Generalized oscillator strengths of the valence-shell excitations of argon studied by fast electron impact

Abstract

The generalized oscillator strengths of the valence-shell excitations from the ground state to 3p5(4s, 4s′, 4p, 4p′, 3d, 3d′, 5p, 5p′, 5s, 4d) of argon have been determined at an incident electron energy of 1500 eV and an energy resolution of about 90 meV. The accuracy of the present generalized oscillator strengths is improved by the adopted relative flow technique. The comprehensive comparison of the present results with the previous experimental and theoretical ones shows that the first Born approximation is satisfied in the lower squared momentum transfer region for the electric dipole excitations, while the deviations from the prediction of the first Born approximation and the inelastic x-ray scattering measurements near the minimum and in the larger K2 region are obvious, which can be attributed to the failure of the first Born approximation in this K2 region. The invalidity of the first Born approximation has also been observed for the electric monopole transitions even at a high impact electron energy of 2500 eV.

Integral cross sections for electron impact excitations of argon and carbon dioxide

“…The GOSs of the low-lying states for argon have been reported before. [19,[26][27][28] Here we only present the extrapolated OOSs and BE-scaled ICSs for comparison with the available data in literature. The associated data for carbon dioxide of the low-lying features are also discussed.…”

“…The major advantage of NRIXS is that the first Born approximation (FBA) is always applicable for x-ray scattering but fails for electron scattering in some cases. [16,18,19] In other words, NRIXS can serve as a high-energy limit for fast electron scattering where the FBA should describe the scattering behaviors well. The comparative study can certainly point out the cases where the FBA fails for electron scattering and the resulted GOSs constitute a set of benchmark data.…”

“…Atomic data associated with electron or x-ray scattering processes are crucial for deriving the elemental abundance in the astrophysical observed spectra and for modeling in lowtemperature plasmas. The GOSs or the equivalent inelastic squared form factors (ISFFs) of the valence-shell excitations below 15 eV for argon were studied by both fast electron [19,[26][27][28] and x-ray [29] scatterings. Note that the earlier experiments by Ji et al [26] and Zhu et al [27,28] were performed with gas cells while crossed-beam method with gas nozzle was adopted in the recent measurement [19] to improve the accuracy.…”

“…The GOSs or the equivalent inelastic squared form factors (ISFFs) of the valence-shell excitations below 15 eV for argon were studied by both fast electron [19,[26][27][28] and x-ray [29] scatterings. Note that the earlier experiments by Ji et al [26] and Zhu et al [27,28] were performed with gas cells while crossed-beam method with gas nozzle was adopted in the recent measurement [19] to improve the accuracy. In addition, theoretical approaches with the Hartree-Fock method, [30] random phase approximation with exchange (RPAE), [31] relativistic distorted wave (RDW), [32] eigenchannel R-matrix method, [33] etc, have also been applied in the calculations of oscillator strengths or cross sections for argon.…”

Probing the delocalized core-hole via inner-shell excitation in N2

“…In addition, a multichannel detection system enhanced the detection efficiency by about 20 times [28], which also facilitated the present experiment. It should be mentioned that the incident electron energy of 1500 eV might be not high enough for the validity of the first Born approximation (FBA) compared to the excitation energy of about 400 eV [29,30]. However, the experiment was designed to determine the energy level structure of the inner-shell transitions in nitrogen molecule, rather than the absolute generalized oscillator strength.…”