Measurements of circular polarization correlations following excitation of Ar and Kr by electron impact

We report measurements of the circular polarization correlation parameter P₃ for the excitation of the 4 s′[1/2]_j=1 state in Ar by 40 eV electrons and for the excitation of the Kr 5 s[3/2]_J=1 state by 30 eV electrons at electron scattering angles up to 50°. The measured Ar data are compared to predictions of a distorted wave Born approximation (DWBA). The agreement is in general not very good with theory predicting P₃ values considerably larger than the measured values in the regime of small scattering angles. In Kr, where the measured data are compared to theoretical predictions from a DWBA, a first-order many-body theory (FOMBT) and a relativistic distorted wave theory (RDW), the level of agreement between experiment and theory is somewhat better. The measured P₃ parameters in conjunction with the previously measured linear coherence parameters P₁ und P₂ under the same scattering conditions yield the total polarization P_tot⁺ which is a measure for the level of coherence in the excitation process. In both cases studied here, we found values of eliminate P_tot⁺ that were consistent with a fully coherent excitation process.