Collisional dissociative recombination of H$_{3}^{+}$ ions with electrons

Plasma afterglow measurements have consistently yielded either much lower (by factors of 10 or more) or higher (by factors of 3 to 4) electron-H$_{3}^{+}$ recombination coefficients then those observed in ion storage rings, and calculated by \textit{ab-initio} theory. The origin of this long-standing discrepancy has not been clearly identified. I will show here that ``collisional dissociative recombination'' in conjunction with angular momentum $l$-mixing can account for the observed increase of recombination rates in plasma experiments at higher neutral densities. In this model, the enhancement of the recombination results from three-body electron capture into Rydberg states of high angular momentum $l$, followed by $l$-reducing collisions with neutral atoms that induce predissociation. Hence, while there is no true ``discrepancy'' between afterglow and storage ring H$_{3}^{+}$ recombination coefficients, recombination in a plasma is not a purely binary process. The same may be true for other ions that recombine by the ``indirect process.'' I also propose that the very low values obtained in some afterglows at low concentrations of neutral hydrogen are flawed by the presence of ion species other than H$_{3}^{+}$, rather than being due to different spin modifications, or vibrational excitation of H$_{3}^{+}$, as has been suggested.