Study of vibrational kinetics of CO2 and CO in CO2-O2 plasmas under non-equilibrium conditions

This work explores the effect of O-2 addition on CO2 dissociation and on the vibrational kinetics of CO2 and CO under various non-equilibrium plasma conditions. A self-consistent model, previously validated for pure CO2 discharges, is further extended by adding the vibrational kinetics of CO, including electron impact excitation and de-excitation (e-V), vibration-to-translation relaxation (V-T) and vibration-to-vibration energy exchange (V-V) processes. The vibrational kinetics considered include levels up to v = 10 for CO and up to v (1) = 2 and v (2) = v (3) = 5, respectively for the symmetric stretch, bending and asymmetric stretch modes of CO2, and accounts for e-V, V-T in collisions between CO, CO2 and O-2 molecules and O atoms and V-V processes involving all possible transfers involving CO2 and CO molecules. The kinetic scheme is validated by comparing the model predictions with recent experimental data measured in a DC glow discharge ignited in pure CO2 and CO2-O-2, operating at pressures in the range 0.4-5 Torr (53.33-666.66 Pa). The experimental results show a lower vibrational temperature of the different modes of CO2 and a decreased dissociation fraction of CO2 when O-2 is added to the plasma but an increase of the vibrational temperature of CO. On the one hand, the simulations suggest that the former effect is the result of the stronger V-T energy-transfer collisions with O atoms which leads to an increase of the relaxation of the CO2 vibrational modes. On the other hand, two main mechanisms contribute to the lower CO2 dissociation fraction with increased O-2 content in the mixture: the back reaction, CO(a(3)pi(r)) + O-2 -> CO2 + O and the recombinative detachment O- + CO -> e + CO2.

Automated summary

This work investigates the impact of O-2 addition on CO2 dissociation and the vibrational kinetics of CO2 and CO in non-equilibrium plasma. The study utilizes a self-consistent model that includes the vibrational kinetics of CO, incorporating e-V, V-T, and V-V processes. The model is validated using experimental data from pure CO2 and CO2-O-2 discharges. The results show changes in vibrational temperature and dissociation fraction due to the addition of O-2, attributed to V-T collisions and two main mechanisms: back reaction and recombinative detachment.