Squared form factors of valence-shell excitations of atomic argon studied by high-resolution inelastic x-ray scattering

摘要

State-resolved squared form factors of the electric monopolar excitations to 3p54p[_(1/2]0) and 3p54p′[_(1/2]0), the electric dipolar excitations to 3p54s[_(3/2]1) and 3p54s′[_(1/2]1), and the electric quadrupolar excitations to 3p54p[_(5/2]2), 3p54p[_(3/2]2), and 3p54p′[_(3/2]2) of argon are determined by inelastic x-ray scattering with a high resolution of 70 meV. Good agreement is observed between the present results and the calculations of the random phase approximation with exchange except that the present results of 3p54s′[_(1/2]1) in q2< 3 a.u. are smaller and 3p54p[_(1/2]0) in q2< 1.5 a.u. are larger than the theoretical results. The difference may be due to the difficulty of obtaining accurate wave functions or dealing with the electronic correlations for a heavier atom such as argon. The disagreements between the present squared form factors and the ones measured by electron energy loss spectroscopy indicate that the first Born approximation is not satisfied, even at an incident electron energy of 2500 eV.