Abstract
Recent simulations by So et al (2002 J. Phys. D 35 2978–87) have shown inter alia that in CF4 where there are two negative ions of comparable density, the plasma is structured, in that there are essentially three regions so far as the negative ions are concerned. In the inner region one negative ion species is concentrated, in the outer region electrons dominate over negative ions, while the intermediate has only one species of negative ion.
This confirms earlier work (Franklin R N 2002a J. Phys. D: Appl. Phys. 35 536–42; 2002b J. Phys. D: Appl. Phys. 35 747–50) and justifies extending that work to cover situations where there is a multiplicity of both positive and negative ions.
In this paper we give explicit results for the central electronegativities and electropositivities for the case of two species of ion of each sign, and also determine the relative sizes of the regions occupied by the negative ions. By effectively varying the electron temperature through the ionization rate, we indicate how these quantities vary with gas pressure.
As an appendix we generalize to the case of `j' positive ions and `k' negative ions.