The generalized oscillator strengths (GOS) of the argon transitions 3p6−3p5(3d, 4d, 5d) and 3p6−3p54f respectively for multiple strengths and are determined using the wavefunctions which have been generated from the CIV3 code of Hibbert. Calculations of these generalized oscillator strengths, as a function of momentum transfer, are also carried out respectively in the configuration interaction method and in the random phase approximation with exchange. The length and velocity forms have been used in this work. The gap between the absolute values of the generalized oscillator strength obtained in the theoretical calculations and those of the experimental results of Zhu et al have been noticeably reduced in the present work for the octupole excitations to 3p5(3d, 4d). This is due to the configuration interaction wavefunctions. The profiles and the positions of the extrema in the generalized oscillator strength have also received particular attention in the evaluation. The results of length and velocity form studies also show that the electron correlation effects are very significant for the excitations to 3p5(3d, 4d) but are found to have no great influence in the positions of the extrema.

The quadrupole, monopole and dipole generalized oscillator strengths (GOSs) as a function of momentum transfer are respectively calculated for these 3p 6 →3p 5 (4p, 5p, 6p) and 3p 6 →3p 5 (4s, 5s, 6s) transitions. Configuration interaction (CI) and random phase approximation with exchange (RPAE) methods are used in the determination of these GOS, in the length and velocity forms. The code of Hibbert has been used to generate the wavefunctions from which a partial of argon GOSs are been computed. The present work has reduced the gap between the absolute values of the theoretical calculations of GOSs and those of the experimental results of Zhu et al for the quadrupole excitations to 3p 5 (4p, 5p). The profile of our quadrupole GOS 3p 6 →3p 5 5p transition agrees well with the experimental result of Zhu. The best agreement (0.7%) is observed between the (length) first maximum position and the experimental one for the quadrupole GOS 3p 6 →3p 5 4p transition. The present velocity GOS minimum position for the dipole excitation in 3p 6 →3p 5 4s and the calculated velocity GOS maximum position of the monopole 3p 6 →3p 5 4p transition are in good agreement with the experimental observations (differences of 1.82% and 3.08%, respectively). Correlation effects decrease with increasing of the excited state principal quantum number and have no great influence on the extrema positions.

The quadrupole and monopole generalized oscillator strengths (GOS) as a function of momentum transfer are calculated for the 2p–3p and 2p–4p transitions of the neon atom using the analytical Hartree–Fock (HF) wavefunctions for the ground-state and the wavefunctions for the excited states which are obtained numerically from the modified HF Slater equation. Calculations are carried out by using the HF method and random phase approximation with exchange in the velocity formulation. The positions and the number of the extrema in the GOS have received particular attention in the evaluation. Our calculated monopole GOS of 2p–3p transition in velocity form reveals one maximum located between the experimental and theoretical results of other authors. The disagreement between our first maximum of the quadrupole GOS 2p–3p transition with the experimental and other theoretical ones is unimportant. The extrema of the monopole and quadrupole GOS of 2p–4p transition are given in this paper. The results of velocity form study also show that the electron correlation effects are important around the maxima and are found to influence the positions of the extrema insignificantly.

The probability, differential, and integral scattering cross sections of the 11S→21S and 11S→21P transitions of helium have been calculated in the first Born approximation. The projectile-target interactions depending on the temperature and the density of plasma are described by the Debye-Hückel model. Wave functions of the target before and after collision were modeled by non orthogonal Hartree-Fock orbitals. The wave functions parameters are calculated with the Ritz variational method. We improve our unscreened first Born approximation integral cross sections by using the BE-scaled (B stands for binding energy and E excitation energy) method. The second Born approximation has also been used to calculate the excitation cross sections in Debye plasma. Our calculations are compared to other theoretical and experimental results where applicable.

The influence of an electric microfield distribution function (EMDF) on line shapes and on Stark broadening parameters is studied. For this purpose, we use different EMDFs obtained by theoretical calculations and computer simulation methods to calculate the allowed 4471 Å neutral helium line and its forbidden 4470 Å component. Correlation effects are shown by considering different categories of plasmas, weakly coupled plasmas and strongly coupled plasmas, with large gaps of temperature and density.