Structures in Electron-Impact Excitation Cross Sections of He from 30 to 70 eV

Close-coupling calculations of $e$-He scattering in the region 30-70 eV reveal structures in the $n=2\mathrm{}{}_{}{}^{1,3}{}_{}{}^{}S$ excitation cross sections between 30 and 50 eV, in agreement with recent experiments. The structures are attributed to open-channel compound-state formation. Additional structures are also predicted at both higher and lower energies. These calculations suggest that temporary negative-ion formation should be considered as a mechanism for triplet excitation.