Knowledge Bank

In situ shock-tube chemical kinetic studies of combustion systems require specific and quantitative spectroscopic methods for concentration-time history measurements of reacting species which do not suffer from interferences by other species. As typical examples for this purpose, we have determined multiple-line correlation-absorption $coefficients1$ at $2259A(\Delta \lambda =39A)$ of low pressure ($\sim 5$ torr) emission lines by high-pressure ($0.5\sim$, atm$\sim 2.1$) and high-temperature $(905\sim T,\circ K\sim 2015)$ lines in the (0,0) band of the NO $\gamma$-band system and near line-center infrared absorption $coefficients2$ at $3.329\mu$ of a He-Ne laser line by a high-pressure ($0.5\sim $p,atm$\sim 2.4$) and high-temperature $(965\sim T,\circ K\sim 2710$) line in the $\nu 3$-fundamental system of $CH4$. The multiple-line absorption obeys an effective absorption coefficient for infinitely narrow emission lines and line-center absorption by isolated Voigt-lines with a common width. This model is applicable for a wide range of experimental conditions encountered in combustion $systems3$ and results in a band f-number which differs by only $+6$ from the preferred value when known line-width data are used. The laser-line absorption can be approximated by the line-center absorption of a Voigt-line for a symmetrical top and agrees at $300\circ K$ (within $-4.5$) with previous data when known line-width data are applied. The outlined methods are generally applicable and show that simple and analytical, quantitative $models4$ for absorption data relevant to combustion studies are feasible. However, they require new experimental data for band-model and line-width parameters for many reactant, intermediate and product species. Examples are given of molecules and radicals of interest.