The gas-phase potential energy surface of [Fe,C-6,H-6,0](+) isomers is examined by collisional activation using a large-scale tandem mass spectrometer, as well as ion/molecule reactions employing the conditions of ion cyclotron resonance mass spectrometry. In addition to the (phenolFe+ complex (1), five other isomers could be distinguished and characterized : (C6H5Fe+(OH) (2), (C6H4Fe+(OH2) (3), (2,4-cyclohexadienoneFe+ (4), (c-C5H6Fe+(CO) (5), and (C6H6)FeO+ (6). The collision-induced fragmentation patterns of these isomers, the results of H/D exchange reactions with C2D4 and D2O, as well as thermochemical estimates, using a simple additivity scheme, permit the construction of a qualitative potential energy surface for [Fe,C6H6,0]+. On the basis of these findings, new insight is provided into the reaction mechanisms of and the intermediates formed in the oxidation of benzene and ethylbenzene by "bare" FeO+. Furthermore, the dissociation of the Fe+ complex of the valence tautomers benzene oxide reversible arrow oxepin is demonstrated to proceed via (phenolFe+ (1) rather than (2,4-cyclohexadienone) Fe+ (4), and evidence is presented for the existence of an additional mechanism for the oxygenation of arenes by iron oxenoids in the gas phase.