Coherence parameter measurements for electrons scattering off heavy noble gas targets

Electron impact excitation of the resonance levels of Ne, Ar, Kr and Xe has been studied for electron scattering angles up to 50' and impact energies between 30 and 80 eV. The P 1 and P 4 Stokes parameters have been measured in each case so that the influence of spin in the excitation process could be studied through evaluation of rho 00 , the relative spin-flip cross section. After careful account was taken of various depolarizing effects due particularly to the finite volume of the interaction region and, in the cases of Kr and Xe, to nuclear spin, very good agreement has been found with theoretical predictions thus resolving a previously reported discrepancy. No evidence has been found for spin-flip under the experimental parameters used in this study, even for the heaviest target studied.