Investigation of Filamentary and Diffuse DBD in CO₂ by Means of InSitu FTIR Absorption Spectroscopy

This work investigates CO2 dielectric barrier discharges (DBDs) at atmospheric pressure in the filamentary and diffuse regimes for the first time using in situ FTIR absorption measurements. The conversion factor of CO2 is determined and is consistent with the results obtained for DBDs in the literature, following a power law with respect to the specific energy input in both regimes. Vibrational temperatures for CO2 and CO molecules as well as rotational temperature are also determined within the discharge. A noticeably high vibrational temperature of CO is observed for low specific energy input (SEI). It drops abruptly when increasing the SEI which is attributed to strong vibrational-to-translational energy transfers by O atoms coming from CO2 dissociation. Except that, the ordering of the different temperatures is similar to the results reported for other CO2 discharges generated at lower pressures: the vibrational temperature of CO is higher than those of the different vibrational modes of CO2. The latter are slightly higher than the rotational temperature of the gas for the diffuse mode, whereas they are almost the same for the filamentary mode. The evolution of the measured parameters as a function of the specific energy input is then discussed and a detailed comparison of the two different regimes is carried out. These data together with the knowledge of the reduced electric field in the diffuse regime, which is included in the range 120–140 Td for all conditions, can be of significant importance for further studies exploring the fundamentals of CO2 plasma chemistry at atmospheric pressure, serving as reference for kinetic models.