Publications by authors named "David Dixon"

Bond dissociation energies (BDEs) and spectroscopic parameters for the ground states of YbO and NoO were calculated at the Brueckner doubles (BD(T)) level and for NoO at the coupled cluster CCSD(T) level based on the closed-shell configurations Yb(4f)O(2p) and No(5f)O(2p). For YbO, the BD(T) BDE (3.93 eV) and vibrational frequency (686.

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  • - A study using anion photoelectron spectroscopy and computational methods investigated the photodetachment of UF, revealing a vertical detachment energy of 0.63 eV, aligning closely with a theoretical value of 0.61 eV from spinor-based relativistic coupled-cluster methods.
  • - The analysis included complex spectral features related to excited electronic states and vibrational movements in UF, facilitated by advanced theoretical techniques like spin-orbit-coupled multireference perturbation theory.
  • - The research confirms that UF exhibits strong ionic bonding characteristics and showcases the effectiveness of the spinor CCSD(T) computational approach in analyzing such systems.
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The nature of the Ni-S bond is investigated due to its role in the absorption of atmospheric Lewis acid gases such as SO and SO onto Ni surfaces. The vibrational frequency and electronic structure of NiS were predicted using CCSD(T), CASSCF, and internally contracted multireference configuration interaction (icMRCI) + Q. 43 density functional theory (DFT) functionals were benchmarked.

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  • Density functional theory combined with small core pseudopotentials was used to calculate the redox potentials of actinides (Ac, Th, Pa) in aqueous solution, taking into account solvation effects through various models.
  • The geometry calculations for Ac(III), Th(IV), and Pa(V) aligned well with experimental data, and the redox potentials were mostly within ±0.2 V of experimental measurements, particularly using the COSMO model.
  • The study explored the redox pathways of Pa(V/IV), revealing that redox potentials shift to more negative values at higher pH, while positive values for Th and Pa in An(I/0) contrasts with negative
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  • The study calculates the free energy of hydration, electron affinities in gas and aqueous phases, and aqueous reduction potentials for halogens and their anions (F, Cl, Br, I, and others) using an advanced electronic structure method, yielding reliable results.
  • Gas phase electron affinities were derived from high-level quantum chemistry calculations, showing strong agreement with existing experimental data.
  • The research also predicts aqueous reduction potentials for various halogen species with a close correlation (within 0.06 V) to experimental values, expanding knowledge on redox couples that lack experimental data, especially for iodine and interhalogen anions.
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A variety of different ground-state structures of carbene and phosphine groups 1 and 2 cationic, group 11 cationic, and group 10 neutral complexes were studied using density functional theory (DFT) and correlated molecular orbital theory (CCSD(T)) methods. Geometries of complexes with phosphines were studied and compared to available experimental data. Among the three analyzed phosphine ligands, PH, PMe, and PPh, PH was found to have noticeably smaller ligand binding energies (LBEs, Δ).

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The redox properties of the actinides in aqueous solution are important for fuel production/reprocessing and understanding the environmental impact of nuclear waste. The redox potentials for U, Np, Pu, and Am in oxidation states from 0 up to VII (as appropriate) in aqueous solutions have been predicted at the density functional theory level with the B3LYP functional, Stuttgart small core pseudopotential basis sets for the actinides, and explicit (30HO molecules)/implicit treatment of the aqueous solvent using the self-consistent reaction field COSMO and SMD approaches for the implicit solvation. The predictions of the structural parameters of clusters incorporating first and second solvation shells are consistent with the available experimental data.

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The nature of the Ni-O bond is relevant to catalytic and environmental applications. The vibrational frequency and electronic structure of NiO were calculated using CASSCF, icMRCI+Q, CCSD(T), and DFT. CASSCF predicted a quintet state (Σ) ground state for the equilibrium bond distance with a state crossing at 1.

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High-level electronic structure calculations were conducted to examine the bonding and spectroscopic properties of the UO and UF diatomic molecules. The low-lying Ω states were described by using multireference SO-CASPT2 calculations. The adiabatic electronic affinity (AEA), adiabatic ionization energy (IE), and bond dissociation energy (BDE) were calculated at the Feller-Peterson-Dixon (FPD) level.

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  • The acidity levels of various hydrated metal dication complexes, including carbonates and bicarbonates, were analyzed using advanced computational methods in both gas and aqueous phases.
  • The study focused on how different metal ions (like Mg, Ca, Mn, and others) affect the acidity of bicarbonate ligands, revealing that group 2 metal complexes generally decrease acidity, while transition-metal complexes can increase it, especially with electron donation from ligands.
  • Results showed that for group 2 and transition metals, the acidity of water in these complexes was usually greater than that of hydrated metal dications, although some exceptions were noted for specific dihydrate complexes.
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Inborn errors of T cell development present a pediatric emergency in which timely curative therapy is informed by molecular diagnosis. In 11 affected patients across four consanguineous kindreds, we detected homozygosity for a single deleterious missense variant in the gene NudC domain-containing 3 () Two infants had severe combined immunodeficiency with the complete absence of T and B cells (TB SCID), whereas nine showed classical features of Omenn syndrome (OS). Restricted antigen receptor gene usage by residual T lymphocytes suggested impaired V(D)J recombination.

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Progress toward the closure of the nuclear fuel cycle can be achieved if satisfactory separation strategies for the chemoselective speciation of the trivalent actinides from the lanthanides are realized in a nonproliferative manner. Since Kolarik's initial report on the utility of bis-1,2,4-triazinyl-2,6-pyridines (BTPs) in 1999, a perfect complexant-based, liquid-liquid separation system has yet to be realized. In this report, a comprehensive performance assessment for the separation of Am from Eu as a model system for spent nuclear fuel using hydrocarbon-actuated alkoxy-BTP complexants is described.

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Activity descriptors are a powerful tool for the design of catalysts that can efficiently utilize H with minimal energy losses. In this study, we develop the use of hydricity and H self-exchange rates as thermodynamic and kinetic descriptors for the hydrogenation of ketones by molecular catalysts. Two complexes with known hydricity, HRh(dmpe) and HCo(dmpe), were investigated for the catalytic hydrogenation of ketones under mild conditions (1.

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A longstanding challenge in catalysis by noble metals has been to understand the origin of enhancements of rates of hydrogen transfer that result from the bonding of oxygen near metal sites. We investigated structurally well-defined catalysts consisting of supported tetrairidium carbonyl clusters with single-atom (apical iridium) catalytic sites for ethylene hydrogenation. Reaction of the clusters with ethylene and H followed by O led to the onset of catalytic activity as a terminal CO ligand at each apical Ir atom was removed and bridging dioxygen ligands replaced CO ligands at neighboring (basal-plane) sites.

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  • The study examines the reactions of halogens (Cl, Br, I) with Na, resulting in the formation of excited states of sodium dimers (Na2*) that emit light in the visible and ultraviolet regions.
  • Experimental findings indicate that this emission is linked to reactions of sodium triplet states (Na3) and specific wavelengths show evidence of population inversion, meaning that more molecules are in excited states than in lower energy states (gain).
  • The research highlights how collision-induced energy transfer creates a buildup of populations in reservoir states, which helps produce laser-like amplification effects in sodium, indicating potential applications in short wavelength laser technologies for chemical propulsion systems.
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  • The study predicts ligand binding energies (LBEs) for various types of carbenes interacting with different metal groups using advanced computational methods.
  • It highlights that alkali and alkaline earth metals exhibit ionic bonding characteristics, while group 10 and 11 metals display covalent-like bonding, influenced by the nature of electron donation.
  • The research improves understanding of how NHCs interact with metals, which can guide the design of new systems utilizing these interactions.
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The aqueous electron affinity and aqueous reduction potentials for F, Cl, Br, I, OH, SH, SeH, TeH, ClO, BrO, and IO were calculated using electronic structure methods for explicit cluster models coupled with a self-consistent reaction field (SMD) to treat the aqueous solvent. Calculations were conducted using MP2 and correlated molecular orbital theory up to the CCSD(T)-F12b level for water tetramer clusters and MP2 for octamer cluster. Inclusion of explicit waters was found to be important for accurately predicting the redox potentials in a number of cases.

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Objective: Musculoskeletal (MSK) causes of chest pain are considered common in emergency care, yet management is limited, reported outcomes are poor and prevalence data in New Zealand are lacking. The present study aims to estimate the prevalence of MSK chest pain in New Zealand EDs and describe the characteristics of MSK chest pain cases.

Methods: A retrospective chart review was conducted based on de-identified clinical notes extracted from four hospitals within the South Island of New Zealand from 3 months spanning 1 March to 31 May 2021.

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  • *Research focused on the effectiveness of nitrogen-strained ring heterocycles in capturing these gases, revealing that reactions with 3- and 4-membered rings are exothermic while those with 5-membered rings are not favorable.
  • *The study found that the structure of the rings influences the capture efficiency and suggests the potential of expanded N-heterocycles for polymerization, enabling the upcycling of materials.
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The interactions between group 1 and 11 monocations and group 2 dications with triphenylphosphine were studied by using a combination of correlated molecular orbital theory and density functional theory. Two binding modes were found: the front side (phosphorus lone pair) and back side (phenyl rings). Group 1 and 2 cations prefer binding to the π system rather than to the lone pair of the phosphorus atom, and their ligand binding energies (LBEs) correlate with the atomic ionic radii as well as the hardness of the atomic ion.

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Transition metal oxide (TMO) clusters are being studied for their ability to absorb acid gases generated by energy production processes. The interaction of SO, a byproduct of common industrial processes, with group 4 metal (Ti, Zr, and Hf) oxide nanoclusters, has been predicted using electronic structure methods. The calculations were done at the density functional theory (DFT) and correlated molecular orbital coupled cluster singles and doubles CCSD(T) theory levels.

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  • * The study tested an antiviral drug, IM-250, which showed promise in reducing future herpes outbreaks by targeting the virus during its latent stage in two animal models.
  • * Results indicate that treating infections during latency can lower the chances of the virus reactivating, suggesting a new approach to managing herpes infections effectively.
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The extraembryonic yolk sac (YS) ensures delivery of nutritional support and oxygen to the developing embryo but remains ill-defined in humans. We therefore assembled a comprehensive multiomic reference of the human YS from 3 to 8 postconception weeks by integrating single-cell protein and gene expression data. Beyond its recognized role as a site of hematopoiesis, we highlight roles in metabolism, coagulation, vascular development, and hematopoietic regulation.

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  • The study examines the hydrolysis reactions of actinide oxides ThO, PaO, UO, and triplet NpO, using advanced computational methods (CCSD(T) and B3LYP) to understand their energetics.
  • Hydrolysis begins with the formation of a Lewis acid/base adduct with water, leading to proton transfer and the formation of dihydroxide, which continues until the oxide is fully hydrolyzed.
  • ThO shows a preference for reacting at terminal oxo groups, while UO and NpO react at bridging oxygens; overall, UO and NpO formations are more favored when more water molecules are added, with stability decreasing as hydroxyl groups increase.
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The purely chemical synthesis of fluorine is a spectacular reaction which for more than a century had been believed to be impossible. In 1986, it was finally experimentally achieved, but since then this important reaction has not been further studied and its detailed mechanism had been a mystery. The known thermal stability of MnF casts serious doubts on the originally proposed hypothesis that MnF is thermodynamically unstable and decomposes spontaneously to a lower manganese fluoride and F .

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