The influence of atoms and vibrationally excited molecules on the electron relaxation in the postdischarge regime of a weakly ionized hydrogen plasma

Abstract

Starting from former investigations of the field-free, collision-dominated temporal relaxation of the electron component in the postdiscarge regime for inert- and molecular-gas plasmas, we studied, in hydrogen, the effect of additional electron collisions with vibrationally excited behavhour. By numerically solving the appropriate electron Boltzmann equation, using the stationary distributions as initial states and suddenly switching off the electric field, the temporal behaviour of the energy distribution and the resulting mean energy and power transfer rates of the electrons were obtained for different physical conditions. Via the introduction of effective collision cross-sections and corresponding effective collision frequencies, the relaxation under different conditions can be analysed and interpreted. The relaxation between temporal evolutions and different types of collision processes have been found. Interesting findings are i) that electron collisions with vibrationally excited molecules, in particular second-kind collisions, are of minor importance in the first stage of relaxation, but become relevant only in the later phase; ii) that an increasing mixture of atoms leads to a sensitive change of the relaxation behaviour and to a marked increase of the corresponding relaxation time.