Optical oscillator strengths of valence-shell excitations of atoms and molecules determined by the newly developed dipole (γ, γ) method

The dipole (γ, γ) method, which is the inelastic x-ray scattering operated at a negligibly small momentum transfer, is newly developed to determine the absolute optical oscillator strengths of the valence-shell excitations of atoms and molecules. This new method is free from the line saturation effect, and the Bethe-Born conversion factor of the dipole (γ, γ) method varies much more slowly with the excitation energy than that of the dipole (e, e) method. Thus the dipole (γ, γ) method provides a reliable approach to obtain the benchmark optical oscillator strengths of the valence-shell excitations for gaseous atoms and molecules, and it is demonstrated by the measurements of absolute optical oscillator strengths for gaseous helium, argon, nitrogen and carbon monoxide. (author)