Quantifying methane vibrational and rotational temperature with Raman scattering

This work describes the theoretical basis and implementation of the measurement of vibrational (T_vib) and rotational (T_rot) 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 T_vib and T_rot 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 T_vib and T_rot, further demonstrating the applicability of this method in fitting non-equilibrium spectra.