Knowledge Bank

Intracavity Laser Absorption Spectroscopy (ICLAS) and Cavity Ring-Down Spectroscopy (CRDS) were used to detect absorption spectra of $CH(C2\Sigma -\leftarrow X2\Pi )$ at 314 nm, $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}CH2(b¯1B1\leftarrow a~1A1)$ at $590$ and $620nm,NH(A3\Pi ,\leftarrow X3\Sigma -)$ at $336nm$, and $NH2(A¯2A1\leftarrow X¯2B1)$ at $598nm$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}CH2$ and $NH2$ 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 $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}CH2$ 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 $NH2$ 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.