oxide acetylene flame. The concentrations measured by absorption were larger by about a factor of 2 for CH and 5 for CN than the values determined by saturated fluorescence. Possible reasons for the discrepancies are discussed.