The IR spectrum of the fluoronium isomer of protonated fluorobenzene (F-C6H6F+, phenylfluoronium) is recorded in the vicinity of the C-H and F-H stretch fundamentals to obtain the first structured spectrum of an isolated protonated aromatic molecule in the gas phase. Stable F-C6H6F+ ions are produced via proton transfer from CH5+ to fluorobenzene (C6H5F) in a supersonic plasma expansion. The F-C6H6F+ spectrum recorded between 2540 and 4050 cm(-1) is consistent with a weakly bound ion-dipole complex composed of HF and the phenyl cation, HF-C6H5+. The strongest transition occurs at 3645 cm(-1) and is assigned to the F-H stretch (sigma(FH)). The antisymmetric C-H stretch of the two ortho hydrogen atoms, sigma(CH) = 3125 cm(-1), is nearly unshifted from bare C6H5+, indicating that HF complexation has little influence on the C-H bond strength Of C6H5+. Despite the simultaneous production of the more stable ring protonated carbenium isomers Of C6H6F+ (fluorobenzenium) in the electron ionization source, F-C6H6F+ can selectively be photodissociated into C6H5+ and HF under the present experimental conditions, because it has a much lower dissociation energy than all carbenium isomers. Quantum chemical calculations at the 83LYP and MP2 levels of theory using the 6-311G(2df,2pd) basis support the interpretation of the experimental data and provide further details on structural, energetic, and vibrational properties of F-C6H6F+, the carbenium isomers Of C6H6F+, and other weakly bound HF-C6H5+ ion-dipole complexes. The dissociation energy of F-C6H6F+ with respect to dehydrofluorination is calculated as D-0 = 4521 cm(-1) (similar to54 kJ/mol). Analysis of the charge distribution in F-C6H6F+ supports the notation of a HF-C6H5+ ion-dipole complex, with nearly the whole positive charge of the added proton distributed over the C6H5+ ring. As a result, protonation at the F atom strongly destabilizes the C-F bond in C6H5F.