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

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 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 compounds 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 two compounds are also studied. Results of our study on the ion kinetics are compared with those from previous studies by other groups. (C) 2001 Elsevier Science B.V.