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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Study of carbon compounds in Apollo 12 and 14 lunar samples.

The results of gas-chromatography and high-resolution mass spectroscopy studies of gases released on deuterium fluoride dissolution of Apollo 12 and 14 lunar samples are reported. The results confirm previous observations that CH4 and C2H6 are released as well as CD4, C2D4, C2D6, and higher deuterated hydrocarbons. The yields correlate with the total carbon content of the samples, and the CH4 and C2H6 released may be regarded as indigenous, while the deuterated products result from hydrolysis of carbide material. The results provide the first experimental confirmation of the hypothesis that the CH4 derives from solar wind interactions.

Holland, P. T.↗
NASA NTRS1974

An inversion in the atmosphere of Titan

A very detailed greenhouse model derives a methane to hydrogen ratio of unity and a minimum surface pressure of 0.4 atm. Based on a surface gravity g = 140 cm sec/2, the minimum CH4 abundance is 30-40 km-A and the minimum H2 abundance varies from 15 to 85 km-A. A model of the atmosphere of Titan is proposed which seems to be consistent with observations and requires a much smaller CH4 abundance (of the order or 2 km-atm). Although no H2 is required, the presence of some H2 is readily accommodated. In this model, a temperature inversion exists in the atmosphere due to absorption of blue and ultraviolet solar radiation by small particles. The absorbed radiation is re-radiated by the dust and by molecules having long wavelength bands such as CH4 7.7 micrometer and ethane at 12.2 micrometer. The brightness temperature at 20 micrometer is primarily due to re-radiation by the dust.

Danielson, R. E.↗
NASA NTRS1976

Scattering of high-velocity He atoms by C/CH3/4 and Si/CH3/4

Fast helium beams are employed to probe short-range potentials in tetramethylmethane and tetramethylsilane, and throw light on the relations between these more complex reactions and such reactions as He-CH4 and He-SiH4. Earlier work on scattering of helium and argon beams by polyatomic molecules (fluorinated methanes, sulfur hexafluoride, silane, germane) are at variance with these results, as neither of the above systems can be represented as a cluster of four CH4 molecules, Effective He-H potentials based on scattering data are identical for the two systems studied but are much larger than the corresponding CH4 potential. A model in which centers of force are located along the bonds rather than at the nuclei is suggested for further testing.

Amdur, I.↗
NASA NTRS1976

Limb brightening on Uranus - The visible spectrum

Results are presented for pinhole and slit narrowband photoelectric area-scanning photometry of the Uranus disk at eight central wavelengths ranging from 5600 to 7500 A. The observations were undertaken to detect limb brightening on the planet and to study the nature of its disk profile as a function of geometrical albedo. A coarse analysis of the results shows that the disk must exhibit limb brightening in the two CH4 bands at 6190 and 7300 A relative to all other wavebands investigated. Except for the two CH4 bands, the shapes and widths of the images are found to be essentially identical; point-spread-function data for all wavebands indicate no significant variation in the representative Gaussian l/e width with wavelength. A fine analysis of the data reveals absolute limb brightening in the 7300-A CH4 band and absolute limb darkening in the adjacent wavebands. These results are shown to be consistent with the hypothesis that clouds are absent from the visible atmosphere of Uranus.

Price, M. J.↗
NASA NTRS1976

Chemistry and spectroscopy of the Jovian atmosphere

A comprehensive review is given of the chemistry and spectroscopic studies of the Jovian atmosphere. Thermochemical equilibrium models for determining atmospheric composition are considered along with possible disequilibrating processes, and studies of the photochemistry of H2, CH4, NH3, H2S, and PH3 using the modeling methods are summarized. It is shown that photodissociation and advection are the major disequilibrating processes in Jupiter's atmosphere, that lightning and charged-particle bombardment are relatively minor factors in the planet's bulk chemistry, and that the existence of living organisms on the planet is highly improbable. Spectroscopic investigations of Jupiter are discussed, emphasizing recent observations of absorption bands due to CH4, NH3, H2, He, and D. Spectroscopic abundance determinations are examined for H2, HD, CH4, CH3D, NH3, C2H6, C2H2, and PH3. Upper limits are given for the abundances of several unobserved gases in the visible atmosphere, including H2S, HCl, SiH4, benzene, purines, pyrimidines, and their derivatives.

Prinn, R. G.↗
NASA NTRS1976

Crossed beam studies of ion-molecule reactions in methane and ammonia

A crossed-beam apparatus is used to measure the product ion velocity and angular distributions for the following ion-molecule reactions in the relative energy range from 2 to 9 eV: CH4(+) + NH3 yields NH4(+) + CH3; CH4(+) + NH3 yields CNH5(+) + H2; NH2(+) + CH4 yields CNH4(+) + H2 (or 2H); and CH3(+) + NH3 yields CNH4(+) + H2 (or 2H). These reactions are also studied by means of deuterium labeling as a further probe of the detailed reaction dynamics. Probability contour plots for the four reactions are constructed in Cartesian velocity space, and product peaks in the plots are discussed. Relative cross sections and Q values are computed for two of the reactions as well as for the corresponding deuterium-labelled reactions. The results show that the present ion-neutral condensation reactions are highly exothermic with a deep well for the internal complex, that little hydrogen scrambling occurs, and that the energy of the reactions is released mainly as internal energy, even to the extent of producing two hydrogen atoms in some cases rather than one hydrogen atom or molecule.

Smith, G. P. K.↗
NASA NTRS1977

A saturation model of the atmosphere of Uranus

A model of the atmospheric structure of Uranus is presented which differs from previous types of models in two important respects: (1) the CH4/H2 ratio is sufficiently large that CH4 is saturated to large depths in the Uranian atmosphere and (2) the internal energy flux is small compared with that due to solar heating. Because of the small internal flux, the thermal flux decreases rapidly with depth and the atmosphere is radiative to large optical depths. A CH4 droplet cloud forms where the atmosphere finally becomes convective due to the internal flux. The model is shown to be in reasonable agreement with published observations of the H2 quadrupole 3-0 and 4-0 bands, the visible (4000-6000 A) CH4 bands, and the infrared emission spectrum.

Danielson, R. E.↗
NASA NTRS1978

Organic chemistry on Titan

Observations of nonequilibrium phenomena on the Saturn satellite Titan indicate the occurrence of organic chemical evolution. Greenhouse and thermal inversion models of Titan's atmosphere provide environmental constraints within which various pathways for organic chemical synthesis are assessed. Experimental results and theoretical modeling studies suggest that the organic chemistry of the satellite may be dominated by two atmospheric processes: energetic-particle bombardment and photochemistry. Reactions initiated in various levels of the atmosphere by cosmic ray, Saturn wind, and solar wind particle bombardment of a CH4 - N2 atmospheric mixture can account for the C2-hydrocarbons, the UV-visible-absorbing stratospheric haze, and the reddish color of the satellite. Photochemical reactions of CH4 can also account for the presence of C2-hydrocarbons. In the lower Titan atmosphere, photochemical processes will be important if surface temperatures are sufficiently high for gaseous NH3 to exist. Hot H-atom reactions initiated by photo-dissociation of NH3 can couple the chemical reactions of NH3 and CH4 and produce organic matter.

Chang, S.↗
NASA NTRS1980

16-30 micron spectroscopy of Titan

Titan has been observed from 16 to 30 micron with a resolution of 1 micron. Earlier broad-band data are consistent with the new measurements, which show that the disk integrated flux is nearly constant over the observed range of wavelengths. Limits on the CH4, H2, and N2 column densities and pressures at the bottom of the upper layer are derived. These indicate that if the atmosphere gas is CH4, an H2-CH4 mix, or N2, the inversion layer must be at pressures less than 30 millibars.

Mccarthy, J. F.↗
NASA NTRS1982

Comments on Pluto's atmosphere

A pure CH4 atmosphere would rapidly escape from Pluto. For such an atmosphere, even CH4 frosts on Pluto's surface would completely sublimate on a time scale short compared to Pluto's life. Observations of CH4 therefore imply that its atmosphere must also contain another gas in significant quantity.

Trafton, L.↗
NASA NTRS1981

Kinetic inhibition of CO and N2 reduction in circumplanetary nebulae - Implications for satellite composition

In contrast to the solar nebula, the conversion of CO to CH4 and of N2 to NH3 in the circumplanetary nebulae of the Jovian planets is fast enough relative to radial mixing and nebula cooling rates that CO and N2 are minor constituents in the circumplanetary nebulae. Thus, although the Jovian planets may have accreted carbon and nitrogen from the solar nebula mainly in the form of CO and N2, these species were then reprocessed within the circumplanetary nebulae to form mainly CH4 and NH3. Satellites of the Jovian planets which accreted in sufficiently cool parts of their circumplanetary nebula are therefore predicted to retain large amounts of NH3 and CH4 in the form of clathrate hydrates and also very small but chemically important amounts of HCN.

Prinn, R. G.↗
NASA NTRS1982

Methane and nonmethane hydrocarbon concentrations in the North and South Atlantic marine boundary layer

Methane and nonmethane hydrocarbon (NMHC) data were collected in the Atlantic marine boundary layer from 40 N to 32 S latitude during October and November 1980. Average volume mixing ratios for CH4 of 1.69 + or - 0.02 ppmv were obtained north of the intertropical convergence zone (ITCZ) and 1.60 + or - 0.02 ppmv south of the ITCZ. The hemispheric CH4 gradient was very sharp, decreasing rapidly between 14 N and 10 N latitude. Gaseous NMHC concentrations (based on response as CH4) were measured simultaneously and found to lie consistently within the standard error for the individual measurements + or - 0.02 ppmv) after correction for water vapor interference. The correction for water vapor response was large, frequently as much as 80% of the raw NMHC signal. Application of the student's t distribution test to the NMHC data set established that the mean northern and southern hemispheric NMHC mixing ratios measured, 0.016 and 0.010 ppmv, respectively, were statistically different at the 95% confidence level. These results indicate volatile NMHC mixing ratios average less than 0.02 ppmv over the Atlantic and represent the first set of semicontinuous NMHC measurements spanning the North and South Atlantic marine boundary layer.

Cofer, W. R., III↗
NASA NTRS1983

The atmosphere of Titan - An analysis of the Voyager 1 radio occultation measurements

The equatorial atmosphere of Titan was probed by means of two coherently related radio signals transmitted from Voyager 1 at 13.0 and 3.6 cm wavelengths during the November 12, 1980 occultation of the spacecraft by the Saturn satellite. An analysis of the differential dispersive frequency measurements did not reveal any ionization layers in the upper atmosphere of Titan. The gas refractivity data, which extend from the surface to about 200 km altitude, were interpreted in two different ways. In the first, it is assumed that N2 makes up virtually all of the atmosphere, with small amounts of CH4 and other hydrocarbons present. In the second interpretation of the refractivity data, it is assumed that the 3.5 km altitude level corresponds to the bottom of a CH4 cloud layer and that N2 and CH4 were perfectly mixed below this level.

Lindal, G. F.↗
NASA NTRS1983

Methane flux across the air-water interface - Air velocity effects

Methane loss to the atmosphere from flooded wetlands is influenced by the degree of supersaturation and wind stress at the water surface. Measurements in freshwater ponds in the St. Marks Wildlife Refuge, Florida, demonstrated that for the combined variability of CH4 concentrations in surface water and air velocity over the water surface, CH4 flux varied from 0.01 to 1.22 g/sq m/day. The liquid exchange coefficient for a two-layer model of the gas-liquid interface was calculated as 1.7 cm/h for CH4 at air velocity of zero and as 1.1 + 1.2 v to the 1.96th power cm/h for air velocities from 1.4 to 3.5 m/s and water temperatures of 20 C.

Sebacher, D. I.↗
NASA NTRS1983

Longitudinal variability of methane and ammonia bands on Jupiter. II - Temporal variations

A set of spectra has been obtained of the Jovian equatorial zone central meridian 6190 A CH4 and 6450 A NH3 bands on the nights of February 26, 27, and 28, 1980, a year after the data reported by Cochran and Cochran (1980), in order to check the previous results and search for possible temporal variations. The new data confirm the results of the previous study. A correlation of the NH3 and CH4 equivalent widths, as well as a lack of any strong correlation of red continuum reflectivity with equivalent width, are found. Longitude regions of larger or smaller than average equivalent width still seem to exist a year later, with some slight drift in longitude. An increase in the average CH4 and NH3 equivalent width over the entire planet was detected during the one year interval. This is easily understood as the result of a global decrease in the mean altitude of the NH3 cloud.

Cochran, W. D.↗
NASA NTRS1983

Photochemistry of methane in the earth's early atmosphere

The photochemical behavior of methane in the early terrestrial atmosphere is investigated with a detailed model in order to determine how much CH4 might have been present and what types of higher hydroocarbons could have been formed. It is found that any primordial methane accumulated during the course of earth accretion would have been dissipated by photochemical reactions in the atmosphere in a geologically short period of time after the segregation of the core. Abiotic sources of methane are not likely to have been large enough to sustain CH4 mixing ratios as high as 10 to the -6th, the threshold for a possible methane greenhouse, with a CO-rich atmosphere being a possible exception. After the origin of life an increasing biogenic source of methane may have driven CH4 mixing ratios well above 10 to the 6th. The rise of atmospheric oxygen in the early Proterozoic may have led to a more rapid photochemical destruction of methane, lowering the mixing ratio to its present value.

Kasting, J. F.↗
NASA NTRS1984

High-resolution spectra of isotopic methanes near 1645 nm

It is demonstrated that the coincidence between Er:YAG laser emission and CH4 absorption is associated with the R(8) multiplet of C-13H4 instead of the R(6) of C-12H4. The Er:YAG emission was characterized as a laser emission at 6079.4/cm with a bandwidh of 2.2/cm and overlapping CH4 emission at 6078.7/cm. The R(6) component of C-12H4 closest to 6078.7/cm is calculated to be 6077.06/cm, corresponding to an absorption coefficient (AC) of 1.12/cm per atm. The F2-prime component of R(8) of C-13H4 has an AC of 0.308/cm per atm, which corresponds well with a range of 1.2-30.30/cm per atm based on a partial pressure of 1.6/89 ppm. The Er:YAG laser is a candidate for use in spectroscopic studies of CH4 atmospheric pollutants, natural gas movement and storage and gas accumulation in coal mines.

Fox, K.↗
NASA NTRS1985

Magmas as Selective Filters of Volatiles Between Planetary Mantles and Surfaces

The composition of early planetary atmospheres and biospheres which is a knowledge of the relationship between mantle volatiles and volcanic gases was analyzed. In the case of Earth it appears that volcanic rocks and gases are relatively oxidized compared to the upper mantle. In the case of the C-O-H volatiles, (H2O, CO2, CO, CH4, H2) the volcanic gases are enriched in H2O and CO2 while the volatiles in the mantle may be dominated by H2O, H2 and possibly CH4. An experimental technique was perfected for phase equilibrium studies in the 5-30 kbar range which allows accurate control of volatile species activities in the fluid phase. The system was used to measure the relative solubilities of H2O, CO2, CO, CH4 and H2 in magmas at 10 kbar pressure. It is found that mantle magmas will selectively screen volatiles from planetary surfaces, forcing volcanic gases towards the neutral QFM oxidation state where H2O is the dominant species.

Holloway, J. R.↗