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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Near-infrared spectroscopy of the proto-planetary nebula CRL 618 and the origin of the hydrocarbon dust component in the interstellar medium

A new 2.8-3.8 micrometers spectrum of the carbon-rich protoplanetary nebula CRL 618 confirms the previous detection of a circumstellar 3.4 micrometers absorption feature in this object (Lequeux & Jourdain de Muizon). The high resolution and high signal-to-noise ratio of our spectrum allow us to derive the detailed profile of this absorption feature, which is very similar to that observed in the spectrum of the Galactic center and also resembles the strong 3.4 micrometers emission feature in some post-asymptotic giant branch stars. A weak 3.3 micrometers unidentified infrared band, marginally detected in the CRL 618 spectrum of Lequeux & Jourdain de Muizon, is present in our spectrum. The existence of the 3.4 micrometers feature implies the presence of relatively short-chained, aliphatic hydrocarbon materials (-CH2-/-CH3 approximately = 2-2.5) in the circumstellar environment around CRL 618. It also implies that the carriers of the interstellar 3.4 micrometers feature are produced at least in part in circumstellar material, and it calls into question whether any are produced by the processing of interstellar ices in dense interstellar clouds, as has been previously proposed. Other features in the spectrum are recombination lines of hydrogen, rotational and vibration-rotation lines of molecular hydrogen, and a broad absorption probably due to a blend of HCN and C2H2 bands.

Spectroscopy, Near-Infrared↗
NASA NTRS1981

Mean molecular weight and hydrogen abundance of Titan's atmosphere

The 200-600/cm continuum opacity in the troposphere and lower stratosphere of Titan is inferred from thermal emission spectra from the Voyager 1 IR spectrometer (IRIS). The surface temperature and mean molecular weight are between 94 and 97 K and between 28.3 and 29.2 AMU, respectively. The mole fraction of molecular hydrogen is 0.002 + or - 0.001, which is equivalent to an abundance of approximately 0.2 + or - 0.1 km amagat.

Samuelson, R. E.↗
DOE OSTI2020

Heterolytic Scission of Hydrogen Within a Crystalline Frustrated Lewis Pair

We report the heterolysis of molecular hydrogen under ambient conditions by the crystalline frustrated Lewis pair (FLP) 1-{2-[bis(pentafluorophenyl)boryl]phenyl}-2,2,6,6-tetramethylpiperidine (KCAT). The gas–solid reaction provides an approach to prepare the solvent-free, polycrystalline ion pair KCATH2 through a single crystal to single crystal transformation. The crystal lattice of KCATH2 increases in size relative to the parent KCAT by approximately 2%. Microscopy was used to follow the transformation of the highly colored red/orange KCAT to the colorless KCATH2 over a period of 2 h at 300 K under a flow of H2 gas. There is no evidence of crystal decrepitation during hydrogen uptake. Inelastic neutron scattering employed over a temperature range from 4–200 K did not provide evidence for the formation of polarized H2 in a precursor complex within the crystal at low temperatures and high pressures. However, at 300 K, the INS spectrum of KCAT transformed to the INS spectrum of KCATH2. Calculations suggest that the driving force is more favorable in the solid state compared to the solution or gas phase, but the addition of H2 into the KCAT crystal is unfavorable. Ab Initio methods were used to calculate the INS spectra of KCAT, KCATH2, and a possible precursor complex of H2 in the pocket between the B and N of crystalline KCAT. Ex-situ NMR showed that the transformation from KCAT to KCATH2 is quantitative and our results suggest that the hydrogen heterolysis process occurs via H2 diffusion into the FLP crystal with a rate-limiting movement of H2 from inactive positions to reactive sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Splitting of multiple hydrogen molecules by bioinspired diniobium metal complexes: a DFT study

Splitting of molecular hydrogen (H 2 ) into bridging and terminal hydrides is a common step in transition metal chemistry. In this paper, we propose a novel organometallic platform for cleavage of multiple H 2 molecules, which combines metal centers capable of stabilizing multiple oxidation states, and ligands bearing positioned pendant basic groups. Using quantum chemical modeling, we show that low-valent, early transition metal diniobium(II) complexes with diphosphine ligands featuring pendant amines can favorably uptake up to 8 hydrogen atoms, and that the energetics are favored by the formation of intramolecular dihydrogen bonds. This result suggests new possible strategies for the development of hydrogen scavenger molecules that are able to perform reversible splitting of multiple H 2 molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1973

Lunar atmospheric composition results from Apollo 17

The Apollo 17 mass spectrometer has confirmed the existence of helium, neon, argon, and possibly molecular hydrogen in the lunar atmosphere. Helium and neon concentrations are in agreement with model predictions based on the solar wind as a source and their being noncondensable gases. Ar-40 and Ar-36 both exhibit a predawn enhancement which indicates that they are condensable gases on the nightside and are re-released into the atmosphere at the sunrise terminator. Hydrogen probably exists in the lunar atmosphere in the molecular rather than atomic state, having been released from the surface in the molecular form. Total nighttime gas concentration of known species in the lunar atmosphere is 200,000 molecules/cu cm.

Hoffmann, J. H.↗
NASA NTRS1977

Stability of the equilibrium for atomic H in solid H2

The previously reported phenomenological rate process theory for the storage of atomic hydrogen free radicals in a tritium-impregnated crystalline molecular hydrogen solid is used to determine the dynamical stability of the constant uniform equilibrium solution. The analysis indicates that the equilibrium is unstable (thus, unattainable experimentally) for storage temperatures in a certain range (specifically between 0.134 and 0.80 K for 0.03% tritium by weight, and between 0.165 and 0.80 K for 1.20% tritium by weight), while being absolutely stable with respect to arbitrary small-amplitude perturbations for all storage temperatures below and above this range. The theory also predicts the maximum size for a stable H/H2 sample with an appreciable concentration of trapped H and a net excess rate of volumetric heating due to the tritium decay.

Rosen, G.↗
NASA NTRS2005

Warm Molecular Gas Traced with CO J = 7 --> 6 in the Galaxy's Central 2 Parsecs: Dynamical Heating of the Circumnuclear Disks

We present an 11" resolution map of the central 2 pc of the Galaxy in the CO J = 7 --> 6 rotational transition. The CO emission shows rotation about Sgr A* but also evidence for noncircular turbulent motion and a clumpy morphology. We combine our data set with available CO measurements to model the physical conditions in the disk. We find that the molecular gas in the region is both warm and dense, with T approx. 200-300 K and n(sub H2) approx. (5-7) x 10(exp 4) cm(exp -3). The mass of warm molecular gas we measure in the central 2 pc is at least 2000 M(solar), about 20 times the UV-excited atomic gas mass, ruling out a UV heating scenario for the molecular material. We compare the available spectral tracers with theoretical models and conclude that molecular gas is heated with magnetohydrodynamic shocks with v approx. 10-20 km s(exp -1) and B approx. 0.3- 0.5 mG. Using the conditions derived with the CO analysis, we include the other important coolants, neutral oxygen and molecular hydrogen, to estimate the total cooling budget of the molecular material. We derive a mass-to-luminosity ratio of approx. 2-3 M(solar)(L(solar)exp -1), which is consistent with the total power dissipated via turbulent decay in 0.1 pc cells with v(sub rms) approx. 15 kilometers per second. These size and velocity scales are comparable to the observed clumping scale and the velocity dispersion. At this rate, the material near Sgr A* is dissipating its orbital energy on an orbital timescale and cannot last for more than a few orbits. Our conclusions support a scenario in which the features near Sgr A* such as the circumnuclear disk and northern arm are generated by infalling clouds with low specific angular momentum.

galatic nuclei↗
DOE OSTI2024

Modeling the Low-Pressure High-Voltage Branch of the Paschen Curve for Hydrogen and Deuterium

A physical and numerical model of the Townsend discharge in molecular hydrogen and deuterium has been developed to meet the needs of designing a plasma-based switching device for power grid applications. Here, the model allows to predict the low-pressure branch of the Paschen curve for applied voltage in the range of several hundred kilovolts. In the regime of interest, electrons are in a runaway state and ionization by ions and fast neutrals sustains the discharge. It was essential to correctly account for both gas-phase and surface interactions (electron emission and electron backscattering), especially in terms of their dependence on particle energy. The model yields results consistent with prior data obtained for lower voltage. The three-species (electrons, ions, and fast neutrals) model successfully captures the essential physics of the process.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Control of hydrogen concentrations by microbial sulfate reduction in two contrasting anoxic coastal sediments

Introduction Molecular hydrogen is produced by the fermentation of organic matter and consumed by organisms including hydrogenotrophic methanogens and sulfate reducers in anoxic marine sediment. The thermodynamic feasibility of these metabolisms depends strongly on organic matter reactivity and hydrogen concentrations; low organic matter reactivity and high hydrogen concentrations can inhibit fermentation so when organic matter is poor, fermenters might form syntrophies with methanogens and/or sulfate reducers who alleviate thermodynamic stress by keeping hydrogen concentrations low and tightly controlled. However, it is unclear how these metabolisms effect porewater hydrogen concentrations in natural marine sediments of different organic matter reactivities. Methods We measured aqueous concentrations of hydrogen, sulfate, methane, dissolved inorganic carbon, and sulfide with high-depth-resolution and 16S rRNA gene assays in sediment cores with low carbon reactivity in White Oak River (WOR) estuary, North Carolina, and those with high carbon reactivity in Cape Lookout Bight (CLB), North Carolina. We calculated the Gibbs energies of sulfate reduction and hydrogenotrophic methanogenesis. Results Hydrogen concentrations were significantly higher in the sulfate reduction zone at CLB than WOR (mean: 0.716 vs. 0.437 nM H 2 ) with highly contrasting hydrogen profiles. At WOR, hydrogen was extremely low and invariant (range: 0.41–0.52 nM H 2 ) in the upper 15 cm. Deeper than 15 cm, hydrogen became more variable (range: 0.312–2.56 nM H 2 ) and increased until methane production began at ~30 cm. At CLB, hydrogen was highly variable in the upper 15 cm (range: 0.08–2.18 nM H 2 ). Ratios of inorganic carbon production to sulfate consumption show AOM drives sulfate reduction in WOR while degradation of organics drive sulfate reduction in CLB. Discussion We conclude more reactive organic matter increases hydrogen concentrations and their variability in anoxic marine sediments. In our AOM-dominated site, WOR, sulfate reducers have tight control on hydrogen via consortia with fermenters which leads to the lower observed variance due to interspecies hydrogen transfer. After sulfate depletion, hydrogen accumulates and becomes variable, supporting methanogenesis. This suggests that CLB’s more reactive organic matter allows fermentation to occur without tight metabolic coupling of fermenters to sulfate reducers, resulting in high and variable porewater hydrogen concentrations that prevent AOM from occurring through reverse hydrogenotrophic methanogenesis.

Microbiology↗
DOE OSTI2019

Hydrogenated Gold Clusters from Helium Nanodroplets: Cluster Ionization and Affinities for Protons and Hydrogen Molecules

We report the mass spectrometric detection of hydrogenated gold clusters ionized by electron transfer and proton transfer. The cations appear after the pickup of hydrogen molecules and gold atoms by helium nanodroplets (HNDs) near zero K and subsequent exposure to electron impact. We focus on the size distributions of the gold cluster cations and their hydrogen content, the electron energy dependence of the ion yield, patterns of hydrogenated gold cluster cation stability, and the presence of “magic” clusters. Ab initio molecular orbital calculations were performed to provide insight into ionization energies and proton affinities of gold clusters as well as into molecular hydrogen affinities of the ionized and protonated gold cluster cations. .

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Radiation-Induced Chemical Yields of Carbon-Centered Radicals and Hydrogen Atoms from the Gamma Irradiation of n -Dodecane

Here, this study investigates the radiolytic yields of carbon-centered radicals and hydrogen atoms in n-dodecane under gamma irradiation. Utilizing molecular iodine (I 2 ) and 2,4,6-tri-tert-butylnitrosobenzene (3tBNB) as radical scavengers, we quantified the yields of molecular hydrogen and various carbon-centered radicals formed from bond scission of the solvent excited states. The yield of primary alkyl radicals was significantly lower than that of the secondary radicals, aligning with expected stabilities and bond dissociation energies. For the overall loss of n-dodecane, total yields of 0.598 ± 0.004 species/100 eV for C–C bond scission, 1.648 ± 0.012 species/100 eV for C–H bond scission, and 3.20 ± 0.10 species/100 eV for unimolecular H 2 elimination were determined. Notably, the I 2 scavenging data provided robust estimates, while the 3tBNB displayed lower efficiency in radical trapping. This research enhances our understanding of radiolytic processes in n-dodecane and offers insights for future studies on the behavior of hydrocarbons under ionizing radiation, with implications for improving UNF reprocessing strategies.

38 - RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCL↗
NASA NTRS1975

Jupiter: Its infrared spectrum from 10 to 40 microns

Spectral measurements of the thermal radiation from Jupiter in the 16-40 micrometer band were analyzed under the assumption that pressure broadened H2 transitions are responsible for the bulk of the infrared opacity over most of this spectral interval. Both the vertical pressure-temperature profile and the hydrogen mixing ratio were determined. The derived value of the molecular hydrogen mixing ratio, 0.89 + or - 0.11, is consistent with the solar value, 0.86.

Houck, J. R.↗
NASA NTRS1988

Aperture synthesis mapping of molecular gas in high-luminosity IRAS galaxies

The Owens Valley millimeter-wave interferometer has been used for high-resolution mapping of the 2.6 mm CO emission from the high-luminosity infrared galaxies NGC 520 (Arp 157), NGC 7469 (Arp 298), and Arp 55. Assuming the same empirical relationship between CO brightness and molecular hydrogen surface mass density as has been found for giant molecular clouds in the Milky Way, it is found that the masses of H2 gas in these concentrations are 10 to the 9th - 10 to the 10th solar masses, typically one-third of the total molecular gas content of these galaxies. The interferometric sizes correspond to radii of 0.8 kpc (NGC 520), 1.4 kpc (NGC 7469), and less than 2.8 kpc (Arp 55). For the same regions the dynamical masses estimated from the CO line width and size of the emission region are only a factor of 3-5 higher. The mean molecular gas surface densities averaged over these regions are in the range 610-825 solar masses/sq pc, a factor of 10 brighter than those obtained for corresponding regions in the nucleus of the Milky Way. The high mass fractions obtained for the interstellar medium in the central regions of these three galaxies strongly suggest that large-scale gravitational instability in the gas may play an important role in the further concentration of the gas in the nucleus and in possibly precipitating a large-scale burst of star formation.

Sanders, D. B.↗
NASA NTRS1995

Development of optical diagnostics for performance evaluation of arcjet thrusters

Laser and optical emission-based measurements have been developed and implemented for use on low-power hydrogen arcjet thrusters and xenon-propelled electric thrusters. In the case of low power hydrogen arcjets, these laser induce fluorescence measurements constitute the first complete set of data that characterize the velocity and temperature field of such a device. The research performed under the auspices of this NASA grant includes laser-based measurements of atomic hydrogen velocity and translational temperature, ultraviolet absorption measurements of ground state atomic hydrogen, Raman scattering measurements of the electronic ground state of molecular hydrogen, and optical emission based measurements of electronically excited atomic hydrogen, electron number density, and electron temperature. In addition, we have developed a collisional-radiative model of atomic hydrogen for use in conjunction with magnetohydrodynamic models to predict the plasma radiative spectrum, and near-electrode plasma models to better understand current transfer from the electrodes to the plasma. In the final year of the grant, a new program aimed at developing diagnostics for xenon plasma thrusters was initiated, and results on the use of diode lasers for interrogating Hall accelerator plasmas has been presented at recent conferences.

Cappelli, Mark A.↗
NASA NTRS1999

The ISO View of Star Forming Galaxies

ISO studies of normal galaxies in the local Universe have revealed basic new properties whose significant implications for the star formation process and cosmology are only starting to be understood. This review will touch on the general results of a statistical nature, and provide a quick summary of the profusion of exciting results on individual objects. In the mid-infrared, PHT-S has established that the spectra of star forming galaxies between 6 and-13microns are dominated by the Aromatic Features in Emission (AFE), and show little variation as a function of the heating intensity. The Carriers of the AFE (CAFE) are thus a universal component of dust with standard properties, and contribute between 10 and 25% of the total dust luminosity. In addition to AFE, the spectra show a low-level continuum detectable at wavelengths longer than 3.5microns whose origin is still under investigation. The mid-infrared colors formed as the ratio of flux densities in the 6.75micron and the 15micron bands of ISO-CAM remain essentially constant and near unity for quiescent and mildly active galaxies. As dust heating increases further, the 15micron flux increases steeply compared to 6.75microns, indicating that dust heated to 100K<T<200K becomes a significant component. Such hot dust is presumably located within or just outside HII regions. At the other end of the spectrum, photometry at 120-200microns using ISO-PHOT is starting to constrain the distribution of dust temperatures at the low end of the temperature scale. From LWS data, the far-infrared fine-structure lines of [CII] and [OI], which provide most of the cooling for warm atomic gas, show variations that have remained controversial in their interpretation. In particular, as the galaxy become more active in star formation, its [CII] flux weakens relative to total dust emission while the [OI] does not. This behavior has attracted much interest because it extrapolates to the most active galaxies, making them weaker in [CII] than previously expected. Several explanations for the effect have been advanced, and will be discussed in this review. Spectroscopy with SWS has measured molecular hydrogen in galaxies, providing a powerful handle on the warm molecular gas content. SWS and CAM-CVF studies targeting ionic fine-structure lines have demonstrated their value as diagnostics of the radiation field.

Helou, George↗
NASA NTRS2015

Resource Prospector: Mission Goals, Relevance and Site Selection

Over the last two decades a wealth of new observations of the moon have demonstrated a lunar water system dramatically more complex and rich than was deduced following the Apollo era. Observation from the Lunar Prospector Neutron Spectrometer (LPNS) revealed enhancements of hydrogen near the lunar poles. This observation has since been confirmed by the Lunar Reconnaissance Orbiter (LRO) Lunar Exploration Neutron Detector (LEND) instrument. The Lunar Crater Observation and Sensing Satellite (LCROSS) mission targeted a permanently shadowed, enhanced hydrogen location within the crater Cabeus. The LCROSS impact showed that at least some of the hydrogen enhancement is in the form of water ice and molecular hydrogen (H2). Other volatiles were also observed in the LCROSS impact cloud, including CO2, CO, an H2S. These volatiles, and in particular water, have the potential to be a valuable or enabling resource for future exploration. In large part due to these new findings, the NASA Human Exploration and Operations Mission Directorate (HEOMD) have selected a lunar volatiles prospecting mission for a concept study and potential flight in CY2020. The mission includes a rover-borne payload that (1) can locate surface and near-subsurface volatiles, (2) excavate and analyze samples of the volatile-bearing regolith (up to 1 meter), and (3) demonstrate the form, extractability and usefulness of the materials.

Moon↗