Relativistic Distorted Wave Theory Research Articles

A comparison of the theoretical and experimental results for keV electron scattering from argon

Experiments studying the scattering of keV electrons from noble gas atoms have been performed in the past, as the first Born approximation (FBA) was thought to be valid under these conditions, and hence it was expected that these experiments could be modelled relatively straightforwardly by theory. Somewhat surprisingly these experiments have so far attracted only very limited theoretical interest and the ability of modern scattering theory to describe them has not been firmly established. In our earlier study of the cross section for the resonant transitions, we established that the FBA was sufficient to describe the results for small scattering angles, but it did not account for the observed intensity at larger angles. Here we extend this comparison for the case of argon to monopole, quadrupole and octopole transitions below the continuum. The experimental results show differential cross sections spanning many orders of magnitude for these transitions. The relativistic distorted wave theory developed here describes these experiments for many transitions and a large range of scattering angles reasonably well.

C-R Model for Ar plasmas using reliable excitation cross-sections

We have used reliable electron excitation cross sections in a simple Collisional-Radiative Model (CRM) to obtain the population densities of various excited levels for low electron temperature Ar discharges. Cross sections are obtained by using relativistic distorted wave theory for transitions from ground as well as excited states to the different higher lying levels of the Ar atom. We have compared our calculated population density results for 3p54s levels with recent exp erimental OES measurements.

Electron impact excitation of the M-shell electrons from Zn-like through Co-like tungsten ions

A detailed study using fully relativistic distorted wave theory for electron impact excitation of Zn-like through Co-like tungsten ions is presented in a wide range of incident electron energies up to 50 keV. We have considered electron impact excitations, namely 3d–4p and 3d–nf (n = 4–8) transitions from the M-shell of the ground state in the Zn-like W44+, Cu-like W45+, Ni-like W46+ and Co-like W47+ ions. We report excitation cross sections for these dipole allowed transitions considered in all the four ions along with the linear polarization of the photon emissions due to the decay of the excited anisotropic states to the ground state. We also provide the analytic fits to our calculated cross sections for plasma application purposes.

Measurements of circular polarization correlations following excitation of Ar and Kr by electron impact

We report measurements of the circular polarization correlation parameterP3 for the excitation of the 4s′[1/2]j=1 state in Ar by 40 eV electrons and for the excitation of the Kr 5s[3/2]J=1 state by 30 eV electrons at electron scattering angles up to 50°. The measured Ar data are compared to predictions of a distorted wave Born approximation (DWBA). The agreement is in general not very good with theory predictingP3 values considerably larger than the measured values in the regime of small scattering angles. In Kr, where the measured data are compared to theoretical predictions from a DWBA, a first-order many-body theory (FOMBT) and a relativistic distorted wave theory (RDW), the level of agreement between experiment and theory is somewhat better. The measuredP3 parameters in conjunction with the previously measured linear coherence parametersP1 undP2 under the same scattering conditions yield the total polarizationPtot+ which is a measure for the level of coherence in the excitation process. In both cases studied here, we found values of eliminatePtot+ that were consistent with a fully coherent excitation process.