A rotational Raman study under non-thermal conditions in pulsed CO2–N2 and CO2–O2 glow discharges.

This work employs in situ rotational Raman spectroscopy to study the effect of N₂ and O₂ addition to CO₂ in pulsed glow discharges in the mbar range. The spatiotemporally resolved measurements are performed in CO₂ and 25%, 50% and 75% of N₂ or O₂ admixture, in a 5–10 ms on-off cycle, 50 mA plasma current and 6.7 mbar total pressure. The rotational temperature profile is not affected by adding N₂, ranging from 400 to 850 K from start to end of the discharge pulse, while the addition of O₂ decreases the temperature at corresponding time points. Molecular number densities of CO₂, CO, O₂ and N₂ are determined, showing the spatial homogeneity along the axis of the reactor and uniformity during the cycle. The measurements in the N₂ containing mixtures show that CO₂ conversion factor α increases from 0.15 to 0.33 when the content of N₂ is increased from 0% to 75%, demonstrating the potential of N₂ addition to enhance the vibrational pumping of CO₂ and its beneficial effect on CO₂ dissociation. Furthermore, the influence of admixtures on CO₂ vibrations is examined by analysing the vibrationally averaged nuclear spin degeneracy. The difference between the fitted odd averaged degeneracy and the calculated odd degeneracy assuming thermal conditions increases with the addition of N₂, demonstrating the growth of vibrational temperatures in CO₂. On the other hand, the addition of O₂ leads to a decrease of α, which might be attributed to quenched vibrations of CO₂, and/or to the influence of the back reaction in the presence of O₂. [ABSTRACT FROM AUTHOR]