Direct current N 2 flowing discharges were generated and conditions for the pink afterglow were obtained. Emissions from N 2 (B, C) and N + 2 (B) radiative states were studied as a function of pressure, flow rate and post-discharge position. A one-dimensional kinetic model accounting for N 2 (X, v), N 2 (A, B, C, a, a , a ), N( 4 S), N + 1−4 (X) and N + 2 (B) species has been developed in order to describe the experimental observations. The analysis on the complete set of processes assumed in this paper has provided possible generation mechanisms for N atoms, N + 2 (B) ions and N 2 (B, C) electronically excited states as well as for metastable ones. It has been shown that ionization, excitation and dissociation processes occur simultaneously at the post-discharge region when the vibrational distribution function of N 2 (X, v) states heats as resulting from the efficient V-V pumping mechanism, which is very sensitive to pressure conditions. Here, the pink afterglow is described as a non-equilibrium plasma, i.e. ambipolar diffusion for ions and the condition of charge neutrality are assumed.

The effect of the addition of molecular nitrogen on the oxygen dissociation is investigated in a low pressure gas discharge. The dissociation efficiency is measured as a function of N2 concentration, for a total pressure ranging from 0.4 to 3 Torr in discharge tubes with diameter between 6 and 21 mm. The concentration of O atoms is obtained by the NO+O chemiluminescent reaction. The authors show that for a few percent of nitrogen the oxygen dissociation degree varies by a factor of 1.5-10 depending on the nitrogen concentration, tube diameter and total pressure. The ratio of the dissociation degree for pure oxygen and mixtures of oxygen and nitrogen is calculated, and the authors show that their results imply that, as the tube diameter tends to infinity, the dissociation efficiency tends to one. The authors conclude that the most important reason for the increase in the dissociation of oxygen in the presence of nitrogen is the reduction of wall diffusion losses.

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This work is devoted to the study of the expansion of a Ar-CH4 microwave plasma. Diagnostics have been performed within the reactor using both an electrostatic Langmuir double probe and spatially resolved emission spectroscopy. We have proven that the plasma jet results from electromagnetic surface wave propagation (ne≥nec=3.6×1011 cm−3, Te∼23 000–46 000 K) and have shown that injection of methane into the jet decreases ne and Te, and thus limits the striking conditions. Such an expanding plasma finds applications in plasma enhanced chemical vapor deposition technology. It can be used to create simple radicals close to a substrate and thus limits their destruction on the reactor walls.

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