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At least 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Proposed geomagnetic control of semiannual waves in the mesospheric zonal wind

The polar semiannual oscillation in zonal wind explains midwinter weakening of the polar vortex and the relatively short stratospheric and mesospheric summer easterlies. The phase of the wind oscillation is equinoctial, as is the phase of the semiannual component in magnetic storm activity. For a given altitude, the contours of amplitude of the semiannual wind oscillation have less variability in geomagnetic than in geographic coordinates. It is suggested that the polar wind oscillations are caused by the semiannual maxima in magnetic storm activity, which lead to electron dissociation of O2 into O, in turn increasing ozone more rapidly than the dissociation of N2 destroys ozone, and inducing a semiannual variation in the thermal and wind fields. This implies that geomagnetic processes may cause or affect the development of sudden warmings. As the tropical semiannual wind oscillation is symmetric about the geomagnetic equator, the same processes may also influence the location of the tropical wind wave.

Belmont, A. D.↗
NASA NTRS1976

Equilibrium properties of chemically reacting gases

The equilibrium energy, enthalpy, entropy, specific heat at constant volume and constant pressure, and the equation of state of the gas are all derived for chemically reacting gas mixtures in terms of the compressibility, the mol fractions, the thermodynamic properties of the pure gas components, and the change in zero point energy due to reaction. Results are illustrated for a simple diatomic dissociation reaction and nitrogen is used as an example. Next, a gas mixture resulting from combined diatomic dissociation and atomic ionization reactions is treated and, again, nitrogen is used as an example. A short discussion is given of the additional complexities involved when precise solutions for high-temperature air are desired, including effects caused by NO produced in shuffle reactions and by other trace species formed from CO2, H2O and Ar found in normal air.

Source record↗
NASA NTRS1976

Abundances of simple oxygen-bearing molecules and ions in interstellar clouds

The abundances of simple oxygen-bearing interstellar molecules in warm (T at least 40 K), diffuse, and moderately thick clouds are calculated on the basis of binary gas-phase reactions. The most important reactions are ion-molecule, charge-exchange, and dissociative-recombination reactions, as suggested mainly by earlier workers. The progenitor of these molecules in diffuse clouds is the cosmic-ray-produced H(+) ion, working through the charge-exchange reaction with O. The ionization of H(+) and He(+) is also discussed. Dissociative charge exchange of He(+) with H2 is an important source of H(+) in regions of large fractional abundance of H2, as well as an important destruction mechanism for He(+) even for small f (at least 0.1). The calculated molecular abundances are consistent with some of the available observational information.

Glassgold, A. E.↗
NASA NTRS1976

MCSCF potential energy surface for photodissociation of formaldehyde

The ground state potential energy surface for the dissociation of formaldehyde (H2CO to H2 and CO) is calculated with the ab initio MCSCF method with an extended (4-31G) basis set. The location, barrier height, and force constants of the transition state are determined, and the normal coordinate analysis is carried out. The calculated barrier height is 4.5 eV. Based on the calculated quantities, the detailed mechanism of the photochemical dissociation is discussed.

Jaffe, R. L.↗
NASA NTRS1976

Isotopic composition of nitrogen - Implications for the past history of Mars' atmosphere

Models are presented for the past history of nitrogen on Mars, based on Viking measurements showing that the atmosphere is enriched in N-15. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N2 and by dissociative recombination of N2(+). The initial partial pressure of N2 should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO2 and HNO3.

Mcelroy, M. B.↗
NASA NTRS1976

Post sunset behavior of the 6300 A atomic oxygen airglow emission

A theoretical model of the 6300 A OI airglow emission was developed based on the assumptions that both the charged and neutral portions of the Earth's upper atmosphere are in steady state conditions of diffusive equilibrium. Intensities of 6300 A OI emission line were calculated using electron density true height profiles from a standard C-4 ionosonde and exospheric temperatures derived from Fabry-Perot interferometer measurements of the Doppler broadened 6300 A emission line shape as inputs to the model. Reaction rate coefficient values, production mechanism efficiencies, solar radiation fluxes, absorption cross sections, and models of the neutral atmosphere were varied parametrically to establish a set of acceptable inputs which will consistently predict 6300 A emission intensities that closely agree with intensities observed during the post-sunset twilight period by an airglow observatory consisting of a Fabry-Perot interferometer and a turret photometer. Emission intensities that can only result from the dissociative recombination of molecular oxygen ions were observed during the latter portion of the observational period. Theoretical calculations indicate that contamination of the 6300 A OI emission should be on the order of or less than 3 percent; however, these results are very sensitive to the wavelengths of the individual lines and their intensities relative to the 6300 A OI intensity. This combination of a model atmosphere, production mechanism efficiencies, and quenching coefficient values was used when the dissociative photoexcitation and direct impact excitation processes were contributing to the intensity to establish best estimates of solar radiation fluxes in the Schumann--Runge continuum and associated absorption cross sections. Results show that the Jacchia 1971 model of the upper atmosphere combined with the Ackerman recommended solar radiation fluxes and associated absorption cross sections produces theoretically calculated intensities that more closely agree with the observed intensities than all the other combinations.

Smith, R. E.↗
NASA NTRS1977

Solar hydrogen generator

An apparatus, using solar energy to manufacture hydrogen by dissociating water molecules into hydrogen and oxygen molecules is described. Solar energy is concentrated on a globe containing water thereby heating the water to its dissociation temperature. The globe is pervious to hydrogen molecules permitting them to pass through the globe while being essentially impervious to oxygen molecules. The hydrogen molecules are collected after passing through the globe and the oxygen molecules are removed from the globe.

Sebacher, D. I.↗
NASA NTRS1977

Evaluation of a spacecraft nitrogen generator

An experiment was completed to demonstrate that low ammonia concentrations in the product nitrogen stream are possible using the staging concept. Mixtures of nitrogen, hydrogen and ammonia were fed into a temperature controlled packed bed ammonia dissociator. An ammonia concentration of 1.03% in the feed stream was reduced to less than 50 ppm at temperatures greater than or equal to 777K. The actual inlet ammonia concentration to the final nitrogen generation module ammonia dissociation stage was only 0.09%.

Marshall, R. D.↗
NASA NTRS1977

Annual variation in temperature and composition of the thermosphere and upper mesosphere

A three-dimensional circulation model, including UV (O2 dissociation) and EUV sources, is used to study the wind field and the effects of temperature and composition on annual thermospheric variations. The results are compared to those of OGO-6 and AE-C. Within an 800-1200 K temperature range, summer to winter temperature variation is studied as a function of solar activity. It is found that the model correctly predicts H, He, O, N2, O2, and Ar measurements. It is suggested that a small winter maximum in mesospheric temperature is caused by large-scale circulation induced by EUV heating. This effect, however, is masked by the energy released in O2 dissociation. The annual temperature amplitude and the winter oxygen bulge are noted to increase with increasing solar activity, whereas the winter helium bulge is noted to decrease with enhanced exospheric return flow. It is felt that the dependence of the F2 region winter anomaly on solar activity may be significantly affected by the solar activity effect in atomic oxygen.

Mayr, H. G.↗
NASA NTRS1979

Determination of the sources and sinks of N/+/ ions in the thermosphere

Measurements of atmospheric parameters made by the Atmosphere Explorer-C satellite used to identify mechanisms for the production and loss of N(+) ions in the ionosphere are presented. Photo-dissociative ionization of N2 is the main source below 250 km. Above 250 km the reaction O(+)(4S) + N(2D) yields N(+)(3P) + O(3P) is dominant, and a possible minor source of N(+) is the reaction O(+)(2P) + N2 yields N(+) + NO. Photoionization of N(4S) and dissociative charge exchange of He(+) with N2 constitute detectable sources above 350 km. Charge exchange of N(+) with O is a significant sink above 300 km, and the rate coefficients for these reactions are derived.

Torr, D. G.↗
NASA NTRS1981

Improved cell for water-vapor electrolysis

Continuous-flow electrolytic cells decompose water vapor in steam and room air into hydrogen and oxygen. Sintered iridium oxide catalytic anode coating yields dissociation rates hundredfold greater than those obtained using platinum black. Cell consists of two mirror-image cells, with dual cathode sandwiched between two anodes. Gas traverses serpentine channels within cell and is dissociated at anode. Oxygen mingles with gas stream, while hydrogen migrates through porous matrix and is liberated as gas at cathode.

Aylward, J. R.↗
NASA NTRS1979

Electron impact study of potassium hydroxide

An attempt is made to measure the sum of the elastic, rotational and vibrational scattering of electrons by KOH at low impact energies (5 to 20 eV) at angles from 10 to 120 deg. Energy loss spectra taken in the 0 to 18 eV range using an electron impact spectrometer are used to identify the species contributing to electric scattering. At temperatures between 300 and 500 C, only inelastic spectral features belonging to water are detected, while at temperatures from 500 to 800 C strong atomic K lines, indicative of molecular dissociation, and H2 energy loss features become prominent. No features attributable to KOH, the KOH dimer, O2 or potassium oxides were observed, due to the effects of the dissociation products, and it is concluded that another technique will have to be developed in order to measure electron scattering by KOH.

Vuskovic, L.↗
NASA NTRS1981

Free radical propulsion concept

A free radical propulsion concept utilizing the recombination energy of dissociated low molecular weight gases to produce thrust was examined. The concept offered promise of a propulsion system operating at a theoretical impulse, with hydrogen, as high as 2200 seconds at high thrust to power ratio, thus filling the gas existing between chemical and electrostatic propulsion capabilities. Microwave energy used to dissociate a continuously flowing gas was transferred to the propellant via three body recombination for conversion to propellant kinetic energy. Power absorption by the microwave plasma discharge was in excess of 90 percent over a broad range of pressures. Gas temperatures inferred from gas dynamic equations showed much higher temperatures from microwave heating than from electrothermal heating. Spectroscopic analysis appeared to corroborate the inferred temperatures of one of the gases tested.

Hawkins, C. E.↗
NASA NTRS1981

Free radical propulsion concept

The concept of a free radical propulsion system, utilizing the recombination energy of dissociated low molecular weight gases to produce thrust, is analyzed. The system, operating at a theoretical impulse with hydrogen, as high as 2200 seconds at high thrust to power ratio, is hypothesized to bridge the gap between chemical and electrostatic propulsion capabilities. A comparative methodology is outlined by which characteristics of chemical and electric propulsion for orbit raising mission can be investigated. It is noted that free radicals proposed in rockets previously met with difficulty and complexity in terms of storage requirements; the present study proposes to eliminate the storage requirements by using electric energy to achieve a continuous-flow product of free radicals which are recombined to produce a high velocity propellant. Microwave energy used to dissociate a continuously flowing gas is transferred to the propellant via three-body-recombination for conversion to propellant kinetic energy. Microwave plasma discharge was found in excess of 90 percent over a broad range of pressure in preliminary experiments, and microwave heating compared to electrothermal heating showed much higher temperatures in gasdynamic equations.

Hawkins, C. E.↗
NASA NTRS1981

The production rate of C/+/ from the photoionization of CO and CO2

The dissociative photoionization cross sections for the production of C(+) ions are presented for the spectral region from the dissociative ionization threshold to 90 A. The cross sections are considerably larger than previously published data and should therefore influence the calculations of the C(+) concentrations in the Mars and Venus ionospheres. It is suggested that the released energy in the C(+) fragment ion could reduce the loss rate of the ions in collisional processes, thereby accounting for the apparent discrepancies between the observed and calculated C(+) ion density in the Venus ionosphere.

Samson, J. A. R.↗
NASA NTRS1981

Hot oxygen atoms in the upper atmosphere of Venus

Using data obtained by an ultraviolet spectrometer on the Pioneer-Venus Orbiter, energy and altitude distribution of nonthermal oxygen atoms in the Venus atmosphere for typical daytime and nighttime conditions are calculated using two different numerical methods. Agreement is found between results obtained by the two-stream transport method and the diffusion equation technique. Dissociative recombination of molecular oxygen ions and charge exchange of atomic oxygen ions with the neutral hydrogen and oxygen gas are the source terms, and calculations show that the dissociative recombination term is the dominant one. It is shown that measured hot atom concentrations exceed estimates of the thermal hydrogen atom concentrations derived from Brinton et al. (1980) over most of the daytime exosphere, and the calculated concentrations do so to an even greater extent. It is concluded that hot oxygen atoms are an important component of the dayside exosphere of Venus, their most important effect being the absorption of solar wind.

Nagy, A. F.↗
NASA NTRS1980

Thermal decomposition of a Si3N4-22 wt% Al2O3 alloy

It is pointed out that materials near the Si3N4 corner of the Si3N4-AlN-Al2O3-SiO2 quaternary, termed sialons are candidate materials for high performance applications. Hot pressed alloys in this system are useful because they possess high flexure strengths and good oxidation and creep resistance. The results of the thermal decomposition studies conducted indicate that dissociation and resulting weight loss lead to inhomogeneous specimens. Material loss comes primarily from near the surface (at least initially) thus causing differences between the composition of the surface material and the bulk. In these specimens, the O-prime phase was found to be the least stable to dissociation and the beta-prime phase the most stable. This result is in accord with the conclusions of Mitomo et al. (1979) that Si2N2O has a larger equilibrium SiO partial pressure than either the X phase or the beta-prime phase.

Ditchek, B. M.↗
NASA NTRS1981

Photochemistry of acetylene at 1470 A

The considered study was conducted to assess the importance of the major primary photochemical process of acetylene at 1470 A, to clarify the role of the metastable excited state, and to obtain information on the rates of C2H reactions with H2 and CH4. Concerning the photodissociation process of acetylene, it was found that at acetylene pressures below 0.8 Torr the direct dissociation process (C2H2 yields C2H + H) is the most important primary photochemical process with a quantum yield of 0.3. Another primary process may be the production of H2 with a quantum yield of approximately 0.1 (C2H2 yields C2 + H2). At acetylene pressures above 0.8 Torr diacetylene is formed by the direct dissociation process followed by the reaction: C2H + C2H2 yields C4H2 + H. At pressures above 20 Torr benzene becomes an important product with a concomitant decrease of diacetylene. The role of acetylene in the photochemistry of the Jovian atmosphere is also considered

Okabe, H.↗