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 3p54pnu0002[1/2]0,nthe electric dipolar excitations to 3p54s[3/2]1 and 3p54snu0002[1/2]1, and the electric quadrupolar excitations ton3p54p[5/2]2, 3p54p[3/2]2, and 3p54pnu0002[3/2]2 of argon are determined by inelastic x-ray scattering with a highnresolution of 70 meV. Good agreement is observed between the present results and the calculations of the randomnphase approximation with exchange except that the present results of 3p54snu0002[1/2]1 in q2 > 3 a.u. are smaller andn3p54p[1/2]0 in q2 < 1.5 a.u. are larger than the theoretical results. The difference may be due to the difficultynof obtaining accurate wave functions or dealing with the electronic correlations for a heavier atom such as argon.nThe disagreements between the present squared form factors and the ones measured by electron energy lossnspectroscopy indicate that the first Born approximation is not satisfied, even at an incident electron energy ofn2500 eV.