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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

H2 molecules and the intercloud medium

The paper discusses expected column densities of H2 in the intercloud medium and the possible use of molecules as indicators of intercloud physical conditions. Molecule formation by the H(-) process and on graphite grains is treated, and it is shown that the Barlow-Silk hypothesis of a 1-eV semichemical hydrogen-graphite bond leads to a large enhancement of the intercloud molecule-formation rate. Rotational-excitation calculations are presented for both cloud and intercloud conditions which show, in agreement with Jura (1975), that the presently observed optically thin H2 absorption components are more likely to originate in cold clouds than in the intercloud medium.

Hill, J. K.↗
NASA NTRS1976

Vibrationally-excited hydroxyl molecules in the lower atmosphere

The vibrational energy distributions of hydroxyl molecules in the lower atmosphere were calculated. As expected, the distributions are found to be highly nonequilibrated. Attention is drawn to the role that vibrationally-excited molecules may play in modifying the chemistry of the lower atmosphere. The most likely role for the OH molecule in the stratosphere is via reactions that may not otherwise be energetically viable.

Nagy, A. F.↗
NASA NTRS1978

Stabilization of He2(A(sup 3)Sigma(sub u)(+)) molecules in liquid helium by optical pumping for vacuum UV laser

A technique is disclosed for achieving large populations of metastable spin-aligned He2(a 3 Sigma u +) molecules in superfluid helium to obtain lasing in the vacuum ultraviolet wavelength regime around 0.0800 micron m by electronically exciting liquid (superfluid) helium with a comparatively low-current electron beam and spin aligning the metastable molecules by means of optical pumping with a modestly-powered (100mW) circularly-polarized continuous wave laser operating at, for example, 0.9096 or 0.4650 micron m. Once a high concentration of spin-aligned He2 (a 3 Sigma u +) is achieved with lifetimes of a few milliseconds, a strong microwave signal destroys the spin alignment and induces a quick collisional transition of He2 (a 3 Sigma u +) molecules to the a 1 Sigma u + state and thereby a lasing transition to the X 1 Sigma g + state.

Zmuidzinas, J. S.↗
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

Interstellar synthesis of the cyanopolyynes and related molecules

The cyanopolyynes HC2CN, HC4CN, HC6CN, and HC8CN, and the molecules CH3CHCN and CH3CH2CN, have recently been detected in the interstellar medium. It is shown that the observed abundances of these molecules can be obtained by gas-phase formation pathways if the reaction of H2CN(+) with C2H2 is rapid at low interstellar temperatures. The molecules CH2CHCN and C3N may be formed also by the reactions of H2CN(+) with C2H2, and CH3CH2CN may be formed by reaction of H2CN(+) with C2H4.

Mitchell, G. F.↗
NASA NTRS1979

Molecule formation and infrared emission in fast interstellar shocks. I Physical processes

The paper analyzes the structure of fast shocks incident upon interstellar gas of ambient density from 10 to the 7th per cu cm, while focusing on the problems of formation and destruction of molecules and infrared emission in the cooling, neutral post shock gas. It is noted that such fast shocks initially dissociate almost all preexisting molecules. Discussion covers the physical processes which determine the post shock structure between 10 to the 4 and 10 to the 2 K. It is shown that the chemistry of important molecular coolants H2, CO, OH, and H2O, as well as HD and CH, is reduced to a relatively small set of gas phase and grain surface reactions. Also, the chemistry follows the slow conversion of atomic hydrogen into H2, which primarily occurs on grain surfaces. The dependence of this H2 formation rate on grain and gas temperatures is examined and the survival of grains behind fast shocks is discussed. Post shock heating and cooling rates are calculated and an appropriate, analytic, universal cooling function is developed for molecules other than hydrogen which includes opacities from both the dust and the lines.

Hollenbach, D.↗
NASA NTRS1980

Detection of energetic hydrogen molecules in Jupiter's magnetosphere by Voyager 2 - Evidence for an ionospheric plasma source

The discovery of energetic (approximately 1 MeV/nuc) H3 and H2 molecules in Jupiter's magnetosphere is reported. The data, obtained with the LECP instrument on Voyager 2, showed these molecules to be present throughout the magnetosphere and as far as 180 Jupiter radii from the planet, in the 'magnetospheric wind' region. Although the relative abundances of H3 and H2 do not show a monotonic trend with distance from Jupiter, the intervals of highest abundance were found in the outer magnetosphere. As an example, in the radial range 51-56 Jupiter radii, of the dayside magnetosphere, the abundances of H3 and H2 (0.60-0.95 MeV/nuc) were about 20 and 13-25% that of He, respectively, and the He abundance was about 1-2% that of H. Since H3(+) is expected to be an important constituent of Jupiter's ionosphere, the data provide strong evidence that, in addition to Io, the ionosphere may be an important local plasma source for the Jovian energetic particles. The measurements reported may represent the first detection in nature of molecules at energies as high as 1 MeV/nucleon.

Hamilton, D. C.↗
NASA NTRS1980

Behavior of molecules on interstellar grains - Application of the Langevin equation and iterative extended Hueckel

The Langevin equation was used to explore an adsorbate desorption mechanism. Calculations were performed using iterative extended Hueckel on a silica model site with various small adsorbates, e.g., H, CH, OH, NO, CO. It was found that barriers to free traversal from one site to another are substantial (about 3-10 eV). A bootstrap desorption mechanism for some molecules in the process of forming at a site also became apparent from the calculations. The desorption mechanisms appear to be somewhat balanced by a counterforce - the attraction of sites for the newly desorbed molecule. The order of attraction to a silica grain site for the diatomic molecules considered was OH greater than CH greater than CO greater than NO, when these entities were sufficiently distant. The nature of the silica grain and that of the 'cold' desorption mechanism, when considered together, suggest that the abundance of very small grains might be less common than anticipated.

Aronowitz, S.↗
NASA NTRS1980

Cosmic ray synthesis of organic molecules in Titan's atmosphere

The possible synthesis of organic molecules by the absorption of galactic cosmic rays in an N2-CH4-H2 Titan model atmosphere has been studied. The cosmic-ray-induced ionization results in peak electron densities of 2000/cu cm, with NH(+), C3H9(+), and C4H9(+) being among the important positive ions. Details of the ion and neutral chemistry relevant to the production of organic molecules are discussed. The potential importance of N(2D) reactions with CH4 and H2 is also demonstrated. Although the integrated production rate of organic matter due to the absorption of the cosmic ray cascade is much less than that by solar ultraviolet radiation, the production of nitrogen-bearing organic molecules by cosmic rays may be greater.

Capone, L. A.↗
NASA NTRS1984

Radical and ion molecule mechanisms in the polymerization of hydrocarbons and chlorosilanes in RF plasmas at low pressures ( 1.0 torr)

The ion-molecule and the radical-molecule mechanisms are responsible for the dissociation of hydrocarbons, and chlorosilane monomers and the formation of polymerized species, respectively, in the plasma state of a RF discharge. In the plasma, of a mixture of monomer with Ar, the rate determining step for both dissociation and polymerization is governed by an ion-molecular type interaction. Additions of H2 or NH3 to the monomer Ar(+) mixture transforms the rate determining step from an ion-molecular interaction to a radical-molecule type interaction for both monomer dissociation and polymerization processes.

Avni, R.↗
NASA NTRS1984

4.6 micron absorption features due to solid phase CO and cyano group molecules toward compact infrared sources

Spectra obtained at a resolving power of 840, for seven protostellar sources in the region of the 4.67-micron fundamental vibrational band of CO, indicate that the deep absorption feature in W33A near 4.61 microns consists of three features which are seen in other sources, but with varying relative strength. UV-irradiation laboratory experiments with 'dirty ice' temperature cycling allow the identification of two of the features cited with solid CO and CO complexed to other molecules. Cyano group-containing molecules have a lower vapor pressure than CO, and can therefore survive in much warmer environments. The formation and location of the CO- and CN-bearing grain mantles and sources of UV irradiation in cold molecular clouds are discussed. Plausible UV light sources can produce the observed cyano group features, but only under conditions in which local heat sources do not cause evaporation of the CO molecules prior to their photoprocessing.

Lacy, J. H.↗
NASA NTRS1984

A new interstellar molecule - Tricarbon monoxide

The C3O molecule, whose pure rotational spectrum has only recently been studied in the laboratory, has been detected in the cold, dark interstellar Taurus Molecular Cloud 1. Since C3O is the first interstelar carbon chain molecule to contain oxygen, its existence places an important new constraint on chemical schemes for cold interstellar clouds. The abundance of C3O can be understood in terms of purely gas-phase ion-molecule chemistry.

Matthews, H. E.↗
NASA NTRS1986

Studies of interstellar vibrationally-excited molecules

Several molecules thus far have been detected in the ISM in vibrationally-excited states, including H2, SiO, HC3N, and CH3CN. In order for vibrational-excitation to occur, these species must be present in unusually hot and dense gas and/or where strong infrared radiation is present. In order to do a more thorough investigation of vibrational excitation in the interstellar medium (ISM), studies were done of several mm-wave transitions originating in excited vibrational modes of HCN, an abundant interstellar molecule. Vibrationally-excited HCN was recently detected toward Orion-KL and IRC+10216, using a 12 meter antenna. The J=3-2 rotational transitions were detected in the molecule's lowest vibrational state, the bending mode, which is split into two separate levels, due to l-type doubling. This bending mode lies 1025K above ground state, with an Einstein A coefficient of 3.6/s. The J=3-2 line mode of HCN, which lies 2050K above ground state, was also observed toward IRC+10216, and subsequently in Orion-KL. Further measurements of vibrationally-excited HCN were done using a 14 meter telescope, which include the observations of the (0,1,0) and (0,2,0) modes towards Orion-KL, via their J=3-2 transitions at 265-267 GHz. The spectrum of the J=3-2 line in Orion taken with the 14 meter telescope, is shown, along with a map, which indicates that emission from vibrationally-excited HCN arises from a region probably smaller than the 14 meter telescope's 20 arcsec beam.

Ziurys, L. M.↗
NASA NTRS1987

The study of excited oxygen molecule gas species production and quenching on thermal protection system materials

The detection of excited oxygen and ozone molecules formed by surface catalyzed oxygen atom recombination and reaction was investigated by laser induced fluorescence (LIF), molecular beam mass spectrometric (MBMS), and field ionization (FI) techniques. The experiment used partially dissociated oxygen flows from a microwave discharge at pressures in the range from 60 to 400 Pa or from an inductively coupled RF discharge at atmospheric pressure. The catalyst materials investigated were nickel and the reaction cured glass coating used for Space Shuttle reusable surface insulation tiles. Nonradiative loss processes for the laser excited states makes LIF detection of O2 difficult such that formation of excited oxygen molecules could not be detected in the flow from the microwave discharge or in the gaseous products of atom loss on nickel. MBMS experiments showed that ozone was a product of heterogeneous O atom loss on nickel and tile surfaces at low temperatures and that ozone is lost on these materials at elevated temperatures. FI was separately investigated as a method by which excited oxygen molecules may be conveniently detected. Partial O2 dissociation decreases the current produced by FI of the gas.

Nordine, Paul C.↗
NASA NTRS1986

Free molecule drag and lift deduced from Shuttle flight experiment

A gas surface interaction experiment was flown on the STS-8 flight of the Space Shuttle in which atomic oxygen was allowed to reflect off a glassy carbon surface. The spatial distribution of the reflected molecules was recorded showing a lobe between the specular and normal directions. Using the Nocilla treatment of the reflected molecules, the speed ratio of the reflected molecules and the angle of the drifting velocity with respect to the surface were determined. This information is used to determine the drag coefficient of a sphere and the drag and lift coefficients of a flat plate.

Karr, Gerald R.↗
NASA NTRS1987

Search for molecules in Comet Halley at millimeter wavelengths

Data collected with the Five College Radio Astronomy Observatory 13.7-m radio telescope are used to search for the possible CN parent molecules HNC, HC3N, and CH3CN in Comet Halley at millimeter wavelengths. Maximum relative abundances for HNC/HCN of 0.3, for HC3N/HCN of 0.4, and for CH3CN/HCN of 0.8 are obtained, showing that these three molecules are not a major source of the CN radical observed in optical and UV spectroscopy. Upper limits to the beam averaged column densities and production rates of these molecules are determined (in addition to an upper limit for the beam averaged column density for the formyl ion of less than 10 to the 11th/sq cm), providing important constraints for chemical models of the coma.

Swade, Daryl A.↗
NASA NTRS1989

Photoabsorption and photodissociation of molecules important in the interstellar medium

Photoabsorption and fluorescence cross sections of molecules important in the interstellar medium were measured in the 90 to 200 nm region using synchrotron radiation, excimer laser, and condensed discharge lamps as light sources. The quantitative spectroscopic data are currently needed for the modeling of formation and destruction rates of molecules by the interstellar radiation field. Fluorescences from excited photofragments produced by vacuum ultraviolet radiation of molecules are dispersed to identify the emitting species. The fluorescence data are useful for the identification of emission sources in interstellar clouds.

Lee, Long C.↗
NASA NTRS1989

Connection between energy relations of solids and molecules

The universal energy relation, discovered for metallic and covalent solids as well as nuclear matter, is tested for diatomic molecules. It is found that it applies well to covalent diatomic bonds, but that ionic diatomic bonds are in a distinct class. A simple extension of the universal binding energy relation that includes the effects of ionicity ensues. It yields accurate prediction of spectroscopic data for both ionic and covalent bonds in 150 molecules. The form of the covalent part is given by the universal relation, suggesting an intimate relationship between the energetics of solids and diatomic molecules.

Smith, John R.↗