Three-Body Capture—Autoionization: A Mechanism for Vibrational Deexcitation of Molecular Ions in a Plasma

The recently measured associative ionization rates in helium plasmas indicate an extremely rapid vibrational relaxation of the resulting molecular ions. Autoionization of weakly bound (high-n) molecular states, in near Saha equilibrium with the molecular ions in the corresponding vibrational level v, is shown to yield the required rates of vibrational deexcitation.