[en] The reactivity and selectivity of radiolytically (⁶⁰Co γ rays) generated unsolvated trifluoromethylium (CF₃⁺) ions toward selected aromatic substrates have been measured under conditions where nonionic processes can be safely ruled out. The same situation could not be attained for the trichloromethylium (CCl₃⁺) ion, owing to the overwhelming interference of CCl₃ radicals, by far the major reactive species produced by the γ radiolysis of gaseous carbon tetrachloride. The unsolvated CF₃⁺ ion is a moderate electrophile, whose attack on differently substituted aromatic substrates is rather indiscriminate; its positional selectivity toward a toluene molecule (para/0.5 meta = 4.3) appears intermediate between the one of i-C₃H₇⁺ ions (para/0.5 meta = 2.7) and that displayed by the very mild t-C₄H₉⁺ cation (para/0.5 meta = 35). 4 figures; 5 tables; 29 references