Resonance Electron Exchange in Large-Angle Scattering ofHe+on He at kev Energies

Recent differential scattering measurements at 5° scattering angle of ${\mathrm{He}}^{+}$ on He at energies of 2 to 250 kev have shown several pronounced resonance peaks when the fraction of the scattered particles which were neutral (electron exchange) was plotted as a function of incident energy. A detailed comparison of those experimental data is made with the theoretical predictions of the impact parameter method for resonance electron capture. The agreement between the theory and experiment is found to be quite good at high energies despite experimental indications of a large amount of excitation. The contribution of electron exchange with excitation is then considered in the light of this fact.