Electron-impact core excitation of SF6. I. S 2p, S 2s, and F 1s spectroscopy

Electron energy-loss spectra (EELS) of SF6 have been recorded in the region of S 2p, S 2s, and F 1s excitation, using both dipole and nondipole electron-scattering conditions. Impact energies between 700 and 3200 eV and scattering angles between 0° and 30° were used. Relative to dipole EELS or photoabsorption, there are large intensity redistributions in both the S 2p and S 2s spectra under nondipole conditions. In contrast, the F 1s spectrum is essentially the same in near-dipole and nondipole scattering regimes. A higher-order electric multiple S 2p spectra feature is observed at 181 eV. It has an unusual multipeaked line shape whose components are more closely spaced than the typical 1.15-eV S 2p spin-orbit splitting. It is attributed to the overlap of several quadrupole-coupled states, which are likely associated with the [S 2p(t1u)-1,t1u] configuration. Ab initio self-consistent field calculations for various open-shell S 2p excited states are used to assist spectral assignments.