Absolute generalized oscillator strengths of 21S and 21P excitations of helium measured by angle-resolved electron-energy-loss spectroscopy

The differential scattering cross sections and the generalized oscillator strengths of the 11S→21S and 11S→21P transitions of helium have been measured by angle-resolved electron-energy-loss spectroscopy with an incident electron energy of 1500 eV and within the range 2 degree endash 11.5 degree of scattering angles. The corrections for angular factors and density effects have also been made for the experimental results. The differential cross sections and generalized oscillator strength values are absolute and are the first to be measured at such a high impact energy. The experimental results are compared with other measurements and theoretical calculations in the literature. copyright 1996 The American Physical Society