Gas-Phase Reactions of Bare and Ligated Uranium Ions with Sulfur Hexafluoride

Reactions of bare and ligated uranium ions with sulfur hexafluoride were studied in a quadrupole ion trap mass spectrometer. Bare U+ was found to react rather efficiently with SF6 (k/kADO ∼ 0.4) to produce both UFn (n ) 1, 2, 3, 4) and SFn (n ) 1, 2, 3). Whereas the UF/SF6 reaction rate was essentially the same as that for U/SF6, both UF2 and UF3 were inert; this is attributed to a repulsive interaction between UFn and SF6 when n exceeds 1. Reactions of UF+ (k/kADO ∼ 0.2) and UF2 (k/kADO ∼ 0.05) with H2O resulted in both F f OH exchange and oxidation. In contrast, UF3 reacted very efficiently with H2O (k/kADO ∼ 1), exhibiting only F f OH exchange. The primary ion products of the UO/SF6 reaction (k/kADO ∼ 0.2) were SF3 and UOF2; those of the UOH/SF6 reaction (k/kADO ∼ 0.3) were SF3 and UOF+. The reaction results are discussed in the context of a previously proposed reaction model, the distinctive chemistry of uranium, and thermodynamic considerations. The results illuminate the nature of uranium as well as general aspects of the interaction of bare and ligated transition-metal ions with SF6. Results for collision-induced dissociation (CID) of selected uranium molecular ions support the concept of CID being a quasithermal process under these experimental conditions, with rearrangements prior to fragmentation possible for certain ions.