Generalized oscillator strengths of the valence-shell excitations of argon studied by fast electron impact

The generalized oscillator strengths of the valence-shell excitations from the ground state to 3p5(4s, 4s', 4p, 4p', 3d, 3d', 5p, 5p', 5s, 4d) of argon have been determined at an incident electron energy of 1500 eV and an energy resolution about 90 meV. The accuracy of the present generalized oscillator strengths is improved by the adopted relative flow technique. The comprehensive comparison of the present results with the previous experimental and theoretical ones shows that the first Born approximation is satisfied in the lower squared momentum transfer region for the electric dipole excitations, while the deviations from the prediction of the first Born approximation and the inelastic X-ray scattering measurements near the minimum and in the larger K2 region are obvious, which can be attributed to the failure of the first Born approximation in this K2 region. The invalidity of the first Born approximation has also been observed for the electric monopole transitions even at a high impact electron energy of 2500 eV.