Collisional dissociative recombination in helium-hydrogen afterglow plasmas

The puzzling dependence of electron-ion recombination in helium-hydrogen afterglows on neutral\footnote{Glos\'{\i}k et al., Phys. Rev.A \textbf{79}, 052707 (2009)} and electron\footnote{Gougousi et al., Int. J. Mass Spec. Ion Proc. \textbf{149-150}, 131 (1995)} densities is shown to be compatible with the ``Collisional Dissociative Recombination'' mechanism, originally proposed by Collins,\footnote{Collins, Phys. Rev.A \textbf{140}, 1850 (1965)} in which three-body capture of electrons into molecular high Rydberg states of H$_{3}^{+}$ leads to predissociation of the molecular core. While both electrons and neutrals play a role in the three-body capture, their effects on recombination do not add in a simple manner, which makes it difficult to distinguish three-body and binary dissociative recombination. Collision-induced angular momentum mixing ($l$-mixing), invoked in earlier models, also occurs but does not provide the rate-limiting step that controls the overall recombination rate.