Search for relativistic effects in electron-impact S→P excitation of heavy alkali atoms:: polarization, alignment and orientation in Cs

This work analyses in detail to what extent relativistic effects can be studied in electron-impact excitation of the S-2(1/2) --> P-2(1/2,3/2)o resonance transitions in heavy alkali atoms. For Cs at 10 eV impact energy as an example, numerical results were obtained in a 40-state semi-relativistic Breit-Pauli R-matrix calculation. For comparison, results were generated in the corresponding 23-state non-relativistic LS model. The standard Stokes parameters obtained with unpolarized electron beams are found to be extremely insensitive to the inclusion of relativistic effects. This insensitivity explains the success of non-relativistic theories in reproducing experimental results for heavy alkali atoms. If spin-polarized electrons are used, however, the generalized Stokes parameters and other spin-asymmetry parameters display small but experimentally accessible relativistic effects. Implications for future experimental studies of these systems are discussed and recommendations are given.