Disturbance of laser-induced-fluorescence measurements of NO in methane-air flames containing chlorinated species by photochemical effects induced by 225-nm-laser excitation

Laser-induced fluorescence measurements of NO in CH4 air flames seeded with CH3Cl and CH2Cl2 are described. The measurements are perturbed by strong photochemical effects characterized by UV emissions. The contribution of these background emissions is taken into account on the basis of an on-line-off-line resonance procedure. First results indicate an important increase of NO in the presence of chlorinated species. Background emissions observed in the range 220-260 nm and at 278 nm are ascribed, respectively, to electronically excited HCl and CCl photofragments. It is shown that C2H3Cl and CHCl2, species are responsible for the formation of HCl and CCl, respectively, and a photolytic mechanism for formation of the photofragments is proposed. (C) 1998 Optical Society of America.