LOW-ENERGY ELASTIC BACKSCATTERING OF ELECTRONS FROM AR+

Measurements of absolute partial cross sections, integrated over the a ngular range 90 degrees-180 degrees, are reported for the elastic scat tering of electrons from Ar+ at impact energies 3.5-6.5 eV. These cons titute the first measurements of backward scattering and for energies below the inelastic threshold in the elastic scattering of free electr ons from positive ions. Comparison with the predictions of the Rutherf ord formula, and partial wave analysis using semiempirical static pote ntials, suggests that low-energy, large-angle scattering from singly c harged positive ions provides an excellent regime for the testing of d ynamic effects in electron-ion collisions.