ELECTRON-IMPACT EXCITATION OF THE NS[3 2]J=2,1(O) AND NS'[1/2]J=0,1(O) LEVELS OF NE, AR, KR AND XE/

Relative differential cross sections for electron-impact excitation of the four lowest electronic levels (ns[3/2]J=2 and 1 and ns'[1/2]J=0 a nd 1) were measured for Ne, Ar, Kr and Xe at 30 eV impact energy and f or Kr and Xe at 20 eV impact energy for a range of scattering angles f rom 0-degrees to 134-degrees. The aim of the present work was: to impr ove 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]2o to ns'[1/2]0 DCS ratios (r) and to com pare the experimental results with the predictions of non-relativistic and relativistic first-order scattering theories. We found that the e xperimental ratios r closely correspond to statistical weight ratios f or Ne and Ar at all scattering angles, for Kr at most angles, but seri ously deviate from statistical weight ratios for Xe at all angles. Fir st-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 b etween experiment and theory. Surprisingly, the DCS ratios (r') obtain ed for the ns[3/2]1o, and ns'[1/2]1o levels by experiment and various first-order theories deviate significantly for all rare-gas species. I t is also surprising that the fully relativistic first-order theory do es not show improved agreement between experiment and theory in the ca se of Xe.