Collision-induced dissociation of [UO 2 (NO 3 )(O 2 )] - and reactions of product ions with H 2 O and O 2 .

We recently reported a detailed investigation of the collision-induced dissociation (CID) of [UO ₂ (NO ₃ ) ₃ ] ^- and [UO ₂ (NO ₃ ) ₂ (O ₂ )] ^- in a linear ion trap mass spectrometer (J. Mass Spectrom. DOI:10.1002/jms.4705). Here, we describe the CID of [UO ₂ (NO ₃ )(O ₂ )] ^- which is created directly by ESI, or indirectly by simple elimination of O ₂ from [UO ₂ (NO ₃ )(O ₂ ) ₂ ] ^- . CID of [UO ₂ (NO ₃ )(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 NO ₂ . DFT calculations identify a pathway by which both product ions can be generated, which involves initial isomerization of [UO ₂ (NO ₃ )(O ₂ )] ^- to create [UO ₂ (O)(NO ₂ )(O ₂ )] ^- , from which elimination of NO ₂ or O ₂ will leave [UO ₂ (O)(O ₂ )] ^- or [UO ₂ (O)(NO ₂ )] ^- , respectively. For the latter product ion, the composition assignment of [UO ₂ (O)(NO ₂ )] ^- rather than [UO ₂ (NO ₃ )] ^- 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 [UO ₂ (NO ₃ )] ^- is not observed. Instead, the species reacts with H ₂ O, which is predicted to be the favored pathway for [UO ₂ (O)(NO ₂ )] ^- . 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 [UO ₂ (O)(NO ₂ )] ^- and [UO ₂ (O)(O ₂ )] ^- form H ₂ O adducts, and calculations suggest these species spontaneously rearrange to create dihydroxides.
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