Ion-molecule reactions in trifluoromethyl iodide and pentafluoroethyl iodide

Abstract

Ion-molecule reactions in trifluoromethyl iodide and pentafluoroethyl iodide were studied using time-of-flight and ion cyclotron resonance mass spectrometry, respectively, to obtain information about reaction rates and mechanistic pathways. In the CF 3I system, CF 3 + reacts with parent via F − transfer (exoergic) or via charge exchange (strongly endoergic). The I + ion reacts by I atom abstraction (exoergic) giving I 2 + or by endoergic charge exchange. The parent ion CF 3I + can decay via collisionally induced dissociation, but also undergoes condensation reactions with neutral CF 3I yielding CF 3I 2 + and the dimer ion (CF 3I) 2 +; the ether-structure product (CF 3) 2I + was not seen. Many of the same reaction types are seen in the C 2F 5I system. The CF + ion undergoes I − and CF 3 − transfer reactions with parent, giving C 2F 5 + and CF 2I +, respectively. As in the CF 3I system, CF 3 + (and also CF 2I + and C 2F 5 +) react with substrate either via energetically favorable F − transfer or via strongly unfavorable charge transfer processes, giving C 2F 4I + and C 2F 4I +, respectively, with each reactant. Again, I − reacts by energetically favorable I atom abstraction or unfavorable charge transfer. Endoergic charge transfer also occurs between parent and C 2F 4 + ion. Two condensation products were seen which are analogous to the methyl case — namely C 2F 5I 2 + and (C 2F 5I) 2 +. In both the CF 3I and C 2F 5I systems, there is strong evidence for participation of ions with as much as 1.5 eV of excitation energy.