Recombination of Electrons and Molecular Helium Ions

The recombination coefficient α(Nₑ, Tₑ) of He₂⁺ is measured in helium afterglow plasmas (12 Torr≤p≤20 Torr; t1 msec) as a function of electron density and gas temperature under conditions where the temperature of electrons and ions equals that of the neutral gas (2.5×10¹²cm^-3≤Nₑ≤2×10¹³ cm^-3; 900^∘K≤T≤2200^∘K). The recombination coefficient is found equal to the theoretical collisional-radiative recombination rate of He⁺. In spite of the high vibrational excitation of the recombining He₂⁺, corresponding to the high gas temperatures, there is no evidence for dissociative processes. In particular, the time decay of the recombination light cannot be reconciled with collisional-dissociative recombination.