Heavy species kinetics in low-pressure dc pulsed discharges in air

A time-dependent kinetic model is presented to study low-pressure (133 and 210 Pa) pulsed discharges in air for dc currents ranging from 20 to 80mA with a pulse duration from 0.1 up to 1000 ms. The model provides the temporal evolution of the heavy species along the pulse within this range time, where the coupling between vibrational and chemical kinetics is taken into account. This work shows that the predicted values for NO(X) molecules and O(P-3) atoms reproduce well previous measured data for these two species. A systematic analysis is carried out on the interpretation of experimental results. It is observed that the N-2(X, nu >= 13) + O -> NO(X) + N(S-4) and the reverse process NO(X) + N(S-4) -> N-2(X, nu similar to 3) + O have practically the same rates for a pulse duration longer than 10 ms, each of them playing a dominant role in the populations of NO(X), N(S-4) and, to a lesser extent, in O(P-3) kinetics. Our simulations show that for shorter pulse durations, from 0.1 to 10 ms, NO(X) is produced mainly via the processes N-2(A) + O -> NO(X) + N(D-2) and N(D-2) + O-2 -> NO(X) + O, while the oxygen atoms are created mostly from electron impact dissociation of O-2 molecules and by dissociative collisions with N-2(A) and N-2(B) molecules.