Knowledge Bank

The technique of Coherent Anti-Stokes Raman Scattering (CARS) has been applied to a study of molecular species present in $CH4/N2O, H2/O2$ and nitramine propellant flames. The coherent nature of this technique facilitates the detection of the CARS signal with minimal interference from the pump beams. It offers orders of magnitude higher sensitivity over that of spontaneous Raman, and often allows spectra to be obtained within seconds. While the present work concentrates on the diagnostic aspect of this method, its application to high resolution spectroscopy cannot be over-looked. The laboratory flame environment leads to the observation of hot bands of many species, such as $N2, N2O$ and $CH4$. Spectral regions of $1260-2400cm-1$ and $3650-4200cm-1$ have been investigated. Of particular interest is the observation of rotational S-transitions and vibrational Q-lines of the $H2$ molecule. At a flame temperature of 2800K, Q-lines have been observed for $J\le 11$ in the (1,0) band and for $J\le 9$ in the (2,1) band. Line positions compare favorably with those calculated from constants derived from the $B\prime \sigma u+-X\prime \Sigma g+$ and $C\prime \prime \pi -X\prime \Sigma g+$ bands of $H2.\mathrm{<mrow\; data-mjx-texclass="ORD">(1)</mrow>}$