Molecular Spectroscopy and Reactions of Actinides in the Gas Phase and Cryogenic Matrices

Gibson, John K.; Marçalo, Joaquim

doi:10.1007/978-94-007-0211-0_38

Cited by 12 publications

(9 citation statements)

References 330 publications

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“…The spectroscopic techniques used in our research, and previous studies of ThO, UO, and UO 2 , have been the subject of a review article in 2006 23 and a book chapter published in 2010. 24 The present article covers recent progress for the molecules UF/UF + and ThX/ThX + (X = F, N, S), with some discussion of the previous work to make this a nearly selfcontained account.…”

Section: ■ Introductionmentioning

confidence: 99%

Spectroscopy and Structure of the Simplest Actinide Bonds

2014

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Understanding the influence of electrons in partially filled f- and d-orbitals on bonding and reactivity is a key issue for actinide chemistry. This question can be investigated by using a combination of well-defined experimental measurements and theoretical calculations. Gas phase spectroscopic data are particularly valuable for the evaluation of theoretical models. Consequently, the primary objectives of our research have been to obtain gas phase spectra for small actinide molecules. To complement the experimental effort, we are investigating the potential for using relativistic ab initio calculations and semiempirical models to predict and interpret the electronic energy level patterns for f-element compounds. Multiple resonance spectroscopy and jet cooling techniques have been used to unravel the complex electronic spectra of Th and U compounds. Recent results for fluorides, sulfides, and nitrides are discussed.

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Section: ■ Introductionmentioning

confidence: 99%

Spectroscopy and Structure of the Simplest Actinide Bonds

2014

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“…A large amount of data already exists for the uranium–oxygen system, − but more data are needed for reactions that occur near phase transition boundaries. The high melting point of UO 2 and sensitivity of condensed UO 2± x stoichiometry to oxygen gas concentration increases the difficulty of experiments in this temperature regime .…”

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confidence: 99%

Experimental Investigation of Uranium Volatility during Vapor Condensation

et al. 2020

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The predictive models that describe the fate and transport of radioactive materials in the atmosphere following a nuclear incident (explosion or reactor accident) assume that uranium-bearing particulates would attain chemical equilibrium during vapor condensation. In this study, we show that kinetically driven processes in a system of rapidly decreasing temperature can result in substantial deviations from chemical equilibrium. This can cause uranium to condense out in oxidation states (e.g., UO3 vs UO2) that have different vapor pressures, significantly affecting uranium transport. To demonstrate this, we synthesized uranium oxide nanoparticles using a flow reactor under controlled conditions of temperature, pressure, and oxygen concentration. The atomized chemical reactants passing through an inductively coupled plasma cool from ∼5000 to 1000 K within milliseconds and form nanoparticles inside a flow reactor. The ex situ analysis of particulates by transmission electron microscopy revealed 2–10 nm crystallites of fcc-UO2 or α-UO3 depending on the amount of oxygen in the system. α-UO3 is the least thermodynamically preferred polymorph of UO3. The absence of stable uranium oxides with intermediate stoichiometries (e.g., U3O8) and sensitivity of the uranium oxidation states to local redox conditions highlight the importance of in situ measurements at high temperatures. Therefore, we developed a laser-based diagnostic to detect uranium oxide particles as they are formed inside the flow reactor. Our in situ measurements allowed us to quantify the changes in the number densities of the uranium oxide nanoparticles (e.g., UO3) as a function of oxygen gas concentration. Our results indicate that uranium can prefer to be in metastable crystal forms (i.e., α-UO3) that have higher vapor pressures than the refractory form (i.e., UO2) depending on the oxygen abundance in the surrounding environment. This demonstrates that the equilibrium processes may not dominate during rapid condensation processes, and thus kinetic models are required to fully describe uranium transport subsequent to nuclear incidents.

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“…Following the approach of Vander Sluis and Nugent [43, 44] we excluded data for ThO [15], ThO + [16, 57] and PaO 2+ from the fits due to strong configuration interactions in all cases. The

D_{0, norm}^{0}

( An O),

D_{0, norm}^{0}

( An O + ) and

D_{0, norm}^{0}

( An O 2+ ) values were weighted according to the estimated experimental uncertainties of the

D_{0}^{0}

( An O)

, D_{0}^{0}

( An O + )

and D_{0}^{0}

( An O 2+ ) values respectively [42, 58] (see column 3 of Tables 1–3). The results, presented in Tables 1–3 and in the left half of Figure 1, show that the normalized bond dissociation energies of An O, An O + and An O 2+ ( An ∈ Th through Cm) [42, 58] as defined by Equations )–) are smooth functions of N within accuracy throughout the first part of the An O, An O + and An O 2+ series for which experimental data are available.…”

Section: Thermodynamic Properties Of Ano and Ano+mentioning

confidence: 99%

“…The D 0 0,norm (AnO), D 0 0,norm (AnO + ) and D 0 0,norm (AnO 2+ ) values were weighted according to the estimated experimental uncertainties of the D 0 0 (AnO) , D 0 0 (AnO + ) and D 0 0 (AnO 2+ ) values respectively [42,58] (see column 3 of Tables 1-3). The results, presented in Tables 1-3 and in the left half of Figure 1, show that the normalized bond dissociation energies of AnO, AnO + and AnO 2+ (An Th through Cm) [42,58] as defined by Equations (12)- (14) are smooth functions of N within accuracy throughout the first part of the AnO, AnO + and AnO 2+ series for which experimental data are available. This trend is in agreement with the result for the normalized bond dissociation energies of LnO as defined by Equation (11) (see figure 2A of Dulick et al [1]).…”

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The electronic structure of the actinide oxides and their singly and doubly charged cations: A ligand field approach

Kaledin

2020

Int J of Quantum Chemistry

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Ligand field theory (LFT) calculations of energy levels were performed for the neutral actinide monooxides (AnO) and their singly and doubly ionized cations (AnO+ and AnO2+) by treating the molecular electronic states as Anm+ free‐ion energy levels (where An ∈ Th through Lr and m = 1, 2, 3, or 4) perturbed by the electric field of O2−or O−. LFT parameters obtained from fits to the energy levels of ThO, ThO+, UO, and UO+ were used to compute molecular energy levels for the lowest energy (maximum Sc, maximum Lc) 5f‐core states of An4+, An3+, An2+, and An+ for the majority of the An4+O2−, An3+O−, An3+O2−, An2+O−, An2+O2−, and An+O− electronic configurations. Simple linear relationships enabled predictions of the dissociation energies for AnO, AnO+ and AnO2+ (where An ∈ Bk through Lr) and ionization energies for AnO and AnO+ (where An ∈ Bk through Lr), mainly based on recent accurate experimental data for the ionization energies of An atoms (where An ∈ Fm, Md, No, and Lr) and correlations with the energetics of the atoms and ions.

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Molecular Spectroscopy and Reactions of Actinides in the Gas Phase and Cryogenic Matrices

Cited by 12 publications

References 330 publications

Spectroscopy and Structure of the Simplest Actinide Bonds

Spectroscopy and Structure of the Simplest Actinide Bonds

Experimental Investigation of Uranium Volatility during Vapor Condensation

The electronic structure of the actinide oxides and their singly and doubly charged cations: A ligand field approach

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