Absolute transition probability measurement of nondipole valence-shell (7–70 eV) electronic transitions of SF6 by angle-resolved electron energy loss spectroscopy

A coplanar electron spectrometer has been constructed for angle-resolved electron energy loss measurements. The experimental arrangement and performance of the spectrometer are described. Absolute absorption transition probabilities (or generalized oscillator strengths) of valence-shell (7–70 eV) electronic transitions of SF6 have been determined as a function of energy loss and momentum transfer at an impact energy of 2.5 keV. New nondipole transitions have been observed at nonzero momentum transfer. Together with the term values obtained from previous dipole electron energy loss and photoabsorption measurements, the momentum transfer dependence of the transition probabilities can be used to provide tentative assignments of the observed nondipole valence-shell transitions of SF6. Despite the complexity of the electronic structure of SF6, the present work demonstrates the feasibility of angle-resolved electron energy loss spectroscopy for investigating nondipole phenomena and related electron-induced excitation processes.