LASER ABSORPTION SPECTROSCOPY OF HYDROCARBON FLAMES

Abstract

Intracavity Laser Absorption Spectroscopy (ICLAS) and Cavity Ring-Down Spectroscopy (CRDS) were used to detect absorption spectra of $CH(C^{2}\Sigma^{-}\leftarrow X^{2}\Pi)$ at 314 nm, $^{1}CH_{2} (\bar{b}^{1}B_{1}\leftarrow \tilde{a}^{1}A_{1})$ at $590$ and $620 nm, NH (A^{3}\Pi,\leftarrow X^{3}\Sigma^{-})$ at $336 nm$, and $NH_{2} (\bar{A}^{2}A_{1}\leftarrow \bar{X}^{2}B_{1})$ at $598 nm$ in a low-pressure (30 Torr) stoichiometric methane/oxygen/nitrogen flat flame doped with a small amount of nitrous oxide. The CH and NH radicals were monitored by CRDS whereas $^{1}CH_{2}$ and $NH_{2}$ were monitored by ICLAS. The absolute concentration profiles of those radicals were measured. The radical absorption spectra were recorded with good signal-to-noise ratio. The spectra of the $^{1}CH_{2}$ radical were measured in different spectral ranges that allowed us better determination of its absorption cross section. For the first time the absolute concentrations of NH and $NH_{2}$ were measured in the flames of this kind. The agreement between experimental results and model predictions based on the GRI-Mech 2.11 mechanism is discussed.