Generalized oscillator strengths for the valence-shell excitations of argon

The generalized oscillator strengths for the valence-shell excitations to 3p{sup 5}(4s,4s{sup '}) and 3p{sup 5}(4p,4p{sup '}) of argon were measured by an angle-resolved fast-electron energy-loss spectrometer at an incident electron energy of 2500 eV. The transition multipolarities for these excitations were elucidated with the help of the calculated intermediate coupling coefficients using the COWAN code. The generalized oscillator strength profiles for the electric dipole excitations to 3p{sup 5}(4s,4s{sup '}), the electric quadrupole and monopole excitations to 3p{sup 5}(4p,4p{sup '}) were analyzed and their positions of the extrema were determined. Furthermore, the generalized oscillator strength of the electric quadrupole excitation in 3p{yields}4p was determined and its profile is in general agreement with the theoretical calculations. However, the generalized oscillator strength profile of the electric monopole excitation in 3p{yields}4p is different from the theoretical calculations.