The potential-energy surface of the triatomic cation [Cr,O-2](+) has been examined by means of ion-cyclotron resonance and sector-field mass spectrometry as well as high-level theoretical methods. Chromium(V) dioxide cation OCrO+ can be generated by electron ionization of CrO2Cl2 and exhibits a doublet ground state. The experimentally determined IE(CrO2) of 9.7 +/- 0.2 eV leads to Delta H-f(OCrO+) = 209 +/- 12 kcal/mol which compares well with a theoretical prediction of 217 kcal/mol. The high-valent chromium(V) dioxide OCrO+ slowly reacts with H-2 to form CrO+ and H2O as products. Activation of saturated and unsaturated hydrocarbons, including methane and benzene, is much more efficient and involves C-H as well as C-C bond activation. In the reaction of OCrO+ with CH4 the by-product OCr(OCH2)(+) points to the operation of a stepwise mechanism in that initially a single oxo unit in OCrO+ is activated in terms of a [2 + 2] cycloaddition of methane across the Cr-O double bond. A structurally different [Cr,O-2](+) cation can be generated by chemical ionization of a mixture of Cr(CO)(6) and O-2. The experimental findings together with the computations propose that the ions formed consist of a mixture of doublet and quartet states of the dioxide OCrO+ and the dioxygen complex Cr(O-2)(+) ((6)A "); in the latter the dioxygen unit is end-on coordinated to the metal. Due to spin conservation, the direct formation of the doublet ground state OCrO+ ((2)A(1)) from the ground state reactants Cr+ (S-6) and O-2 ((3) Sigma(g)(-)) is not possible; rather, two curve crossings from the sextet via the quartet to the doublet surface in the sequence Cr-6(+) + O-3(2) --> Cr-6(O-2)(+) --> (OCrO+)-O-4 --> (OCrO+)-O-2 are suggested.