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Results for “HYDROFLUORIC ACID”

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
DOE OSTI2016

Analysis of the possibility of designing more compact DF lasers driven by combustion of preheated fuels

We report a theoretical calculation of the processes proceeding in the combustor of combustion-driven cw DF/HF chemical lasers with different mixtures of fuels preheated to high temperatures. Calculation results demonstrate a great effect of the preheating temperature on the yield of F atoms and strongest deactivator, on the primary dilution ratio Ψp and on the estimated specific power. When fuels are preheated to about 1300 K, the specific power is improved by about 74.2 %, and the total mass of the fuel is reduced by about 43 %, which makes it possible to realise a more compact and efficient design of combustion-driven cw DF/HF chemical lasers at elevated combustor pressures. Fuel preheating can facilitate the development of chemical lasers and high-power lasers based not only on airborne and space-borne platforms, but also on mobile ground-based platforms. (active media)

42 ENGINEERING↗
DOE OSTI2017

Numerical simulation of a high efficiency combustion-driven HF laser with preheated fuels

We report a simulation calculation of the processes proceeding in a nozzle array and an optical cavity of a combustion-driven cw HF chemical laser with preheated fuels. Investigation results demonstrate that fuel preheating can dramatically improve the output characteristics of combustion-driven HF chemical lasers. The available output power and specific output power are improved by ∼13% and ∼46%, respectively, when fuels are preheated to 1200 K. It is shown that the fuel consumption in the combustor is reduced by ∼36%, which allows one to improve the performance of combustion-driven HF lasers and make them more compact due to fuel preheating. (paper)

42 ENGINEERING↗
DOE OSTI2019

Tetrafluoroethylene as a fuel component for an atomic fluorine generator of a supersonic continuous-wave chemical HF laser

A cheap and widely accessible combination (one of non-saturated perfluorocarbons), i.e. C{sub 2}F{sub 4} tetrafluoroethylene, is proposed as an alternative fuel component for an atomic fluorine generator of a supersonic cw chemical HF laser of self-contained type. Combustion products of the hypergolic F{sub 2} – C{sub 2}F{sub 4} – He mixture do not contain active relaxants of vibrationally excited HF(v) molecules. According to estimates, the atomic fluorine yield under comparable conditions is about 70 % in relation to that of the atomic fluorine generator operating on the F{sub 2} – D{sub 2} – He mixture which is the ‘basic’ one for a HF laser. The specific power is reduced by 23 % with an improvement in a set of the fuel performance and a significant reduction in the cost of triggering the laser in the course of its bench tests. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Energy characteristics of a supersonic continuous-wave chemical HF laser using hydrazine decomposition products

We report the results of calculations and experimental studies of specific energy characteristics of a supersonic cw chemical HF laser with a flat nozzle block corresponding to the nozzle – nozzle reagent mixing scheme, in which catalytic decomposition products of hydrazine N{sub 2}H{sub 4} (H{sub 2} + N{sub 2} + NH{sub 3}) are used as a secondary fuel. As a result of experiments with cold (300 K) model mixtures, the specific energy extraction of the laser is found to decrease in this case by 43 % compared with the laser utilising pure hydrogen. The calculations show that the main reason for a decrease in the specific energy of the laser is an increase in the temperature in the mixing zone of the oxidising gas and secondary fuel jets. A strong effect of ammonia is revealed. Taking into account the actual heating of the products (up to 1000 K) during the catalytic decomposition of N{sub 2}H{sub 4} allows the level of specific energy extraction from the laser to approach that of energy extraction from the laser operated on pure hydrogen by 13 %, which will lead to a decrease in the specific energy extraction by only 30 % in the absence of NH{sub 3} decomposition products. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Efficiency of using nitrogen trifluoride as an oxidiser in a supersonic continuous-wave chemical HF laser

We report the results of an experimental study of possible ways to increase the efficiency of using NF{sub 3} nitrogen trifluoride as an oxidiser in an atomic fluorine generator of a supersonic continuous-wave chemical HF laser with a flat nozzle block corresponding to the nozzle – nozzle reagent mixing scheme. As such ways, we consider increasing the residence time of reagents in the combustion chamber and rising temperature in the chemical reaction zone. Comparison of specific energy characteristics of an HF laser operating with the use of the studied (NF{sub 3}) and ‘basic’ (F{sub 2}) oxidisers shows that the replacement of molecular fluorine with nitrogen trifluoride during the burning with deuterium in the combustion chamber of an atomic fluorine generator with allowance for the proposed measures leads to a reduction in the specific laser energy output by no more than 23 % – 24 % at high burning completeness. (paper)

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

Comparative analysis of characteristics of a supersonic cw chemical HF laser on molecular fluorine and nitrogen trifluoride

We have experimentally studied the characteristics of a supersonic cw chemical HF laser with a flat nozzle array based on a nozzle – nozzle reagent mixing scheme operating with the use of F{sub 2} – D{sub 2} – He and NF{sub 3} – D{sub 2} – He fuel compositions in an atomic fluorine generator. The active medium flow field pattern, its gas-dynamic characteristics, and the laser radiation spectrum are considered. The comparison of these characteristics has made it possible to establish a strong impact on the flow field (lasing zone length) of the chemical composition of the combustion products from the atomic fluorine generator. The gas-dynamic parameters of the active medium formed by using a NF{sub 3} – D{sub 2} – He fuel have turned out to be less acceptable in terms of the gas flow pressure recovery than in the case of F{sub 2} – D{sub 2} – He fuel, while the radiation spectrum was more preferable from the viewpoint of passing through the atmosphere. (paper)

36 MATERIALS SCIENCE↗
DOE OSTI2013

The abundance of fluorine in the Hyades, NGC 752, and M67

The abundance of fluorine is determined from the 2.3358 μm feature of the molecule HF for several giants in the Hyades, NGC 752, and M67 open clusters from spectra obtained with the Phoenix IR spectrometer on the 2.1 m telescope at Kitt Peak. The abundance of fluorine in cluster giants is consistent with that observed in field stars, and may indicate that stars with super-solar metallicities and young ages may be enhanced in fluorine by perhaps 0.2-0.3 dex compared to older or lower-metallicity field stars. Multiple sources probably contribute to the fluorine abundance in the Galactic disk, although the relative contributions of possible sources remain uncertain. Fluorine production in asymptotic giant branch stars, however, is unlikely to be the dominant source.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

HYDROGEN FLUORIDE IN HIGH-MASS STAR-FORMING REGIONS

Hydrogen fluoride (HF) has been established to be an excellent tracer of molecular hydrogen in diffuse clouds. In denser environments, however, the HF abundance has been shown to be approximately two orders of magnitude lower. We present Herschel/HIFI observations of HF J = 1-0 toward two high-mass star formation sites, NGC 6334 I and AFGL 2591. In NGC 6334 I the HF line is seen in absorption in foreground clouds and the source itself, while in AFGL 2591 HF is partially in emission. We find an HF abundance with respect to H{sub 2} of 1.5 Multiplication-Sign 10{sup -8} in the diffuse foreground clouds, whereas in the denser parts of NGC 6334 I we derive a lower limit on the HF abundance of 5 Multiplication-Sign 10{sup -10}. Lower HF abundances in dense clouds are most likely caused by freezeout of HF molecules onto dust grains in high-density gas. In AFGL 2591, the view of the hot core is obstructed by absorption in the massive outflow, in which HF is also very abundant (3.6 Multiplication-Sign 10{sup -8}) due to the desorption by sputtering. These observations provide further evidence that the chemistry of interstellar fluorine is controlled by freezeout onto gas grains.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

DIRECT DETERMINATION OF THE HF/H{sub 2} ABUNDANCE RATIO IN INTERSTELLAR GAS

We report the first detection of the v = 1-0, R(0) ro-vibrational transition of HF at 2.499385 {mu}m arising from interstellar gas. The line is seen in absorption toward three background sources-HD 154368, Elias 29, and AFGL 2136 IRS 1-all of which have reported H{sub 2} column densities determined from observations of H{sub 2}. This allows for the first direct determination of the HF/H{sub 2} abundance ratio. We find values of N(HF)/N(H{sub 2}) = 1.15 Multiplication-Sign 10{sup -8} and 0.69 Multiplication-Sign 10{sup -8} for HD 154368 and Elias 29, respectively. The sight line toward AFGL 2136 IRS 1 also shows absorption from the v = 1-0, R(1) transition of HF, indicating warm, dense (n {sub H} {approx}> 10{sup 9} cm{sup -3}) gas, likely very close to the central protostar. Ascribing portions of the HF absorption to warm and cold gas, we find N(HF)/N(H{sub 2}) = (1.7-2.9) Multiplication-Sign 10{sup -8} and (0.33-0.58) Multiplication-Sign 10{sup -8} for the two components, respectively. Except for the warm component toward AFGL 2136 IRS 1, all observed HF/H{sub 2} ratios are well below N(HF)/N(H{sub 2}) = 3.6 Multiplication-Sign 10{sup -8}, the value predicted if nearly all gas phase fluorine is in the form of HF. Models of fluorine chemistry that account for depletion onto grains are able to reproduce the results toward HD 154368, but not in the cold, dense gas toward AFGL 2136 IRS 1 and Elias 29. Most likely, some combinations of simplifying assumptions made in the chemical models are responsible for these discrepancies.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

FLUORINE ABUNDANCES OF GALACTIC LOW-METALLICITY GIANTS

With abundances and 2{sigma} upper limits of fluorine (F) in seven metal-poor field giants, nucleosynthesis of stellar F at low metallicity is discussed. The measurements are derived from the HF(1-0) R9 line at 23358 A using near-infrared K-band high-resolution spectra obtained with CRIRES at the Very Large Telescope. The sample reaches lower metallicities than previous studies on F of field giants, ranging from [Fe/H] = -1.56 down to -2.13. Effects of three-dimensional model atmospheres on the derived F and O abundances are quantitatively estimated and shown to be insignificant for the program stars. The observed F yield in the form of [F/O] is compared with two sets of Galactic chemical evolution models, which quantitatively demonstrate the contribution of Type II supernova (SN II) {nu}-process and asymptotic giant branch/Wolf-Rayet stars. It is found that at this low-metallicity region, models cannot well predict the observed distribution of [F/O], while the observations are better fit by models considering an SN II {nu}-process with a neutrino energy of E {sub {nu}} = 3 Multiplication-Sign 10{sup 53} erg. Our sample contains HD 110281, a retrograde orbiting low-{alpha} halo star, showing a similar F evolution as globular clusters. This supports the theory that such halo stars are possibly accreted from dwarf galaxy progenitors of globular clusters in the halo.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE HYPERFINE STRUCTURE OF THE ROTATIONAL SPECTRUM OF HDO AND ITS EXTENSION TO THE THz REGION: ACCURATE REST FREQUENCIES AND SPECTROSCOPIC PARAMETERS FOR ASTROPHYSICAL OBSERVATIONS

The rotational spectrum of the mono-deuterated isotopologue of water, HD{sup 16}O, has been investigated in the millimeter- and submillimeter-wave frequency regions, up to 1.6 THz. The Lamb-dip technique has been exploited to obtain sub-Doppler resolution and to resolve the hyperfine (hf) structure due to the deuterium and hydrogen nuclei, thus enabling the accurate determination of the corresponding hf parameters. Their experimental determination has been supported by high-level quantum-chemical calculations. The Lamb-dip measurements have been supplemented by Doppler-limited measurements (weak high-J and high-frequency transitions) in order to extend the predictive capability of the available spectroscopic constants. The possibility of resolving hf splittings in astronomical spectra has been discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A Herschel/HIFI legacy survey of HF and H{sub 2}O IN the galaxy: Probing diffuse molecular cloud chemistry

We combine Herschel observations for a total of 12 sources to construct the most uniform survey of HF and H{sub 2}O in our Galactic disk. Both molecules are detected in absorption along all sight lines. The high spectral resolution of the Heterodyne Instrument for the Far-infrared (HIFI) allows us to compare the HF and H{sub 2}O distributions in 47 diffuse cloud components sampling the disk. We find that the HF and H{sub 2}O velocity distributions follow each other almost perfectly and establish that HF and H{sub 2}O probe the same gas-phase volume. Our observations corroborate theoretical predictions that HF is a sensitive tracer of H{sub 2} in diffuse clouds, down to molecular fractions of only a few percent. Using HF to trace H{sub 2} in our sample, we find that the N(H{sub 2}O)-to-N(HF) ratio shows a narrow distribution with a median value of 1.51. Our results further suggest that H{sub 2}O might be used as a tracer of H{sub 2}—within a factor of 2.5—in the diffuse interstellar medium (ISM). We show that the measured factor of ∼2.5 variation around the median is driven by true local variations in the H{sub 2}O abundance relative to H{sub 2} throughout the disk. The latter variability allows us to test our theoretical understanding of the chemistry of oxygen-bearing molecules in the diffuse gas. We show that both gas-phase and grain-surface chemistry are required to reproduce our H{sub 2}O observations. This survey thus confirms that grain surface reactions can play a significant role in the chemistry occurring in the diffuse ISM (n{sub H} ⩽ 1000 cm{sup −3}).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

SUBMILLIMETER-WAVE ROTATIONAL SPECTROSCOPY OF H{sub 2}F{sup +}

Five pure rotational transitions of H{sub 2}F{sup +} generated by a discharge in an HF/H{sub 2}/Ar mixture were observed in the range 473-774 GHz with a backward-wave oscillator based submillimeter-wave spectrometer. A simultaneous analysis of the rotational lines with 120 combination differences for the ground state derived from the infrared spectra was carried out to determine the precise molecular constants for the ground state. The rotational transition frequencies that lie below 2 THz were calculated, together with their estimated uncertainties, to facilitate future astronomical identifications. The chemistry for H{sub 2}F{sup +} formation in interstellar space is discussed in comparison with a case for recently detected H{sub 2}Cl{sup +}.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

HERSCHEL/HIFI OBSERVATIONS OF HYDROGEN FLUORIDE TOWARD SAGITTARIUS B2(M)

Herschel/HIFI observations have revealed the presence of widespread absorption by hydrogen fluoride (HF) J = 1-0 rotational transition, toward a number of Galactic sources. We present observations of HF J = 1-0 toward the high-mass star-forming region Sagittarius B2(M). The spectrum obtained shows a complex pattern of absorption, with numerous features covering a wide range of local standard of rest velocities (-130 to 100 km {sup -1}). An analysis of this absorption yields HF abundances relative to H{sub 2} of {approx}1.3 x 10{sup -8}, in most velocity intervals. This result is in good agreement with estimates from chemical models, which predict that HF should be the main reservoir of gas-phase fluorine under a wide variety of interstellar conditions. Interestingly, we also find velocity intervals in which the HF spectrum shows strong absorption features that are not present, or are very weak, in spectra of other molecules, such as {sup 13}CO (1-0) and CS (2-1). HF absorption reveals components of diffuse clouds with small extinction that can be studied for the first time. Another interesting observation is that water is significantly more abundant than hydrogen fluoride over a wide range of velocities toward Sagittarius B2(M), in contrast to the remarkably constant H{sub 2}O/HF abundance ratio with average value close to unity measured toward other Galactic sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

DISCOVERY OF HYDROGEN FLUORIDE IN THE CLOVERLEAF QUASAR AT z = 2.56

We report the first detection of hydrogen fluoride (HF) toward a high-redshift quasar. Using the Caltech Submillimeter Observatory, we detect the HF J = 1-0 transition in absorption toward the Cloverleaf, a broad absorption line quasi-stellar object at z = 2.56. The detection is statistically significant at the {approx}6{sigma} level. We estimate a lower limit of 4 Multiplication-Sign 10{sup 14} cm{sup -2} for the HF column density and using a previous estimate of the hydrogen column density, we obtain a lower limit of 1.7 Multiplication-Sign 10{sup -9} for the HF abundance. This value suggests that, assuming a Galactic N(HF)/N{sub H} ratio, HF accounts for at least {approx}10% of the fluorine in the gas phase along the line of sight to the Cloverleaf quasar. This observation corroborates the prediction that HF should be a good probe of the molecular gas at high redshift. Measurements of the HF abundance as a function of redshift are urgently needed to better constrain the fluorine nucleosynthesis mechanism(s).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE LU ISOTOPIC COMPOSITION OF ACHONDRITES: CLOSING THE CASE FOR ACCELERATED DECAY OF {sup 176}LU

Studies of Lu–Hf isotope systematics in meteorites have produced apparent “ages” that are older than Pb–Pb ages and older than the estimated age of our solar system. One proposed explanation for this discrepancy is that irradiation by cosmic rays caused excitation of {sup 176}Lu to its short-lived isomer that then underwent rapid decay to {sup 176}Hf. This explanation can account for apparent excesses in {sup 176}Hf that correlate with Lu/Hf ratio. Mass balance requires that samples with measurable excess in {sup 176}Hf should also have measurable deficiencies in {sup 176}Lu on the order of 1‰–3‰. To unambiguously test the accelerated decay hypothesis, we have measured the {sup 176}Lu/{sup 175}Lu ratio in terrestrial materials and achondrites to search for evidence of depletion in {sup 176}Lu. To a precision of 0.1‰ terrestrial standards, cumulate and basaltic eucrites and angrites all have the same {sup 176}Lu/{sup 175}Lu ratio. Barring a subsequent mass-dependent fractionation event, these results suggest that the apparent excesses in {sup 176}Hf are not caused by accelerated decay of {sup 176}Lu, and so another hypothesis is required to explain apparently old Lu–Hf ages.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

Photoelectron angular distributions from polar molecules probed by intense femtosecond lasers

We present numerical calculations of molecular-frame photoelectron angular distributions in strong-field ionization of oriented polar HF and LiF molecules by linearly polarized laser pulses with durations of about 20 fs (seven cycles at 800 nm). The calculations are performed within the single-active-electron and frozen-nuclei approximations. Our analysis shows that for the HF and LiF molecules, anisotropies in the molecular potential and the probed orbital lead to enhanced ionization during laser half cycles with the field pointing antiparallel to the permanent dipole of the dipole term in a multipolar expansion of the anisotropic molecular potential. This is manifested as a strong asymmetry in the computed photoelectron angular distributions: The photoelectrons are preferentially detected opposite to the permanent dipole of the molecular potential. This phenomenon is very sensitive to the probed system (the probed orbital and the molecular potential) and the orientation angle between the molecular axis and the laser polarization.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Combining density-functional theory and density-matrix-functional theory

We combine density-functional theory with density-matrix-functional theory to draw the best from both worlds. This is achieved by range separation of the electronic interaction which permits one to rigorously combine a short-range density functional with a long-range density-matrix functional. The short-range density functional is approximated by the short-range version of the Perdew-Burke-Ernzerhof functional (srPBE). The long-range density-matrix functional is approximated by the long-range version of the Buijse-Baerends functional (lrBB). The obtained srPBE+lrBB method accurately describes both the static and dynamic electron correlation at a computational cost similar to that of standard density-functional approximations. This is shown for the dissociation curves of the H{sub 2}, LiH, BH, and HF molecules.

74 ATOMIC AND MOLECULAR PHYSICS↗