High-resolution measurements of near-edge resonances in the core-level photoionization spectra ofSF6

The x-ray-absorption near-edge structure (XANES) of sulfur hexafluoride, ${\mathrm{SF}}_6$, in the gas phase has been measured with high energy resolution at the sulfur ${\mathit{L}}_{2,3}$ and fluorine K ionization thresholds using synchrotron radiation from the SX700/II monochromator at BESSY. Besides dominant transitions to core-excited inner-well states, several series of Rydberg states with vibrational fine structure were resolved below the sulfur ${\mathit{L}}_{2,3}$ thresholds. Using the Rydberg formula, quantum defects of ${\mathrm{\delta }}_{\mathit{s}}$=1.80 and ${\mathrm{\delta }}_{\mathit{d}}$=-0.03 were obtained for the s and d Rydberg orbitals of the central sulfur atom. A Franck-Condon analysis was used to determine the vibrational spacing and the S-F bond length of the (S 2${\mathit{p}}_{3/2}$ ${)}^{\mathrm{-}1}$4${\mathit{s}}^1$ core-excited state. The presence of vibronically coupled transitions below the sulfur ${\mathit{L}}_{2,3}$ edges was confirmed. The derived natural linewidths of the (S 2${\mathit{p}}_{1/2,3/2}$ ${)}^{\mathrm{-}1}$ Rydberg states were found to be strikingly narrower than those of the (S 2${\mathit{p}}_{1/2,3/2}$ ${)}^{\mathrm{-}1}$ inner-well resonances. Line-shape analysis also revealed significant inhomogeneous broadening of the (S 2${\mathit{p}}_{1/2,3/2}$ ${)}^{\mathrm{-}1}$ ${\mathit{a}}_{1\mathit{g}}^1$ states, which is attributed to unresolved vibrational structure. Large Lorentzian contributions to the line shapes of the (S 2${\mathit{p}}_{1/2,3/2}$ ${)}^{\mathrm{-}1}$ ${\mathit{t}}_{2\mathit{g}}^1$ resonances suggest that vibrational effects are relatively small for those states.