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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Programmable topotaxis of magnetic rollers in time-varying fields

We discuss how spatially uniform, time-periodic magnetic fields can be designed to power and direct the migration of ferromagnetic spheres up (or down) local gradients in the topography of a solid substrate. Our results are based on a dynamical model that considers the time-varying magnetic torques on the particle and its motion through the fluid at low Reynolds number. We use both analytical theory and numerical simulation to design magnetic fields that maximize the migration velocity up (or down) an inclined plane. We show how “topotaxis” of spherical particles relies on differences in the hydrodynamic resistance to rotation about axes parallel and perpendicular to the plane. Importantly, the designed fields can drive multiple independent particles to move simultaneously in different directions as determined by gradients in their respective environments. Experiments on ferromagnetic spheres provide evidence for topotactic motions up inclined substrates. The ability to program the autonomous navigation of driven particles within anisotropic environments is relevant to the design of colloidal robots.

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DOE OSTI2021

Inelastic scattering in isotopologues of O 2 –Ar: the effects of mass, symmetry, and density of states

The two species considered here, O 2 (oxygen molecule) and Ar (argon-atom), are both abundant components of Earth's atmosphere and hence familiar collision partners in this medium. O 2 is quite reactive and extensively involved in atmospheric chemistry, including Chapman's cycle of the formation and destruction of ozone; while Ar, like N 2 , typically plays the nevertheless crucial role of inert collider. Inert species can provide stabilization to metastable encounter-complexes through the energy transfer associated with inelastic collisions. The interplay of collision frequency and energy transfer efficiency, with state lifetimes and species concentrations, contributes to the rich and varied chemistry and dynamics found in diverse environments ranging from planetary atmospheres to the interstellar and circumstellar media. The nature and density of bound and resonance states, coupled electronic states, symmetry, and nuclear spin-statistics can all play a role. Here, we systematically investigate some of those factors by looking at the O 2 –Ar system, comparing rigorous quantum-scattering calculations for the 16 O 16 O– 40 Ar, 18 O 16 O– 40 Ar, and 18 O 18 O– 40 Ar isotope combinations. A new accurate potential energy surface was constructed for this purpose holding the O 2 bond distance at its vibrationally averaged distance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Imidazole-graphyne: a new 2D carbon nitride with a direct bandgap and strong IR refraction

Six-membered rings are common building blocks of many carbon structures. Recent studies have shown that penta-graphene composed of five-membered carbon rings have properties very different from that of graphene. This has motivated the search for new carbon structures. Among this is cp-graphyne, composed of carbon pentagons and bridged by acetylenic linkers. However, the bandgap of cp-graphyne, like that of graphene, is zero, making it unsuitable for applications in electronics. Herein, we show that a new two-dimensional (2D) carbon nitride structure formed by assembling the five-membered imidazole molecules with acetylenic linker can overcome this limitation. Named ID-GY, this new material not only has a direct band gap of 1.10 eV, but it is dynamically and mechanically stable and can withstand temperatures up to 1200 K. In addition, due to its porous and anisotropic geometry, the Young's modulus of ID-GY along the diagonal direction is lower than that of most 2D materials reported previously. Equally important, ID-GY exhibits strong refraction near infrared (IR) and has potential for applications in nanoelectronics and optical devices. These results, based on density functional theory, can stimulate experimental studies.

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DOE OSTI2021

Failure of molecular dynamics to provide appropriate structures for quantum mechanical description of the aqueous chloride ion charge-transfer-to-solvent ultraviolet spectrum

The lowest band in the charge-transfer-to-solvent ultraviolet absorption spectrum of aqueous chloride ion is studied by experiment and computation. Interestingly, the experiments indicate that at concentrations up to at least 0.25 M, where calculations indicate ion pairing to be significant, there is no notable effect of ionic strength on the spectrum. The experimental spectra are fitted to aid comparison with computations. Classical molecular dynamic simulations are carried out on dilute aqueous Cl - , Na + , and NaCl, producing radial distribution functions in reasonable agreement with experiment and, for NaCl, clear evidence of ion pairing. Clusters are extracted from the simulations for quantum mechanical excited state calculations. Accurate ab initio coupled-cluster benchmark calculations on a small number of representative clusters are carried out and used to identify and validate an efficient protocol based on time-dependent density functional theory. The latter is used to carry out quantum mechanical calculations on thousands of clusters. The resulting computed spectrum is in excellent agreement with experiment for the peak position, with little influence from ion pairing, but is in qualitative disagreement on the width, being only about half as wide. It is concluded that simulation by classical molecular dynamics fails to provide an adequate variety of structures to explain the experimental CTTS spectrum of aqueous Cl - .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Theoretical and experimental study on the O( 3 P) + 2,5-dimethylfuran reaction in the gas phase

In this work we report a joint experimental and computational study on the 2,5-dimethylfuran oxidation reaction in the gas phase initiated by atomic oxygen O( 3 P). The experiments have been performed by using vacuum-ultraviolet synchrotron radiation at the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory (LBNL), at a temperature of 550 K and a pressure of 8 Torr. The experimental data were supported by quantum-chemical calculations along with a kinetic model, also taking into account the possible involvement of different magnetic states, performed in the framework of the RRKM theory. Propyne, acetaldehyde, methylglyoxal, dimethylglyoxal, 3-penten-2-one, 2,5-dimethylfuran-3(2 H )-one, and 1,2-diacetyl ethylene have been identified as the main primary products arising under the conditions of the experiment. Our computational model suggests that these species can be formed at the concentration and branching ratio experimentally observed only in the presence of a non-negligible fraction of non-thermalized intermediates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

The CH(X 2 Π) + H 2 O reaction: two transition state kinetics

he reaction of ground state methylidyne (CH) with water vapor (H 2 O) is theoretically re-investigated using high-level coupled cluster computations in combination with semi-classical transition state theory (SCTST) and two-dimensional master equation simulations. Insertion of CH into a H–O bond of H 2 O over a submerged barrier via a well-skipping mechanism yielding solely H and CH 2 O is characterized. The reaction kinetics is effectively determined by the formation of a pre-reaction van der Waals complex (PRC, HC—OH 2 ) and its subsequent isomerization to activated CH 2 OH in competition with PRC re-dissociation. The tunneling effects are found to be minor, while variational effects in the PRC → CH 2 OH step are negligible. The calculated rate coefficient k ( T ) is nearly pressure-independent, but strongly depends on temperature with pronounced down-up behavior: a high value of 2 x 10 -10 cm 3 s -1 at 50 K, followed by a fairly steep decrease down to 8 × 10 -12 cm 3 s -1 at 900 K, but increasing again to 5 × 10 -11 cm 3 s -1 at 3500 K. Over the T-range of this work, k ( T ) can be expressed as: k ( T , P = 0) = 2.31 × 10 -11 ( T /300 K) -1.615 exp(-38.45/ T ) cm 3 s -1 for T = 50-400 K k ( T , P = 0) = 1.15 × 10 -12 ( T /300 K) 0.8637 exp(892.6/ T ) cm 3 s -1 for T = 400-1000 K k ( T , P = 0) = 4.57 × 10 -15 ( T /300 K) 3.375 exp(3477.4/ T ) cm 3 s -1 for T = 1000–3500 K.

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DOE OSTI2021

Reactive force fields for aqueous and interfacial magnesium carbonate formation

Here we develop Mg/C/O/H ReaxFF parameter sets for two environments: an aqueous force field for magnesium ions in solution and an interfacial force field for minerals and mineral–water interfaces. Since magnesium is highly ionic, we choose to fix the magnesium charge and model its interaction with C/O/H through Coulomb, Lennard-Jones, and Buckingham potentials. We parameterize the forcefields against several crystal structures, including brucite, magnesite, magnesia, magnesium hydride, and magnesium carbide, as well as Mg 2+ water binding energies for the aqueous forcefield. Then, we test the forcefield for other magnesium-containing crystals, solvent separated and contact ion-pairs and single-molecule/multilayer water adsorption energies on mineral surfaces. We also apply the forcefield to the forsterite–water and brucite–water interface that contains a bicarbonate ion. We observe that a long-range proton transfer mechanism deprotonates the bicarbonate ion to carbonate at the interface. Free energy calculations show that carbonate can attach to the magnesium surface with an energy barrier of about 0.22 eV, consistent with the free energy required for aqueous Mg–CO 3 ion pairing. Also, the diffusion constant of the hydroxide ions in the water layers formed on the forsterite surface are shown to be anisotropic and heterogeneous. These findings can help explain the experimentally observed fast nucleation and growth of magnesite at low temperature at the mineral–water–CO 2 interface in water-poor conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Pressure-induced order–disorder transitions in β-In 2 S 3 : an experimental and theoretical study of structural and vibrational properties

We report this joint experimental and theoretical study of the structural and vibrational properties of β-In 2 S 3 upon compression shows that this tetragonal defect spinel undergoes two reversible pressure-induced order–disorder transitions up to 20 GPa. We propose that the first high-pressure phase above 5.0 GPa has the cubic defect spinel structure of α-In 2 S 3 and the second high-pressure phase ($\phi$-In 2 S 3 ) above 10.5 GPa has a defect α-NaFeO 2 -type (R$\bar{3}$) structure. This phase, related to the NaCl structure, has not been previously observed in spinels under compression and is related to both the tetradymite structure of topological insulators and to the defect LiTiO 2 phase observed at high pressure in other thiospinels. Structural characterization of the three phases shows that α-In 2 S 3 is softer than β-In 2 S 3 while $\phi$-In 2 S 3 is harder than β-In 2 S 3 . Vibrational characterization of the three phases is also provided, and their Raman-active modes are tentatively assigned. Our work shows that the metastable α phase of In 2 S 3 can be accessed not only by high temperature or varying composition, but also by high pressure. On top of that, the pressure-induced β–α–$\phi$ sequence of phase transitions evidences that β-In 2 S 3 , a B III 2 X V 3 compound with an intriguing structure typical of A II B III 2 X VI 4 compounds (intermediate between thiospinels and ordered-vacancy compounds) undergoes: (i) a first phase transition at ambient pressure to a disordered spinel-type structure (α-In 2 S 3 ), isostructural with those found at high pressure and high temperature in other B III 2 X V 3 compounds; and (ii) a second phase transition to the defect α-NaFeO 2 -type structure ($\phi$-In 2 S 3 ), a distorted NaCl-type structure that is related to the defect NaCl phase found at high pressure in A II B III 2 X VI 4 ordered-vacancy compounds and to the defect LiTiO 2 -type phase found at high pressure in A II B III 2 X VI 4 thiospinels. This result shows that In 2 S 3 (with its intrinsic vacancies) has a similar pressure behaviour to thiospinels and ordered-vacancy compounds of the A II B III 2 X VI 4 family, making β-In 2 S 3 the union link between such families of compounds and showing that group-13 thiospinels have more in common with ordered-vacancy compounds than with oxospinels and thiospinels with transition metals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

High-fidelity first principles nonadiabaticity: diabatization, analytic representation of global diabatic potential energy matrices, and quantum dynamics

We report nonadiabatic dynamics, which goes beyond the Born–Oppenheimer approximation, has increasingly been shown to play an important role in chemical processes, particularly those involving electronically excited states. Understanding multistate dynamics requires rigorous quantum characterization of both electronic and nuclear motion. However, such first principles treatments of multi-dimensional systems have so far been rather limited due to the lack of accurate coupled potential energy surfaces and difficulties associated with quantum dynamics. In this Perspective, we review recent advances in developing high-fidelity analytical diabatic potential energy matrices for quantum dynamical investigations of polyatomic uni- and bi-molecular nonadiabatic processes, by machine learning of high-level ab initio data. Special attention is paid to methods of diabatization, high fidelity construction of multi-state coupled potential energy surfaces and property surfaces, as well as quantum mechanical characterization of nonadiabatic nuclear dynamics. To illustrate the tremendous progress made by these new developments, several examples are discussed, in which direct comparison with quantum state resolved measurements led to either confirmation of the observation or sometimes reinterpretation of the experimental data. The insights gained in these prototypical systems greatly advance our understanding of nonadiabatic dynamics in chemical systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Coordination and thermophysical properties of select trivalent lanthanides in LiCl–KCl

The coordination chemistry of various fission and decay products, such as actinides and lanthanides, are crucial to the commercial deployment of molten salt reactors as they can affect the thermophysical properties. In this report we examined the structure, coordination environment, and physical properties such as the density and the vibrational density of states for three lanthanide species, namely Ce, Eu, and Sm in the LiCl–KCl eutectic system using a combination of quantum mechanics simulations and spectroscopic experiments. Quantum mechanics molecular dynamics (QM-MD) modelling was employed to determine the physical properties of each system resulting in accurate local coordination of each species. Then, the vibrational density of states (DOS) was determined using a two-phase thermodynamic modelling which was then compared to the experimentally obtained Raman spectra of the species in molten LiCl–KCl having the eutectic composition. We find that Ce 3+ , Eu 3+ and Sm 3+ all adopt octahedral local coordination environments in the eutectic salt composition in good agreement with experimental results. Ce3+ is found to fluctuate between an octahedral six-coordinated and a seven-coordinated structure due to the increased local proximity of Cl in the eutectic salt, resulting in a lower fluidicity/diffusivity than the other trivalent lanthanides studied. The thermophysical properties of the eutectic composition with trivalent lanthanides were not significantly different from the pure eutectic salt composition, but several changes were noted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Two-bond 13 C– 13 C spin-coupling constants in saccharides: dependencies on exocyclic hydroxyl group conformation

Seven doubly 13 C-labeled isotopomers of methyl β-D-glucopyranoside, methyl β-D-xylopyranoside, methyl β-D-galactopyranoside, methyl β-D-galactopyranosyl-(1→4)-β-D-glucopyranoside and methyl β-D-galactopyranosyl-(1→4)-β-D-xylopyranoside were prepared, crystallized, and studied by single-crystal X-ray crystallography and solid-state 13 C NMR spectroscopy to determine experimentally the dependence of 2 J C1,C3 values in aldopyranosyl rings on the C1–C2–O2–H torsion angle, θ 2 , involving the C2 carbon of the C1–C2–C3 coupling pathway. Using X-ray crystal structures to determine θ 2 in crystalline samples and by selecting compounds that exhibit a relatively wide range of θ 2 values in the crystalline state, 2 J C1,C3 values measured in crystalline samples were plotted against θ 2 and the resulting plot compared to that obtained from density functional theory (DFT) calculations. For θ 2 values ranging from ~90° to ~240°, very good agreement was observed between the experimental and theoretical plots, providing strong validation of DFT-calculated spin-coupling dependencies on exocyclic C–O bond conformation involving the central carbon of geminal C–C–C coupling pathways. we report that these findings provide new experimental evidence supporting the use of 2 J CCC values as non-conventional spin-coupling constraints in MA'AT conformational modeling of saccharides in solution, and the use of NMR spin-couplings not involving coupled hydroxyl hydrogens as indirect probes of C–O bond conformation. Solvomorphism was observed in crystalline βGal-(1→4)-βGlcOCH 3 wherein the previously-reported methanol solvate form was found to spontaneously convert to a monohydrate upon air-drying, leading to small but discernible conformational changes in, and a new crystalline form of, this disaccharide.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Predicting 1 H NMR relaxation in Gd 3+ -aqua using molecular dynamics simulations

Atomistic molecular dynamics simulations are used to predict 1 H NMR T 1 relaxation of water from paramagnetic Gd 3+ ions in solution at 25 °C. Simulations of the T 1 relaxivity dispersion function r 1 computed from the Gd 3+ – 1 H dipole–dipole autocorrelation function agree within ≃8% of measurements in the range f 0 ≃ 5 ↔ 500 MHz, without any adjustable parameters in the interpretation of the simulations, and without any relaxation models. Here the simulation results are discussed in the context of the Solomon-Bloembergen-Morgan inner-sphere relaxation model, and the Hwang-Freed outer-sphere relaxation model. Below f 0 ≲ 5 MHz, the simulation overestimates r 1 compared to measurements, which is used to estimate the zero-field electron-spin relaxation time. The simulations show potential for predicting r 1 at high frequencies in chelated Gd 3+ contrast-agents used for clinical MRI.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Ellipticity controlled dissociative double ionization of ethane by strong fields

We report the yields of all dissociation channels of ethane dications produced by strong field double ionization were measured. It was found that the branching ratios can be controlled by varying the ellipticity of laser pulses. The CH 3 + formation and H + formation channels show a clear competition, producing the highest and lowest branching ratios at ellipticity of ~0.6, respectively. With the help of theoretical calculations, such a control was attributed to the ellipticity dependent yields of different sequential ionization pathways.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Ballistic Δ S = 2 intersystem crossing in a cobalt cubane following ligand-field excitation probed by extreme ultraviolet spectroscopy

We report femtosecond M 2,3 -edge X-ray absorption near-edge structure (XANES) spectroscopy is used to probe the excited-state dynamics of the cobalt cubane [Co III 4 O 4 ](OAc) 4 (py) 4 (OAc = acetate, py = pyridine), a model for water oxidation catalysts. After ligand-field excitation, intersystem crossing (ISC) to a metal-centered quintet occurs in 38 fs. 30% of the hot quintet undergoes ballistic back-ISC directly to the singlet ground state, with the remainder relaxing to a long-lived triplet.

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