Flame Temperature Measurement by Redistribution of Rotational Population in Laser-Excited Fluorescence: An Application to the OH Radical in a Methane-Air Flame

Expressions for the rotationally relaxed population densities, under steady state laser excitation, have been derived with particular concern to the temperature measurement in flames. Agreement has been found between the developed theory and the measured rotational distribution. The experiments were carried out with both a flash lamp dye laser (long pulses) and a nitrogen laser-pumped dye laser (short pulses). The two distributions were found identical, showing that fast collisional rate constants are involved in the relaxation of the OH radical in a methane-air flame. The thermally assisted fluorescence technique has been proved to give reliable results in combustion diagnostics.