Inapplicability of the Born Exchange Scattering Amplitude for the He (11S→23S) Transition

Differential cross sections are calculated for the $\mathrm{He}{\text{(1}}^1{\text{S→2}}^3\mathrm{S)}$ transition within the Born–Oppenheimer approximation. The Bonham–Ochkur (OB) approximation is compared to the exact exchange scattering amplitude and it is found to yield semiquantitative agreement, especially at high incident energies. However, the theoretical results show qualitatively different behavior from recent experimental results. Experimental differential cross sections peak in the forward direction while theory predicts a maximum at large angles.