Gas-phase plutonium nitrate anion complexes were produced by electrospray ionization (ESI) of a plutonium nitrate solution. The ESI mass spectrum included species with all four of the common oxidation states of plutonium: Pu(III), Pu(IV), Pu(V), and Pu(VI). Plutonium nitrate complexes were isolated in a quadrupole ion trap and subjected to collision-induced dissociation (CID). CID of complexes of the general formula PuOx(NO3)(y) resulted in the elimination of NO2 to produce PuOx+1(NO3)(y-1)(-), which in most cases corresponds to an increase in the oxidation state of plutonium. Plutonyl species, PuVO2(NO3)(2) and PuVIO2(NO3)(3), were produced from PuIII(NO3)(4) and PuIV(NO3)(5)(-) , respectively, by the elimination of two NO2 molecules. CID of (PuO2)-O-VI(NO3)(3)(-) resulted in NO2 elimination to yield PuO3(NO3)(2)(-) , in which the oxidation state of plutonium could be VII, a known oxidation state in condensed phase but not yet in the gas phase. Density functional theory confirmed the nature of (PuO2)-O-V(NO3)(2)(-) and (PuO2)-O-VI(NO3)(3)(-) as plutonyl(V/VI) cores coordinated by bidentate equatorial nitrate ligands. The computed structure of PuO3(NO3)(2)(-) is essentially a plutonyl(VI) core, PuVIO2 (2+) , coordinated in the equatorial plane by two nitrate ligands and one radical oxygen atom. The computations indicate that in the ground spinorbit free state of PuO3(NO3)(2)(-) , the unpaired electron of the oxygen atom is antiferromagnetically coupled to the spin-triplet state of the plutonyl core. The results indicate that Pu(VII) is not a readily accessible oxidation state in the gas phase, despite that it is stable in solution and solids, but rather that a Pu(VI)-O. bonding configuration is favored, in which an oxygen radical is involved.