Quantifying methane vibrational and rotational temperature with Raman scattering

•Vibrational and rotational temperatures of methane are obtained by fitting the methane Raman spectrum.•Technique is validated using available data up to 860 K, but believed to be accurate at least up to 1500 K.•Vibrational-rotational non-equilibrium spectra are generated using pulsed microwave plasmas. This work describes the theoretical basis and implementation of the measurement of vibrational (Tvib) and rotational (Trot) temperatures in CH4 by fitting spontaneous Raman scattering spectra in the Pentad region. This method could be applied for thermal equilibrium temperature measurements applications, e.g. in combustion, or vibrational-rotational non-equilibrium applications, such as in plasma chemistry. The method of calculating these temperatures is validated against known temperature thermal equilibrium spectra up to 860 K from published data, giving an estimated relative error of 10%. This demonstrates that both the calculated stick spectrum and the algorithm to determine Tvib and Trot for CH4 is robust to 860 K, but we expect it is valid to 1500 K. Additionally, a number of non-equilibrium spectra generated with a pulsed microwave plasma are fitted to find Tvib and Trot, further demonstrating the applicability of this method in fitting non-equilibrium spectra.