Kinetics of excited states and radicals in a nanosecond pulse discharge and afterglow in nitrogen and air

The present kinetic modelling calculation results provide key new insights into the kinetics of vibrational excitation of nitrogen and plasma chemical reactions in nanosecond pulse, ‘diffuse filament’ discharges in nitrogen and dry air at a moderate energy loading per molecule, ∼0.1 eV per molecule. It is shown that it is very important to take into account Coulomb collisions between electrons because they change the electron energy distribution function and, as a result, strongly affect populations of excited states and radical concentrations in the discharge. The results demonstrate that the apparent transient rise of N₂ ‘first level’ vibrational temperature after the discharge pulse, as detected in the experiments, is due to the net downward V–V energy transfer in N₂–N₂ collisions, which increases the N₂(X ¹Σ, v = 1) population. Finally, a comparison of the model's predictions with the experimental data shows that NO formation in the afterglow occurs via reactive quenching of multiple excited electronic levels of nitrogen molecule, N₂^∗, by O atoms. (paper)