A measurement of the cross section for proton production in collisions between electrons and H₂⁺ ions

A crossed beam method has been used to measure the cross section for proton production in single collisions between H₂⁺ ions and electrons at incident electron energies from 5.0 eV to 1000 eV. The measured cross section is the sum of the dissociative excitation cross section plus twice the dissociative ionization cross section. Its magnitude is in good agreement with other experimental data and with theory, but there is some disagreement over the rate of fall-off of the cross section at high energies. The present data at electron energies above 40 eV can be represented approximately by Q = (255/E)log(E/13.8) where Q is in units of πa₀² and E in eV. The measured cross section was found to be independent of ion source pressure over a wide pressure range, and the implications of this with regard to the vibrational-state population distribution of the H₂⁺ ions are discussed.