Influence of N2 on the CO2 vibrational distribution function and dissociation yield in non-equilibrium plasmas

This work explores the effect of nitrogen addition on CO2 dissociation under various non-equilibrium plasma conditions. Experiments are performed in non-thermal plasmas sustained by DC pulsed discharges, for pressure and current ranges of 1 to 5 Torr and 20 to 50 mA, respectively. A self-consistent model, previously validated for pure CO2 discharges, is further extended to take into account e-V, V-T and V-V reactions involving N-2. Both model predictions and experimental data reveal a maximum of the asymmetric vibrational temperature T-3 at 5 Torr during the discharge around 1 ms, while no such maximum is visible at 1 Torr before the saturation occurs. It is shown that V-T deactivation by O atoms can have a strong influence on the vibrational kinetics, by directly affecting the relaxation of N-2 vibrational excited states and, as a consequence, the very important energy transfers between vibrationally excited N-2 and CO2 molecules. The experimental results show a twice as large CO2-conversion rate when N-2 gas is added to the plasma. The simulations suggest this effect cannot be the result of an increased dissociation by direct electron impact due to modifications in the reduced electric field, but rather of some other contribution to dissociation and/or inhibition of reactions giving back CO2.