Triplet-triplet excitation in helium

Differential cross sections for the electron impact excitation from the metastable 2 ${}_{}{}^3{}_{}{}^{}\mathrm{S}$ state to the 3 ${}_{}{}^3{}_{}{}^{}\mathrm{S}$ state of helium, at impact energies 50 to 500 eV, are calculated in the two-potential model and the modified Born approximation using Coulomb waves with a screened nuclear charge. The exchange effect is included in the framework of the Ochkur-Rudge approximation. The results are compared with recent theoretical calculations. It is shown that the present approach provides a significant improvement over the plane-wave Born approximation at large scattering angles.