Comparisons of electron impact ionization and ion chemistries of CF3Br and CF3I

Abstract

Comparisons of the electron impact ionization and of the ion-molecule reactions for CF3Br and CF3I are made from a study of the two compounds using Fourier-transform mass spectrometry. The ionization of the compounds over the energy range from threshold to 70 eV produces primarily the molecular ion and 6 fragment ions, with the dominant ion from CF3Br being CF3+ and, from CF3I, CF3I+. The total cross sections at 70 eV are 8.3 ± 0.8 and 9.0 ± 0.9 × 10−16 cm2 for CF3Br and CF3I, respectively. These results appear to be the first for the molecules. The ion-molecule reactions in the two compounds are similar, with CF+ and X+ (X = Br or I) being the most reactive ions (k ∼ (8–13) × 10−10 cm3 s−1). Ar+ reactions with the two compounds are also studied. Results of our study on the ion kinetics are compared with those from previous studies by other groups.