ELECTRON-IMPACT CORE EXCITATION OF SF6 .1. S-2P, S-2S, AND F-1S SPECTROSCOPY

Electron energy-loss spectra (EELS) of SF6 have been recorded in the r egion of S 2p, S 2s, and F 1s excitation, using both dipole and nondip ole electron-scattering conditions. Impact energies between 700 and 32 00 eV and scattering angles between 0 degrees and 30 degrees were used . Relative to dipole EELS or photoabsorption, there are large intensit y redistributions in both the S 2p and S 2s spectra under nondipole co nditions. In contrast, the F 1s spectrum is essentially the same in ne ar-dipole and nondipole scattering regimes. A higher-order electric mu ltiple S 2p spectra feature is observed at 181 eV. It has an unusual m ultipeaked line shape whose components are more closely spaced than th e typical 1.15-eV S 2p spin-orbit splitting. It is attributed to the o verlap of several quadrupole-coupled states, which are likely associat ed with the [S 2p(t(1u))(-1),t(1u)] configuration. Ab initio self-cons istent field calculations for various open-shell S 2p excited states a re used to assist spectral assignments.