Laser-induced fluorescence of the CH radical is used to determine the flame-front temperature of an 8-Torr premixed CH<sub>4</sub>/O<sub>2</sub> flame. The <i>A</i><sup>2</sup>Δ–<i>X</i><sup>2</sup>Π (0, 0) and <i>B</i><sup>2</sup>Σ<sup>−</sup> − <i>X</i><sup>2</sup>Π (0, 0) bands give values of 1960 ∓ 60 and 1920 ∓ 70 K, respectively. This is an improvement over a previous study that found discrepancies up to 20% between these bands. New rotational-level-dependent transition probabilities are the main reason for this improvement. The weaker off-diagonal bands <i>A</i>–<i>X</i> (0, 1) and <i>B</i>–<i>X</i> (0, 1) yield temperatures of 1930 ∓ 90 and 1830 ∓ 100 K, respectively. The influence of rotational transfer on the predissociated levels that have <i>N</i>′ > in <i>B</i><sup>2</sup>Σ<sup>−</sup>, <i>v</i>′ = 0 was investigated with fluorescence scans and a statistical power-gap law model of the relaxation; deviations up to 8% in temperature can occur because of this process.
© 1999 Optical Society of America
Jorge Luque and David R. Crosley, "Radiative, Collisional, and Predissociative Effects in CH Laser-Induced-Fluorescence Flame Thermometry," Appl. Opt. 38, 1423-1433 (1999)