Positron Impact Excitation for the Lowest Autoionizing State of Cesium using the Distorted Wave Method
Munywoki, Abednego Wambua
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Atomic collision cross sections are of interest because they can show the collision dynamics involved in the scattering process. There has been an upsurge in interest on positron collision processes due to recent advancement in positron beam experiments. In these studies, alkali metal atoms receive preference due to their simple electronic structure and spectra. We have calculated differential cross-sections, integral cross-sections, lambda (λ) parameter and the alignment parameter (A20) for positron impact excitation for the lowest autoionizing state of cesium have been calculated using the distorted wave method for projectile energies between 13.5 and 1000 eV. This was meant to provide data for comparison with existing positron scattering results as well as form a basis for comparison with future experimental results on positron scattering. We used Roothan- Hatree- Fock atomic wave functions both multi-zeta and double zeta. We also used the ground state static potential as the distorting potential in the initial channel. For the final channel, we used a linear combination of the ground state static potential and the excited state static potential. The obtained results have shown a general agreement with available theoretical results at high energies but a slight disagreement at low energies due to the change in the distorting potential. However, the positron cross-sections do not show dominant features at energies near excitation threshold as observed in most electron scattering results. This indicates the inability of positrons to excite an atom to autoionizing states. The lambda parameter and alignment parameters point to a higher possibility of the promotion of the m=0 electron from the 5p electron at low energies compared to the m=1 electron. At high energies, the cross-sections merge an indication that the choice of distorting potential has no effect on the scattering process.