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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Detection of small molecules with a flow immunosensor

We describe the development of an easy-to-use sensor with widespread applications for detecting small molecules. The flow immunosensor can analyze discrete samples in under one minute or continuously monitor a flowing stream for the presence of specific analytes. This detection system is extremely specific, and achieves a level of sensitivity which meets or exceeds the detection limits reported for rival assays. Because the system is also compact, transportable, and automated, it has the potential to impact diverse areas. For example, the flow immunosensor has successfully detected drugs of abuse and explosives, and may well address many of the needs of the environmental community with respect to continuous monitoring for pollutants. Efforts are underway to engineer a portable device in the field.

Kusterbeck, Anne W.↗
NASA NTRS1991

Molecules and chains in a strong magnetic field - Statistical treatment

A Thomas-Fermi-Dirac-Weizsaecker statistical model is developed and employed to investigate diatomic molecules and infinite molecular chains in strong magnetic fields. The standard magnetic Thomas-Fermi-Dirac kinetic, potential, and exchange energy functionals are supplemented by a gradient correction to the kinetic energy. The numerical method used for solving this system in two spatial dimensions is detailed. Numerical solutions for a wide range of magnetic strengths and elements are presented to demonstrate the robustness, as well as the limitations, of the statistical approach. These calculations qualitatively reproduce many of the results of detailed quantum mechanical treatments. For example, the fractional binding energy is greatest for low atomic numbers and for strong magnetic fields.

Abrahams, Andrew M.↗
NASA NTRS1990

Solvent-tuned intramolecular charge-recombination rates in a conjugated donor-acceptor molecule

The nonradiative charge-recombination rates from the charge-transfer state of a new conjugated donor-acceptor molecule (p-cyano-p-prime-methylthiodiphenylacetylene) can be tuned over almost an order of magnitude by varying the polarity of the solvent. These measurements of intramolecular recombination show a turnover of rates as a function of emission energy, consistent with the 'normal' and 'inverted' behavior of Marcus theory. Steady-state spectra and time-resolved measurements make it possible to quantitatively compare thermal and optical electron-transfer rates as a function of driving force and demonstrate their correspondence.

Khundkar, Lutfur R.↗
NASA NTRS1992

The effect of H2O gas on volatilities of planet-forming major elements. I - Experimental determination of thermodynamic properties of Ca-, Al-, and Si-hydroxide gas molecules and its application to the solar nebula

The vapor pressures of Ca(OH)2(g), Al(OH)3(g), and Si(OH)4(g) molecules in equilibrium with solid calcium-, aluminum, and silicon-oxides, respectively, were determined, and were used to derive the heats of formation and entropies of these species, which are expected to be abundant under the currently postulated physical conditions in the primordial solar nebula. These data, in conjunction with thermodynamic data from literature, were used to calculate the relative abundances of M, MO(x), and M(OH)n gas species and relative volatilities of Fe, Mg, Si, Ca, and Al for ranges of temperature, total pressure, and H/O abundance ratio corresponding to the plausible ranges of physical conditions in the solar nebula. The results are used to explain how Ca and Al could have evaporated from Ca,Al-rich inclusions in carbonaceous chondrites, while Si, Mg, and Fe condensed onto them during the preaccretion alteration of CAIs.

Hashimoto, Akihiko↗
NASA NTRS1992

Theoretical study of the BeLi, BeNa, MgLi, MgNa, and AlBe molecules and their negative ions

The alkaline earth-alkali diatomics are found to have weak bonds, because the diffuse alkali valence s orbitals cannot form a bond of sufficient strength to pay the promotion energy of the alkaline-earth atoms. This leads to van der Waals bonding in the neutrals as well as the negative ions. In fact, the negative ions have larger binding energies than the neutrals as a result of the much larger polarizability of the negative ion. The binding energy of AlBe is significantly larger than the Be-alkali molecules, due to a covalent contribution to the bonding. The binding energy in AlBe(-) is considerably larger than AlBe; the binding energy of the X 3Sigma(-) state of AlBe(-) is computed to be 1.36 eV, as compared with 0.57 eV for the X 2Pi state of AlBe.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1992

Concerted hydrogen atom exchange between three HF molecules

The termolecular reaction involving concerted hydrogen-atom exchange between three HF molecules was investigated with particular attention given to the effects of correlation at the various stationary points along the reaction. Using large segmented Gaussian basis sets to locate the (HF)3 stationary points at the SCF level, the geometries of the stable hydrogen-bonded trimer, which is of C(3h) symmetry, were located, together with the transition state for hydrogen exchange, which is of D(3h) symmetry. Then, using a large atomic natural orbital basis and correlating all valence electrons, the energetics of the exchange reaction were evaluated at the correlated level.

Komornicki, Andrew↗
NASA NTRS1992

The optimization of single mode basis functions for polyatomic vibrational problems with application to the water molecule

The optimization of the wave functions is considered for coupled vibrations represented by linear combinations of products of functions depending only on a single vibrational coordinate. The functions themselves are optimized as well as configuration list. For the H2O molecule highly accurate results are obtained for the lowest 15 levels using significantly shorter expansions than would otherwise be possible.

Schwenke, David W.↗
NASA NTRS1993

Electrostatic Propulsion Using C60 Molecules

Report proposes use of C60 as propellant material in electrostatic propulsion system of spacecraft. C60, C70, and similar molecules, have recently been found to have characteristics proving advantageous in electrostatic propulsion. Report discusses these characteristics and proposes experiments to determine feasibility of concept.

Leifer, Stephanie D.↗
NASA NTRS1992

Observations of cometary parent molecules with the IRAM radio telescope

Several rotational transitions of HCN, H2S, H2CO, and CH3OH were detected in comets P/Brorsen-Metcalf 1989 X, Austin (1989c1) and Levy (1990c) with the Institute for Millimeter Radioastronomy (IRAM) 30-m radio telescope. This allows us to determine the production rates of these molecules and to probe the physical conditions of the coma.

Colom, P.↗
NASA NTRS1992

Calculations of ion-molecule deuterium fractionation reactions involving HD

Gas-phase chemical models of deuterium fractionation in dense interstellar clouds utilize a small number of exothermic reactions to achieve fractionation. Although HD is a major repository of deuterium, it appears not to exchange deuterium with many molecular ions. Useful semiquantitative reasons have been given for the unusual lack of reactivity of exothermic ion-HD deuterium exchange systems, but quantum chemical studies are needed to understand these ideas in more detail and to determine if the lack of reactivity pertains at very low temperatures not studied in the laboratory, or whether tunneling can drive the reactions. Accordingly, the potential energy surfaces of three representative ion-molecule exchange reactions involving protonated ions and HD have been investigated with ab initio quantum chemical techniques. Our results generally confirm the semiquantitative picture as to which reactions are likely to occur and show that tunneling at low temperatures is unlikely to alter this picture.

Maluendes, Sergio A.↗
NASA NTRS1991

Infrared spectroscopy of cometary parent molecules

The wealth of information on cometary physics provided by high-resolution spectroscopy of the IR water transitions is discussed. Specifically, the absolute line intensities and spatial brightness profiles are used to determine water production rates and lifetimes; the relative line intensities and spatial brightness profiles are used to determine water production rates and lifetimes; the relative line intensities probe the kinetic temperature profile in the coma; the line widths and line positions shed light on the coma outflow dynamics; and the temporal variability in the lines provides information on the structure of the nucleus. These observations also make it possible to determine the water ortho-to-para ratio, which may elucidate the origin and/or evolution of cometary nuclei. Recent advances in IR instrumentation promise to extend sensitivities for parent molecule searches to relative abundances well below 1 percent, especially if cooled, earth-orbiting facilities are available.

Weaver, H. A.↗
NASA NTRS1992

Ab initio multireference study of the BN molecule

The lowest 1Sigma(+) and 3Pi states of the BN molecule are studied using multireference configuration interaction (MRCI) and averaged coupled-pair functional (ACPF) methods and large atomic natural orbital (ANO) basis sets, as well as several coupled cluster methods. Our calculations strongly support a 3Pi ground state, but the a1Sigma(+) state lies only 381 +/- 100/cm higher. The a1Sigma(+) state wave function exhibits strong multireference character and, consequently, the predictions of the perturbationally-based single-reference CCSD(T) coupled cluster method are not as reliable in this case as the multireference results. The theoretical predictions for the spectroscopic constants of BN are in good agreement with experiment for the Chi3Pi state, but strongly suggest a misassignment of the fundamental vibrational frequency for the a1Sigma(+) state.

Martin, J. M. L.↗
NASA NTRS1993

A survey of bimolecular ion-molecule reactions for use in modeling the chemistry of planetary atmospheres, cometary comae, and interstellar clouds - 1993 supplement

This is a supplement to a previous paper (Anicich & Huntress 1986). It is a survey of bimolecular positive ion-molecule reactions with potential importance to the chemistry of planetary atmospheres, cometary comae, and interstellar clouds. This supplement covers the literature from 1986 through 1991, with some additional citations missed in the original survey. Over 200 new citations are included. A table of reactions is listed by reactant ion, and cross-references are provided for both ionic and neutral reactants and also for both ionic and neutral products.

Anicich, V. G.↗
NASA NTRS1993

Intercomparison of stratospheric water vapor observed by satellite experiments - Stratospheric Aerosol and Gas Experiment II versus Limb Infrared Monitor of the Stratosphere and Atmospheric Trace Molecule Spectroscopy

A comparison is made of the stratospheric water vapor measurements made by the satellite sensors of the Stratospheric Aerosol and Gas Experiment II (SAGE II), the Nimbus-7 LIMS, and the Spacelab 3 Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment. It was found that, despite differences in the measurement techniques, sampling bias, and observational periods, the three experiments have disclosed a generally consistent pattern of stratospheric water vapor distribution. The only significant difference occurs at high southern altitudes in May below 18 km, where LIMS measurements were 2-3 ppmv greater than those of SAGE II and ATMOS.

Chiou, E. W.↗
NASA NTRS1993

Formaldehyde and organic molecule production in astrophysical ices at cryogenic temperatures

Thermally promoted formaldehyde (H2CO) reactions in cryogenic ices have been studied to test their importance as a source of organic molecules in comets and interstellar ices. Ices containing H2CO, H2O, CH3OH, CO, and NH3 were investigated by using infrared spectroscopy. Small traces of NH3 (NH3/H2CO equal to or greater than 0.005) are sufficient to convert significant fractions (40 percent or greater) of the H2CO into more complex organics. However, H2CO reactions do not proceed without NH3. Spectral evidence for reaction onset appeared between 40 and 80 K, depending on the ice. Five distinct products were formed. These principally consist of polyoxymethylene and related derivatives. Polyoxymethylene itself was not made in significant amounts in cometary analogs. These products differ from those produced by ultraviolet and particle irradiation. The nature and relative amounts of the products depend on the initial composition, making these materials excellent tracers of a comet's history. About 3 percent of the organics in p-Halley's coma could have been produced by thermal H2CO reactions.

Schutte, W. A.↗
NASA NTRS1993

The formation of cyanopolyyne molecules in IRC + 10216

Molecule formation in the outer envelope of the carbon-rich star IRC + 10216 is investigated, with special emphasis on the chemistry of the cyanopolyynes HC(i)N (i = 3, 5, 7). Basic elements of the photochemical model of Glassgold et al. (1986) are revised. A dust model suitable to IRC + 10216 is used for which the extinction properties in the far-UV are those of 500 A amorphous carbon particles. A new chemical route to the formation of large cyanopolyynes is proposed, based on reactions of the radicals C3N and C5N with acetylene, and shown to be efficient. Our results agree qualitatively with observations of the spatial distributions of HCN, CN, HC3N, and C3N, but the calculated column densities of the higher-order cyanopolyynes appear to be too small. The amount of the allenic radical HC2N produced by molecular ion reactions with atomic N agrees with recent observations.

Cherchneff, Isabelle↗
NASA NTRS1993

Structure and energetics of model amphiphilic molecules at the water liquid-vapor interface - A molecular dynamics study

A molecular dynamics study of adsorption of p-n-pentylphenol at infinite dilution at the water liquid-vapor interface is reported. The calculated free energy of adsorption is -8.8 +/- 0.7 kcal/mol, in good agreement with the experimental value of -7.3 kcal/mol. The transition between the interfacial region and the bulk solution is sharp and well-defined by energetic, conformational, and orientational criteria. At the water surface, the phenol head group is mostly immersed in aqueous solvent. The most frequent orientation of the hydrocarbon tail is parallel to the interface, due to dispersion interactions with the water surface. This arrangement of the phenol ring and the alkyl chain requires that the chain exhibits a kink. As the polar head group is being moved into the solvent, the chain length increases and the tail becomes increasingly aligned toward the surface normal, such that the nonpolar part of the molecule exposed to water is minimized. The same effect was achieved when phenol was replaced by a more polar head group, phenolate.

Pohorille, Andrew↗
NASA NTRS1992

Electron attachment to molecules at ultralow electron energies

Experimental techniques, both single-collision and multiple-collision, for studying electron attachment to molecules at energies below 0.1 eV are reviewed. Recent attachment results in HI, DI, F2, SF6, CCl4, and CFCl3 are examined from the point of view of threshold behavior (s- or p-wave), threshold energetics, and the temperature dependence of the attachment rate constant. An interesting application of the s-wave phenomenon to trace-species detection is given.

Chutjian, Ara↗