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

摘要

This work employs in situ rotational Raman spectroscopy to study the effect of N_2 and O_2 addition to CO_2 in pulsed glow discharges in the mbar range. The spatiotemporally resolved measurements are performed in CO_2 and 25%, 50% and 75% of N_2 or O_2 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 N_2, ranging from 400 to 850 K from start to end of the discharge pulse, while the addition of O_2 decreases the temperature at corresponding time points. Molecular number densities of CO_2, CO, O_2 and N_2 are determined, showing the spatial homogeneity along the axis of the reactor and uniformity during the cycle. The measurements in the N_2 containing mixtures show that CO_2 conversion factor α increases from 0.15 to 0.33 when the content of N_2 is increased from 0% to 75%, demonstrating the potential of N_2 addition to enhance the vibrational pumping of CO_2 and its beneficial effect on CO_2 dissociation. Furthermore, the influence of admixtures on CO_2 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 N_2, demonstrating the growth of vibrational temperatures in CO_2. On the other hand, the addition of O_2 leads to a decrease of α, which might be attributed to quenched vibrations of CO_2, and/or to the influence of the back reaction in the presence of O_2.