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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Validation and Recalibration of the Solubility Models in Support of the Heater Test in Salt Formations

The US Department of Energy Office of Nuclear Energy is conducting a brine availability heater test to characterize the thermal, mechanical, hydrological and chemical response of salt at elevated temperatures. In the heater test, brines will be collected and analyzed for chemical compositions. In order to support the geochemical modeling of chemical evolutions of the brines during the heater test, we are recalibrating and validating the solubility models for the mineral constituents in salt formations up to 100°C, based on the solubility data in multiple component systems as well as simple systems from literature. In this work, we systematically compare the model-predicted values based on the various solubility models related to the constituents of salt formations, with the experimental data. As halite is the dominant constituent in salt formations, we first test the halite solubility model in the Na-Mg-Cl dominated brines. We find the existing halite solubility model systematically over-predict the solubility of halite. We recalibrate the halite model, which can reproduce halite solubilities in Na-Mg-Cl dominated brines well. As gypsum/anhydrite in salt formations controls the sulfate concentrations in associated brines, we test the gypsum solubility model in NaCl solutions up to 5.87 mol•kg –1 from 25 ° C to 50 ° C. The testing shows that the current gypsum solubility model reproduces the experimental data well when NaCl concentrations are less than 1 mol•kg –1 . However, at NaCl concentrations higher than 1, the model systematically overpredicts the solubility of gypsum. In the Na + —Cl – —SO 4 2– —CO 3 2– system, the validation tests up to 100 ° C demonstrate that the model excellently reproduces the experimental data for the solution compositions equilibrated with one single phase such as halite (NaCl) or thenardite (Na 2 SO 4 ), with deviations equal to, or less than, 1.5 %. The model is much less ideal in reproducing the compositions in equilibrium with the assemblages of halite + thenardite, and of halite + thermonatrite (Na 2 CO 3 •H 2 O), with deviations up to 31 %. The high deviations from the experimental data for the multiple assemblages in this system at elevated temperatures may be attributed to the facts that the database has the Pitzer interaction parameters for Cl – —CO 3 2– and SO 4 2– —CO 3 2– only at 25 ° C. Finally, in the Na + —Ca 2+ —SO 4 2– —HCO 3 – system, the validation tests also demonstrate that the model reproduces the equilibrium compositions for one single phase such as gypsum better than the assemblages of more than one phase.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Dynamics of Product Branching from Radical Intermediates in Elementary Combustion Reactions (Final Technical Report)

While the total rate constant for many elementary reactions is well-characterized, understanding the product branching in complex reactions presents a formidable challenge. To gain an incisive probe of such reactions, our experiments investigate the dynamics of the product channels that arise from transient radical intermediates along the bimolecular reaction coordinates. Our recent published work uses the methodology developed in my group in the last fifteen years, using both imaging and scattering apparatuses. The experiments generate a particular isomeric form of an unstable radical intermediate along a bimolecular reaction coordinate and study the branching between the ensuing product channels of the energized radical as a function of its internal rotational and vibrational energy under collision-less conditions. The experiments use a combination of: 1) measurement of product velocity and angular distributions in a crossed laser-molecular beam apparatus, with electron bombardment detection in my lab in Chicago or 2) with tunable vacuum ultraviolet photoionization detection at Taiwan's National Synchrotron Radiation Research Center (NSRRC), and 3) velocity map imaging using state-selective REMPI and single photon VUV ionization of radical intermediates and reaction products. We also employ tunable VUV photoionization detection in our imaging apparatus, using difference frequency four-wave mixing to produce photoionization light tunable from 8 to 10.8 eV. This year of support funded our work to photolytically generate the radical intermediate important in the OH + propene reaction when OH adds to an end carbon. Our other major result this past year was on the photoionization detection of vinoxy radicals. Our experiments at the NSRRC definitively show that vinoxy dissociatively ionizes to both CH 3 + and HCO + , and establishes the absolute partial photoionization cross section of vinoxy to CH 3 + at 10.5 and 11.44 eV. This should allow experimentalists detecting vinoxy radicals produced in bimolecular reactions such as OH + propene to get good branching fractions to that product channel. Finally we initiated studies of the photodissociation of 1-bromo-2-chloroethane and 1,1-bromochloroethane at 193 nm at the NSRRC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

A comprehensive strategy for stable, high productivity cultivation of microalgae with controllable biomass composition

This project was performed primarily as a partnership between three Universities – The University of Toledo (UToledo), Montana State University (MSU) and The University of North Carolina at Chapel Hill (UNC). North Carolina State University also contributed to the project through a sub-subcontract. The project developed fundamental and applied knowhow for cultivation systems that are not restricted by (i) proximate availability of flue gas or other high concentration CO 2 sources and (ii) the energy and infrastructure burden to deliver CO 2 over long distances. To overcome these constraints, this project focused on cultivation of alkaliphilic algal cultures in high pH, high alkalinity media (pH>10, alkalinity >100mEq) and demonstrated high biomass productivity, improvement of biomass composition for fuel production, and culture stability. The high media alkalinity ensured availability of sufficient HCO 3 - in solution for high rates of carbon fixation while the high pH of the media facilitated rapid scavenging of atmospheric CO 2 . Overall, the direct air capture rates (DAC) in our system were sufficient to achieve high biomass productivities using atmospheric CO 2 alone. The project also developed and validated toolkits related to metabolic flux modeling and microbiome characterization.

09 BIOMASS FUELS↗
DOE OSTI2024

ELECTRONIC STRUCTURE METHODS AND PROTOCOLS WITH APPLICATION TO DYNAMICS, KINETICS AND THERMOCHEMISTRY

Hydrocarbon combustion involves the reaction dynamics of a tremendous number of species beginning with many-component fuel mixtures and proceeding via a complex system of intermediates to form primary and secondary products. Combustion conditions corresponding to new advanced engines and/or alternative fuels rely increasingly on autoignition and low-temperature-combustion chemistry. In these regimes various transient radical species such as HO2, ROO·, ·QOOH, HCO, NO2, HOCO, and Criegee intermediates play important roles in determining the detailed as well as more general dynamics. A clear understanding and accurate representation of these processes is needed for effective modeling. Given the difficulties associated with making reliable experimental measurements of these systems, computation can play an important role in developing these energy technologies. Accurate calculations have their own challenges since even within the simplest dynamical approximations such as transition state theory, the rates depend exponentially on critical barrier heights and these may be sensitive to the level of quantum chemistry. Moreover, it is well-known that in many cases it is necessary to go beyond statistical theories and consider the dynamics. Quantum tunneling, resonances, radiative transitions, and non-adiabatic effects governed by spin-orbit or derivative coupling can be determining factors in those dynamics. Building upon progress made during a period of prior support through the DOE Early Career Program, this project combines developments in the areas of potential energy surface (PES) fitting and multistate multireference quantum chemistry to allow spectroscopically and dynamically/kinetically accurate investigations of key molecular systems (such as those mentioned above), many of which are radicals with strong multireference character and have the possibility of multiple electronic states contributing to the observed dynamics. An ongoing area of investigation is to develop general strategies for robustly convergent electronic structure theory for global multichannel reactive surfaces including diabatization of energy and other relevant surfaces such as dipole transition. Combining advances in ab initio methods with automated interpolative PES fitting allows the construction of high-quality PESs (incorporating thousands of high-level data) to be done rapidly through parallel processing on high-performance computing (HPC) clusters. In addition, new methods and approaches to electronic structure theory will be developed and tested through applications. This project will explore limitations in traditional multireference calculations (e.g., MRCI) such as those imposed by internal contraction, lack of high-order correlation treatment and poor scaling. Methods such as DMRG-based extended active-space CASSCF and various Quantum Monte Carlo (QMC) methods will be applied (including VMC/DMC and FCIQMC). Insight into the relative significance of different orbital spaces and the robustness of application of these approaches on leadership class computing architectures will be gained. Synergy with other components of this research program such as automated PES fitting and multireference quantum chemistry will be used to address challenges encountered by the standard approaches to computational thermochemistry (those being single-reference quantum chemistry and perturbative treatments of the anharmonic vibrational energy, which break down for some cases of electronic structure or floppy strongly coupled vibrational modes).

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Enhanced Arsenic (III and V) Removal in Anoxic Environments by Hierarchically Structured Citrate/FeCO 3 Nanocomposites

Novel citrate/FeCO 3 nanocomposites (CF-NCs) were synthesized for effective arsenic (III and V) sorption with constant addition of Fe2+ into HCO 3 - solution in the presence of citrate. This paper is the first report on the formation of CF-NCs, and in this study we investigate the mechanisms of arsenic uptake by the sorbent under anoxic conditions through various solid- and liquid-phase spectroscopic methods, including X-ray absorption spectroscopy. In CF-NCs, citrate was found to be incorporated into the structure of siderite (up to 17.94%) through (Fe 2+ citrate) - complexes. The crystal morphology of rhombohedral siderite was changed into hierarchically nanostructured spherical aggregates composed of several sheet-like crystals, which improved the surface reactivity in the presence of sufficient citrate. Compared to pure siderite (15.2%), enhanced removal of As(III) in the range of 19.3% to 88.2% was observed, depending on the amount of incorporated citrate. The maximum sorption capacities of CF-NCs for As(III) and As(V) were 188.97 and 290.22 mg/g, respectively, which are much higher than those of previously reported siderite-based adsorbents. It was found that arsenic (III and V) sorption on CF-NCs occurred via bidentate corner-sharing surface complexation, predominantly without changes in the arsenic oxidation states. These results suggest that arsenic (III and V) can be attenuated by siderite in anoxic environments, and this attenuation can be even more effective when siderite is modified by incorporation of organic compounds such as citrate.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Outflow from Outer-arm Starburst in a Grazing Collision between Galaxies

Gemini NIFS K-band spectra and Atacama Large Millimeter/submillimeter Array {sup 12}CO J=1→0, HCO{sup +}, and 100 GHz continuum observations are used to study a bright starburst clump on an outer arm of the interacting galaxy NGC 2207. This clump emits 23% of the total 24 μm flux of the galaxy pair and has an optically opaque dust cone extending out of its 170 pc core. The measured CO accounts for the dark cone extinction if almost all the gas and dust there are in front of the star clusters. An associated approaching CO outflow has v {sub z} ~ 16 km s{sup -1}, an estimated molecular mass 8 × 10{sup 6} M {sub ⊙}, and rises to heights ~0.9 kpc. A receding CO outflow on the far side with v {sub z} ~ 28 km s{sup -1} is less extensive. The observed star formation in the core over 10 Myr can supply the dark cone kinetic energy of roughly 2 × 10{sup 52} erg via supernovae and stellar winds. Other signs of intense activity are a variable radio continuum, suggesting an embedded supernova or other outburst; X-ray emission possibly from an X-ray binary or intermediate-mass black hole, depending on the extinction; and Brγ and He i lines with 82 km s{sup -1} line widths and fluxes consistent with excitation by embedded O-type stars. According to previous models, the retrograde encounter suffered by NGC 2207 caused the loss of angular momentum. This compressed its outer disk. We suggest that the resulting inward crashing stream hit a massive H i clump on the preexisting spiral arm and triggered the observed starburst.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Chemical Inventory of the Planet-hosting Disk PDS 70

As host to two accreting planets, PDS 70 provides a unique opportunity to probe the chemical complexity of atmosphere-forming material. We present ALMA Band 6 observations of the PDS 70 disk and report the first chemical inventory of the system. With a spatial resolution of 0."4–0."5 (~50 au), 12 species are detected, including CO isotopologs and formaldehyde, small hydrocarbons, HCN and HCO{sup +} isotopologs, and S-bearing molecules. SO and CH{sub 3}OH are not detected. All lines show a large cavity at the center of the disk, indicative of the deep gap carved by the massive planets. The radial profiles of the line emission are compared to the (sub)millimeter continuum and infrared scattered light intensity profiles. Different molecular transitions peak at different radii, revealing the complex interplay between density, temperature, and chemistry in setting molecular abundances. Column densities and optical depth profiles are derived for all detected molecules, and upper limits obtained for the nondetections. Excitation temperature is obtained for H{sub 2}CO. Deuteration and nitrogen fractionation profiles from the hydrocyanide lines show radially increasing fractionation levels. Comparison of the disk chemical inventory to grids of chemical models from the literature strongly suggests a disk molecular layer hosting a carbon-to-oxygen ratio C/O > 1, thus providing for the first time compelling evidence of planets actively accreting high C/O ratio gas at present time.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

The State of the Molecular Gas in Post-starburst Galaxies

The molecular gas in galaxies traces both the fuel for star formation and the processes that can enhance or suppress star formation. Observations of the molecular gas state can thus point to when and why galaxies stop forming stars. In this study, we present Atacama Large Millimeter/submillimeter Array observations of the molecular gas in galaxies evolving through the post-starburst phase. These galaxies have low current star formation rates (SFRs), regardless of the SFR tracer used, with recent starbursts ending within the last 600 Myr. We present CO (3–2) observations for three post-starburst galaxies, and dense gas HCN/HCO+/HNC (1–0) observations for six (four new) post-starburst galaxies. The post-starbursts have low excitation traced by the CO spectral-line energy distribution up to CO (3–2), more similar to early-type than starburst galaxies. The low excitation indicates that lower density rather than high temperatures may suppress star formation during the post-starburst phase. One galaxy displays a blueshifted outflow traced by CO (3–2). MaNGA observations show that the ionized gas velocity is disturbed relative to the stellar velocity field, with a blueshifted component aligned with the molecular gas outflow, suggestive of a multiphase outflow. Low ratios of HCO + /CO, indicating low fractions of dense molecular gas relative to the total molecular gas, are seen throughout post-starburst phase, except for the youngest post-starburst galaxy considered here. These observations indicate that the impact of any feedback or quenching processes may be limited to low excitation and weak outflows in the cold molecular gas during the post-starburst phase.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

The Rest-frame Submillimeter Spectrum of High-redshift, Dusty, Star-forming Galaxies from the SPT-SZ Survey

We present the average rest-frame spectrum of the final catalog of dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope's SPT-SZ survey and measured with Band 3 of the Atacama Large Millimeter/submillimeter Array. This work builds on the previous average rest-frame spectrum, given in Spilker et al. (2014) for the first 22 sources, and is comprised of a total of 78 sources, normalized by their respective apparent dust masses. The spectrum spans 1.9 < z < 6.9 and covers rest-frame frequencies of 240–800 GHz. Combining this data with low-J CO observations from the Australia Telescope Compact Array, we detect multiple bright line features from 12 CO, [Ci], and H 2 O, as well as fainter molecular transitions from 13 CO, HCN, HCO + , HNC, CN, H 2 O + , and CH. We use these detections, along with limits from other molecules, to characterize the typical properties of the interstellar medium (ISM) for these high-redshift DSFGs. We are able to divide the large sample into subsets in order to explore how the average spectrum changes with various galaxy properties, such as effective dust temperature. We find that systems with hotter dust temperatures exhibit differences in the bright 12 CO emission lines, and contain either warmer and more excited dense gas tracers or larger dense gas reservoirs. These observations will serve as a reference point to studies of the ISM in distant luminous DSFGs (L IR > 10 12 L ⊙ ), and will inform studies of chemical evolution before the peak epoch of star formation at z = 2–3.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Properties of a coronal 'hole' derived from extreme-ultraviolet observations.

A description is given of the results of an analysis of EUV observations of a large coronal hole observed by the Harvard College Observatory (HCO) experiment on OSO-4 in 1967, November. Models were constructed for the chromospheric-coronal transition and coronal layers of the two types of regions. A comparison of the model of the hole and the normal quiet sun indicates that the electron pressure in the hole is reduced by a factor of three and the coronal temperature is lower by 600,000 K.

Munro, R. H.↗
NASA NTRS1974

Observations of the chromospheric network - Initial results from the Apollo Telescope Mount

A preliminary analysis of early data taken by the HCO spectrometer on Skylab shows that the solar chromospheric network can be clearly seen with varying contrast in the extreme-ultraviolet emission characteristic of temperatures between 10,000 K (the Lyman continuum) and 300,000 K (O VI). In the emission of Mg X, a coronal line formed at about 1,500,000 K, the network is generally unrecognizable. This is interpreted as being due to a spreading of the magnetic field lines of the network boundary in the height interval corresponding to the temperature difference between 300,000 and 1,500,000 K. We note that in certain anomalous cases, bright points of the network are seen to extend with high contrast and essentially unchanged in their cross-section through the full range of temperatures characteristic of the chromosphere, transition region, and low corona.

Reeves, E. M.↗
NASA NTRS1975

Theoretical description of the 2A/double prime/ and 2A/prime/ states of the peroxyformyl radical

Simple orbital ideas are used to describe the lowest two states of the peroxyformyl radical, and ab initio Hartree-Fock calculations in these states are reported. It is found that both states may be formed exothermically by association of O2 and HCO in their ground states; however, the excited state may decompose readily to OH and CO2. The possible role of such processes in oxidation of aldelydes is discussed.

Winter, N. W.↗
NASA NTRS1978

The energetics of molecular clouds. II - The S140 molecular cloud

Techniques of analysis which allow estimates of kinetic temperature, gas density, gas cooling rate, and dust cooling rate are applied to the S140 molecular cloud. Maps of this cloud in various molecular lines are examined which reveal the existence of a strong temperature and density peak near the H-alpha rim and the presence of a strong near-IR source very near that peak. This source is found to have an energy distribution which is very similar to that of the Becklin-Neugebauer object, including the silicate feature at 9.5 microns. The heating and cooling rates for the gas and dust in S140 are estimated, and the predicted cooling rate for dust is shown to be much greater than that for gas. The molecular-line observations are compared with a spherical large-velocity-gradient trapping calculation. An optimum cloud model is developed which indicates that: (1) (C-13)O, HCO(+), and H2CO are about 10 times less abundant in S140 than in dark clouds; (2) the HCN abundance is approximately 4 times the H2CO abundance in S140, compared with roughly equal values in dark clouds; and (3) the (C-13)O/C(O-18) ratio is consistent with terrestrial isotope ratios.

Blair, G. N.↗
NASA NTRS1978

An ion cyclotron resonance study of reactions of some atomic and simple polyatomic ions with water

Reactions of various positive ions with water vapor were studied by ion cyclotron resonance mass spectrometric techniques. Rate constants and product distributions were determined for reactions of the ions: Ar(+), Co(+), N2(+), and CO2(+), CH2(+), and CH4(+), CH2Cl(+), HCO(+), H2CO(+), H2COH(+), H2S(+) and HS(+). The results obtained in this work are compared with earlier reported data where available.

Karpas, Z.↗
NASA NTRS1979

The synthesis of complex molecules in interstellar clouds

The abundances of polyatomic molecules that may be formed by CH3(+) radiative association reactions in dense interstellar molecular clouds are reevaluated. The formation of a number of complex interstellar molecules via radiative association reactions involving ionic precursors other than CH3(+) is also investigated; these additional precursors include CH3O(+), CH3CO(+), CH5(+), HCO(+), NO(+), H2CN(+), C2H2(+), and NH3(+). The results indicate that the postulated gas-phase ion-molecule radiative association reactions could potentially explain the synthesis of most of the more complex species observed in dense molecular clouds such as Sgr B2. It is concluded, however, that in order to be conclusive, laboratory data are needed to show whether or not these reactions proceed at the required rates at low temperatures.

Huntress, W. T., Jr.↗
NASA NTRS1979

Reaction rate and products for the reaction O/3P/ + H2CO

A study of reaction kinetics of O + H2CO in a discharge-flow system using mass spectrometric detection of reactants and products is presented. It was performed under both oxygen-atom-rich and formaldehyde-rich conditions over the 296 to 437 K range, showing that the global bimolecular rate constant is in agreement with other studies. This study differs from others in that the reaction products can be observed, and a substantial yield of a primary reaction product was measured with a mass spectral peak at m/e=44. This suggests that the global reaction rate probably consists of combination, as well as of simple abstraction. For the combination, one hypothesis is that triplet dioxymethylene is formed which polymerizes to triplet formic acid; the vibrationally excited triplet formic acid may decompose to form several sets of products, including HCO + OH and HCO2 + H.

Chang, J. S.↗
NASA NTRS1979

The determination of electron abundances in interstellar clouds

An independent method is proposed for the determination of electron abundances in dense clouds based upon the abundance ratio of HCO(+) and CO. The method is derived from a simple application of gas phase ion molecule interstellar chemistry. It is noted that unlike the fractionation of deuterated molecules, it applies to warm as well as to cool clouds. The method is illustrated with the results of the recent abundance survey of Wooten et al. (1978). Finally, it is shown that in cases where deuterium enhancement is measured, an upper limit can be obtained for the cosmic ray ionization rate.

Wootten, A.↗
NASA NTRS1980

Further observational studies of the high velocity molecular source /'plateau'/ in Orion

Sensitive measurements have been made of the profiles of various molecular lines in the direction of the BN/KL infrared complex in Orion. Similar line shapes are found for the high velocity wings ('plateau') of most lines observed. The position of the high velocity source was found in SO and HCO(+) relative to the SiO maser. A search for high velocity emission in other sources was unsuccessful.

Kuiper, T. B. H.↗