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DOE OSTI2016

Investigation of sodium insertion–extraction in olivine Na x FePO 4 (0 ≤ x ≤ 1) using first-principles calculations

Olivine NaFePO4 has recently attracted the attention of the scientific community as a promising cathode material for Na-ion batteries. In this work we combine density functional theory (DFT) calculations and high resolution synchrotron X-ray diffraction (HRXRD) experiments to study the phase stability of NaxFePO4 along the whole range of sodium compositions (0 ≤ x ≤ 1). DFT calculations reveal the existence of two intermediate structures governing the phase stability at x = 2/3 and x = 5/6. This is in contrast to isostructural LiFePO4, which is a broadly used cathode in Li-ion batteries. Na2/3FePO4 and Na5/6FePO4 ground states both align vacancies diagonally within the ab plane, coupled to a Fe2+/Fe3+ alignment. HRXRD data for NaxFePO4 (2/3 < x < 1) materials show common superstructure reflections up to x = 5/6 within the studied compositions. The computed intercalation voltage profile shows a voltage difference of 0.16 V between NaFePO4 and Na2/3FePO4 in agreement with the voltage discontinuity observed experimentally during electrochemical insertion.

Saracibar, A.↗

DOE OSTI2023

Quantum and anharmonic effects in non-adiabatic transition state theory

Quantitative descriptions of non-adiabatic transition rates at intermediate temperatures are challenging due to the simultaneous importance of quantum and anharmonic effects. Here, in this paper, the interplay between quantum effects—for motion across or along the seam of crossing—and anharmonicity in the seam potential is considered within the weak coupling limit. The well-known expression for quantized 1-D motion across the seam (i.e., tunneling) in the linear terms approximation is derived in the thermal domain using the Lagrangian formalism, which is then applied to the case when tunneling is distributed along the seam of crossing (treating motion along the seam classically). For high-frequency quantum modes, a vibrationally adiabatic (VA) approach is developed that introduces to the non-adiabatic rate constant a factor associated with high-frequency wavefunction overlap; this approach treats the high-frequency motion along the seam quantum mechanically. To test these methodologies, the reaction N 2 O ↔ N 2 + O( 3 P) was chosen. CCSD(T)-F12b/cc-pVTZ-F12 explorations of the 3 A'- 1 A' seam of N 2 O revealed that seam anharmonicity has a strong effect on the rate constant (a factor of ~20 at 2000 K). Several quantum effects were found to be significant at intermediate/lower temperatures, including the quantum N–N vibration that was coupled with seam anharmonicity using the VA approach. Finally, a 1-D approximation to non-adiabatic instanton theory is presented to estimate the validity limit of the linear terms model at low temperatures (⁠~ 250 K for N 2 O). We recommend that the assumptions built into many statistical theories for non-adiabatic reactions—harmonic behavior, classical motion, linear terms, and weak coupling—should be verified on a case-by-case basis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Spin-orbit exciton in a honeycomb lattice magnet CoTiO 3 : Revealing a link between magnetism in d - and f -electron systems

We carried out inelastic neutron scattering to study the spin-orbital (SO) exciton in a single crystal sample of CoTiO 3 as a function of temperature. CoTiO 3 is a honeycomb magnet with dominant XY-type magnetic interaction and an A-type antiferromagnetic order below T N ≈ 38 K. We found that the SO exciton becomes softer, but acquires a larger bandwidth in the paramagnetic phase, compared to that in the magnetically ordered phase. Moreover, an additional mode is only observed in the intermediate temperature range, as the sample is warmed up above the lowest accessible temperature below T N . Such an unusual temperature dependence observed in this material suggests that its ground states (an S eff = 1 2 doublet) and excited states multiplets are strongly coupled, and therefore cannot be treated independently, as often done in a pseudo-spin model. Furthermore, our observations can be explained by a multi-level theory within random phase approximation that explicitly takes into account both the ground and excited multiplets. The success of our theory, which is originally developed to explain temperature dependence of magnetic excitations in the rare-earth magnets, highlight the similarity between the magnetic excitations in rare-earth systems and those in transition metal systems with strong spin orbit coupling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Numerical Simulation Applications in the Design of EGS Collab Experiment 1

The United States Department of Energy, Geothermal Technologies Office (GTO) is funding a collaborative investigation of enhanced geothermal systems (EGS) processes at the meso-scale. This study, referred to as the EGS Collab project, is a unique opportunity for scientists and engineers to investigate the creation of fracture networks and circulation of fluids across those networks under in-situ stress conditions. The EGS Collab project is envisioned to comprise three experiments and the site for the first experiment is on the 4850 Level (4,850 feet below ground surface) in phyllite of the Precambrian Poorman formation, at the Sanford Underground Research Facility, located at the former Homestake Gold Mine, in Lead, South Dakota. Principal objectives of the project are to develop a number of intermediate-scale field sites and to conduct well-controlled in situ experiments focused on rock fracture behavior and permeability enhancement. Data generated during these experiments will be compared against predictions of a suite of computer codes specifically designed to solve problems involving coupled thermal, hydrological, geomechanical, and geochemical processes. Comparisons between experimental and numerical simulation results will provide code developers with direction for improvements and verification of process models, build confidence in the suite of available numerical tools, and ultimately identify critical future development needs for the geothermal modeling community. Moreover, conducting thorough comparisons of models, modelling approaches, measurement approaches and measured data, via the EGS Collab project, will serve to identify techniques that are most likely to succeed at the Frontier Observatory for Research in Geothermal Energy (FORGE), the GTO's flagship EGS research effort. As noted, outcomes from the EGS Collab project experiments will serve as benchmarks for computer code verification, but numerical simulation additionally plays an essential role in designing these meso-scale experiments. This paper describes specific numerical simulations supporting the design of Experiment 1, a field test involving hydraulic stimulation of two fractures from notched sections of the injection borehole and fluid circulation between sub-horizontal injection and production boreholes in each fracture individually and collectively, including the circulation of chilled water. Whereas the mine drift allows for accurate and close placement of monitoring instrumentation to the developed fractures, active ventilation in the drift cooled the rock mass within the experimental volume. Numerical simulations were executed to predict seismic events and magnitudes during stimulation, initial fracture orientations for smooth horizontal wellbores, pressure requirements for fracture initiation from notched wellbores, fracture propagation during stimulation between the injection and production boreholes, tracer travel times between the injection and production boreholes, produced fluid temperatures with chilled water injections, pressure limits on fluid circulation to avoid fracture growth, temperature environment surrounding the 4850 Level drift, and fracture propagation within a stress field altered by drift excavation, ventilation cooling, and dewatering.

15 GEOTHERMAL ENERGY↗

DOE OSTI2019

The Necessity for Iteration in the Application of Numerical Simulation to EGS: Examples from the EGS Collab Test Bed 1

The United States Department of Energy, Geothermal Technologies Office (GTO) is funding a collaborative investigation of enhanced geothermal systems (EGS) processes at the meso-scale. This study, referred to as the EGS Collab project, is a unique opportunity for scientists and engineers to investigate the creation of fracture networks and circulation of fluids across those networks under in-situ stress conditions. The EGS Collab project is envisioned to comprise three experiments and the site for the first experiment is on the 4850 Level in phyllite of the Precambrian Poorman formation, at the Sanford Underground Research Facility, located at the former Homestake Gold Mine, in Lead, South Dakota. Principal objectives of the project are to develop a number of intermediate-scale field sites and to conduct well-controlled in situ experiments focused on rock fracture behavior and permeability enhancement. Data generated during these experiments will be compared against predictions of a suite of computer codes specifically designed to solve problems involving coupled thermal, hydrological, geomechanical, and geochemical processes. Comparisons between experimental and numerical simulation results will provide code developers with direction for improvements and verification of process models, build confidence in the suite of available numerical tools, and ultimately identify critical future development needs for the geothermal modeling community. Moreover, conducting thorough comparisons of models, modelling approaches, measurement approaches and measured data, via the EGS Collab project, will serve to identify techniques that are most likely to succeed at the Frontier Observatory for Research in Geothermal Energy (FORGE), the GTO's flagship EGS research effort. As noted, outcomes from the EGS Collab project experiments will serve as benchmarks for computer code verification, but numerical simulation additionally plays an essential role in designing these meso-scale experiments. This paper reviews specific numerical simulations supporting the design of experiments within Test Bed 1, a volume of phyllite rock under in-situ stress conditions off the western side of the West Access Drift on the 4850 Level, near Governor's Corner. Numerical simulations were executed prior to the start of hydraulic stimulation activities within Test Bed 1 following standard practices, using best estimates of principal stress conditions, thermal conditions, and the rock petrophysical properties, including geomechanical properties. These simulations indicated notching of the borehole would promote the initiation of transverse fractures, seismic magnitudes during the hydraulic stimulation would be below 0.1 magnitude on the Richter scale, a rock thermal conductivity of 5.0 W/m K yielded agreement with kISMET borehole temperature logs, back pressure on the production borehole would increase circulation across the test bed, and the production borehole would serve to halt propagation of the hydraulic fracture to the drift. Pre-existing natural fractures, heterogeneities in the rock properties, monitoring boreholes, and overlooked mine elements have prompted a second look at numerically modeling stimulation, fluid circulation, tracer migration, and thermal breakthrough. Numerical simulation is an invaluable tool for providing insight and understanding to complex physical processes. The success of simulations, however, often depends on including all of the salient features of the system in the founding conceptual model. This paper takes a retrospective look at examples where the conceptual model and simulation was sufficient to provide accurate forecasts and those where elements were missing, necessitating rethinking of the simulation.

15 GEOTHERMAL ENERGY↗

DOE OSTI2019

The Necessity for Iteration in the Application of Numerical Simulation to EGS: Examples from the EGS Collab Test Bed 1

The United States Department of Energy, Geothermal Technologies Office (GTO) is funding a collaborative investigation of enhanced geothermal systems (EGS) processes at the meso-scale. This study, referred to as the EGS Collab project, is a unique opportunity for scientists and engineers to investigate the creation of fracture networks and circulation of fluids across those networks under in-situ stress conditions. The EGS Collab project is envisioned to comprise three experiments and the site for the first experiment is on the 4850 Level in phyllite of the Precambrian Poorman formation, at the Sanford Underground Research Facility, located at the former Homestake Gold Mine, in Lead, South Dakota. Principal objectives of the project are to develop a number of intermediate-scale field sites and to conduct well-controlled in situ experiments focused on rock fracture behavior and permeability enhancement. Data generated during these experiments will be compared against predictions of a suite of computer codes specifically designed to solve problems involving coupled thermal, hydrological, geomechanical, and geochemical processes. Comparisons between experimental and numerical simulation results will provide code developers with direction for improvements and verification of process models, build confidence in the suite of available numerical tools, and ultimately identify critical future development needs for the geothermal modeling community. Moreover, conducting thorough comparisons of models, modelling approaches, measurement approaches and measured data, via the EGS Collab project, will serve to identify techniques that are most likely to succeed at the Frontier Observatory for Research in Geothermal Energy (FORGE), the GTO’s flagship EGS research effort. As noted, outcomes from the EGS Collab project experiments will serve as benchmarks for computer code verification, but numerical simulation additionally plays an essential role in designing these meso-scale experiments. This paper reviews specific numerical simulations supporting the design of experiments within Test Bed 1, a volume of phyllite rock under in-situ stress conditions off the western side of the West Access Drift on the 4850 Level, near Governor’s Corner. Numerical simulations were executed prior to the start of hydraulic stimulation activities within Test Bed 1 following standard practices, using best estimates of principal stress conditions, thermal conditions, and the rock petrophysical properties, including geomechanical properties. These simulations indicated notching of the borehole would promote the initiation of transverse fractures, seismic magnitudes during the hydraulic stimulation would be below 0.1 magnitude on the Richter scale, a rock thermal conductivity of 5.0 W/m K yielded agreement with kISMET borehole temperature logs, back pressure on the production borehole would increase circulation across the test bed, and the production borehole would serve to halt propagation of the hydraulic fracture to the drift. Pre-existing natural fractures, heterogeneities in the rock properties, monitoring boreholes, and overlooked mine elements have prompted a second look at numerically modeling stimulation, fluid circulation, tracer migration, and thermal breakthrough. Numerical simulation is an invaluable tool for providing insight and understanding to complex physical processes. The success of simulations, however, often depends on including all of the salient features of the system in the founding conceptual model. This paper takes a retrospective look at examples where the conceptual model and simulation was sufficient to provide accurate forecasts and those where elements were missing, necessitating rethinking of the simulation.

numerical simulation, EGS Collab, enhanced geother↗

DOE OSTI2018

Numerical Simulation Applications in the Design of EGS Collab Experiment 1

The United States Department of Energy, Geothermal Technologies Office (GTO) is funding a collaborative investigation of enhanced geothermal systems (EGS) processes at the meso-scale. This study, referred to as the EGS Collab project, is a unique opportunity for scientists and engineers to investigate the creation of fracture networks and circulation of fluids across those networks under in-situ stress conditions. The EGS Collab project is envisioned to comprise three experiments and the site for the first experiment is on the 4850 Level in phyllite of the Precambrian Poorman formation, at the Sanford Underground Research Facility, located at the former Homestake Gold Mine, in Lead, South Dakota. Principal objectives of the project are to develop a number of intermediate-scale field sites and to conduct well-controlled in situ experiments focused on rock fracture behavior and permeability enhancement. Data generated during these experiments will be compared against predictions of a suite of computer codes specifically designed to solve problems involving coupled thermal, hydrological, geomechanical, and geochemical processes. Comparisons between experimental and numerical simulation results will provide code developers with direction for improvements and verification of process models, build confidence in the suite of available numerical tools, and ultimately identify critical future development needs for the geothermal modeling community. Moreover, conducting thorough comparisons of models, modelling approaches, measurement approaches and measured data, via the EGS Collab project, will serve to identify techniques that are most likely to succeed at the Frontier Observatory for Research in Geothermal Energy (FORGE), the GTO’s flagship EGS research effort. As noted, outcomes from the EGS Collab project experiments will serve as benchmarks for computer code verification, but numerical simulation additionally plays an essential role in designing these meso-scale experiments. This paper describes specific numerical simulations supporting the design of Experiment 1, a field test involving hydraulic stimulation of two fractures from notched sections of the injection borehole and fluid circulation between sub-horizontal injection and production boreholes in each fracture individually and collectively, including the circulation of chilled water. Whereas the mine drift allows for accurate and close placement of monitoring instrumentation to the developed fractures, active ventilation in the drift cooled the rock mass within the experimental volume. Numerical simulations were executed to predict seismic events and magnitudes during stimulation, initial fracture orientations for smooth horizontal wellbores, pressure requirements for fracture initiation from notched wellbores, fracture propagation during stimulation between the injection and production boreholes, tracer travel times between the injection and production boreholes, and produced fluid temperatures with chilled water injections, and pressure limits on fluid circulation to avoid fracture growth.

Numerical Simulation, EGS Collab, EGS, Sanford Und↗

DOE OSTI2017

The Role of Numerical Simulation in the Design of Stimulation and Circulation Experiments for the EGS Collab Project

Numerical Simulation, EGS Collab, EGS, Sanford Und↗

DOE OSTI2015

Development of nanosecond time-resolved infrared detection at the LEAF pulse radiolysis facility

When coupled with transient absorption spectroscopy, pulse radiolysis, which utilizes high-energy electron pulses from an accelerator, is a powerful tool for investigating the kinetics and thermodynamics of a wide range of radiation-induced redox and electron transfer processes. The majority of these investigations detect transient species in the UV, visible, or near-IR spectral regions. Unfortunately, the often-broad and featureless absorption bands in these regions can make the definitive identification of intermediates difficult. Time-resolved vibrational spectroscopy would offer much improved structural characterization, but has received only limited application in pulse radiolysis. In this paper, we describe in detail the development of a unique nanosecond time-resolved infrared (TRIR) detection capability for condensed-phase pulse radiolysis on a new beam line at the LEAF facility of Brookhaven National Laboratory. The system makes use of a suite of high-power, continuous wave external-cavity quantum cascade lasers as the IR probe source, with coverage from 2330-1051 cm⁻¹. The response time of the TRIR detection setup is ~40 ns, with a typical sensitivity of ~100 µOD after 4-8 signal averages using a dual-beam probe/reference normalization detection scheme. As a result, this new detection method has enabled mechanistic investigations of a range of radiation-induced chemical processes, some of which are highlighted here.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Toward sustainable production of N-containing products via nonthermal plasma-enhanced conversion of natural gas resources

Nonthermal plasmas can directly activate and cleave the strong chemical bonds in molecular nitrogen and methane to facilitate the transformation of these inherently stable molecules through the application of electrical energy. Here, we report a low temperature, atmospheric pressure, nonthermal plasma for the “one-pot” synthesis of olefins, alkynes, higher molecular weight hydrocarbons, ammonia, and nitrogen-containing liquids from a representative shale gas feed enriched with nitrogen. Furthermore, we reproducibly observe a wide range of valuable and synthetically challenging gas-phase and liquid-phase products containing C-N, C-C, and N-H bonding by controlling the N 2 concentration in the inlet feed stream. In nitrogen-lean regimes, hydrocarbon products dominate (e.g., ethylene, acetylene, etc.), while nitrogen-rich regimes promote incorporation of nitrogen into the products, leading to the formation of ammonia and liquid products containing a variety of functionalities (e.g., nitriles, amines, heterocycles). High resolution electrospray ionization mass spectrometry was used to measure molecular weights and identify the chemical formulas of the liquid products. Van Krevelen diagrams were created and showed many products with compositions around H/C = 2 and N/C = 0.5, indicating the potential importance of intermediate species with these ratios for liquid formation (e.g., CH 3 CN + H).

03 NATURAL GAS↗

DOE OSTI2019

Propanol Amination over Supported Nickel Catalysts: Reaction Mechanism and Role of the Support

Ni-supported hydroxyapatite catalyst (Ni/HAP) was characterized and evaluated for propanol amination to propylamine at 423 K. The reaction proceeds via dehydroamination, a process that involves sequential dehydrogenation, condensation, and hydrogenation. Kinetic and isotopic studies indicate that α-H abstraction from propoxide species limits the rate of the dehydrogenation step and hence the overall rate of reaction. The rate of propanol dehydrogenation depends on the composition of the support and on the concentration of Ni sites located at the interface between Ni nanoparticles and the support. Ni/HAP is an order of magnitude more active than Ni/SiO 2 and displays a higher selectivity toward the primary amine. In conclusion, the superior performance of Ni/HAP is attributed to the high density of basic sites on HAP, which are responsible for stabilizing alkoxide intermediates and suppressing the disproportionation and secondary amination of amines.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2012

Studies of top quark properties at the Tevatron

An overview of the recent measurements of the top quark properties in proton antiproton collisions at {radical}s = 1.96 TeV is presented. These measurements are based on 5.4-8.7 fb{sup -1} of data collected with the D0 and CDF experiments at the Fermilab Tevatron collider. The top quark mass and width measurements, studies of the spin correlation in top quark pair production, W boson helicity measurement, searches for anomalous top quark couplings and Lorentz invariance violation are discussed.

43 PARTICLE ACCELERATORS↗

DOE OSTI2011

Phase separation versus supersolid behavior in frustrated antiferromagnets

We investigate the competition between spin supersolidity and phase separation in a frustrated spin-half model of weakly coupled dimers. We start by considering systems of hard-core bosons on the square lattice, onto which the low-energy physics of the herein investigated spin model can be mapped, and devise a criterion for gauging the interplay between supersolid order and domain-wall formation based on strong-coupling arguments. Effective bosonic models for the spin model are derived via the contractor renormalization (CORE) algorithm and we propose to combine a self-consistent cluster mean-field solution with our criterion for the occurrence of phase separation to derive the phase diagram as a function of frustration and magnetic field. In the limit of strong frustration, the model is shown to be unstable toward phase separation, in contradiction with recently published results. However, a region of stable supersolidity is identified for intermediate frustration, in a parameter range of possible experimental relevance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Ab Initio Unimolecular Reaction Kinetics of CH 2 C(＝)OCH 3 and CH 3 C(＝O)OCH 2 Radicals

The unimolecular dissociation and isomerization kinetics of the methyl ester combustion intermediates methoxycarbonylmethyl (CH 2 C(＝O)OCH 3 ) and acetyloxylmethyl (CH 3 C(＝O)OCH 2 ) are theoretically investigated using high-level ab initio methods and the Rice–Ramsperger–Kassel–Marcus (RRKM)/master equation (ME) theory. Potential energy surfaces (PESs) are obtained using coupled cluster singles and doubles with perturbative triples correction (CCSD(T)), multireference singles and doubles configuration interaction (MRSDCI) with the Davidson–Silver (DS) correction, and multireference averaged coupled pair functional (MRACPF2) theory. The transition states exhibit high T1 diagnostics in coupled cluster calculations, suggesting the need for a multireference correlated wave function treatment. MRSDCI+DS and MRACPF2 capture their multiconfigurational character well, yielding lower barrier heights than CCSD(T) for these reactions. Additionally, the rate coefficients are computed using the RRKM/ME theory over a 500–2500 K temperature range and at a pressure range of 0.01 atm to the high-pressure limit. The temperature- and pressure-dependent rate coefficients are given in modified Arrhenius expressions. The β-scission of CH 2 C(＝O)OCH 3 is predicted to have a much higher barrier than the corresponding isomerization reaction and the β-scission of CH 3 C(＝O)OCH 2 . Consequently, the rate coefficients for β-scission of CH 2 C(＝O)OCH 3 are the smallest among the three reactions and the isomerization followed by decomposition to CH 3 C(＝O) and HCHO is the dominant reaction pathway for CH 2 C(＝O)OCH 3 . Furthermore, both radicals CH 2 C(＝O)OCH 3 and CH 3 C(＝O)OCH 2 are predicted to mainly decompose to CH 3 C(＝O) + HCHO rather than to the bimolecular product CH 2 C(＝O) + CH 3 O. A newly developed MA combustion mechanism, using our theoretical rate coefficients for the MA-related reactions, predicts combustion properties in good agreement with available experimental data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Open Circuit Potential Method for Thermodynamic Hydricity Measurements of Metal Hydrides

Metal hydrides are prevalent in many catalytic reactions, and thermodynamic hydricity has emerged as a useful parameter for understanding and predicting key hydride transfer steps with these intermediates. An open circuit potentiometry method for determining the hydricity of metal hydrides with a single thermodynamic parameter is reported. The open circuit potential (OCP) of a solution containing a metal hydride and its conjugate hydride acceptor, along with a conjugate acid/base pair, is coupled with known values for the acid pK a and H + /H – reduction potential to determine the hydricity. Here, the reliability of the method was established by using potentiometry to obtain the hydricity of three hydride complexes with varying supporting ligands and transition metal elements in acetonitrile solvent, all within error of previously reported values. Advantages and drawbacks of this method are discussed, and a recommended workflow for practitioners is introduced.

Anions↗

DOE OSTI2011

Reactivity of Chemisorbed Oxygen Atoms and Their Catalytic Consequences during CH 4 –O 2 Catalysis on Supported Pt Clusters

Kinetic and isotopic data and density functional theory treatments provide evidence for the elementary steps and the active site requirements involved in the four distinct kinetic regimes observed during CH4 oxidation reactions using O2, H2O, or CO2 as oxidants on Pt clusters. These four regimes exhibit distinct rate equations because of the involvement of different kinetically relevant steps, predominant adsorbed species, and rate and equilibrium constants for different elementary steps. Transitions among regimes occur as chemisorbed oxygen (O*) coverages change on Pt clusters. O* coverages are given, in turn, by a virtual O2 pressure, which represents the pressure that would give the prevalent steady-state O* coverages if their adsorption–desorption equilibrium was maintained. The virtual O2 pressure acts as a surrogate for oxygen chemical potentials at catalytic surfaces and reflects the kinetic coupling between C–H and O=O activation steps. O* coverages and virtual pressures depend on O2 pressure when O2 activation is equilibrated and on O2/CH4 ratios when this step becomes irreversible as a result of fast scavenging of O* by CH4-derived intermediates. In three of these kinetic regimes, C–H bond activation is the sole kinetically relevant step, but occurs on different active sites, which evolve from oxygen–oxygen (O*–O*), to oxygen–oxygen vacancy (O*–*), and to vacancy–vacancy (*–*) site pairs as O* coverages decrease.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Oxidation, Reduction, and Condensation of Alcohols over (MO3)3 (M=Mo, W) Nanoclusters

The reactions of deuterated methanol, ethanol, 1-propanol, 1-butanol, 2-propanol, 2-butanol and t-butanol over cyclic (MO3)3 (M = Mo, W) clusters were studied experimentally with temperature programmed desorption (TPD) and theoretically with coupled cluster CCSD(T) theory and density functional theory. The reactions of two alcohols per M3O9 cluster are required to provide agreement with experiment for D2O release, dehydrogenation and dehydration. The reaction begins with the elimination of water by proton transfers and forms an intermediate dialkoxy species which can undergo further reaction. Dehydration proceeds by a β hydrogen transfer to a terminal M=O. Dehydrogenation takes place via an α hydrogen transfer to an adjacent MoVI = O atom or a WVI metal center with redox involved for M = Mo and no redox for M = W. The two channels have comparable activation energies. H/D exchange to produce alcohols can take place after olefin is released or via the dialkoxy species depending on the alcohol and the cluster. The Lewis acidity of the metal center with WVI being larger than MoVI results in the increased reactivity of W3O9 over Mo3O9 for dehydrogenation and dehydration.

Environmental Molecular Sciences Laboratory↗

DOE OSTI2014

Electron spin-lattice relaxation of low-symmetry Ni{sup 2+} centers in LiF

The spin-lattice relaxation times of charge-compensated Ni{sup 2+} centers in LiF single crystals were measured using the electron spin echo technique. An analysis of the results revealed a very high relaxation rate with a linear dependence on temperature within the intermediate temperature range of 5–15 K. This acceleration of the relaxation rate was found to be due to the inhomogeneous distribution of Ni{sup 2+} ions in the LiF lattice. It seems that the effective cross-relaxation mechanism through the exchange-coupled clusters of Ni{sup 2+} ions can play a dominant role. Two-phonon Raman type relaxation dominates at higher temperatures involving the Debye phonon spectrum of the LiF lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗