Time-dependence of the electron energy distribution function in the nitrogen afterglow

In this paper, we present an investigation of the time-relaxation of the electron energy distribution function EEDF) in the nitrogen afterglow of an omega/2pi = 433 MHz flowing discharge at p = 3.3 torr, in a tube with inner radius R = 1.9 cm. We solve the time-dependent Boltzmann equation, including. the term for creation of new electrons in associative/Penning reactions, coupled to a system of rate balance equations for the heavy-particles. The EEDFs are also obtained experimentally from second derivatives of digitized probe characteristics measured using a triple probe technique, and compared with the calculations. It is shown that an equilibrium between the vibrational distribution function of ground-state molecules N-2 (X (1)Sigma(g)(+),upsilon) and low-energy electrons is rapidly established, in times similar to10(-7) s. In these early instants of the postdischarge, a dip is formed in the EEDF around 4 eV. The EEDF finally reaches a quasi-stationary state for t greater than or similar to 10(-6) s, although the electron density still continues to decrease beyond this instant. Collisions of highly excited N-2(X (1)Sigma(g)(+),upsilon greater than or similar to 35) molecules with N (S-4) atoms are in the origin of a maximum in the electron density occurring downstream from the discharge at similar or equal to2 x 10(-2) s. These reactions create locally the metastable states N-2(A (3)Sigma(u)(+)) and N-2(a' (1)Sigma(u)(-)), which in turn ionize the gas in associative/Penning processes. Slow electrons remain for very long times in the postdischarge and can be. involved in electron stepwise processes with energy thresholds smaller than similar to2-3 eV.