Electron detachment in collisions of negative ions:H+He

Abstract
Contrary to the expectation from a compound-state model, observation shows that the detachment cross section increases with energy in the "adiabatic" region below 2 keV. The compound-state model is not appropriate because a strong s-wave component in the wave function allows the extra electron to run away as soon as its state becomes unbound. The detachment cross section increases with collision velocity because detachment is induced by a breakdown of the Born-Oppenheimer approximation, which shifts to larger separations of the nuclei as the collision velocity increases.