No abstract

No abstract

The electron-impact excitation of the individual levels that constitute the 4p 5 5s configuration of Kr is experimentally and theoretically investigated at incident electron energies of 20.0, 15.0, 13.5 and 12.0 eV, for scattering angles ranging from 10 • to 135 • . High resolution electron energy-loss spectroscopy is used to obtain spectral intensities for the excitation of each of the four 4p 5 5s levels from the ground state. The intensities lead to three differential cross section ratios. Absolute electron-impact excitation cross sections are then determined by normalization to elastic scattering cross sections using the conventional inelastic to elastic normalization method. The present theoretical cross sections are calculated using two different methods, namely the R-matrix method and the unitarized first-order many-body theory. Comparisons between the experimental and the theoretical results show some good agreement, but reveal areas where significant improvement of the present models is needed. Additionally, it is shown that in the present case, just as in general for the rare gases, differential cross section ratios provide a sensitive test of theoretical models as well as unique insights concerning relativistic effects in the scattering process. Comparisons with existing models and other experimental data are also presented.

We present measurements of the (e, 2e) cross sections of xenon for transitions leading to the 5p 3/2 and 5p 1/2 states of the residual ion using an incident polarized electron beam in coplanar asymmetric kinematics and in the intermediate energy regime. The results show that the spin up-down asymmetry for the 5p 3/2 and 5p 1/2 transitions can be understood as an analogue of the so-called fine-structure effect in inelastic scattering. However, our present measurements also point to significant contributions from relativistic effects in the electron-atom system under certain conditions. The measured spin up-down asymmetry is analysed using the density matrix formalism. This approach reveals that different exchange interactions contribute to the fine-structure effect for ionization. The contribution of relativistic interactions in the observed parameters is also investigated by using a semirelativistic DWBA model to evaluate the scattering amplitudes.

Using beams of polarised electrons and polarised hydrogen atoms we measured the spin antiparallel-parallel ionisation asymmetry from threshold to 500 eV. Our measurements are generally more precise than those of earlier studies and, more significantly, are characterised by an energy spread that is at least an order of magnitude smaller than that of the earlier work. We compare our results with several theoretical models as well as with the results from similar experiments using polarised alkali atoms.