Oxidation Studies of Dipositive Actinide Ions, An²⁺ (An = Th, U, Np, Pu, Am) in the Gas Phase:  Synthesis and Characterization of the Isolated Uranyl, Neptunyl, and Plutonyl Ions UO₂²⁺(g), NpO₂²⁺(g), and PuO₂²⁺(g)

Abstract

Reactions of atomic and ligated dipositive actinide ions, An2+, AnO2+, AnOH2+, and AnO2(2+) (An = Th, U, Np, Pu, Am) were systematically studied by Fourier transform ion cyclotron resonance mass spectrometry. Kinetics were measured for reactions with the oxidants, N2O, C2H4O (ethylene oxide), H2O, O2, CO2, NO, and CH2O. Each of the five An2+ ions reacted with one or more of these oxidants to produce AnO2+, and reacted with H2O to produce AnOH2+. The measured pseudo-first-order reaction rate constants, k, revealed disparate reaction efficiencies, k/k(COL): Th2+ was generally the most reactive and Am2+ the least. Whereas each oxidant reacted with Th2+ to give ThO2+, only C2H4O oxidized Am2+ to AmO2+. The other An2+ exhibited intermediate reactivities. Based on the oxidation reactions, bond energies and formation enthalpies were derived for the AnO2+, as were second ionization energies for the monoxides, IE[AnO+]. The bare dipositive actinyl ions, UO2(2+), NpO2(2+), and PuO2(2+), were produced from the oxidation of the corresponding AnO2+ by N2O, and by O2 in the cases of UO2+ and NpO2+. Thermodynamic properties were derived for these three actinyls, including enthalpies of formation and electron affinities. It is concluded that bare UO2(2+), NpO2(2+), and PuO2(2+) are thermodynamically stable toward Coulomb dissociation to [AnO+ + O+] or [An+ + O2+]. It is predicted that bare AmO2(2+) is thermodynamically stable. In accord with the expected instability of Th(VI), ThO(2+) was not oxidized to ThO2(2+) by any of the seven oxidants. The gas-phase results are compared with the aqueous thermochemistry. Hydration enthalpies were derived here for uranyl and plutonyl; our deltaH(hyd)[UO2(2+)] is substantially more negative than the previously reported value, but is essentially the same as our deltaH(hyd)[PuO2(2+)].

Gas-Phase Reactions of Doubly Charged Lanthanide Cations with Alkanes and Alkenes. Trends in Metal(2+) Reactivity

“…Collisional and radiative cooling as performed in the present study is usually sufficient to remove excess translational energy of the ions formed by LDI. In several previous studies of the reactivity of singly-charged lanthanide ions, Ln + , [38] and of doubly-charged actinide ions, An 2+ , [39][40][41][42], performed under experimental conditions similar to those employed in this work, no evidence was found for the involvement of excited states in the observed chemistries. In the present work, as in previous studies using this technique, effective thermalization was established by the measured reproducible pseudo first-order kinetics.…”

Gas-Phase Oxidation of Cm+ and Cm2+ − Thermodynamics of Neutral and Ionized CmO

“…Estimates for the IE[MO + ] are based on comparison with electron-transfer efficiencies for selected bare "calibration" M 2+ ions (M = Sn, Pb, Mn, Ge, Bi). These latter efficiencies for the "calibration" M 2+ ions, reported previously [13,14], are summarized in Table 8. The results in Table 8 suggest that the thermodyanmic onset for electron transfer occurs in the approximate range of 1 eV (from the Pb 2+ /CO reaction) and 1.2 eV (from the Pb/CO2 reaction), which is in accord with the estimate of ~1 eV given by Roth and Freiser [50].…”

Ions generated from uranyl nitrate solutions by electrospray ionization (ESI) and detected with fourier transform ion-cyclotron resonance (FT-ICR) mass spectrometry

“…Many of these studies have focused on the reactions of U ϩ and UO ϩ with alkanes [6,7], alkenes [8], alcohols, thiols and ethers [9], arenes [10], and other small molecules [11][12][13][14][15][16]. Recently, the hydration reactivities of UO ϩ , UO 2 ϩ , and UO 2 2ϩ were examined using secondary ion mass spectrometry [17].…”