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

Abstract

Electron impact ionization and ion–molecule reactions of octafluoro-2-butene ( 2-C 4F 8) 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 C 4F 7,8 +, C 3F 3,5,6 +, C 2F 4 + and CF 1–3 + as the major ions. The total ionization cross-section reaches a maximum of 1.2 × 10 −15 cm 2 at 90 eV. From threshold to 18 eV, the ion population is dominated by the parent ion C 4F 8 +, and from 18 to 70 eV, by C 3F 5 +. Above 70 eV, CF 3 + becomes the dominant ion. Among the major ions formed by electron impact ionization of 2-C 4F 8, only CF +, CF 2 + and CF 3 + are found to react with the parent molecule, via F − transfer or charge transfer mechanisms. The charge transfer reaction of Ar + with 2-C 4F 8 produces mainly C 4F 7 +. The ion chemistries in 2-C 4F 8 are significantly different from those in c-C 4F 8 that we have previously studied.