Electron impact ionization and ion–molecule reactions of octafluoro-2-butene

Electron impact ionization and ion–molecule reactions of octafluoro-2-butene (2-C4F8) were studied using Fourier transform mass spectrometry (FTMS). Fifteen product ions are formed by electron impact ionization over the energy range 10–200 eV, with C4F7,8+, C3F3,5,6+, C2F4+ and CF1–3+ as the major ions. The total ionization cross-section reaches a maximum of 1.2 × 10−15 cm2 at 90 eV. From threshold to 18 eV, the ion population is dominated by the parent ion C4F8+, and from 18 to 70 eV, by C3F5+. Above 70 eV, CF3+ becomes the dominant ion. Among the major ions formed by electron impact ionization of 2-C4F8, only CF+, CF2+ and CF3+ are found to react with the parent molecule, via F− transfer or charge transfer mechanisms. The charge transfer reaction of Ar+ with 2-C4F8 produces mainly C4F7+. The ion chemistries in 2-C4F8 are significantly different from those in c-C4F8 that we have previously studied.