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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Advances in actinide thin films: synthesis, properties, and future directions

Actinide-based compounds exhibit unique physics due to the presence of 5f electrons, and serve in many cases as important technological materials. Targeted thin film synthesis of actinide materials has been successful in generating high-purity specimens in which to study individual physical phenomena. These films have enabled the study of the unique electron configuration, strong mass renormalization, and nuclear decay in actinide metals and compounds. The growth of these films, as well as their thermophysical, magnetic, and topological properties, have been studied in a range of chemistries, albeit far fewer than most classes of thin film systems. This relative scarcity is the result of limited source material availability and safety constraints associated with the handling of radioactive materials. Here, we review recent work on the synthesis and characterization of actinide-based thin films in detail, describing both synthesis methods and modeling techniques for these materials. Further, we review reports on pyrometallurgical, solution-based, and vapor deposition methods. We highlight the current state-of-the-art in order to construct a path forward to higher quality actinide thin films and heterostructure devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Electronic correlation induced expansion of Fermi pockets in δ-plutonium

Plutonium is a critically important material as the behavior of its 5f electrons stands midway between the metalliclike itinerant character of the light actinides and localized atomic-core-like character of the heavy actinides. The δ phase of plutonium (δ-Pu), whereas still itinerant, has a large coherent Kondo peak and strong electronic correlations coming from its near-localized character. Here, using sophisticated Gutzwiller wave function and dynamical mean-field theory correlated theories, we study the Fermi surface and associated mass renormalizations of δ-Pu together with calculations of the de Haas–van Alphen frequencies. We find a large (~200%) correlation induced volume expansion in both the hole and the electron pockets of the Fermi surface in addition to an intermediate mass enhancement. All of the correlated electron theories predict, approximately, the same hole pocket placement in the Brillouin zone, which is different from that obtained in conventional density-functional band-structure theory, whereas the electron pockets from all theories are in, roughly, the same place.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Topological band and superconductivity in UTe 2

UTe 2 is a likely spin-triplet superconductor that also exhibits evidence for chiral Majorana edge states. A characteristic structural feature of UTe 2 is inversion-symmetry related pairs of U atoms, forming rungs of ladders. Here we show how each rung's two sublattice degrees of freedom play a key role in understanding the electronic structure and the origin of superconductivity. In particular, DFT + U calculations generically reveal a topological band near the chemical potential originating from a band inversion associated with 5f electrons residing on these rungs, necessitating a microscopic description that includes these rung degrees of freedom. Furthermore, we show that a previously identified strong ferromagnetic interaction within a U-U rung leads to a pseudospin-triplet superconducting state that accounts for a nonzero polar Kerr angle, the observed magnetic field-temperature phase diagrams, and nodal Weyl fermions. Finally, our analysis may also be relevant for other U-based superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Machine learning study of magnetism in uranium-based compounds

Actinide and lanthanide-based materials display exotic properties that originate from the presence of itinerant or localized f electrons and include unconventional superconductivity and magnetism, hidden order, and heavy-fermion behavior. Due to the strongly correlated nature of the 5f electrons, magnetic properties of these compounds depend sensitively on applied magnetic field and pressure, as well as on chemical doping. However, precise connection between the structure and magnetism in actinide-based materials is currently unclear. In this investigation, we established such structure-property links by assembling and mining two datasets that aggregate, respectively, the results of high-throughput density functional theory simulations and experimental measurements for the families of uranium- and neptunium-based binary compounds. Various regression algorithms were utilized to identify correlations among accessible attributes (features or descriptors) of the material systems and predict their cation magnetic moments and general forms of magnetic ordering. Descriptors representing compound structural parameters and cation f-subshell occupation numbers were identified as most important for accurate predictions. The best machine learning model developed employs the random forest regression algorithm. It can predict both spin and orbit moment size with root-mean-square error of 0.17 μ B and 0.19 μ B , respectively. Lastly, the random forest classification algorithm is used to predict the ordering (paramagnetic, ferromagnetic, and antiferromagnetic) of such systems with 76% accuracy.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The insufficiency of the charge transfer model for resonant $\text{XES}$ in $\text{UF}$ 4

Recently, it was suggested that the single-electron charge transfer model (ligand 2p to Uranium 5f transition) could be used to explain the U M 4,5 Resonant X-ray Emission Spectroscopy (XES) of uranium dioxide (UO 2 ) and uranium tetrafluoride (UF 4 ). Here in this report, it is shown that this model produces results inconsistent with a joint consideration of both of the bandgaps of UO 2 and UF 4 and is thus insufficient to explain the observed behavior. An alternative Raman-based model is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba8B5N10F by Materials Project

Ba8(BN2)5F crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are seventeen inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to six N3- atoms to form edge-sharing BaN6 octahedra. There are a spread of Ba–N bond distances ranging from 2.85–2.97 Å. In the second Ba2+ site, Ba2+ is bonded in a 7-coordinate geometry to seven N3- atoms. There are a spread of Ba–N bond distances ranging from 2.74–3.22 Å. In the third Ba2+ site, Ba2+ is bonded to five N3- and one F1- atom to form distorted BaN5F octahedra that share corners with three BaN4F2 octahedra and edges with two equivalent BaN5F octahedra. The corner-sharing octahedra tilt angles range from 53–72°. There are a spread of Ba–N bond distances ranging from 2.78–3.10 Å. The Ba–F bond length is 2.71 Å. In the fourth Ba2+ site, Ba2+ is bonded in a 7-coordinate geometry to seven N3- atoms. There are a spread of Ba–N bond distances ranging from 2.74–3.25 Å. In the fifth Ba2+ site, Ba2+ is bonded in a 7-coordinate geometry to seven N3- atoms. There are a spread of Ba–N bond distances ranging from 2.74–3.23 Å. In the sixth Ba2+ site, Ba2+ is bonded in a 7-coordinate geometry to seven N3- atoms. There are a spread of Ba–N bond distances ranging from 2.74–3.19 Å. In the seventh Ba2+ site, Ba2+ is bonded in a 3-coordinate geometry to six N3- atoms. There are a spread of Ba–N bond distances ranging from 2.72–3.23 Å. In the eighth Ba2+ site, Ba2+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Ba–N bond distances ranging from 2.76–3.15 Å. In the ninth Ba2+ site, Ba2+ is bonded in a 5-coordinate geometry to five N3- atoms. There are a spread of Ba–N bond distances ranging from 2.74–3.09 Å. In the tenth Ba2+ site, Ba2+ is bonded to four N3- and two equivalent F1- atoms to form BaN4F2 octahedra that share corners with two equivalent BaN5F octahedra and edges with six BaN6 octahedra. The corner-sharing octahedra tilt angles range from 53–72°. There are a spread of Ba–N bond distances ranging from 2.81–2.88 Å. There are one shorter (2.71 Å) and one longer (2.78 Å) Ba–F bond lengths. In the eleventh Ba2+ site, Ba2+ is bonded to four N3- and two equivalent F1- atoms to form BaN4F2 octahedra that share corners with two equivalent BaN5F octahedra and edges with six BaN4F2 octahedra. The corner-sharing octahedra tilt angles range from 56–72°. There are a spread of Ba–N bond distances ranging from 2.82–2.85 Å. There are one shorter (2.70 Å) and one longer (2.75 Å) Ba–F bond lengths. In the twelfth Ba2+ site, Ba2+ is bonded to six N3- atoms to form edge-sharing BaN6 octahedra. There are a spread of Ba–N bond distances ranging from 2.86–2.95 Å. In the thirteenth Ba2+ site, Ba2+ is bonded to five N3- and one F1- atom to form a mixture of edge and corner-sharing BaN5F octahedra. The corner-sharing octahedral tilt angles are 66°. There are a spread of Ba–N bond distances ranging from 2.82–2.97 Å. The Ba–F bond length is 2.69 Å. In the fourteenth Ba2+ site, Ba2+ is bonded to five N3- and one F1- atom to form BaN5F octahedra that share a cornercorner with one BaN5F octahedra and edges with six BaN4F2 octahedra. The corner-sharing octahedral tilt angles are 64°. There are a spread of Ba–N bond distances ranging from 2.82–2.91 Å. The Ba–F bond length is 2.71 Å. In the fifteenth Ba2+ site, Ba2+ is bonded to five N3- and one F1- atom to form distorted BaN5F octahedra that share corners with three BaN4F2 octahedra and edges with two equivalent BaN5F octahedra. The corner-sharing octahedra tilt angles range from 56–72°. There are a spread of Ba–N bond distances ranging from 2.78–3.11 Å. The Ba–F bond length is 2.69 Å. In the sixteenth Ba2+ site, Ba2+ is bonded in a 3-coordinate geometry to seven N3- atoms. There are a spread of Ba–N bond distances ranging from 2.70–3.24 Å. In the seventeenth Ba2+ site, Ba2+ is bonded to six N3- atoms to form edge-sharing BaN6 octahedra. There are a spread of Ba–N bond distances ranging from 2.82–3.03 Å. There are ten inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.35 Å) and one longer (1.36 Å) B–N bond length. In the second B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.35 Å) B–N bond length. In the third B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. Both B–N bond lengths are 1.35 Å. In the fourth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.35 Å) B–N bond length. In the fifth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.36 Å) B–N bond length. In the sixth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. Both B–N bond lengths are 1.35 Å. In the seventh B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.36 Å) B–N bond length. In the eighth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.35 Å) and one longer (1.36 Å) B–N bond length. In the ninth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.35 Å) B–N bond length. In the tenth B3+ site, B3+ is bonded in a linear geometry to two N3- atoms. There is one shorter (1.34 Å) and one longer (1.35 Å) B–N bond length. There are twenty inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the second N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the third N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the fourth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the fifth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the sixth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the seventh N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the eighth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the ninth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the tenth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the eleventh N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the twelfth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the thirteenth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the fourteenth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the fifteenth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the sixteenth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the seventeenth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the eighteenth N3- site, N3- is bonded in a distorted single-bond geometry to four Ba2+ and one B3+ atom. In the nineteenth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. In the twentieth N3- site, N3- is bonded in a distorted single-bond geometry to five Ba2+ and one B3+ atom. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded to four Ba2+ atoms to form corner-sharing FBa4 tetrahedra. In the second F1- site, F1- is bonded to four Ba2+ atoms to form corner-sharing FBa4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

EFRC Materials Science of Actinides (Final Report)

The Energy Frontier Research Center Materials Science of Actinides (MSA) conducted basic research from 2009-2019. The scientific personnel and participating institutes changed several times during the evolution of the Center, and in total included 24 senior investigators, four national laboratories, and ten universities. Workforce development was a motivating goal of the university-led Center, which included many undergraduate, graduate, and post-doctoral researchers. The center focused on the actinide elements, which arise from the sequential filling of the 5f electron orbitals. Although the specific themes evolved during the Center’s history, the final research themes were: (1) Nanoscale Cage Clusters, (2) Complex Ceramic and Metallic Materials, and (3) Materials Under Extreme Environments. To date, the Center has produced 254 peer-reviewed journal publications and book chapters that acknowledged only the EFRC funding, and an additional 161 journal publications and book chapters that acknowledged funding from the EFRC and additional sources (a few manuscripts are still in preparation). Broad highlights include: (1) Development of an extensive family of actinide nanomaterials that self-assemble in aqueous solution, an understanding of their formation mechanisms and stabilities, and possible uses in nuclear fuel cycles; (2) Establishment of facilities and methodologies to conduct high-temperature calorimetry on transuranium materials, and extensive thermodynamic-based studies of uranium and thorium compounds important to the nuclear fuel cycle; (3) A vastly improved understanding of the behavior of actinide materials in extreme conditions, including high radiation fields, temperatures, and pressures, as well coupled effects of two or more of these; (4) Development of resonance ultrasound spectroscopy and direct measurement of aging of plutonium alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The First Neptunium Dioxide Neutron Diffraction Experiment at HFIR

Here we present the first neutron diffraction experiment of a 50 mg sample of neptunium(IV) dioxide (NpO 2 ) powder at the High Flux Isotope Reactor (HFIR) using the wide-angle neutron diffractometer (WAND 2 ) HB-2C. We also provide a brief literature survey to pinpoint gaps in the crystal, electronic, and magnetic structure of NpO 2 to determine the optimum experiment to be pursued in the next HFIR user proposal cycle. Characterizing actinide materials with neutron diffraction, inelastic scattering, neutron imaging, polarized neutron studies, and small-angle neutron scattering techniques will increase our understanding of 5f electron behavior and elucidate atomic and magnetic structural properties. This strategy will help fill gaps in the literature and provide theoretical physicists with the data needed to build physical and chemical models to guide and validate computational methods. These methods may be used for predicting structural and chemical features of actinide-based materials. This proof-of-principle effort begins to uncover how to advance actinide science and technology at Oak Ridge National Laboratory (ORNL) using neutron capabilities. This effort has already sparked collaborative discussions between researchers outside the Radioisotope Science and Technology Division, including theoretical physicists from the Nuclear Nonproliferation Division and beamline scientists in the Neutron Scattering Division. We intend to continue pursuing neutron experiments and develop a scientific strategy focused on studying transuranium elements (e.g., Np, Pu, Am, and Cm) using the advanced neutron capabilities at ORNL.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Examination of Exogenous and Endogenous Irradiation Effects on PuO2 and its Precursors via EPR Spectroscopy

The spectroscopic examination of actinide compounds are of con-siderable interest for elucidating the role of 5f electrons in chemical bonding. For example, this could be directly detected via EPR spectroscopy through the hyperfine interaction of an unpaired Pu electron with a given ligand. However, typically fast spin-lattice re-laxation times [1] require the use of low temperatures, multiplying the difficulty of working with radio-toxic Pu compounds. Instead, we looked for radicals at room temperature produced from endoge-nous α-decay or exogenous γ-irradiation. PuO2 and its precursor PuIII2(C2O4)3∙nH2O were used as examples because of their ubiquity in the literature.

Kinyon, Jared S.↗
DOE OSTI2023

Unmasking f -electron physics: Exploring novel phases of actinide materials using extreme environments [Slides]

There are a multitude of compounds to study. Actinide-based systems stand out as being especially attractive, because they have been shown to be a deep reservoir for exotic phenomena (e.g., heavy fermion behavior, unconventional superconductivity, unconventional magnetism, topological states) that originate from their 5f-electron states.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Indications of flat bands driving the δ to α volume collapse of plutonium

On cooling from the melt, plutonium (Pu) undergoes a series of structural transformations accompanied by a ≈ 28% reduction in volume from its δ phase to its α phase at low temperatures. While Pu’s partially filled 5f -electron shells are known to be involved, their precise role in the transformations has remained unclear. By using calorimetry measurements on α-Pu and gallium-stabilized δ-Pu combined with resonant ultrasound and X-ray scattering data to account for the anomalously large softening of the lattice with temperature, we show here that the difference in electronic entropy between the α and δ phases dominates over the difference in phonon entropy. Rather than finding an electronic specific heat characteristic of broad $f$-electron bands in α-Pu, as might be expected to occur within a Kondo collapsed phase in analogy with cerium, we find it to be indicative of flatter subbands. An important role played by Pu’s 5$f$ electrons in the formation of its larger unit cell α phase comprising inequivalent lattice sites and varying bond lengths is therefore suggested.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Ab Initio Study of the Effect of Mono-Vacancies on the Metastability of Ga-Stabilized δ-Pu

Most experimental studies on metallic Pu are on the room temperature monoclinic α-phase or the fcc Ga stabilized δ-phase. Stabilized δ-phase Pu-Ga alloys are metastable and exhibit a martensitic phase transformation to α’-phase at low temperatures, or applied shear, with concentrations lower than three atomic percent Ga. By using first principles, we explore the metastability of δ-phase by investigating the structural and electronic behavior induced by Ga alloying and by a mono-vacancy point defect. We find that a site substitutional Ga induces a tetragonal distortion in the lattice affected by hybridization of Ga 4p and Pu 6d states. With the addition of a mono-vacancy, a monoclinic or tetragonal distortion forms locally (dependent on its distance from Ga), and decoupling of the Pu 5f and 6d states and broadening of the 6d states occurs. This response enables hybridization of Pu 6d with the Ga 4p states affecting the mono-vacancy formation energy. Thus, stabilization of the fcc lattice correlates with hybridization of Pu 6d states with Ga 4p states, and this becomes more evident in the presence of a mono-vacancy.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Thermodynamics Modeling for Actinide Monocarbides and Mononitrides from First Principles

The high-temperature thermodynamical properties for the actinide monocarbides and mononitrides ThC, ThN, UC, UN, PuC, and PuN are calculated from first-principles electronic-structure theory. The electronic structure is modeled with density-functional theory (DFT) and is fully relativistic, including the spin-orbit interaction. Furthermore, the DFT is extended to account for orbital–orbital interactions, by means of a parameter-free orbital-polarization (OP) technique, that has proven to be essential for the 5f electrons in plutonium. Strong anharmonicity and the temperature dependence of the lattice vibrations are captured with the self-consistent ab initio lattice dynamics (SCAILD) method. The calculated free energies and heat capacities are compared to published results from quasi-harmonic (QH) theory, and experiments, where available. For the uranium and plutonium compounds, we make use of CALPHAD assessments to help evaluate the theory. Generally, our anharmonic relativistic approach compares well with both CALPHAD and experiments. For the thorium compounds, our theory is in good accord with QH modeling of the free energy at lower temperatures but for the heat capacity the comparison is less favorable.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1972

Recent results of the Goddard rocket program for observing stars.

Rockets flown by A. M. Smith have yielded spectra of Alpha Vir, Bl V, Zeta Puppis, O 5f, Zeta Ori, O9.5 Ib, Zeta Oph, O9.5 V and Zeta Per, Bl Ib, at about 0.5 A resolution. Many weak subordinate lines are visible in the range 924 to 1700 A as well as strong resonance lines, some of which have P Cygni profiles. Sharp interstellar lines from C I, C II, O I and Si II are seen. Stecher and Smith have confirmed the presence of CO in the interstellar medium from lines in the ultraviolet spectra of Zeta Oph and Zeta Per. Absolute energy calibrations of the ultraviolet energy distribution of Alpha Leo, Alpha CMa, Gamma Ori and Kappa Ori have been derived with accuracy to about plus or minus 15% over the range 1350-3100 A from rocket spectra at 10 A resolution obtained by D. C. Evans.

Underhill, A. B.↗
NASA NTRS1975

Research for preparation of cation-conducting solids by high-pressure synthesis and other methods

It was shown that two body-centered-cubic skeleton structures, the Im3 KSbO3 phase and the defect-pyrochlore phase A(+)B2X6, do exhibit fast Na(+)-ion transport. The placement of anions at the tunnel intersection sites does not impede Na(+)-ion transport in (NaSb)3)(1/6 NaF), and may not in (Na(1+2x)Ta2 5F)(Ox). The activation energies are higher than those found in beta-alumina. There are two possible explanations for the higher activation energy: breathing of the bottleneck (site face or edge) through which the A(+) ions must pass on jumping from one site to another may be easier in a layer structure and/or A(+)-O bonding may be stronger in the cubic structures because the O(2-) ion bonds with two (instead of three) cations of the skeleton. If the former explanation is dominant, a lower activation energy may be achieved by optimizing the lattice parameter. If the latter is dominant, a new structural principle may have to be explored.

Goodenough, J. B.↗
NASA NTRS1979

Transition probabilities and Stark-broadening parameters of neutral and singly ionized lead

Strengths and Stark widths of the prominent visible PbI and PbII lines are measured in emission by means of a gas-driven shock tube. Absolute ionic line strengths for 7s-7p and 7p-7d arrays conform well to quantum-mechanical sum rules and agree with theoretical predictions, but 6d-5f results differ markedly from central-field approximations. Neutral-line strengths agree satisfactorily with available comparison data. Semiempirical theory predicts the widths of PbII lines with characteristic reliability of better than 25%.

Miller, M. H.↗
NASA NTRS1988

Full configuration interaction benchmark calculations for TiH

Full configuration interaction (FCI) results for the 3F and 5F states of Ti and the 4Phi and 2Delta states of TiH are presented. While the coupled pair functional (CPF) or modified CPF approaches are found to work well for the 4Phi state of TiH, they do not perform as well for the 2Delta state. Although for mu, the CASSCF/MRCI methods do well for the 2Delta state, when the active space is expanded outside the normal valence definition, the dipole moment is only brought into agreement with the FCI results by natural orbital iterations.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1991

An ab initio study of Fe(CO)n, n = 1,5, and Cr(CO)6

Ab initio calculations have been performed for Cr(CO)6 and Fe(CO)n, n = 1,5. Basis sets of better than double zeta quality are used, and correlation is included using the modified coupler-pair functional method. The computed geometries and force constants are in reasonable agreement with experiment. The sequential bond dissociation energies of CO from Fe(CO)5 are estimated to be: 39, 31, 25, 22, and greater than 5 kcal/mol. It is noted that the first bond dissociation energy is relative to the singlet ground state of Fe(CO)5 and the lowest singlet state of Fe(CO)4, whereas the second is relative to the ground triplet states of Fe(CO)4 and Fe(CO)3. In addition, the binding energy for Fe-CO would be modified to 18 kcal/mol if dissociation occurred to the Fe(5F) excited state asymptote. The CO binding energies for Fe and Cr are found to be in poorer agreement with experiment than those found in a previous study on Ni(CO)4. The origins of this difference are discussed.

Barnes, Leslie A.↗