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DOE OSTI2020

Materials Data on Th(Al10V)2 by Materials Project

ThV2Al20 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Th is bonded in a 4-coordinate geometry to sixteen Al atoms. There are four shorter (3.15 Å) and twelve longer (3.23 Å) Th–Al bond lengths. V is bonded to twelve Al atoms to form VAl12 cuboctahedra that share corners with six equivalent VAl12 cuboctahedra, edges with eighteen equivalent AlThAl10V cuboctahedra, and faces with six equivalent AlThAl10V cuboctahedra. There are six shorter (2.58 Å) and six longer (2.81 Å) V–Al bond lengths. There are three inequivalent Al sites. In the first Al site, Al is bonded in a distorted linear geometry to two equivalent Th and twelve equivalent Al atoms. All Al–Al bond lengths are 3.12 Å. In the second Al site, Al is bonded in a 12-coordinate geometry to two equivalent V and ten Al atoms. There are a spread of Al–Al bond distances ranging from 2.73–2.86 Å. In the third Al site, Al is bonded to one Th, one V, and ten Al atoms to form distorted AlThAl10V cuboctahedra that share corners with fifteen equivalent AlThAl10V cuboctahedra, edges with two equivalent AlThAl10V cuboctahedra, edges with three equivalent VAl12 cuboctahedra, a faceface with one VAl12 cuboctahedra, and faces with fifteen equivalent AlThAl10V cuboctahedra. There are a spread of Al–Al bond distances ranging from 2.72–2.92 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Chemical and environmental stability of monazite-cheralite solid solutions Ln 1-2 x Ca x Th x PO 4 (Ln = Pr, Nd; x = 0–0.15): A thermodynamic study

Monazite-cheralite ceramics are a promising waste form for actinides. To elucidate the long-term behavior of this matrix in aqueous solutions, this study measured thermodynamic data for Th-rhabdophanes Ln 1-2 x Ca x Th x PO 4 ·nH 2 O (with Ln = Pr, Nd; x = 0–0.15) and the associated anhydrous monazite-cheralites Ln 1-2 x Ca x Th x PO 4 . Further, solubility experiments at 298K and high temperature oxide melt solution calorimetry were combined for calculation of ΔG$^°_f$, ΔH$^°_f$ and S$^°_m$ of Th-rhabdophanes and associated monazite-cheralites. Standard solubility constants were employed in a geochemical simulation using the PHREEQC software, the results of which confirmed the high chemical stability of the monazite-cheralite phases and supported their use as a specific conditioning matrix for the long-term immobilization of actinides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Metal–Oxo Cluster Formation Using Ammonium and Sulfate to Differentiate M IV (Th, U, Ce) Chemistries

Isolating isostructural compounds of tetravalent metals M IV (Zr, Hf, Ce, Th, U, Pu, Np) improves our understanding of metal hydrolysis and coordination behavior across the periodic table. These metals form polynuclear clusters typified by the hexamer [M IV 6 O 4 (OH) 4 ] 12+ . Exploiting the ammonium M IV -sulfate (Ce IV , Th IV , and U IV ) phase space targeting rapid crystallization, we isolate the common hexamer [M IV 6 (OH) 4 (O) 4 ] 12+ but with different numbers of capping sulfates and water molecules for Ce IV , Th IV , and U IV . Furthermore, these phases allowed a direct comparison of bonding trends across the series. Upon cocrystallization with the hexamers, higher complex structures can be identified. Thorium features assemblies with monomer-linked hexamer chains. Uranium features assemblies with sulfate-bridged hexamers and the supramolecular assembly of 14 hexamers into the U 84 , [U 6 (OH) 4 (O) 4 ) 14 (SO 4 ) 120 (H 2 O) 42 ] 72– . Last, cerium showcases the isolation from monomers to the Ce 62 , [Ce 62 (OH) 30 (O) 58 (SO 4 ) 71 (H 2 O) 33.25 ] 41– . Furthermore, small-angle X-ray scattering (room temperature) shows ammonium-induced cluster assembly for Ce IV but minimal reactivity for U IV and Th IV . In this study, because the phases crystallized at elevated temperature demonstrates favorable cluster assembly, these solution phase results were surprising and suggest some other characteristics such as Ce’s facile redox behavior, contributes to its solution-phase speciation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Mining for Metal–Organic Systems: Chemistry Frontiers of Th-, U-, and Zr-Materials

The conceptual framework presented in this Perspective overviews the design principles of innovative thorium-based materials that could address urgent needs of the medicinal, nuclear energy, and waste remediation sectors from the lens of zirconium and uranium analogs. We survey the intersections of Zr, Th, and U chemistry with a focus on how the intrinsic behavior of each metal translates to broader material properties, including, but not limited to, structural and topological diversity, preferential metal–ligand binding, and reactivity. On the example of several classes of materials, including organometallic complexes, polyoxometalates, and the primary focus of this Perspective, metal–organic frameworks (MOFs), the design principles that govern the preparation of Zr-, Th-, and U-compounds, including oxophilicity, variation in oxidation states, and stable coordination environments have been considered. Further, we highlight how the impact of the mentioned variables may shift throughout the progression from discrete molecular systems to extended structures. We discuss the common assumption that zirconium-organic materials are typically considered a close analog of thorium-based congeners in areas such as material design and preparation. Through consideration of fundamental chemistry principles, we shed light on the relationships between Zr-, Th-, and U-based materials and highlight how a critical analysis of their distinct properties can be used to target a desired material performance. Finally, we provide a detailed understanding of Th-based materials chemistry by anchoring their fundamental properties between two well-studied reference points, zirconium- and uranium-containing analogs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1972

U, Th, Pb and REE abundances and Pb 207/Pb 206 ages of individual minerals in returned lunar material by ion microprobe mass analysis.

Results of ion microprobe analyses of Apollo 11, 12 and 14 material, showing that U, Th, Pb and REE are concentrated in accessory minerals such as apatite, whitlockite, zircon, baddeleyite, zirkelite, and tranquillityite. Th/U ratios are found to vary by over a factor of 40 in these minerals. K, Ba, Rb and Sr have been localized in a K rich, U and Th poor glass phase that is commonly associated with the U and Th bearing accessory minerals. Li is observed to be fairly evenly distributed between the various accessory phases. The phosphates have been found to have REE abundance patterns (normalized to the chondrite abundances) that are fairly flat, while the Zr bearing minerals have patterns that rise steeply, by factors of ten or more, from La to Gd. All the accessory minerals have large negative Eu anomalies. Radiometric age dates (Pb 207/Pb 206) of the individual U and Th bearing minerals compare favorably with the Pb 207/Pb 206 age of the bulk rocks.

Andersen, C. A.↗

NASA NTRS1990

Calibration of the C-14 timescale over the past 30,000 years using mass spectrometric U-Th ages from Barbados corals

Uranium-thorium ages obtained by mass spectrometry from corals raised off the island of Barbados confirm the high precision of this technique over at least the past 30,000 years. Comparison of the U-Th ages with C-14 ages obtained on the Holocene samples shows that the U-Th ages are accurate, because they accord with the dendrochronological calibration. Before 9,000 yr BP, the C-14 ages are systematically younger than the U-Th ages, with a maximum difference of about 3500 yr at about 20,000 yr BP. The U-Th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration.

Bard, Edouard↗

NASA NTRS2014

Preliminary Report on U-Th-Pb Isotope Systematics of the Olivine-Phyric Shergottite Tissint

Geochemical studies of shergottites suggest that their parental magmas reflect mixtures between at least two distinct geochemical source reservoirs, producing correlations between radiogenic isotope compositions, and trace element abundances.. These correlations have been interpreted as indicating the presence of a reduced, incompatible-element- depleted reservoir and an oxidized, incompatible-element-rich reservoir. The former is clearly a depleted mantle source, but there has been a long debate regarding the origin of the enriched reservoir. Two contrasting models have been proposed regarding the location and mixing process of the two geochemical source reservoirs: (1) assimilation of oxidized crust by mantle derived, reduced magmas, or (2) mixing of two distinct mantle reservoirs during melting. The former clearly requires the ancient martian crust to be the enriched source (crustal assimilation), whereas the latter requires a long-lived enriched mantle domain that probably originated from residual melts formed during solidification of a magma ocean (heterogeneous mantle model). This study conducts Pb isotope and U-Th-Pb concentration analyses of the olivine-phyric shergottite Tissint because U-Th-Pb isotope systematics have been intensively used as a powerful radiogenic tracer to characterize old crust/sediment components in mantle- derived, terrestrial oceanic island basalts. The U-Th-Pb analyses are applied to sequential acid leaching fractions obtained from Tissint whole-rock powder in order to search for Pb isotopic source components in Tissint magma. Here we report preliminary results of the U-Th-Pb analyses of acid leachates and a residue, and propose the possibility that Tissint would have experienced minor assimilation of old martian crust.

Moriwaki, R.↗

NASA NTRS2014

Humic Acid Complexation of Th, Hf and Zr in Ligand Competition Experiments: Metal Loading and Ph Effects

The mobility of metals in soils and subsurface aquifers is strongly affected by sorption and complexation with dissolved organic matter, oxyhydroxides, clay minerals, and inorganic ligands. Humic substances (HS) are organic macromolecules with functional groups that have a strong affinity for binding metals, such as actinides. Thorium, often studied as an analog for tetravalent actinides, has also been shown to strongly associate with dissolved and colloidal HS in natural waters. The effects of HS on the mobilization dynamics of actinides are of particular interest in risk assessment of nuclear waste repositories. Here, we present conditional equilibrium binding constants (Kc, MHA) of thorium, hafnium, and zirconium-humic acid complexes from ligand competition experiments using capillary electrophoresis coupled with ICP-MS (CE- ICP-MS). Equilibrium dialysis ligand exchange (EDLE) experiments using size exclusion via a 1000 Damembrane were also performed to validate the CE-ICP-MS analysis. Experiments were performed at pH 3.5-7 with solutions containing one tetravalent metal (Th, Hf, or Zr), Elliot soil humic acid (EHA) or Pahokee peat humic acid (PHA), and EDTA. CE-ICP-MS and EDLE experiments yielded nearly identical binding constants for the metal- humic acid complexes, indicating that both methods are appropriate for examining metal speciation at conditions lower than neutral pH. We find that tetravalent metals form strong complexes with humic acids, with Kc, MHA several orders of magnitude above REE-humic complexes. Experiments were conducted at a range of dissolved HA concentrations to examine the effect of [HA]/[Th] molar ratio on Kc, MHA. At low metal loading conditions (i.e. elevated [HA]/[Th] ratios) the ThHA binding constant reached values that were not affected by the relative abundance of humic acid and thorium. The importance of [HA]/[Th] molar ratios on constraining the equilibrium of MHA complexation is apparent when our estimated Kc, MHA values attained at very low metal loading conditions are compared to existing literature data. Overall, experimental data suggest that the tetravalent transition metal/-actinide-humic acid complexation is important over a wide range of pH values, including mildly acidic conditions, and thus, these complexes should be included in speciation models.

humic acid↗

NASA NTRSDate not supplied

Zircon (U-TH)/He Impact Crater Thermochronometry and the Effects of Shock Microstructures on Helium Diffusion Kinetics

Accurate age determinations of hyper-velocity impact and cratering events remains difficult and often controversial, while less than half of all known impact craters are regarded as accurately and precisely dated. Besides 40Ar/39Ar and U-Pb methods, zircon (U-Th)/He dating of impactites is a burgeoning technique to date large- to medium-sized impact structures. Zircon (U-Th)/He ages can be fully reset in minutes at 1000°C, T commonly reached in and directly adjacent to impact melt domains, whereas complete resetting of zircon (U-Th)/He at <300°C, which might be encountered near the crater margins or persist in post-impact hydrothermal systems, may take >103-4 years. However, there is a critical need to test the reliability of (U-Th)/He impact dating in shock deformed zircon, and to quantify helium diffusion kinetics in well-characterized grains with a broad spectrum of shock-induced defect substructures. For this purpose, we investigated samples from two impact structures, the 66 Ma Chicxulub multi-ring basin and the 15 Ma Ries complex crater, to compare zircon diffusion kinetics from impact structures with varying parameters, including size, age, and hydrothermal system longevity. Shock microstructures were characterized by backscattered-electron (BSE) imaging prior to determination of diffusion step-heating fractional release experiments using light-bulb furnace with prograde and retrograde incrementally 10°C steps from 300°C to 600°C. We find that zircon with low-level shock microstructures exhibit no significant deviation from helium diffusion kinetics of undamaged zircon. In contrast, zircon grains with planar deformation features and granular textures classified by SEM are characterized by a dramatic decrease in helium retentivity, similar to radiation damage, due to the reduction in the effective domain size and the introduction of fast diffusion pathways. This likely renders shocked grains more susceptible to impact-induced hydrothermal resetting. Hence, characterization of impact microstructure is critical for determining accurate impact ages, but also offers the opportunity to determine the magnitude and duration of post-impact hydrothermal circulation.

Catherine Ross↗

DOE OSTI2020

Materials Data on Th(PS3)2 by Materials Project

Th(PS3)2 crystallizes in the tetragonal P4_2/m space group. The structure is one-dimensional and consists of one Th(PS3)2 ribbon oriented in the (0, 0, 1) direction. Th4+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are four shorter (2.84 Å) and four longer (3.04 Å) Th–S bond lengths. P4+ is bonded in a trigonal non-coplanar geometry to three S2- atoms. There are two shorter (2.02 Å) and one longer (2.06 Å) P–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 1-coordinate geometry to two equivalent Th4+ and one P4+ atom. In the second S2- site, S2- is bonded in an L-shaped geometry to one Th4+ and one P4+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Th(InBr3)2 by Materials Project

Th(InBr3)2 crystallizes in the monoclinic C2/c space group. The structure is one-dimensional and consists of two Th(InBr3)2 ribbons oriented in the (0, 0, 1) direction. Th4+ is bonded in a 8-coordinate geometry to eight Br1- atoms. There are a spread of Th–Br bond distances ranging from 2.90–3.15 Å. In1+ is bonded in a 1-coordinate geometry to three Br1- atoms. There are a spread of In–Br bond distances ranging from 3.39–3.50 Å. There are three inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a single-bond geometry to one Th4+ atom. In the second Br1- site, Br1- is bonded in a distorted water-like geometry to two equivalent Th4+ and one In1+ atom. In the third Br1- site, Br1- is bonded in a 1-coordinate geometry to one Th4+ and two equivalent In1+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Th(PO3)4 by Materials Project

Th(PO3)4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are two inequivalent Th4+ sites. In the first Th4+ site, Th4+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Th–O bond distances ranging from 2.38–2.47 Å. In the second Th4+ site, Th4+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Th–O bond distances ranging from 2.36–2.45 Å. There are eight inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.62 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.61 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.61 Å. In the fourth P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.50–1.61 Å. In the fifth P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There is two shorter (1.50 Å) and two longer (1.60 Å) P–O bond length. In the sixth P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.61 Å. In the seventh P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.61 Å. In the eighth P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There is two shorter (1.50 Å) and two longer (1.61 Å) P–O bond length. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two P5+ atoms. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the seventh O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the ninth O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one P5+ atom. In the tenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the eleventh O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one P5+ atom. In the twelfth O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one P5+ atom. In the thirteenth O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one P5+ atom. In the fourteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the fifteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the sixteenth O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one P5+ atom. In the seventeenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one P5+ atom. In the eighteenth O2- site, O2- is bonded in a distorted linear geometry to one Th4+ and one P5+ atom. In the nineteenth O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one P5+ atom. In the twentieth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the twenty-first O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the twenty-second O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the twenty-third O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one P5+ atom. In the twenty-fourth O2- site, O2- is bonded in a distorted single-bond geometry to one Th4+ and one P5+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Th(Ge3Pt)4 by Materials Project

ThPt4Ge12 crystallizes in the cubic Im-3 space group. The structure is three-dimensional. Th is bonded to twelve equivalent Ge atoms to form ThGe12 cuboctahedra that share faces with eight equivalent PtGe6 octahedra. All Th–Ge bond lengths are 3.37 Å. Pt is bonded to six equivalent Ge atoms to form PtGe6 octahedra that share corners with six equivalent PtGe6 octahedra and faces with two equivalent ThGe12 cuboctahedra. The corner-sharing octahedral tilt angles are 60°. All Pt–Ge bond lengths are 2.52 Å. Ge is bonded in a 2-coordinate geometry to one Th, two equivalent Pt, and two equivalent Ge atoms. There are one shorter (2.54 Å) and one longer (2.65 Å) Ge–Ge bond lengths.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Th(SiO)2 by Materials Project

Th(SiO)2 crystallizes in the tetragonal I4_1/amd space group. The structure is zero-dimensional and consists of eight Th(SiO)2 clusters. Th4+ is bonded in a linear geometry to two equivalent O2- atoms. Both Th–O bond lengths are 2.14 Å. Si is bonded in a single-bond geometry to one O2- atom. The Si–O bond length is 1.72 Å. O2- is bonded in a water-like geometry to one Th4+ and one Si atom.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Measurement of the $\textrm{t}\overline{\textrm{t}}\textrm{H}$ and tH production rates in the H → $\textrm{b}\overline{\textrm{b}}$ decay channel using proton-proton collision data at $\sqrt{s}$ = 13 TeV

An analysis of the production of a Higgs boson (H) in association with a top quark-antiquark pair ($\textrm{t}\overline{\textrm{t}}\textrm{H}$) or a single top quark (tH) is presented. The Higgs boson decay into a bottom quark-antiquark pair (H → $\textrm{b}\overline{\textrm{b}}$) is targeted, and three different final states of the top quark decays are considered, defined by the number of leptons (electrons or muons) in the event. The analysis utilises proton-proton collision data collected at the CERN LHC with the CMS experiment at $\sqrt{s}$ = 13 TeV in 2016–2018, which correspond to an integrated luminosity of 138 fb −1 . The observed $\sqrt{s}$ production rate relative to the standard model expectation is 0.33 ± 0.26 = 0.33 ± 0.17(stat) ± 0.21(syst). Additionally, the $\textrm{t}\overline{\textrm{t}}\textrm{H}$ production rate is determined in intervals of Higgs boson transverse momentum. An upper limit at 95% confidence level is set on the tH production rate of 14.6 times the standard model prediction, with an expectation of ${19.3}_{-6.0}^{+9.2}$. Finally, constraints are derived on the strength and structure of the coupling between the Higgs boson and the top quark from simultaneous extraction of the $\textrm{t}\overline{\textrm{t}}\textrm{H}$ and tH production rates, and the results are combined with those obtained in other Higgs boson decay channels.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

10-th order of accuracy for numerical solution of 3-D elasticity equations for heterogeneous materials on unfitted Cartesian meshes

We have developed the Optimal Local Truncation Error Method (OLTEM) with 10-th order of accuracy on unfitted Cartesian meshes for a system of 3-D elasticity equations with smooth irregular interfaces. 5 x 5 x 5 = 125-point stencils (similar to those for quadratic finite elements) for elastic heterogeneous materials are used for OLTEM. There are no unknowns at the interface points between different materials; the structure of the global discrete equations is the same for homogeneous and heterogeneous materials. The calculation of unknown stencil coefficients is based on the minimization of the local truncation error of the stencil equations and yields the optimal 10-th order of accuracy for OLTEM on unfitted Cartesian meshes, i.e., the increase by 7 orders in accuracy compared to quadratic finite elements on conformal meshes. A new post-processing procedure provides the 9-th order of accuracy for stresses in the 3-D case. Similar to basic computations it uses OLTEM with the 125-point stencils, the interface conditions and the elasticity equations. It was shown that the use of the elasticity equations for post-processing improves the accuracy of 0.1% stresses by 6 orders compared to post-processing without the use of PDEs. At an accuracy of for stresses, OLTEM with the new post-processing procedure reduces the number of degrees of freedom by 360 - 8000 times compared to quadratic finite elements with similar stencils. OLTEM with the 125-point stencils yields even more accurate results than high-order finite elements with much wider stencils. OLTEM provides accurate numerical results for compressible and nearly incompressible materials.

elasticity equations↗

DOE OSTI2021

Analyses of the excited 5f 1 optical spectra of Th 3+ compounds

We look at the electronic structure of Th(Cp") 3 (Cp" = η 5 -C 5 H 3 (SiMe 3 -1,3), a molecule which has a 6d 1 ground configuration and an excited 5f 1 configuration beginning approximately 14,000 cm -1 higher, is reexamined. The ground state of the 6d 1 configuration in a crystal field of D 3h symmetry is shown to be an orbitally quenched 2 A 1' state, best described as a pure 2 D 1/2 state. Electric dipole selection rules from this state to the states for the 5f 1 configuration in a D 3h crystal field result in the 5f 1 truncated optical spectrum observed. The optical spectrum of the square planar Th 3+ compound [Li(THF) 4 ][Th(OAr') 4 ], where (OAr' = OC 6 H 2 tBu 2 -2,6-Me-4), is discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Activation of CO 2 by Actinide Cations (Th + , U + , Pu + , and Am + ) as Studied by Guided Ion Beam and Triple Quadrupole Mass Spectrometry

Reactions of CO 2 with Th+ have been studied using guided ion beam tandem mass spectrometry (GIBMS) and with An + (An + = Th + , U + , Pu + , and Am + ) using triple quadrupole inductively coupled plasma mass spectrometry (QQQ-ICP-MS). Additionally, the reactions ThO + + CO and ThO + + CO 2 were examined using GIBMS. Modeling the kinetic energy dependent GIBMS data allowed determination of bond dissociation energies (BDEs) for D o (Th + -O) and D o (OTh + -O) that are in reasonable agreement with previous GIBMS measurements. The QQQ-ICP-MS reactions were studied at higher pressures where multiple collisions between An + and the neutral CO 2 occur. As a consequence, both AnO + and AnO 2 + products were observed for all An + except Am + , where only AmO + was observed. Here, the relative abundances of the observed monoxides compared to the dioxides are consistent with previous reports of the AnO n + (n = 1, 2) BDEs. Comparison of the periodic trends of the group 4 transition metal, lanthanide (Ln), and actinide atomic cations in reactions with CO 2 (a formally spin-forbidden reaction for most M + ground states), and O 2 (a spin unrestricted reaction) indicate that spin conservation plays a minor role, if any, for the heavier An + metals. Further correlation of Ln + and An + + CO 2 reaction efficiencies with the promotion energy (E p ) to the first electronic state with two valence d-electrons (E p (5d 2 ) for Ln + and E p (6d 2 ) for An + ) indicates that the primary limitation in the activation of CO 2 is the energetic cost to promote from the electronic ground state of the atomic metal ion to a reactive state.

bond activation↗