The methane Raman spectrum from 1200 to 5500 cm: A first step toward temperature diagnostic using methane as a probe molecule in combustion systems

We present a study of the spontaneous Raman spectra of ¹²CH₄ from 1200 to 5500 cm⁻¹ at various temperatures. This study is of interest from a fundamental as well as from a practical point of view with regards to the temperature diagnostic in hydrocarbon combustion. The present investigation shows that the spontaneous ¹²CH₄ Raman spectra are very sensitive to temperature and that the complexity of methane spectra is not an obstacle to use methane as a probe molecule in laser-diagnostic techniques. Our study consists in determining the polarisability parameters of methane ¹²CH₄, unknown at the present time, from spontaneous Raman spectra recorded at pressure less than one atmosphere to minimize the problem of line-mixing. This diagnostic method technique based on spontaneous Raman spectroscopy may be applied to temperature measurements in a uni-element rocket combustion chamber using methane-oxygen propellants.