The Formation of Negative Ions of Sulfur Hexafluoride

Abstract

Negative ion production in SF₆ has been studied in a mass spectrometer; SF₆⁻, SF₅⁻, F₂⁻, and F⁻ were identified. The SF₆⁻ and SF₅⁻ are produced in very large quantities by a resonance capture process at an electron energy of about 2 ev, and are formed in approximately equal amounts. At higher electron energies, the same capture occurs by a secondary process, in which low energy electrons released by other excitation and ionization processes suffer the resonance capture. Partial dissociation after electron capture accounts for the appearance of F⁻ and F₂⁻ ions below 16 ev. Above this energy, other processes will also produce these ions. Possible explanations of the primary resonance capture mechanism are discussed.