Comparisons of electron impact ionization and ion chemistries of CF3Br andCF3I

Comparisons of the electron impact ionization and of the ion-molecule react ions for CF3Br and CF3I are made from a study of the two compounds using Fo urier-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 x 10(-16) cm(2) for CF3Br and CF3I, respectively. These results appear to be the first for the molecules. The ion-molecule reactions in the two co mpounds are similar, with CF+ and X+ (X = Br or I) being the most reactive ions (k similar to (8 -13) x 10(-10) cm(3) s(-1)). Ar+ reactions with the t wo compounds are also studied. Results of our study on the ion kinetics are compared with those from previous studies by other groups. (C) 2001 Elsevi er Science B.V.