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DOE OSTI2022

Thermal expansion of plasma-exposed tungsten

We report results from a systematic analysis of thermal expansion of plasma-exposed tungsten based on molecular-dynamics simulations using models of tungsten with distributions of helium (He) bubbles in the tungsten matrix. We distinguish between two approaches of filling the bubbles with He, where the amount of He in the bubble can or cannot vary with temperature. In the former case, the thermal expansion coefficient decreases monotonically with the porosity and He content of the tungsten matrix, while in the latter case, the thermal expansivity increases monotonically with increasing porosity and He content. The latter condition, where the He content in the bubble is determined at the implantation temperature and remains constant with varying temperature in the tungsten matrix, is consistent with He species transport in tungsten used as a plasma-facing component (PFC) in nuclear fusion reactors and implies the development of biaxial compressive thermal strains in the PFC material that contribute to accelerating the growth of a nanostructure on PFC tungsten surfaces. Furthermore our analysis advances the fundamental understanding of thermal expansion in PFC tungsten and contributes to the development of a thermophysical property database for properly incorporating effects of realistic heat loads into modeling the dynamical response of PFC tungsten under fusion reactor operating conditions.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Spectroscopy and dynamics of the v = 1 levels derived from the OH(D) stretching modes in the I‾∙HDO complex using CW and time-resolved, resonant two-photon infrared excitation of the cryogenically cooled ions

The vibrational energy levels of the two isotopomers adopted by the I‾∙HDO ion-molecule complex occur such that the OH(D) stretching fundamentals span its dissociation energy, thus enabling a spectroscopic investigation of the dynamics displayed by a system prepared in the vicinity of the dissociation threshold. This regime is explored using infrared photoexcitation of the mass-selected complexes cooled in a cryogenic radiofrequency (Paul) ion trap. Survey spectra are obtained at modest resolution using two-color, IR-IR photodissociation with nanosecond lasers to establish the level structure and unimolecular decay dynamics of the v = 1 and 2 levels of the bound OH(D) oscillator. The v = 1 levels are prepared by fixed frequency excitation in the trap and the absorption spectra arising from this excited state are probed by photofragmentation of the complex with a second pulsed IR laser after a variable delay time (0 to 20 ms). The transitions to levels above the dissociation threshold for I‾ + HDO formation are observed to be sharp (~5 cm -1 FWHM). At low pressure, the bound OD (v = 1) population relaxes very slowly (~3 ms), consistent with resonant fluorescence in the IR. The collisional quenching rate constants of this level by the He buffer gas were estimated to be on the order 3 x 10 -12 cm 3 /s based on a crude Stern-Volmer analysis. Here, the rotational fine structure and linewidths (≲0.01 cm -1 FWHM) arising from transitions of the non-bonded OH stretch fundamental of the OD-bound isotopomer that lies just above the dissociation energy are determined using single photon photodissociation by excitation of the 10 K ions with a single-frequency, CW IR laser in the ion trap.

Cryogenic ion infrared spectroscopy↗

NASA NTRS1979

Experimental investigation of flow and heating in a resonance tube

Experiments have been performed to determine the basic mechanism of heating in resonance tubes of square section with constant area excited by underexpanded jet flows. The jet flow between the nozzle exit and the tube inlet plays a key role in the performance of a resonance tube. A detailed and systematic investigation of the unsteady complex shock structure in this part of the flow region has led to a better understanding of the fundamental mechanisms associated with the gas heating in such tubes. A study of the effects of tube location in relation to free-jet shock location (without the presence of the resonance tube) has shed further light on the underlying mechanism of sustained oscillations of the flow in a resonance tube.

Sarohia, V.↗

NASA NTRS1974

Kinetics of the reaction of nitric oxide with hydrogen

Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The reaction kinetics were studied in the temperature range 2400-4500 K using a shock-tube technique. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principle result of the study was the determination of the rate constant for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k sub 1 were obtained for each test through comparisons of measured and numerically predicted NO profiles.

Flower, W. L.↗

NASA NTRS1987

Collision detection for spacecraft proximity operations

Collision Detection for Spacecraft Proximity Operations This thesis describes the development of a new collision detection algorithm to be used when two spacecraft are operating in the same vicinity. The two spacecraft are modelled as unions of convex polyhedra, where the polyhedron resulting from the union may be either convex or nonconvex. The relative motion of the two spacecraft is assumed to be such that one vehicle is moving with constant linear and angular velocity with respect to the other. The algorithm determines if a collision is possible and, if so, predicts the time when the collision will take place. The theoretical basis for the new collision detection algorithm is the C-function formulation of the configuration space approach recently introduced by researchers in robotics. Three different types of C-functions are defined that model the contacts between the vertices, edges, and faces of the polyhedra representing the two spacecraft. These C-functions are used to formulate three "collision" conditions. The first of these conditions limits the points representing potential collisions to the zeros of the C-functions. The new algorithm is fundamentally a search for the smallest zero of any C-function that satisfies the second and third collision conditions. The C-functions are shown to be transcendental functions of time for the assumed trajectory of the moving spacecraft. The zeros of these functions cannot be expressed in dosed form. Therefore, numerical search procedures are developed to find aLl of the zeros of a C-function in specified bounded intervals of time. These bounded intervals of time are found by examining the second and third collision conditions. The capabilities of the new algorithm are demonstrated for several example cases. These include examples of collisions determined by zeros of each of the three different types of C-functions. In addition to predicting the time of first contact of the polyhedra, the algorithm identifies the features of the two polyhedra that are touching at this time. The new collision detection algorithm is the first such algorithm that is capable of solving the collision detection problem exactly for the case where the moving object has constant linear and angular velocities. This is a significant improvement on previous collision detection algorithms described in the literature. In particular, the ability to handle constant angular velocity represents a more realistic type of rotational motion than those which have been used in other algorithms.

Robin M Vaughan↗

NASA NTRS2001

Band-gap Engineering in Sputter Deposited Amorphous/Microcrystalline Sc(x)Ga(1-x)N

Reactive sputtering was used to grow thin films of Sc(x)Ga(1-x)N with scandium concentrations of 20%-70% on quartz substrates at temperatures of 300-675 K. X-ray diffraction (XRD) of the films showed either weak or no structure, suggesting the films are amorphous or microcrystalline. Optical absorption spectra were taken of each sample and the optical band gap was determined. The band gap varied linearly with increasing Ga concentration between 2.0 and 3.5 eV. Ellipsometry was used to confirm the band gap measurements and provide optical constants in the range 250-1200 nm. ScN and GaN have different crystal structures (rocksalt and wurzite, respectively), and thus may form a heterogeneous mixture as opposed to an alloy. Since the XRD data were inconclusive, bilayers of ScN/GaN were grown and optical absorption spectra taken. A fundamental difference in the spectra between the bilayer films and alloy films was seen, suggesting the films are alloys, not heterogeneous mixtures.

Little, Mark E.↗

NASA NTRS2006

On the Discovery of CO Nighttime Emissions on Titan by Cassini/VIMS: Derived Stratospheric Abundances and Geological Implications

We present a quantitative analysis of CO thermal emissions discovered on the nightside of Titan by Baines et al. [2005. The atmospheres of Saturn and Titan in the near-infrared: First results of Cassini/VIMS. Earth, Moon, and Planets, 96, 119-147] in Cassini/VIMS spectral imagery. We identify these emission features as the P and R branches of the 1-0 vibrational band of carbon monoxide (CO) near 4.65 microns. For CH3D, the prominent Q branch of the nu(2) fundamental band of CH3D near 4.55 microns is apparent. CO2 emissions from the strong nu(3) vibrational band are virtually absent, indicating a CO2 abundance several orders of magnitude less than CO, in agreement with previous investigations. Analysis of CO emission spectra obtained over a variety of altitudes on Titan's nightside limb indicates that the stratospheric abundance of CO is 32 +/- 15 ppm, and together with other recent determinations, suggests a vertical distribution of CO nearly constant at this value from the surface throughout the troposphere to at least the stratopause near 300 km altitude. The corresponding total atmospheric content of CO in Titan is similar to 2.9 +/- 1.5 x 10(exp 14) kg. Given the long lifetime of CO in the oxygen-poor Titan atmosphere (similar to 0.5-1.0 Gyr), we find a mean CO atmospheric production rate of 6 +/- 3 x 10(exp 5) kg yr(exp -1). Given the lack of primordial heavy noble gases observed by Huygens [Niemann et al., 2005. The abundances of constituents of Titan's atmosphere from the GCMS on the Huygens probe. Nature, 438, 779-784], the primary source of atmospheric CO is likely surface emissions. The implied CO/CH4 mixing ratio of near-surface material is 1.8 +/- 0.9 x 10(exp -4), based on an average methane surface emission rate over the past 0.5 Gyr of 1.3 x 10(exp -13) gm cm(exp -2) s(exp -1) as required to balance hydrocarbon haze production via methane photolysis [Wilson and Atreya, 2004. Current state of modeling the photochemistry of Titan's mutually dependent atmosphere and ionosphere. J. Geophys. Res. 109, E06002 Doi: 10.1029/2003JE002181]. This low CO/CH4 ratio is much lower than expected for the sub-nebular formation region of Titan and supports the hypothesis [e.g., Atreya et al., 2005. Methane on Titan: photochemical-meteorological-hydrogeochemical cycle. Bull. Am. Astron. Soc. 37, 735] that the conversion of primordial CO and other carbon-bearing materials into CH4-enriched clathrate-hydrates occurs within the deep interior of Titan via the release of hydrogen through the serpentinization process followed by Fischer-Tropsch catalysis. The time-averaged predicted emission rate of methane-rich surface materials is approximately 0.02 km(exp 3) yr (exp -1), a value significantly lower than the rate of silicate lava production for the Earth and Venus, but nonetheless indicative of significant geological processes reshaping the surface of Titan.

carbon compounds↗

DOE OSTI2025

Pd–Methyl Bond Energy─Property Correlations, Noncorrelations, Machine Learning Models, and Application to Polymerization Catalysis

Metal–carbon bonds are a key intermediate in a variety of homogeneous organometallic transformations and often determine the critical thermodynamics and kinetics of catalytic processes. Surprisingly, the influence of different ligands on metal–carbon bond strengths has been largely overlooked. Here, in this study, we evaluated nearly 700 experimental Pd–methyl complexes by calculating their bond dissociation energies using density functional theory (DFT) and compared these bond strengths to several fundamental molecular properties, and this revealed several surprising correlations and noncorrelations. Most surprising was that several fundamental properties, such as the bond length, bond force constant, and bond electron density, have no correlation with bond strength, despite these correlations often holding for main-group compounds. We were indeed able to identify key ligand-dependent chemical features/descriptors that provided a highly accurate machine learning model and provided insight into the general factors that control the Pd–carbon bond strength, such as radical delocalization and nucleophilicity. Insights gained from the Pd–Me bond energy analysis were then applied to CO migratory insertion steps that are part of copolymerization reactions.

binding energy↗

NASA NTRS2010

Prolegomena to the Study of Friction Stir Welding

The literature contains many approaches toward modeling of the friction stir welding (FSW) process with varying treatments of the weld metal properties. It is worthwhile to consider certain fundamental features of the process before attempting to interpret FSW phenomena: Because of the unique character of metal deformation (as opposed to, say, viscous deformation) a velocity "discontinuity" or shear surface occurs in FSW and determines much of the character of the welding mechanism. A shear surface may not always produce a sound bond. Balancing mechanical power input against conduction and convection heat losses yields a relation, a "temperature index", between spindle speed and travel speed to maintain constant weld temperature. But many process features are only weakly dependent upon temperature. Thus, unlike modeling of metal forming processes, it may be that modeling the FSW process independently of the material conditions has some merit.

Nunes, Arthur C., Jr.↗

DOE OSTI2022

Formation and detection of metastable formic acid in a supersonic expansion: High resolution infrared spectroscopy of the jet-cooled cis -HCOOH conformer

High-resolution direct absorption infrared spectra of metastable cis-formic acid (HCOOH) trapped in a cis-well resonance behind a 15 kcal/mol barrier are reported for the first time, with the energetically unstable conformer produced in a supersonic slit plasma expansion of trans-formic acid/H 2 mixtures. We present a detailed high-resolution rovibrational analysis for cis-formic acid species in the OH stretch (ν 1 ) fundamental, providing first precision vibrational band origin, rotational constants, and term values, which in conjunction with ab initio calculations at the couple-cluster with single, double, and perturbative triple [CCSD(T)]/ANOn (n = 0, 1, 2) level support the experimental assignments and establish critical points on the potential energy surface for internal rotor trans-to-cis isomerization. Relative intensities for a- and b-type transitions observed in the spectra permit the transition dipole moment components to be determined in the body fixed frame and prove to be in good agreement with ab initio CCSD(T) theoretical estimates but in poor agreement with simple bond-dipole predictions. As a result, the observed signal dependence on H 2 in the discharge suggests the presence of a novel H atom radical chemical mechanism for strongly endothermic “up-hill” internal rotor isomerization between trans- and cis-formic acid conformers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Superconducting vortices carrying a temperature-dependent fraction of the flux quantum

Magnetic field penetrates type-II bulk superconductors by forming quantum vortices that enclose a magnetic flux equal to the magnetic flux quantum. The flux quantum is a universal quantity that depends only on fundamental constants. In this study, we investigated isolated vortices in the hole-overdoped Ba 1–x K x Fe 2 As 2 (x = 0.77) by using scanning superconducting quantum interference device (SQUID) magnetometry. In many locations, we observed objects that carried only part of a flux quantum, with a magnitude that varied continuously with temperature. Here, we demonstrated mobility and manipulability of these objects and interpreted them as quantum vortices with nonuniversally quantized (fractional) magnetic flux whose magnitude is determined by the temperature-dependent parameters of a multicomponent superconductor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS2005

Characterizing the Early Impact Bombardment

The early bombardment revealed in the larger impact craters and basins on the moon was a major planetary process that affected all bodies in the inner solar system, including the Earth and Mars. Understanding the nature and timing of this bombardment is a fundamental planetary problem. The surface density of lunar impact craters within a given size range on a given lunar surface is a measure of the age of that surface relative to other lunar surfaces. When crater densities are combined with absolute radiometric ages determined on lunar rocks returned to Earth, the flux of large lunar impactors through time can be estimated. These studies suggest that the flux of impactors producing craters greater than 1 km in diameter has been approximately constant over the past approx. 3 Gyr. However, prior to 3.0 - 3.5 Gyr the impactor flux was much larger and defines an early bombardment period. Unfortunately, no lunar surface feature older than approx. 4 Gyr is accurately dated, and the surface density of craters are saturated in most of the lunar highlands. This means that such data cannot define the impactor flux between lunar formation and approx. 4 Gyr ago.

Bogard, Donald D.↗

DOE OSTI2024

Underestimation of multi-decadal global O 2 loss due to an optimal interpolation method

Abstract. The global ocean's oxygen content has declined significantly over the past several decades and is expected to continue decreasing under global warming, with far-reaching impacts on marine ecosystems and biogeochemical cycling. Determining the oxygen trend, its spatial pattern, and uncertainties from observations is fundamental to our understanding of the changing ocean environment. This study uses a suite of CMIP6 Earth system models to evaluate the biases and uncertainties in oxygen distribution and trends due to sampling sparseness. Model outputs are sub-sampled according to the spatial and temporal distribution of the historical shipboard measurements, and the data gaps are filled by a simple optimal interpolation method using Gaussian covariance with a constant e-folding length scale. Sub-sampled results are compared to full model output, revealing the biases in global and basin-wise oxygen content trends. The simple optimal interpolation underestimates the modeled global deoxygenation trends, capturing approximately two-thirds of the full model trends. The North Atlantic and subpolar North Pacific are relatively well sampled, and the simple optimal interpolation is capable of reconstructing more than 80 % of the oxygen trend in the non-eddying CMIP models. In contrast, pronounced biases are found in the equatorial oceans and the Southern Ocean, where the sampling density is relatively low. The application of the simple optimal interpolation method to the historical dataset estimated the global oxygen loss to be 1.5 % over the past 50 years. However, the ratio of the global oxygen trend between the sub-sampled and full model output has increased the estimated loss rate in the range of 1.7 % to 3.1 % over the past 50 years, which partially overlaps with previous studies. The approach taken in this study can provide a framework for the intercomparison of different statistical gap-filling methods to estimate oxygen content trends and their uncertainties due to sampling sparseness.

Ito, Takamitsu (ORCID:000000019873099X)↗

NASA NTRS1997

Positive Anharmonicities: The Oxonide Anion as an Example

An accurate ab initio quartic force field for the ozonide anion has been determined at the singles and doubles coupled-cluster level of theory that includes a perturbational estimate of the effects of connected triple excitations, denoted CCSD(T), using the augmented valence triple-zeta correlation consistent one-particle basis set. Convergence of the harmonic frequencies with respect to the one-particle basis set has been demonstrated by computing quadratic force fields at the CCSD(T) level using augmented valence double-zeta and quadruple-zeta basis sets. Fundamental vibrational frequencies have been determined via second-order ro-vibrational perturbation theory and also using exact variational methods. Agreement is very good, and they both show that the antisymmetric O-O stretch, v 3, possesses a positive anharmonic correction (that is, the fundamental frequency is predicted to be higher in energy than the harmonic frequency). Comparison of the O_3 and O3 quartic force fields shows that the positive anharmonic correction is the result of a particularly large F3333 symmetry internal coordinate force constant. The reasonableness of this force constant has been tested by computing both F33 and F3333 at the CCSD, CCSD(T), and CASPT2 levels of theory. A discussion of known positive anharmonicities for stretching modes is presented.

Lee, Timothy J.↗

DOE OSTI2023

Analysis of the rotationally-resolved infrared spectrum of CD 3 79 Br and CD 3 81 Br between 900 and 1400 cm -1

We report the infrared spectrum of CD 3 79 Br and CD 3 81 Br between 900 cm -1 and 1400 cm -1 has been analyzed at high resolution. In this region, two fundamental vibrational states, v 2 = 1 and v 5 = 1, an overtone state, v 3 = 2, and a combination state, v 3 = v 6 = 1, have been analyzed for both isotopologues. As found in other halomethane molecules, strong Coriolis resonances couple the v 2 = 1 state to the v 5 = 1 state, and similar resonances were also used to describe the coupling found between the v 5 = 1 state to the v 3 = 2 state. A new determination of the K-dependent constant A 0 was performed for each isotopologue through the use of perturbation-allowed transitions. The values for A 0 determined from the analysis are 2.6001898(26) and 2.6001905(27) for CD 3 79 Br and CD 3 81 Br, respectively. Ab initio calculations were performed to examine the efficacy of high-level theoretical calculations to accurately predict spectroscopic constants. The ab initio calculations had variable success with the largest errors associated with the prediction of the ΔB rotational constants of the interacting states

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Carbon Dioxide Insertion into Rhenium Hydrides as a Probe for the Impact of Solvent on Linear Free Energy Relationships between Thermodynamic and Kinetic Hydricity

The kinetics of CO 2 insertion into electronically different Re( R bpy)(CO) 3 H ( R bpy = 4,4'-R-2,2'- bipyridine; R = OMe, t Bu, Me, H, Br, COOMe, CF 3 ) complexes to form Re( R bpy)(CO) 3 {OC(H)O} compounds were determined in acetone, dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), and 3-methoxypropionitrile (3-MPN) and compared with previous data in acetonitrile (MeCN). The rates of CO 2 insertion for any one complex of the type Re(Rbpy)(CO) 3 H in different solvents correlates with the Dimroth-Reichardt (E T (30)) solvent parameter. Hammett plots in each solvent indicate that insertion reactions are faster for bpy ligands with electron-donating groups. There is, however, no correlation between the slope of the Hammett plot in different solvents and any common solvent parameter. Similarly, the enthalpies and entropies of activation and kinetic isotope effects associated with CO 2 insertion into Re(bpy)(CO) 3 H in different solvents do not correlate with any common solvent parameters. Theoretical calculations were used to determine the relative thermodynamic hydricities of Re( R bpy)(CO) 3 H type complexes in MeCN, acetone, DMF, and DMSO and in each solvent complexes with more electron-donating substituents on the bpy ligand are stronger hydride donors. Linear Free Energy Relationships (LFERs) between calculated thermodynamic and experimental kinetic hydricity, as measured through CO 2 insertion reactions, were observed in MeCN, acetone, DMF, and DMSO. Furthermore, the slopes of the LFERs correlate with the dielectric constant of the solvent. Overall, this work provides fundamental information about the thermodynamics and kinetics of hydride transfer reactions in different solvents, which is valuable for catalyst design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1977

An empirical model for ocean radar backscatter and its application in inversion routine to eliminate wind speed and direction effects

Several regression models were tested to explain the wind direction dependence of the 1975 JONSWAP (Joint North Sea Wave Project) scatterometer data. The models consider the radar backscatter as a harmonic function of wind direction. The constant term accounts for the major effect of wind speed and the sinusoidal terms for the effects of direction. The fundamental accounts for the difference in upwind and downwind returns, while the second harmonic explains the upwind-crosswind difference. It is shown that a second harmonic model appears to adequately explain the angular variation. A simple inversion technique, which uses two orthogonal scattering measurements, is also described which eliminates the effect of wind speed and direction. Vertical polarization was shown to be more effective in determining both wind speed and direction than horizontal polarization.

Dome, G. J.↗

NASA NTRS2005

Reliable Spectroscopic Constants for CCH-, NH2- and Their Isotopomers from an Accurate Potential Energy Function

Accurate quartic force fields have been determined for the CCH- and NH2- molecular anions using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, CCSD(T). Very large one-particle basis sets have been used including diffuse functions and up through g-type functions. Correlation of the nitrogen and carbon core electrons has been included, as well as other "small" effects, such as the diagonal Born-Oppenheimer correction, and basis set extrapolation, and corrections for higher-order correlation effects and scalar relativistic effects. Fundamental vibrational frequencies have been computed using standard second-order perturbation theory as well as variational methods. Comparison with the available experimental data is presented and discussed. The implications of our research for the astronomical observation of molecular anions will be discussed.

Lee, Timothy J.↗