Collision-induced dissociation of [UO2(NO3)(O-2)](-) and reactions of product ions with H2O and O-2

We recently reported a detailed investigation of the collision-induced dissociation (CID) of [UO2(NO3)(3)](-) and [UO2(NO3)(2)(O-2)](-) in a linear ion trap mass spectrometer (J. Mass Spectrom. DOI:10.1002/jms.4705). Here, we describe the CID of [UO2(NO3)(O-2)](-) which is created directly by ESI, or indirectly by simple elimination of O-2 from [UO2(NO3)(O-2)(2)](-). CID of [UO2(NO3)(O-2)](-) creates product ions as at m/z 332 and m/z 318. The former may be formed directly by elimination of O-2, while the latter required decomposition of a nitrate ligand and elimination of NO2. DFT calculations identify a pathway by which both product ions can be generated, which involves initial isomerization of [UO2(NO3)(O-2)](-) to create [UO2(O)(NO2)(O-2)](-), from which elimination of NO2 or O-2 will leave [UO2(O)(O-2)](-) or [UO2(O)(NO2)](-), respectively. For the latter product ion, the composition assignment of [UO2(O)(NO2)](-) rather than [UO2(NO3)](-) is supported by ion-molecule reaction behavior, and in particular, the fact that spontaneous addition of O-2, which is predicted to be the dominant reaction pathway for [UO2(NO3)](-) is not observed. Instead, the species reacts with H2O, which is predicted to be the favored pathway for [UO2(O)(NO2)](-). This result in particular demonstrates the utility of ion-molecule reactions to assist the determination of ion composition. As in our earlier study, we find that ions such as [UO2(O)(NO2)](-) and [UO2(O)(O-2)](-) form H2O adducts, and calculations suggest these species spontaneously rearrange to create dihydroxides.