Low-energy elastic backscattering of electrons from Ar+

Measurements of absolute partial cross sections, integrated over the angular range 90 degrees -180 degrees , are reported for the elastic scattering of electrons from Ar+ at impact energies 3.5-6.5 eV. These constitute the first measurements of backward scattering and for energies below the inelastic threshold in the elastic scattering of free electrons from positive ions. Comparison with the predictions of the Rutherford formula, and partial wave analysis using semi-empirical static potentials, suggests that low-energy, large-angle scattering from singly charged positive ions provides an excellent regime for the testing of dynamic effects in electron-ion collisions.