Ionization Processes in Decaying Plasmas. I. Helium

The current theories of the helium afterglow are shown not to be substantiated by published experimental results. The experimental data are reanalyzed to obtain a more consistent interpretation of the ionization mechanisms. The primary conclusion of this analysis is that the enhancement of ionization in the afterglow occurs by the conversion of metastable helium atoms to molecular ions: ${\mathrm{He}}^{*}+{\mathrm{He}}^{*}\to {{\mathrm{He}}_2}^{+}+e$. The analysis yields specific rate constants for the important reactions in the plasma.