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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Probing the presently tenuous link between comets and the origin of life

The possibilities of using millimeter-wave technology to probe the subsurface processes of comets to investigate links between cometary materials and the origins of life are explored. It is noted that current theories hold that the necessities for life to begin comprise a fairly uniform temperature, the presence of a solvent to give materials mobility, and the presence of atoms which can form long chains of molecules. Consideration is given to two cometary nuclei models: a core with an equal amount of liquid water and lunar material, and a nucleus with equal amounts of frozen water ice and lunar material. Solutions to the radiative transfer equation for the two models are presented to characterize identifiable emissions using radiometric spectrometer instrumentation on a spacecraft. Particular species such as OH, CN, HCN, and glycine are expected to be detectable if present.

Hobbs, R. W.↗
NASA NTRS1983

The atmosphere of the primitive earth and the prebiotic synthesis of organic compounds

The prebiotic synthesis of organic compounds is investigated using a spark discharge on various simulated prebiotic atmospheres at 25 C. It is found that glycine is almost the only amino acid produced from the model atmospheres containing CO and CO2. These results show that the maximum yield is about the same for the three carbon sources (CO, CO2, and CH4) at high H2/carbon ratios, but that CH4 is superior at low H2/carbon ratios. CH4 is found to yield a much greater variety of amino acids than either CO or CO2. If it is assumed that amino acids more complex than glycine were required for the origin of life, then these findings indicate the need for CH4 in the primitive atmosphere. The yields of cyanide and formaldehyde are shown to parallel the amino acid results, with yields of HCN and H2CO as high as 13 percent based on carbon. Ammonia is also found to be produced from N2 in experiments with no added NH3 in yields as high as 4.9 percent. These results indicate that large amounts of NH3 would have been synthesized on the primitive earth by electric discharges.

Miller, S. L.↗
NASA NTRS1983

Prebiotic synthesis and reactions of nucleosides and nucleotides

The potential of diiminosuccinonitrile (DISN) as a prebiotic phosphorylating agent is studied. This compound is formed readily by the oxidation of diaminomaleonitrile, a tetramer of HCN. DISN is shown to produce the cyclization of 3'-adenosine monophosphate to adenosine 2',3'-cyclic phosphate in up to 40 percent yield. The DISN-mediated phosphorylation of uridine to uridine monophosphate is determined not to proceed efficiently in aqueous solution. The reaction of DISN and BrCN with uridine-5'-phosphate and uridine is found to result in the formation of 2,2'-anhydronucleotides and 2,2'-anhydronucleosides, respectively, and other reaction products resulting from an initial reaction at the 2' and 3'-hydroxyl groups. Homoionic montmorillonites were employed to study the clay mineral catalysis of the cyclization of adenosine-3'-phosphate.

Ferris, J. P.↗
NASA NTRS1984

NGC 2024: Far-infrared and radio molecular observations

Far infrared continuum and millimeter wave molecular observations are presented for the infrared and radio source NGC 2024. The measurements are obtained at relatively high angular resolution, enabling a description of the source energetics and mass distribution in greater detail than previously reported. The object appears to be dominated by a dense ridge of material, extended in the north/south direction and centered on the dark lane that is seen in visual photographs. Maps of the source using the high density molecules CS and HCN confirm this picture and allow a description of the core structure and molecular abundances. The radio molecular and infrared observations support the idea that an important exciting star in NGC 2024 has yet to be identified and is centered on the dense ridge about 1' south of the bright mid infrared source IRS 2. The data presented here allows a presentation of a model for the source.

Thronson, H. A., Jr.↗
NASA NTRS1982

Characterization and degradation studies on synthetic polymers for aerospace application

The anti-misting additive for jet fuels known as FM-9 (proprietary polymer) was characterized by elemental analysis, solubility studies and molecular weight determination. Physical properties of surface tension, viscosity, specific gravity and other physical parameters were determined. These results are compared with properties of polyisobutylene and fuels modified with the same; the misting characteristics of polyisobutylene and FM-9 in Jet A fuel are included. Characterization and degradation of phthalocyanine and its derivatives were accomplished by use of a mass spectrometer and a pyroprobe solid pyrolyzer. Metal phthalocyanine tetracarboxylic acids and phthalocyanine-tetraamine cured epoxies were studied. Epoxy/graphite composite panels were exposed to a NASA-Ames radiant panel fire simulator in the flaming and non-flaming modes; toxic gases of HCN and HZS were measured along with oxygen, Co2, Co, and organic gases.

Hsu, M. T. S.↗
NASA NTRS1984

CN and C2H in IRC +10216

The effects of the production of the radicals CN and C2H from the dissociation of HCN and C2H2 by ambient UV photons in the outer envelope of IRC +10216 are investigated. The spatial distribution of the radicals and their observable millimeter emission-line characteristics are calculated from the inferred abundances of the progenitor species in the envelope of IRC +10216 using photochemical and radiative transfer models. These are compared with available observations to examine whether photoproduction is a possible explanation of the observed emission from these species. The results suggest that the variable abundances induced by photodestruction of their progenitors do affect the observed emission from the radicals.

Huggins, P. J.↗
NASA NTRS1984

NGC 2024 - Far-infrared and radio molecular observations

New far-infrared continuum and millimeter-wave molecular observations of NGC 2024 are presented. The measurements were obtained at relatively high angular resolution making it possible to describe the source energetics and mass distribution in greater detail than previously reported. The object appears to be dominated by a dense ridge of material, extended in the north-south direction and centered on the dark lane that is seen in visual photographs. The maps of the source using the 'high-density' molecules CS and HCN confirm this picture and makes it possible to describe the core structure and molecular abundances. The radio molecular and infrared observations support the idea that an important exciting star in NGC 2024 has yet to be identified and is centered on the dense ridge about 1 arcmin south of the bright mid-infrared source IRS 2. The data presented here, along with other observations, make it possible to describe a model for the source.

Thronson, H. A., Jr.↗
NASA NTRS1984

The cometary connection with prebiotic chemistry

The latent heat of water ice has been established to control the sublimation of most cometary nuclei. The next most abundant molecules are CO and/or CO2, typically reaching 10-30 percent of the water content. The other species are in the range of 1-10 percent or less and include the newly discovered NH3. HCN and CH3CN are two other important prebiotic molecules present at a comparable (1 percent) level. Attention is drawn to similarities between these compositions and those inferred for the primordial earth.

Delsemme, A. H.↗
NASA NTRS1984

Photodissociation rates of molecules by the interstellar radiation field

The photodissociation rates of CO, NO, H2O, HCN, NO2, SO2, CS2, OCS, NH3, CH4, H2O2, and C2H2 dissociated by the interstellar ultraviolet background in the solar neighborhood are calculated for the 106-200 nm wavelength region. The processes for photodissociation of various interstellar molecules into fragments are discussed.

Lee, L. C.↗
NASA NTRS1984

Cyanide and isocyanide abundances in the cold, dark cloud TMC-1

Cold, dark molecular clouds are particularly useful for the study of interstellar chemistry because their physical parameters are better understood than those of heterogeneous, complex giant molecular clouds. Another advantage is their relatively small distance from the solar system. The present investigaation has the objective to provide accurate abundance ratios for several cyanides and isocyanides in order to constrain models of dark cloud chemistry. The relative abundances of such related species can be particularly useful for the study of chemical processes. The cloud TMC-1 considered in the current study has a remarkably high abundance of acetylene and polyacetylene derivatives. Data at 3 mm, corresponding to the J = 1 to 0 transitions of HCN, H(C-13)N, HN(C-13), HC(N-15), and H(N-15)C were obtained.

Irvine, W. M.↗
NASA NTRS1984

NGC 2024: Multi-wavelength Infrared and Radio Observations

A series of far-infrared maps obtained on the KAO find the total IR luminosity of NGC 2024 is to the 4th power L, and show a peak in flux density and optical depth about 1' south of IRS 2. High resolution spectra of IRS 2 in Brackett alfa and Pfund gamma indicate the presence of an optically thick wind with M approx. 7 x 10 to the minus 7 power M sub yr to minus 1 power, from which we infer that IRS 2 is unable to supply the luminosity observed. A six centimeter continuum map peaks near the location of the far-infrared peak and confirms it as a likely site for a source to provide this luminosity. Maps in HCN, CS, and H2CO show the gas is dense in the direction of the far IR peak. Velocity analysis shows the H2 region created by the far IR source and IRS 2 forms an expanding bubble in front of which the H2CO is seen in absorption, and which is bounded in the south and behind by dense material.

Smith, H. A.↗
NASA NTRS1984

Radioastronomical observations of comets IRAS-Araki-Alcock (1983d) and Sugano-Saigusa-Fujikawa (1983e)

Continuum and spectral-line radio observations of the comets IRAS-Araki-Alcock and Sugano-Saigusa-Fujikawa obtained at a number of observatories during May and June, 1983, are compiled in tables and briefly characterized. The species NH3, H2O, CO, and HCN are considered in detail; visible-range observations of CN are compared; and the implications of the results and the experience gained in performing and coordinating the observations for the detection of important species in other comets, especially Halley's Comet, are explored.

Irvine, W. M.↗
NASA NTRS1984

Possible production by lightning of aerosols and trace gases in Titan's atmosphere

Although lightning has not yet been observed in Titan's atmosphere, the presence of condensable vapors and the deposition of a significant amount of solar energy at the surface suggest the possibility of lightning activity. Based on an understanding of the relationship of lightning activity to the amount of convective energy available on Titan, a lightning energy dissipation rate of 4 x 10 to the -6th W/sq m can be expected. This value is much lower than that for earth or Jupiter, and is a result of both the reduced solar flux at Titan and the absorption of sunlight by the aerosols that lie above the convective layer. For this dissipation rate, the amount of HCN and C2N2 produced by lightning should be greater than that by solar UV, but could be less than that produced by electron precipitation and galactic cosmic rays. Equilibrium calculations indicate that large mole fractions of elemental solid phase carbon will also be produced. Using a simplified model of aerosol formation, coagulation, and settling, it is estimated that a lightning-produced aerosol could have a typical optical depth of 0.01, with values as high as 0.1. The accumulation of soot over geological time might reach a meter or more in depth.

Borucki, W. J.↗
NASA NTRS1985

Chemistry in dynamically evolving clouds

A unified model of chemical and dynamical evolution of isolated, initially diffuse and quiescent interstellar clouds is presented. The model uses a semiempirically derived dependence of the observed cloud temperatures on the visual extinction and density. Even low-mass, low-density, diffuse clouds can collapse in this model, because the inward pressure gradient force assists gravitational contraction. In contrast, previous isothermal collapse models required the low-mass diffuse clouds to be unrealistically cold before gravitational contraction could start. Theoretically predicted dependences of the column densities of various atoms and molecules, such as C and CO, on visual extinction in diffuse clouds are in accord with observations. Similarly, the predicted dependences of the fractional abundances of various chemical species (e.g., CO, H2CO, HCN, HCO(+)) on the total hydrogen density in the core of the dense clouds also agree with observations reported to date in the literature. Compared with previous models of interstellar chemistry, the present model has the potential to explain the wide spectrum of chemical and physical properties of both diffuse and dense clouds with a common formalism employing only a few simple initial conditions.

Tarafdar, S. P.↗
NASA NTRS1984

The high resolution submillimetre spectrum of the stratosphere

The structure of the stratospheric spectrum, measured with a resolution of 0.0033/cm unapodized in the 7-90/cm spectral interval is described. The spectra from measurements recorded on April 24, 1979 from a balloon-borne platform at about 39 km altitude launched from the National Scientific Balloon Facility of Palestine, TX are presented. The main spectroscopic constituents include a few strong and saturated lines due to the rotational spectrum of water vapor, to magnetic dipole transitions of oxygen, and to the rotational spectrum of ozone. It is shown that the lines of ozone prevent the positive identification of the contribution to the submillimeter spectrum of several minor constituents such as HF, HCl, HCN, HNO3, and N2O. The assignments which are possible in the spectra are revised.

Carli, B.↗
NASA NTRS1984

A balloon-borne microwave limb sounder for stratospheric measurements

The balloon-borne microwave limb sounder (BMLS) measures atmospheric thermal emission from millimeter wavelength spectral lines to determine vertical profiles of stratospheric species. The instrument flown to date operates at 205 GHz to measure ClO, O3, and H2O2. A 63 GHz radiometer will be added to test the technique for determining tangent point pressure from the MLS experiment on the upper atmosphere research satellite (UARS). Many additional species could also be measured by the BMLS. A radiometer at 270 GHz would provide measurements of HO2, NO2, HNO3, N2O, O-16O-18O-16, and HCN. With this addition, the BMLS can test the current theory of O3 photochemical balance in the upper stratosphere.

Waters, J. W.↗
NASA NTRS1984

Chemical evolution on the giant planets and Titan

The atmospheres of Jupiter, Saturn, Neptune and Uranus, and Titan are characterized chemically in a review of recent observational and theoretical investigations. Compositions are indicated in tables, and special emphasis is given to the formation of HCN on Jupiter, the differentiation of polar and equatorial zones in the Jovian atmosphere, the mechanisms responsible for the color of the Great Red Spot, and the possible origin of the N2-dominated atmosphere of Titan.

Caldwell, J.↗
NASA NTRS1985

Theoretical investigation of the interstellar CH3NC/CH3CN ratio

Calculations have been performed to determine the abundance ratio of the metastable isomer CH3NC to the stable isomer CH3CN in dense interstellar clouds. According to gas phase, ion-molecule treatments, these molecules are both synthesized via protonated ion precursors. A calculation has been made of the ratio of the formation rates of the protonated precursor ions, CH3NCH(+) and CH3CNH(+), synthesized via the radiative association reaction between CH3(+) and HCN, which is thought to be the dominant formation process of the two isomeric ions. The calculations, which involve both ab initio quantum chemistry and equilibrium determinations, lead to a predicted CH3NCH(+)/CH3CNH(+) formation rate ratio between 0.1 and 0.4. If this ratio is maintained in the neutral species formed from the precursor ions, theory predicts a sizable abundance for methyl isocyanide (CH3NC) and lends credence to its tentative observation.

Defrees, D. J.↗