Gas-Phase Reactions of Hydrocarbons with An⁺ and AnO⁺ (An = Th, Pa, U, Np, Pu, Am, Cm):  The Active Role of 5f Electrons in Organoprotactinium Chemistry

Abstract

Activation of small (C1−C4) alkanes and alkenes by bare and oxo-ligated actinide cations (Th+ through Cm+) has been systematically examined using Fourier transform ion cyclotron resonance mass spectrometry. The reduced reactivities of Pu+, Am+, and Cm+ correlate with the energies for electronic excitation to a 5f n- 26d7s configuration, which indicates that their 5f electrons are chemically inert. The reactivity trend identified for the highly reactive early actinide ions, Th+ > Pa+ > U+ > Np+, is interpreted to indicate significant 5f electron participation in organoactinide σ-type bond formation for Pa+. Among the seven studied AnO+ ions, only ThO+, PaO+, and UO+ activated at least one hydrocarbon, with the reactivity of PaO+ being distinctively high. Electronic structure calculations for PaO+ show that its ground state is Pa(5f6d)O+, i.e., with one 5f and one 6d nonbonding electrons available on the metal, and all of its excited states up to 1.8 eV have a 5f orbital occupancy of ≥0.8. The high reactivity and substantial 5f character of PaO+ indicate participation of 5f electrons in hydrocarbon bond activation for oxo-ligated Pa+. The results of this work reveal that 5f electrons play a distinctive role in protactinium chemistry involving σ-type organometallic bonding.

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

“…Because the ThO + ion distinctively produces the radical-like ThOC5H5 + product in its reaction with isoprene [11], the reactivity of UO + with dienes is considered to better represent the characteristic electrophilic attack mechanism seen with the LnO + [37].…”

“…The results for reactions of CmO + with dienes are given in Table 4. Other than inefficient adduct formation with ThO + [11] and significant reactivity with PaO + , which constitutes a special case in the An series [37], no other AnO + ions (An = U, Np, Pu, Am, Cm) reacted with butadiene [11].…”

Can water continuously oxidize the PuO molecule? Mechanisms, topological analysis and rate constant calculations

“…Besides, exploring the most stable plutonium oxide and whether plutonium oxide further oxidizes are also important issues in plutonium science. 2,3 Therefore, over the last few decades, the reaction of plutonium with small molecules in the gas phase has attracted signicant attention both in experimental [1][2][3][4][5][6][7][8][9][10][11][12] and theoretical studies. [13][14][15][16][17][18][19][20][21] In addition, the reaction of plutonium with water which can provide some insight into the corrosive mechanism of steam on nuclear fuel is a more imperative and challenging research eld.…”

Ab initio molecular dynamics study of the interaction of plutonium with oxygen in the gas phase

“…Some theoretical studies have provided important insights into the electronic structure of plutonium elements, [5][6][7] where the 5f electrons are relatively high in energy and are spatially extended. Furthermore, numerous investigations have been executed and provided a wealth of insight concerning the reactions of actinide with small molecules, both experimentally 1,2,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] and theoretically, 3,4,[22][23][24] which can be used as reference when investigating plutonium corrosion.…”