Radiative, collisional, and predissociative effects in CH laser-induced-fluorescence flame thermometry

Laser-induced fluorescence of the CH radical is used to determine the flame -front temperature of an 8-Torr premixed CH4/O-2 flame. The A (2)Delta-X (2 )Pi (0, 0) and B (2)Sigma(-) - X (2)Pi (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 rotation al-level-dependent transition probabilities are the main reason for this im provement. The weaker off-diagonal bands A-X (0, 1) and B-X(0, 1) yield tem peratures of 1930 +/- 90 and 1830 +/- 100 K, respectively. The influence of rotational transfer on the predissociated levels that have N' > 14 in B (2 )Sigma(-), v' = 0 was investigated with fluorescence scans and a statistica l power-gap law model of the relaxation; deviations up to 8% in temperature can occur because of this process. (C) 1999 Optical Society of America.