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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

High Resolution Spectroscopy to Support Atmospheric Measurements

Spectroscopic parameters (such as line position, intensity, broadening and shifting coefficients and their temperature dependences, line mixing coefficients etc.) for various molecular species of atmospheric interest are determined. In order to achieve these results, infrared spectra of several molecular bands are obtained using high-resolution recording instruments such as tunable diode laser spectrometer and Fourier transform spectrometers. Using sophisticated analysis routines (Multispectrum nonlinear least squares technique) these high-resolution infrared spectra are processed to determine the various spectral line parameters that are cited above. Spectra were taken using the McMath-Pierce Fourier transform spectrometer (FTS) at the National Solar Observatory on Kitt Peak, Arizona as well as the Bruker FTS at the Pacific Northwest National Laboratory (PNNL) at Richland, Washington. Most of the spectra are acquired not only at room temperature, but also at several different cold temperatures. This procedure is necessary to study the variation of the spectral line parameters as a function of temperature in order to simulate the Earth's and other planetary atmospheric environments. Depending upon the strength or weakness of the various bands recorded and analyzed, the length(s) of the absorption cells in which the gas samples under study are kept varied from a few centimeters up to several meters and the sample temperatures varied from approximately +30 C to -63 C. Research on several infrared bands of various molecular species and their isotopomers are undertaken. Those studies are briefly described.

Venkataraman, Malathy Devi↗
NASA NTRS2017

A Library of ATMO Forward Model Transmission Spectra for Hot Jupiter Exoplanets

We present a grid of forward model transmission spectra, adopting an isothermal temperature-pressure profile, alongside corresponding equilibrium chemical abundances for 117 observationally significant hot exoplanets (equilibrium temperatures of 547-2710 K). This model grid has been developed using a 1D radiative-convective-chemical equilibrium model termed ATMO, with up-to-date high-temperature opacities. We present an interpretation of observations of 10 exoplanets, including best-fitting parameters and X(exp 2) maps. In agreement with previous works, we find a continuum from clear to hazy/cloudy atmospheres for this sample of hot Jupiters. The data for all the 10 planets are consistent with subsolar to solar C/O ratio, 0.005 to 10 times solar metallicity and water rather than methane-dominated infrared spectra. We then explore the range of simulated atmospheric spectra for different exoplanets, based on characteristics such as temperature, metallicity, C/O ratio, haziness and cloudiness. We find a transition value for the metallicity between 10 and 50 times solar, which leads to substantial changes in the transmission spectra. We also find a transition value of C/O ratio, from water to carbon species dominated infrared spectra, as found by previous works, revealing a temperature dependence of this transition point ranging from approximately 0.56 to approximately 1-1.3 for equilibrium temperatures from approximately 900 to approximately 2600 K. We highlight the potential of the spectral features of HCN and C2H2 to constrain the metallicities and C/O ratios of planets, using James Webb Space Telescope (JWST) observations. Finally, our entire grid (approximately 460 000 simulations) is publicly available and can be used directly with the JWST simulator PandExo for planning observations.

techniques: spectroscopic – planets and satellit↗
NASA NTRS1975

Infrared emission spectra of elastohydrodynamic contacts

A small diamond disk mounted as a window in a steel plate was covered with test fluid, and a weighted steel ball was rotated over the window so as to form a sliding elastohydrodynamic (EHD) contact region. Some of the radiant energy generated in this region, both in the fluid and at the boundaries, passed through the window into an infrared interferometer, giving rise to an emission spectrum. This spectrum could be separated into contributions from the fluid and from the ball surface, making it possible, by appropriate calibrations, to estimate their temperatures separately under operating conditions. Moreover, the shape of the discrete spectral bands of the fluid permitted some inferences on its state. Two fluids were studied under identical mechanical conditions, a polyester and a naphthenic oil, each containing an equal amount of polymethylstyrene as a spectral indicator. Differences of band intensity, band width, and frequency could, therefore, be attributed to differences in the behavior of the base fluid.

Lauer, J. L.↗
NASA NTRS1982

The Reiner Gamma Formation - Composition and origin as derived from remote sensing observations

In order to investigate the composition and origin of Reiner Gamma, near-infrared spectra and vidicon images were obtained and interpreted. The 0.40/0.56 micron ratio image shows that the high albedo portion of Reiner Gamma is surrounded by a 'red halo' and the 0.95/0.56 micron image indicates that Reiner Gamma exhibits a strong pyroxene absorption band. Analysis of the near-infrared spectra of various portions of the formation indicated the presence of major amounts of fresh mare basalt. Spectral mixing models demonstrate that the Reiner Gamma spectra can be reproduced by mixing major amounts of local fresh mare material (Reiner K crater) with small amounts of fresh highlands material (Oelbers A crater). No evidence was found for the presence of 'exotic' components (i.e., magnetite, free iron, cometary material). Together with photogeologic considerations, these results suggest that Reiner Gamma is quite young and is composed of a mixture of fresh highland materials with much larger quantities of local mare basalt.

Bell, J. F.↗
NASA NTRS1987

On the nitrogen-induced far-infrared absorption spectra

The rototranslational absorption spectrum of gaseous N2 is analyzed, considering quadrupolar and hexadecapolar induction mechanisms. The available experimental data are accounted for by using a line-shape analysis in which empirical profiles describe the single-line translational profiles. Thus, a simple procedure is derived that allows the prediction of the N2 spectrum at any temperature. On the basis of the results obtained for the pure gas, a procedure to compute the far-infrared spectrum of the N2-Ar gaseous mixture is also proposed. The good agreement between computed and experimental N2-Ar data indicates that it is possible to predict the far-infrared absorption induced by N2 on the isotropic polarizability of any interacting partner.

Dore, P.↗
NASA NTRS1984

The helium abundance of Saturn from Voyager measurements

The helium abundance in the atmosphere of Saturn is obtained from Voyager measurements by two methods. The first method combines infrared spectra and vertical profiles derived from radio occultation measurements and yields a hydrogen mole fraction of q = 0.963 + or - 0.024 corresponding to a helium mass fraction of Y = 0.06 + or - 0.05. The estimated errors are primarily due to uncertainties in the radio occultation profile and in the abundance of methane, which contributes significantly to the mean molecular weight. The second method is based on the direct inversion of infrared spectra and yields values consistent with those from the first method; however, examination of the sensitivities of the two methods indicates that in the Saturnian case the first approach provides more accurate results. Comparison of the helium abundance of Saturn with that of Jupiter and the sun suggests that helium precipitation is significant in Saturn but may not have begun in Jupiter.

Conrath, B. J.↗
DOE OSTI2022

SERDP PFAS Database

The PNNL-PFAS database was constructed to provide quantitative infrared spectra of per- and polyfluoroalkyl substances (PFAS) in the gas phase. These fluorine-rich, organic compounds have been used as non-flammable solvents, cleaning agents, and in the manufacture of a diverse variety of consumer products. Due to their widespread use and relative inertness, PFAS have accumulated in the natural environment, and exposure to these chemicals may be linked to harmful health effects. Development of methods for detecting and remediating PFAS contamination are thus active areas of research. This database supports PFAS investigations where gas-phase infrared signatures may be measured (e.g., during treatment by thermal decomposition). The database currently contains infrared spectra for 15 compounds; these were selected based on the potential of these compounds being thermal degradation products of the manufactured chemicals mentioned above. • Additional compounds will be added to the database in the future. • Additional information about the database may be obtained from [link to future paper about the PFAS database].

PFAS, infrared(IR)spectroscopy, DATABASE, FTIR, sp↗
NASA NTRS1986

Modeling of infrared flux spectra from disk-shaped interstellar dust clouds

Although there is growing observational and theoretical evidence for many disk-shaped objects of astrophysical interest, spherical geometry is assumed in most radiative transfer models. Recently we generalized the quasi-diffusion method developed by Leung (1975, 1976) for spherical geometry to solve the problem of scattering, absorption, and reemission by dust grains in a medium of disk geometry. The method is applicable to a variety of astronomical sources whose dynamics are angular-momentum dominated and hence not accurately treated by spherical geometry, e.g., protoplanetary nebulae, circumstellar disks, bipolar-flow molecular clouds, accretion disks and disk galaxies. Using this technique and realistic grain opacities we construct theoretical models to determine self-consistently the dust temperature distribution and infrared emission from disk-shaped, quiescent dark globules heated externally by the intersteller radiation field. The effects of the following parameters on the temperature structure and the emergent spectrum are studied: grain type (graphite and silicate), optical depth, density inhomogeneity, and degree of disk flattening. The disk models are characterized by an aspect ratio and an optical depth at 0.55 microns. For inhomogeneous models, a gaussian density distribution is assumed such that the ratio of central to surface density is 100. To study the effects of source geometry, we also compare results for models with spherical and disk geometry. In this case both models have the same radius and central optical depth, the disk models having a 1:1 aspect ratio. While the dust temperature distributions in the two cases are very similar, the emergent flux for the disk model depends sensitively on the viewing angle. For clouds which are unresolved, one would expect, since the thermal emission is isotropic in the neighborhood of an emitting grain, and since the emission (in the far infrared) is optically thin, that the emergent flux spectrum should be characteristic only of the dust temperature, and independent of viewing angle. However, because of the lack of complete symmetry and the resulting radiation anisotropy, this is found not to be the case for the disk models. Angle is that it implies a large uncertainty in estimating the radiation dust mass.

Spagna, G. F., Jr.↗
DOE OSTI2021

The Galactic Chemical Evolution of Chlorine

We measured {sup 35}Cl abundances in 52 M giants with metallicities in the range −0.5 < [Fe/H] < 0.12. Abundances and atmospheric parameters were derived using infrared spectra from CSHELL on the NASA Infrared Telescope Facility and from optical echelle spectra. We measured Cl abundances by fitting a H{sup 35}Cl molecular feature at 3.6985 μm with synthetic spectra. We also measured the abundances of O, Ca, Ti, and Fe using atomic absorption lines. We find that the [Cl/Fe] ratio for our stars agrees with chemical evolution models of Cl, and the [Cl/Ca] ratio is broadly consistent with the solar ratio over our metallicity range. Both indicate that Cl is primarily made in core-collapse supernovae with some contributions from Type Ia supernovae. We suggest that other potential nucleosynthesis processes, such as the ν-process, are not significant producers of Cl. Finally, we also find our Cl abundances are consistent with H ii and planetary nebular abundances at a given oxygen abundance, although there is scatter in the data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2012

Widespread Weathered Glass on the Surface of Mars

Low albedo sediments cover >10(exp 7) sq km in the northern lowlands of Mars, but the composition and origin of these widespread deposits have remained ambiguous despite many previous investigations. Here we use near-infrared spectra acquired by the Mars Express OMEGA (Observatoire pour la Mineralogie, l'Eau, les Glaces, et l'Activite') imaging spectrometer to show that these sediments exhibit spectral characteristics that are consistent with both high abundances of iron-bearing glass and silica-enriched leached rinds on glass. This interpretation is supported by observations of low-albedo soil grains with possible rinds at the Phoenix Mars Lander landing site in the northern lowlands. By comparison with the extensive glass-rich dune fields and sand sheets of Iceland, we propose an explosive volcanic origin for these glass-rich sediments. We also propose that the glassy remnant rinds on the sediments are the result of post-depositional alteration, as these rinds are commonly formed in arid terrestrial volcanic environments during water-limited, moderately acidic leaching. These weathered, glass-rich deposits in the northern lowlands are also colocated with the strongest concentrations of a major global compositional surface type previously identified in mid-infrared spectra, suggesting that they may be representative of global processes. Our results provide potential confirmation of models suggesting that explosive volcanism has been widespread on Mars, and also raise the possibilities that glass-rich volcaniclastics are a major source of eolian sand on Mars and that widespread surficial aqueous alteration has occurred under Amazonian climatic conditions.

Horgan, Briony↗
DOE OSTI2020

Higher-order phonon scattering: advancing the quantum theory of phonon linewidth, thermal conductivity and thermal radiative properties

Phonon scattering plays a central role in the quantum theory of phonon linewidth, which in turn governs important properties including infrared spectra, Raman spectra, lattice thermal conductivity, thermal radiative properties, and also signifi- cantly affects other important processes such as hot electron relaxation. Since Maradudin and Fein’s classic work in 1962, three-phonon scattering had been considered as the dominant intrinsic phonon scattering mechanism and has seen tremendous advances. However, the role of the higher-order four-phonon scattering had been persistently unclear and so was ignored. The tremendous complexity of the formalism and computational challenges stood in the way, prohibiting the direct and quantitative treatment of four-phonon scattering. In 2016, a rigorous four-phonon scattering formalism was developed, and the prediction was realized using empirical potentials. In 2017, the method was extended using first-principles calculated force constants, and the thermal conductivities of boron arsenides (BAs), Si and diamond were predicted. The predictions for BAs were later confirmed by several independent experiments. Four-phonon scattering has since been investigated in a range of materials and established as an important intrinsic scattering mechanism for thermal transport and radiative properties. Specifically, four-phonon scattering is important when the fourth-order scattering potential or phase space becomes relatively large. The former scenario includes: (i) nearly all materials when the temperature is high; (ii) strongly anharmonic (low thermal conductivity) materials, including most rocksalt compounds, halides, hydrides, chalcogenides and oxides. The latter scenario includes: (iii) materials with large acoustic–optical phonon band gaps, such as XY compounds with a large atomic mass ratio between X and Y; (iv) two- dimensional materials with reflection symmetry, such as single-layer graphene, single-layer boron nitride and carbon nanotubes; and (v) phonons with a large density of states, such as optical phonons, which are important for Raman, infrared and thermal radiative properties. Four-phonon scattering is expected to gain broad interest in various technologically important materials for thermoelectrics, thermal barrier coatings, thermal energy storage, phase change, nuclear power, ultra-high temperature ceramics, infrared spectra, Raman spectra, radiative transport, hot electron relaxation and radiative cooling. Four-phonon scattering has been, and will continue to be, established as an important intrinsic phonon scattering mechanism beyond three-phonon scattering. The prediction of four-phonon scattering will transition from a breakthrough to a new routine in the next decade.

Feng, Tianli↗
DOE OSTI2024

Competition between Water–Water Hydrogen Bonds and Water–π Bonds in Pyrene–Water Cluster Anions

We present infrared spectra and density functional theory calculations of hydrated pyrene anion clusters with up to four water molecules. The experimental spectra were acquired using infrared Ar messenger photodissociation spectroscopy. Water molecules form clusters on the surface of the pyrene, forming hydrogen bonds with the pi-system. The structures of the water clusters and their interaction with the π-system are encoded in the OH stretching vibrational modes. Here, we find that the interactions between water molecules are stronger than they are between water molecules and the π-system. While all clusters show multiple conformers, three- and four-membered rings are the lowest energy structures in the larger hydrates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗