Electron and heavy particle kinetics in a low-pressure nitrogen glow discharge

A detailed kinetic model is used to investigate the mechanisms for ionization, dissociation and atomic re-association in a low-pressure N-2 positive column. The approach is based on the self-consistent solutions to the electron Boltzmann equation coupled to a system of rate balance equations for the N-2(X (1) Sigma(g)(+), v) levels, the electronically excited states of N-2 and the N-2(+) and N-4(+) ions. The maintenance electric field is self-consistently determined from the continuity equations for electrons and ions. The model provides a satisfactory explanation of measurements conducted in these conditions, in the range p = 0.6-2.5 Torr and I = 10-100 mA, for the reduced electric field and the concentrations of N(S-4) atoms and N-2(A (3) Sigma(u)(+)) and N-2(B (3) Pi(g)) states. The rate coefficients 10(-11) and 5 x 10(-11) cm(3) s(-1) are derived here for the two reactions leading to associative ionization by collisions between electronic metastables N-2(A (3) Sigma(u)(+)) + N-2(a' (1) Sigma(u)(-)) --> N-4(+) + e and N-2(a' (1) Sigma(u)(-)) + N-2(a' (1) Sigma(u)(-)) --> N-4(+) + e, respectively. The dissociation due to the vibration-vibration (V-V) and vibration-translation (V-T) energy exchanges is shown to represent only a minor contribution for the total rate of dissociation, in opposition to previous studies, due to the effects of fast V-T exchanges associated with N-2-N collisions. Finally, it is shown that the reaction N-2(A (3) Sigma(u)(+) + N(S-4) --> N-2(X (1) Sigma(g)(+), v) N(P-2) does not constitute an effective depopulating mechanism of N(S-4) atoms as most of the N(P-2) atoms so created are reconverted to the N(S-4) by collisions on the wall and quenching.