Electron transfer to SF6 and oriented CH3Br

Previous experiments have suggested that different negative ions are formed by electron transfer to different ends of a molecule. To investigate this possibility, a crossed molecular beam apparatus has been constructed to mass-analyze the ions produced in collisions between fast K atoms and oriented molecules. Initial studies are reported on ion formation in collisions of unoriented SF6 and oriented CH3Br. For lab energies ≈ 5-30 eV, Br- is the only ion observed from CH3Br, and its formation is favored by attack at the Br-end of CH3Br. The Br and CH3 ends have the same energetic threshold for forming Br-. SF5-, SF6-, and F- ions are observed from SF6 and O2- from O2. These ions are formed over a range of energies unlike those formed by electron attachment and suggest that the nascent negative ion can be stabilized by the accompanying positive K+. © 1999 American Chemical Society.