(e, eγ)-coincidence studies to determine spin-resolved Stokes parameters of the 185 nm emission line in mercury

Direct measurements of the three Stokes parameters (polarization components) P1, P2 and P3 of the VUV Hg transition 6s6p1P1 → 6s21S 0 (185 nm) have been carried out at electron impact energies of 15 eV, 50 eV and 100 eV. Within the experimental uncertainty, no influence of the electron spin was discovered for scattering angles ≤ 30°. At 15 eV excitation energy and scattering angles ≥ 80°, increasing spin effects become apparent. The experimental data are compared to theoretical predictions from a first-order full-relativistic distorted-wave model, a five-state Breit-Pauli R-matrix (close-coupling) approach, and a convergent close-coupling model, in which relativistic effects are accounted for by adding non-relativistic amplitudes using known intermediate-coupling coefficients. At scattering angles ≤ 15°, all of the theories reproduce the experimental data well, whereas the CCC model exhibits the best overall agreement with experiment at large scattering angles