Dynamic effects in electron momentum spectroscopy of sulfur hexafluoride

Abstract

Electron momentum spectroscopy (EMS) results are presented for the sulfur hexafluoride (${\mathrm{SF}}_{6}$) molecule using a high-resolution binary ($e$, $2e$) spectrometer at incident energies (${E}_{i}$) of 600, 1200, and 2400 eV plus the binding energy. The valence orbital momentum profiles were measured with a binding energy resolution of 0.68 eV and angular resolutions of $\mathrm{\ensuremath{\Delta}}\ensuremath{\theta}=\ifmmode\pm\else\textpm\fi{}0.{6}^{\ensuremath{\circ}}$, $\mathrm{\ensuremath{\Delta}}\ensuremath{\phi}=\ifmmode\pm\else\textpm\fi{}0.{85}^{\ensuremath{\circ}}$. Whereas the two higher incident energies are in the range where normally EMS measurements do not exhibit an impact-energy dependence, the current experimental data display a dynamic dependence on the impact energies. The measured momentum profiles are compared with predictions from a plane-wave impulse approximation (PWIA) calculation using molecular orbitals obtained from a density-functional-theory quantum-chemistry calculation. The PWIA calculations are in fairly good agreement with experiment only for 2400 eV impact energy, particularly for the summed $1{t}_{2u}$ and $5{t}_{1u}$ orbitals. We have also compared the experimental results for the $5{a}_{1g}$ state with the molecular three-body distorted-wave (M3DW) approach using the orientation-averaged molecular orbital approximation. Unlike the PWIA, the M3DW results are in very good agreement with the experimental data at all three measured incident energies for small momenta, which indicates that dynamical distortion effects are important for this molecule.