Optical emission spectroscopy and modeling of DC CO2−N2−He mixture plasma

In this study, a direct current carbon dioxide-helium-nitrogen CO2-N2-He mixture plasma was studied to evaluate its dependence on pressure. Optical emission spectroscopy (OES), and a Langmuir probe analysis were used to characterize the plasma. The ion number density and electron temperature were determined by a dual Langmuir probe; both values exhibited a slight dependence on the pressure. The species observed via OES exhibited a slight dependence on pressure, and the results were in good agreement with the behavior of the electron temperature and ion density measurements. The N2/N+2 , N/N2, and N/N+2 ratios as a function of pressure (obtained via OES measurements) were quantitatively correlated with the electron impact excitation and dissociation cross sections ratios. The carbon monoxide/oxygen CO/O2 ratio as a function of pressure (obtained via OES) indicated that more CO than O2 was produced, which corresponded with the most important process pertaining to CO2 splitting. This paper also presents the calculated electron transport coefficients, rate coefficients, electron energy distribution functions, and electron temperatures to support the trends observed during the experiment using BOLSIG+, a two-term Boltzmann solver. The rate coefficient due to excitation of the CO2, N2, and He obtained by BOLSIG+ are in good agreement with the present OES observation.