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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Kinetics of the reaction OH + HO2 yields H2O + O2 from 254 to 382 K

The discharge-flow resonance fluorescence technique has been used to determine the absolute rate constant for the reaction OH + HO2 yields H2O + O2 from 254 to 382 K at a total pressure of 1 Torr. Pseudo-=first-order conditions were used with HO2 in large excess over OH. The rate constant was obtained directly from observed decays of OH and measured concentrations of HO2. Since the observed rate constant was found to be very sensitive to small background concentrations of O and H atoms, NO2 was used to remove both atom species from the system. With added NO2 the result at 299 K is (1.1 + or - 0.3) x 10 to the -10th cu cm/molecule where the error limits are one standard deviation and include an estimate of overall experimental uncertainty. The temperature dependence expressed in Arrhenius form is (4.8 + or - 0.8) x 10 to the -11th exp (250 + or - 50)/T. The results are independent of the type of reactor surface and the precursor used to produce OH and HO2. The present results agree well with earlier measurements near 1-atm total pressure and suggest that this rate constant exhibits little or no pressure dependence between 1 and 1000 Torr.

Keyser, Leon F.↗
NASA NTRS1988

Intermolecular potential for thermal H2O-He collisions

Theoretical potentials for rotational excitation of H2O by He were constructed via several methods, all of which start with a large basis set SCF interaction. The semiempirical Hartree-Fock with damped dispersion model adds a damped long-range attraction with parameters adjusted to fit experimental total differential cross sections. Purely ab initio potentials add correlation energies obtained via perturbation theory (MP2 and MP4) or a variational method (ICF1). Scattering calculations were performed on all surfaces to compare wih available beam scattering and pressure broadening data and to assess sensitivity of state-to-state rates to uncertainties in the potential. From comparison with the limited experimental data, the ICF1 surface appears to be marginally better than the MP4 surface. Thermal rates calculated from this surface should be accurate to better than 50 percent, at least for the larger, more important rates.

Palma, Amedeo↗
NASA NTRS1988

Heterogeneous reactions of N2O5 with H2O and HCl on ice surfaces - Implications for Antarctic ozone depletion

This paper reports on the measurements of reaction probabilities for heterogeneous reaction of N2O5 with H2O and HCl on ice surfaces at 195 K, using a fast-flow reactor coupled with a quadrupole mass spectrometer. The reaction probability for N2O5 on pure-water ice was found to be 0.028 + or - 0.011, with nitric acid in the solid phase as the sole product. In the presence of HCl in ice, the probability of N2O5 reaction was enhanced (to 0.037); the reaction produced, besides solid-phase nitric acid, ClNO2 and ClONO which were released into the gas phase within a few milliseconds. The latter two compounds can be readily photolyzed in the austral spring to form active chlorine which would remove stratospheric ozone. It is suggested that, since the polar stratospheric clouds are believed to contain HCl-ice mixture on the surface, the reactions of N2O5 on H2O/HCl particles is a major factor in the Antarctic springtime ozone depletion.

Leu, Ming-Taun↗
NASA NTRS1989

Proton irradiation of SiH4-Fe(CO)5-H2O ices - Production of refractory silicates and implications for the solar nebula

The results of a number of experiments are reported in which SiH4-Fe(CO)5-H2O ice mixtures were irradiated by 1 MeV protons at 15 K and then warmed to room temperature in approximately 50 K steps. The properties of a sample were monitored by observing its infrared absorption spectrum as a function of its processing history. In each experiment in which ice samples containing SiH4 were irradiated, a refractory amorphous silicate residue remained after warming to room temperature. In addition to the usual broad silicate features at 10 and 20 microns, features due to water or hydroxyl at 3 and 6.2 microns, and a feature due to CO at 5 microns, a surprisingly stable infrared feature at 4.6 microns, attributed to the SiH stretching fundamental, was observed.

Nuth, J. A.↗
NASA NTRS1989

Solid organic residues produced by irradiation of hydrocarbon-containing H2O and H2O/NH3 ices - Infrared spectroscopy and astronomical implications

Plasma-discharge irradiations were conducted for the methane clathrate expected in outer solar system satellites and cometary nuclei; also irradiated were ices prepared from other combinations of H2O with CH4, C2H6, or C2H2. Upon evaporation of the yellowish-to-tan irradiated ices, it is found that a colored solid film adheres to the walls of the reaction vessel at room temperature. These organic films are found to exhibit IR band identifiable with alkane, aldehide, alcohol, and perhaps alkene, as well as substituted aromatic functional groups. These spectra are compared with previous studies of UV- or photon-irradiated nonclathrated hydrocarbon-containing ices.

Khare, B. N.↗
NASA NTRS1989

Ground-based measurements of O 1D and the H2O production rate from comets

High spectral resolution 6300.3 A line profiles of Comet Halley are modeled to determine the relative contributions to the emission that can be expected from the distant O 1D daughters produced by photodissociation H2O, CO2, and CO. The results are compared with profiles measured with a single etalon Fabry-Perot interferometer interfaced with a 0.4-m telescopre. To accurately calculate Q O 1D using the 6300.3 A intensity, the line profile must be known. It is shown that the outflow velocity of the parent molecules from the nucleus can be determined using the interferometer profiles.

Kerr, R. B.↗
NASA NTRS1990

Energy storage for a lunar base by the reversible chemical reaction: CaO+H2O reversible reaction Ca(OH)2

A thermochemical solar energy storage concept involving the reversible reaction CaO + H2O yields Ca(OH)2 is proposed as a power system element for a lunar base. The operation and components of such a system are described. The CaO/H2O system is capable of generating electric power during both the day and night. The specific energy (energy to mass ratio) of the system was estimated to be 155 W-hr/kg. Mass of the required amount of CaO is neglected since it is obtained from lunar soil. Potential technical problems, such as reactor design and lunar soil processing, are reviewed.

Perez-Davis, Marla E.↗
NASA NTRS1989

Measurements of CH4, N2O, CO, H2O and O3 in the middle atmosphere by the ATMOS experiment on Spacelab 3

The volume mixing ratios of five minor gases (CH4, N2O, CO, H2O, and O3) were retrieved through the middle atmosphere from the analysis of 0.01/cm resolution infrared solar occultation spectra recorded near 28 N and 48 S latitudes with the ATMOS (Atmospheric Trace Molecule Spectroscopy) instrument, flown on board Spacelab 3. The results, which constitute the first simultaneous observations of continuous profiles through the middle atmosphere for these gases, are in general agreement with reported measurements from ground, balloon and satellite-based instruments for the same seasons. In detail, the vertical profiles of these gases show the effects of the upper and middle atmospheric transport patterns dominant during the season of these observations. The profiles inferred at different longitudes around 28 N suggest a near-uniform zonal distribution of these gases. Although based on fewer observations, the sunrise occultation measurements point to a larger variability in the vertical distribution of these gases at 48 S.

Gunson, M. R.↗
NASA NTRS1989

Photochemistry of CO and H2O - Analysis of laboratory experiments and applications to the prebiotic earth's atmosphere

The role photochemical reactions in the early earth's atmosphere played in the prebiotic synthesis of simple organic molecules was examined, extending an earlier calculation of formaldehyde production rates to more reduced carbon species, such as methanol, methane, and acetaldehyde. The experimental results of Bar-Nun and Chang (1983) are simulated as an aid in the construction of the photochemical scheme and as a way of validating the model. The results indicate that some fraction of CO2 and H2 present in the primitive atmosphere could have been converted to simple organic molecules. The exact amount is dependent on the partial pressure of CO2 and H2 in the atmosphere and on what assumptions are made concerning the shape of the absorption spectra of CO2 and H2O.

Wen, Jun-Shan↗
NASA NTRS1990

Comet Halley O(1D) and H2O production rates

Ground-based dual-etalon Fabry-Perot spectrometer observations have been made of Comet Halley's forbidden O I 6300 A emission. The 0.2 A resolution of the spectral scans was sufficient to resolve the O I forbidden line emissions from both nearby cometary NH2 and telluric emissions. On the basis of these measurements, the production rate Q of O(1D) was determined; it is then found, by taking into account the photodissociation of H2O and OH as sources of O(1D), that the ratio of H2O/O(1D) production rates is of the order of 6.

Magee-Sauer, K.↗
NASA NTRS1990

Hydrogen constituents of the mesosphere inferred from positive ions - H2O, CH4, H2CO, H2O2, and HCN

The concentrations in the mesosphere of H2O, CH4, H2CO, H2O2, and HCN were inferred from data on positive ion compositions, obtained from one mid-latitude and four high-latitude rocket flights. The inferred concentrations were found to agree only partially with the ground-based microwave measurements and/or model prediction by Garcia and Solomon (1985). The CH4 concentration was found to vary between 70 and 4 ppb in daytime and 900 and 100 ppbv at night, respectively. Unexpectedly high H2CO concentrations were obtained, with H2CO/H2O ratios between 0.0006 and 0.1, and a mean HCN volume mixing ratio of 6 x 10 to the -10th was inferred.

Kopp, E.↗
NASA NTRS1990

Fabry-Perot observations of Comet Halley H2O(+)

Fabry-Perot scanning spectrometer observations of Comet Halley's H2O(+) emissions have yielded 6158.64 and 6158.85 A spin doublet data at distances in the range of 0 to 2 million km from the comet heat in the antisunward direction. Cometary plasma outflow velocities were ascertained on the basis of the emissions' Doppler shifts, yielding results that were mostly but not exclusively consistent with the plasma's constant antisunward acceleration; the acceleration varied from night to night of observations over a 30-300 cm/sec range. The unusual plasma kinematics of December 14-15, 1985, and January 10, 1986, may be associated with the tail-disconnection activity observed by others.

Scherb, F.↗
NASA NTRS1990

Measurements of CH4, N2O, CO, H2O, and O3 in the middle atmosphere by the Atmospheric Trace Molecule Spectroscopy Experiment on Spacelab 3

The volume mixing ratios of five minor gases (CH4, N2O, CO, H2O, and O3) have been retrieved through the middle atmosphere from the analysis of 0.01/cm resolution infrared solar occultation spectra recorded near 28 deg N and 48 deg S latitudes with the Atmospheric Trace Molecule Spectroscopy instrument, flow on board Spacelab 3 (April 30 through May 6, 1985). The results are in general agreement with reported measurements from ground-, balloon-, and satellite-based instruments for the same seasons. In detail, the vertical profiles of these gases show the effects of the upper and middle atmospheric transport patterns dominant during the season of these observations. The profiles inferred at different longitudes around 28 deg N suggest a near-uniform zonal distribution of these gases, for conditions corresponding to late spring. The sunrise occultation measurements point to a larger longitudinal variability in the vertical distribution of these gases at 48 deg S.

Gunson, M. R.↗
NASA NTRS1990

The volume- and surface-binding energies of ice systems containing CO, CO2, and H2O

Laboratory-measured, temperature-dependent sticking efficiencies are presently used to derive the surface-binding energies of CO and CO2 on H2O-rich ices, with a view to determining the condensation and vaporization properties of these systems as well as to the measured energies' implications for both cometary behavior and the evolution of interstellar ices. The molecular volume and the surface binding energies are not found to be necessarily related on the basis of simple nearest-neighbor scaling in surface and bulk sites; this may be due to the physical constraints associated with matrix structure-associated physical constraints, which sometimes dominate the volume-binding energies.

Sandford, Scott A.↗
NASA NTRS1989

H2 extraction and H2O and O2 production from lunar soil

Direct extraction and reaction of the 50 ppm H found in mature lunar soil with a small fraction of the 1 percent ilmenite found in even the most Ti-poor lunar soils is a viable method of producing H2O2 and H2O for propellants and life support. A plant with a mass of approximately 62 metric tons can produce about 8 metric tons of LOX and 1.2 metric tons of LH2 per month. The concept is viable in even Ti-poor regions if the soils have long exposure to solar wind. The plant processes over 29,000 tons of soil with about 50 ppm H per month. The mine that feeds the plant excavates over 8600 sq m per month with a fleet of three front-end loaders and five haulers. Trade studies demonstrate that nuclear power accompanied by a high process plant duty cycle results in a far smaller installation than a solar-powered unit.

Simonds, Charles H.↗
NASA NTRS1991

Calculations of H2O microwave line broadening in collisions with He atoms - Sensitivity to potential energy surfaces

Theoretical computations of broadening parameters are reported for three microwave lines of H2O in a bath of He atoms. The potential-energy surfaces employed are corrected for basis-set superposition error, and their reliability is checked by repeating the calculations with a different basis set for orbital expansion. The results are presented in extensive tables and discussed in detail. The corrections applied are shown to have a significant impact on the accuracy of the room-temperature broadenings determined: 8.9 sq A for the 22.2-GHz line, 11.8 sq A for the 183,3-GHz line, and 10.0 sq A for the 380.2-GHz line, in good agreement with published experimental data. The importance of collisional broadening for the atmospheric transmission of radiation and for remote-sensing applications is indicated.

Green, Sheldon↗
NASA NTRS1991

The binding energies of Cu(+)-(H2O)n and Cu(+)-(NH3)n (n = 1-4)

The successive binding energies of up to four H2O and NH3 ligands to Cu(+) are computed at the self-consistent-field and modified coupled-pair functional levels. The most stable structures are those where all ligands are equivalent. Replacing Cu(+) by a point charge gives binding energies that are in good agreement with ab initio and experimental results, and is consistent with bonding that is largely charge dipole in nature. About two-thirds of the large reduction in ligand binding energy between the second and third ligand is due to ligand-ligand repulsion, while one-third is due to increased metal-ligand repulsion resulting from a loss of sd-sigma hybridization. The first and second ligand binding energies increase substantially at the correlated level due to an improved description of sd-sigma hybridization.

Bauschlicher, Charles W., Jr.↗