The reactivity of CF3CO+ ions, formed via two different routes, has been studied in the gas phase by the joint use of mass spectrometric and radiolytic techniques, spanning a pressure range from 10(-8) Torr to ca. 1 atm. The 23 kcal mol(-1) exothermic addition of CF3+ to CO provides a route to CF3CO+ requiring third-body stabilization of the adduct ion. In the 10(-8) Torr pressure regime of Fourier transform ion cyclotron resonance (FT-ICR) spectrometry, CF3CO+ ions from electron ionization (EI) induced fragmentation of trifluoroacetic anhydride yield NuCF(3)(+) products from oxygen-centered nucleophiles (Nu) and XC(6)H(4)CO(+) ions from aromatics (C(6)H(5)X) At ca. 1 atm trifluoroacetylated products are efficiently formed even with strongly deactivated aromatics, showing distinct intra- and intermolecular selectivity features pertaining to the reactant CF3CO+ ions. The reactivity pattern is interpreted according to a kinetic interplay of collisional and chemical events depending on the activation of C(6)H(5)X toward electrophilic attack.