Electron-impact excitation of the ns[3/2]oJ=2,1 and ns'[ 1/2]oJ=0,1 levels of Ne, Ar, Kr and Xe

Relative differential cross sections for electron-impact excitation of the four lowest electronic levels ns[3/2]oJ=2 and 1 ns'[1/2]oJ=0 and 1 were measured for Ne, Ar, Kr and Xe at 30 eV impact energy and for Kr and Xe at 20 eV impact energy for a range of scattering angles from 0 degrees to 134 degrees . The aim of the present work was: to improve the quality of existing data, to extend the measurements to small scattering angles, to determine whether statistical weight (branching) ratios represent the ns[3/2]o2 to ns'[1/2]o DCS ratios (r) and to compare the experimental results with the predictions of non-relativistic and relativistic first-order scattering theories. We found that the experimental ratios r closely correspond to statistical weight ratios for Ne and Ar at all scattering angles, for Kr at most angles, but seriously deviate from statistical weight ratios for Xe at all angles. First-order scattering theories yield good and reasonable predictions for Ne, Ar and Kr, respectively. For Xe theories also predict significant deviations from statistical weight ratios but there is no agreement between experiment and theory. Surprisingly, the DCS ratios (r') obtained for the ns[3/2]o1, and ns'[1/2]o1, levels by experiment and various first-order theories deviate significantly for all rare-gas species. It is also surprising that the fully relativistic first-order theory does not show improved agreement between experiment and theory in the case of Xe.