Absolute Differential Elastic- and Inelastic-Scattering Cross Sections in 25-140 keVHe++ He Collisions

Data obtained as energy-loss spectra at angles from 0 to 7.3×${10}^{-3\mathrm{}}$ rad (c.m.) with typical energy-loss resolution of 0.7 eV and angular resolution of 2×${10}^{-3\mathrm{}}$ rad (c.m.) were used to calculate average differential cross sections ${〈\frac{d\sigma }{d\Omega }〉}_{\mathrm{av}}$ for elastic scattering, direct excitation of the individual $\mathrm{He}\mathrm{}(n=2\mathrm{})\mathrm{}$ states, and direct excitation of the ${\mathrm{He}}^{+}\mathrm{}(n=2\mathrm{})\mathrm{}$ states. The total cross section for excitation of the $\mathrm{He}\mathrm{}(n=2\mathrm{})\mathrm{}$ states obtained by integrating the differential cross sections was found to be 20×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$ at 25 keV (lab) decreasing to 7×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$ at 140 keV. At incident lab energies below 100 keV the $\mathrm{He}\left(2\mathrm{}{}_{}{}^2{}_{}{}^{}S\right)$ and $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}P\right)$ states dominate the $\mathrm{He}\mathrm{}(n=2\mathrm{})\mathrm{}$ structure at angles close to zero, while the $\mathrm{He}\left(2\mathrm{}{}_{}{}^1{}_{}{}^{}P\right)$ state dominates at larger angles. The contribution of the $\mathrm{He}\left(2\mathrm{}{}_{}{}^1{}_{}{}^{}S\right)$ state remains below 25% at all angles and energies.