Plasma chemistry in repetitively pulsed discharges in air at low pressures

Repetitively pulsed discharges in dry air (N sub(2)-20%O sub(2)) at low pressures (1 Torr) are studied by means of a time-dependent kinetic model. Simulations are carried out for both pulse and afterglow phases, accounting for the temporal evolution of the composition of the gas between each pulse. Modelling results are computed for a dc current of 40 mA, pulse durations between 200 mu s and 10 ms, and pulse repetition rates ranging from 20 up to 1000 Hz. This work shows that the vibrational distribution function of N sub(2) molecules becomes more populated by increasing the pulse duration or the pulse repetition rate. A similar behaviour is also predicted for the final concentrations of NO(X), N( super(4)S) and O( super(3)P). It is shown that [NO(X)] increases with the duty cycle ratio independently of the pulse repetition rate, as observed experimentally under similar conditions. The influence of the pulse duration, repetition rate and number of pulses in the overall kinetics is analysed and discussed in detail.