Observation of strong relativistic and distorted-wave effects in (e, 2e) electron-momentum spectroscopy of mercury

摘要

We report a measurement of the valence orbital-momentum profiles of mercury (Hg) using a high-sensitivity binary (e, 2e) electron-momentum spectrometer at incident energies of 600 and 1200 eV plus the binding energy. The 6s_(1/2) orbital and the spin-orbit components of 5d_(5/2) and 5d_(3/2) orbitals are well separated in the measured binding-energy spectra. The experimental momentum distributions for the individual orbitals and the branching ratio of 5d_(5/2) to 5d_(3/2) are obtained and compared with predictions from a plane-wave impulse approximation (PWIA) in which the orbital wave functions are calculated using the nonrelativistic (NR) and spin-orbital (SO) relativistic theories. The SO relativistic calculations are in better agreement with experiment than the NR, indicating clearly the importance of relativistic effects in the electronic structure of Hg. We also observe some discrepancies between experiment and PWIA calculations in the high-momentum region of 6s_(1/2) and the low-momentum region of 5d orbitals which display a dynamic dependence on the impact energy. These discrepancies become smaller at a higher energy of about 1200 eV and thus can be qualitatively assigned to the distorted-wave effect in the (e, 2e) reaction of Hg.