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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

An intercomparison of nitrogen-containing species in Nimbus 7 LIMS and SAMS data

Odd-nitrogen chemistry and transport are analyzed using a two-dimensional model and Nimbus 7 data. The Nimbus 7 data include: measurements of O3, NO2, HNO3, H2O, and temperature by the LIMS instrument; N2O, CH4, and temperature measurements by the SAMS instrument; and O3 data from the SBUV instrument. The characteristics of the two-dimensional model used in the study, a modified Guthrie et al. (1984) model, are described. NO2 and HNO3 are calculated using the two-dimensional model, and the computed data are compared with the LIMS NO2 and HNO3 measurements. The model uncertainties are computed based on the photochemical equilibrium assumption, and the role of stratospheric dynamics in determining NO2 and HNO3 is discussed. It is observed that there is good correlation between the LIMS and model data in the upper stratosphere; however, the data do not correspond in the lower stratosphere. The effect of nitrogen sources, such as lightning, on the stratospheric odd nitrogen distribution is examined.

Jackman, Charles H.↗
NASA NTRS1987

Infrared spectroscopy of the lower stratosphere with a balloon-borne cryogenic Fourier spectrometer

The IR limb emission of the lower stratosphere has been measured using a balloon-borne liquid nitrogen-cooled Michelson interferometer with liquid helium-cooled Si:Ga detectors. Portions of the thermal emission spectrum have been recorded between 650 and 2000/cm with an unapodized spectral resolution of 0.03/cm. This is the highest spectral resolution limb emission thus far obtained. A preliminary description is given of these data along with a discussion of the significant features. Species identified to date include CO2, O3, CFCl3, CF2Cl2, H2O, CH4, HNO3, N2O, NO2, and ClONO2. A tentative identification is made for NO, representing the first direct spectroscopic detection of NO in emission.

Kunde, Virgil G.↗
NASA NTRS1987

Electron impact excitation cross section studies of methane and acetylene

The 40-200-nm emission features of electron-impact-excited CH4 and C2H2 are investigated experimentally using the crossed-beam apparatus and VUV calibration techniques described by Ajello et al. (1982 and 1985). The results are presented in extensive tables and graphs and characterized in detail. All of the features are attributed to the atomic dissociation fragments C I, C II, and H, and the long lifetimes and high kinetic energies of the excited H fragments are shown to truncate the H Lyman series near principal quantum number n = 10.

Pang, K. D.↗
NASA NTRS1987

Measurement of methane and other light hydrocarbons in the troposphere and lower stratosphere

The volume mixing ratios of methane, acetylene, ethane, and propane were measured in the troposphere and stratosphere on April 5, 1984, at 33 deg N, over New Mexico, using the technique of grab sampling by evacuated spheres on a balloon platform. Tropospheric volume mixing ratios were CH4, 1.59 ppm; C2H2, 358 ppt (parts per trillion); C2H6, 365 ppt; and C3H8, 1440 ppt. In the stratosphere, acetylene was 60 ppt. For ethane and propane the mixing ratios at 11.6 km were 441 ppt and 84 ppt, respectively.

Aikin, A. C.↗
NASA NTRS1987

The spectra of Uranus and Neptune at 8-14 and 17-23 microns

The 3-m NASA Infrared Telescope Facility was used to observe the disks of Uranus and Neptune between May 30 and June 1, 1985 in the 7-14 and 17-23 micron spectral regions. Maximum stratospheric mixing ratios of 9 x 10 to the -9th for C2H2, and of 2 x 10 to the -8th for C2H6, are found for Uranus, and the spectrum is otherwise smooth, consistent with the opacity provided by H2 collision-induced absorption and spectrally continuous stratospheric emission. Strong emission features of CH4 and C2H6 are found in the short-wavelength spectrum of Neptune, and the spectrum near 13.5 microns is consistent with C2H2 emission in local saturation equilibrium with a maximum mixing ratio of 9 x 10 to the -7th.

Orton, Glenn S.↗
NASA NTRS1987

The rotation rate of Uranus, its internal structure, and the process of planetary accretion

It is investigated whether Uranus models with higher values of the total planetary ice to rock ratio (I/R) can be made consistent with the rotation period of 17.24 hr. measured by Voyager 2, and with the 16-pole moment of the gravitational field (J4) derived from the observations of French et al. (1986). An atmospheric enhancement of H2O, NH3, and CH4 of not more than about 30 times the solar value, and an I/R value of greater than 16, are implied by these models. A planetary accretion scenario whereby such I/R values are possible for a large range of planetesimal radii and initial velocities is discussed.

Podolak, M.↗
NASA NTRS1987

Structure, vibrational spectrum, and energetics of the CH5(+) ion - A theoretical investigation

Analytic derivative techniques are utilized to determine molecular geometries, vibration spectra, molecular force field, proton affinity, and energetics of clustering of protonated methane. It is observed that the geometries are gradient optimized, while the harmonic force fields and IR intensities are also determined analytically at the SCF level. It is determined that the frequency of the torsional model for rotation of the H2 about the pseudothreefold axis of the CH3(+) group is extremely low, and the proton affinity of CH4 is calculated as 129.0 kcal/mol.

Komornicki, Andrew↗
NASA NTRS1987

Infrared observations of circumstellar molecules

A current listing of IR observations of circumstellar molecules is presented. These observations were performed using Fabry-Perot, Fourier transform, and laser heterodyne spectroscopy. The most abundant species were CO, SiO, and HCN, while trace species included NH3, CH4, SiH4, and CS. Among the undetected species were H2, HCl, and CH2.

Betz, Albert↗
NASA NTRS1987

Methane absorption variations in the spectrum of Pluto

The lightcurve phases of 0.18, 0.35, 0.49, and 0.98 covered by 5600-10,500 A absolute spectrophotometry of Pluto during four nights include minimum (0.98) light and one near-maximum (0.49) light. The spectra are noted to exhibit significant methane band absorption depth variations at 6200, 7200, 7900, 8400, 8600, 8900, and 10,000 A, with the minimum absorption occurring at minimum light and thereby indicating a 30-percent change in the methane column abundance in the course of three days. An attempt is made to model this absorption strength variation with rotational phase terms of an isotropic surface distribution of methane frost and a clear layer of CH4 gas.

Buie, Marc W.↗
NASA NTRS1986

Current status of the prebiotic synthesis of small molecules

Experiments designed to simulate conditions on the primitive earth and to demonstrate how the organic compounds that made up the first living organisms were synthesized are described. Simulated atmospheres with CH4, N2, NH3, and H2O were found to be most effective for synthesis of small prebiotic molecules, although atmospheres with H2, CO, N2, and H2O, and with H2, CO2, N2, and H2O also give good yields of organic compounds provided the H2/CO and H2/CO2 ratios are above 1 and 2, respectively. The spark discharge (which is a good source of HCN) and UV light are also important. Reasonable prebiotic syntheses were worked out for the amino acids that occur in proteins (with the exception of lysine, arginine, and histidine), and for purines, pyrimidines, sugars, and nicotinic acid. Many of the molecules that have been produced in these simulated primitive-earth experiments are found in carbonaceous chondrites.

Miller, Stanley L.↗
NASA NTRS1987

The potential impact on atmospheric ozone and temperature of increasing trace gas concentrations

The response of the atmosphere to emissions of chlorofluorocarbons (CFCs) and other chlorocarbons, and to increasing concentrations of other radiatively active trace gases such as CO2, CH4, and N2O is calculated by a coupled chemical-radiative transport one-dimensional model. It is shown that significant reductions in the ozone concentration and in the temperature are expected in the upper stratosphere as a result of increasing concentrations of active chlorine produced by photodecomposition of the CFCs. The ozone content is expected to increase in the troposphere, as a consequence of increasing concentrations of methane and nitrogen oxides. Due to enhanced greenhouse effects, the Earth's surface should warm up by several degrees. The amplitude and even the sign of future changes in the ozone column are difficult to predict as they are strongly scenario-dependent. An early detection system to prevent noticeable ozone changes as a result of increasing concentrations of source gases should thus be based on a continuous monitoring of the ozone amount in the upper stratosphere rather than on measurements of the ozone column only. Measurements of NOx, Clx, and HOx are also required for unambiguous trend detection and interpretation.

Brasseur, G.↗
NASA NTRS1987

Elucidation of the organometallic vapor phase epitaxial growth mechanism for InP

A new technique for tracing the organometallic vapor epitaxial growth is reported. The pyrolysis of PH3, alone and in the presence of trimethylindium (TMIn), and of TMIn alone was studied by conducting the epitaxial growth of InP in D2 as the carrier gas, tracing growth reactions by mass spectrometric analysis of the product molecules. The TMIn alone pyrolyzes mostly homogeneously in the gas phase, while the PH3 pyrolysis is completely heterogeneous at the InP surface. Adding TMIn to PH3 results in a dramatic decrease in the pyrolysis temperature. PH3 molecules which interact with TMIn in the gas phase pyrolyze at temperatures as low as 250, and those decomposing without TMIn interaction pyrolyze at temperatures approximately 200 C higher. Similarly, the presence of PH3 lowers the TMIn pyrolysis temperature by at least 50 C. TMIn alone in D2 produces mainly CH3D molecules. For high PH3:TMIn ratios, CH4 is the only carbon-containing reaction product.

Buchan, N. I.↗
NASA NTRS1987

Electric discharge synthesis of HCN in simulated Jovian atmospheres

Corona discharge is presently considered as a possible source of the HCN detected in the Jovian atmosphere at 2.2 x 10 to the -7th moles/sq cm column density, for the cases of gas mixtures containing H2, CH4, and NH3, with H2/CH4 ratios from 4.4 to 1585. A 3:1 ratio of corona discharge to lightning energy similar to that of the earth is applied to Jupiter. Depending on the lightning energy available on Jupiter and the eddy diffusion coefficients in the synthesis region, HCN column densities generated by corona discharge could account for about 10 percent of the HCN observed.

Stribling, Roscoe↗
NASA NTRS1987

Mass spectrometric studies of phosphine pyrolysis and OMVPE growth of InP

The mechanism of PH3 decomposition was studied by using D2 as a carrier gas and analyzing the reaction products with a mass spectrometer. The effects of InP and silica surfaces were investigated. The only gaseous product below 600 C is H2. Since any gas-phase H atoms would produce HD, the reaction occurs entirely on the surface. The slow step is the unimolecular removal of the first hydrogen atom, with an activation energy of 36.0 kcal/mole on InP surfaces. The reaction on InP is first-order for PH3 concentrations as high as 15 percent, so the surface is not saturated at those conditions. When trimethylindium (TMIn) is added to the gas mixture, the mechanism changes dramatically, probably proceeding via an unstable intermediate adduct of TMIn and PH3 which eliminates CH4 upon formation. This concerted reaction lowers the pyrolysis temperatures of both PH3 and TMIn.

Larsen, C. A.↗
NASA NTRS1987

Mechanisms and observations for isotope fractionation of molecular species in planetary atmospheres

Chemcial and physical processes which may give rise to isotope fractionation of molecular species in the atmospheres of both earth and other planets are reviewed, along with observations of isotopically substituted molecules in planetary atmospheres. Mechanisms for production of isotope fractionation considered include atmospheric escape and the effect of isotope substitution on equilibrium constants (including those of phase changes), photolysis rates, and chemical reaction rates. The isotopes considered for compounds in the terrestrial atmosphere include D, T, C-13, C-14, N-15, O-18, and S-34. Compounds for which data about isotopic composition in the terrestrial atmosphere are summarized include CO, CO2, O3, N2O, NH3, SO2, H2S, H2O, H, H2, and CH4. Planetary atmospheres discussed include those of Venus, Mars, Jupiter, Saturn, Uranus, and Titan; isotopes reviewed are D, C-13, N-15, and O-18. Suggestions for additional research in the area of isotopically substituted molecules in atmospheres are offered.

Kaye, Jack A.↗
NASA NTRS1988

The separate spectra of Pluto and its satellite Charon

The March 3, 1987 occultation of Charon by Pluto was observed spectroscopically from 5400 to 10,200 A at a resolution of 12 A. The midpoint of the event occurred at 11:06 UT; the depth of the event at 6800 A was 0.162 mag. The spectrum of Charon is completely featureless and almost perfectly flat; the red slope and the CH4 absorption features can be attributed solely to Pluto.

Fink, Uwe↗
NASA NTRS1987

Evidence for methane and ammonia in the coma of comet P/Halley

Methane and ammonia abundances in the coma of Halley are derived from Giotto ion mass spectrometer data using an Eulerian model of chemical and physical processes inside the contact surface to simulate Giotto high-intensity spectrometer ion mass spectral data for mass-to-charge ratios (m/q) from 15 to 19. The ratio m/q = 19/18 as a function of distance from the nucleus is not reproduced by a model for a pure water coma. It is necessary to include the presence of NH3, and uniquely NH3, in coma gases in order to explain the data. A ratio of production rates Q(NH3)/Q(H2O) = 0.01 = 0.02 results in model values approximating the Giotto data. Methane is identified as the most probable source of the distinct peak at m/q = 15. The observations are fit best with Q(CH4)/Q(Q2O) = 0.02. The chemical composition of the comet nucleus implied by these production rate ratios is unlike that of the outer planets. On the other hand, there are also significant differences from observations of gas phase interstellar material.

Allen, M.↗