Absolute Measurement of Differential Cross Sections for Electron Scattering in Helium

Absolute measurements of cross sections for electron-impact scattering in helium at an angle of 5° have been made for elastic scattering and excitation of the $2{}_{}{}^1{}_{}{}^{}P$ and $2{}_{}{}^1{}_{}{}^{}S$ states and for incident energies of 50-400 eV. Cross-section values of $\sigma (2\mathrm{}{}_{}{}^1{}_{}{}^{}P,5^{\circ })$ are found to be lower than theoretical Born values by (9.5 ± 5.4)% at 400 eV, (31.5 ± 4.6)% at 100 eV, and (62.5 ± 3.4)% at 50 eV. Deduced values of total $2{}_{}{}^1{}_{}{}^{}P$ excitation cross sections ($E\ge 100$ eV) are in agreement with other experimental values. Our measurements for elastic scattering agree well with recent theoretical calculations.