Electron-impact dissociative ionization of SF6 studied by angle-resolved (e, e plus ion) spectroscopy

We study the electron-impact dissociative ionization of SF6 using a scattered electron-ion coincidence technique. The ion-yield spectra are obtained at an incident electron energy of 1.4 keV for scattering angles ranging from 2.2 degrees to 8.2 degrees to investigate the momentum transfer dependences of the fragment-ion yields and shape resonance features. It is found that the 4t1u -> epsilon t2g resonance is evident over a wide momentum transfer range, indicating its strong influence on the SF3+ production by electron impact, while resonance bands in the SF5+ and SF4+ yield spectra rapidly diminish with increasing momentum transfer. In addition, the angular distribution of SF5+ reveals the significant difference in stereodynamics between electron-impact-induced and photon-induced ionization of SF6. We also discuss the dissociation mechanisms of SF6+ using the kinetic energy distributions of the fragment ions. Analysis of the data strongly suggests that many of the SF6+ ions in the D 2T2g state decay by internal conversion to a lower electronic state and dissociate to SF5+ + F, followed by statistical emission of F or F2.