Interatomic contributions to high-energy electron-molecule scattering

Within the independent atom scattering model, we derive an approximate formula for the rotationally and vibrationally averaged three-atom terms in the series expansion of the electron scattering cross section. This formula uses the atomic scattering factors as well as the atomic scattered wavefunctions as input, and rotational averaging is performed numerically. We compare our results to previous theoretical multiple scattering approaches for the molecules F 3 , F 4 , and S F 6 and to experimental data for Te F 6 . Our results are consistent with those of previous calculations and inclusion of the three-atom term produces a dramatically better least squares fit of the Te F 6 data. The algorithm presented here is sufficiently fast and simple to be incorporated easily into existing electron diffraction codes.