Effects of the Wannier Ridge on Secondary-Electron Spectra in Proton-Helium Collisions

We present high-resolution electron spectra for electrons ejected in the forward direction by protons and neutral hydrogen in collisions with He gas. The spectra show the expected electron transfer to the continuum peak, but also show a 0^∘{} ridge extending to the lowest electron energies measured. We propose that this new secondary-electron component represents electrons which propagate on the saddle of the potential surface produced by the two positive ions H⁺ and He⁺ in the intermediate collision complex.