The spectroscopic data, particularly those from NMR, are sufficiently accurate to unambiguously identify the protonation sites in aromatic compounds. Experimental information on protonation in the gas phase also comes from mass spectrometry studies involving proton transfer reactions . Even though these studies have shown the existence of several protonated isomers of many aromatic ions, and in some cases also the specific locations of the protons, the details of their structures constantly remained confused. For these cases, the structural attribution of the various isomers sometimes depended on computational chemical calculations .