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At least 253 records · Page 14

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NASA NTRS1983

Reactions of NaCl with Gaseous SO3, SO2, and O2

Hot corrosion of gas turbine engine components involves deposits of Na2SO4 which are produced by reactions between NaCl and oxides of sulfur. For the present investigation, NaCl single crystals were exposed at 100 to 850 C to gaseous mixtures of SO3, SO2, and O2. The products formed during this exposure depend, primarily, on the temperatures. The four product films were: NaCl-SO3; Na2S2O7; Na2SO4; and NaCl-Na2SO4. The kinetics of the reactions were measured.

Fielder, W. L.↗

NASA NTRS1984

Low-energy proton stopping power of N2, O2 and water vapor and deviations from Bragg's rule

A modified local plasma model, based on the works of Lindhard and Winther; and Bethe, Brown, and Walske, is established. The Gordon-Kim model for molecular electron density is used to calculate stopping power of N2, O2, and water vapor for protons of energy ranging from 40 keV to 2.5 MeV, resulting in good agreement with experimental data. Deviations from Bragg's rule are evaluated and are discussed under the present theoretical model.

Xu, Y. J.↗

NASA NTRS1983

Spatially and spectrally resolved multipoint coherent anti-Stokes Raman scattering from N2 and O2 flows

Single-shot spectrally resolved broadband rotational coherent anti-Stokes Raman scattering (CARS) from multiple points along a line intersecting a flow has been observed for N2 and O2. A large-angle phase-matching configuration was used to achieve spatial resolution of 0.1 mm x 0.1 mm x 0.1 mm for each of 20 points in the interaction volume. Single-shot multipoint CARS of N2 at different temperatures and of several species in a coflowing jet was observed.

Snow, J. B.↗

NASA NTRS1984

Feasibility of measuring temperature and density fluctuations in air using laser-induced O2 fluorescence

A tunable line-narrowed ArF laser can selectively excite several rotation al lines of the Schumann-Runge band system of O2 in air. The resulting ultraviolet fluorescence can be monitored at 90 deg to the laser beam axis, permitting space and time resolved observation of density and temperature fluctuations in turbulence. Experiments and calculations show that + or - 1 K, + or - 1 percent density, 1 cu mm spatial, and 1 microsecond temporal resolution can be achieved simultaneously under some conditions.

Massey, G. A.↗

NASA NTRS1984

Kinetics of the reaction O + ClO yields Cl + O2

The bimolecular rate constant for the reaction O + ClO yields Cl + O2 has been measured over the temperature range 236-422 K in a discharge flow system using atomic oxygen resonance fluorescence at 130 nm to monitor the decay of O in an excess of ClO. The results are found to be independent of the method used to produce the ClO radical. At 296 K, the rate constant is given by (3.6 + or - 0.7) x 10 to the -11th cu cm/sec and the temperature dependence expressed in Arrhenius form by k2 = (5.0 + or - 1.0) x 10 to the -11th exp-(96 + or - 20)/T cu cm/sec. The results are compared with earlier values, and the implications for stratospheric chemistry are discussed briefly.

Leu, M.-T.↗

NASA NTRS1984

Radiative lifetimes of the second negative system of O2(+)

The dipole moment of the A2Pi(u)-X2Pi(g) transition of O2(+) is calculated as a function of internuclear distance using ab initio methods. The band absorption oscillator strengths and band transition probabilities of the second negative system are derived and the resulting lifetimes are compared with experimental data. The high-lying v double prime levels of the ground state may decay into low-lying v prime levels of the excited state. The corresponding radiative lifetimes are calculated.

Wetmore, R. W.↗

NASA NTRS1984

Reactions of NaCl with gaseous SO3, SO2, and O2

Fielder, W. L.↗

NASA NTRS1984

Kinetics of the reaction O + ClO yields Cl + O2

The kinetics of the reaction O + ClO yields Cl + O2 (k1) were studied by using resonance fluorescence to monitor the decay of O atoms which had been generated from the laser photolysis of ClO. A discharge flow system was used to generate the ClO and its concentration was measured directly by multipass absorption spectrometry. The results are k1(298) = (4.2 + or -0.8) x 10 to the -11th cu cm/s (including systematic errors) with E/R determined to lie in the range + or - 200 K. The literature data are reviewed and a composite value of k1(T) = 6.0 x 10 to the -11th exp-(100/T) is recommended for stratospheric modeling calculations. The atmospheric implications of the revised rate constant are discussed briefly.

Margitan, J. J.↗

NASA NTRS1985

Self-shielding in O2 - A possible explanation for oxygen isotopic anomalies in meteorites?

The production of isotopic effects in oxygen due to self-shielding of photolysing radiation by the Schumann-Runge bands of (O-16)2 is investigated. The model studied is the simple case of incoming radiation falling on a gaseous medium of uniform composition. The enhancement of O-17 and O-18 production upon photodissociation of O2 is calculated for various column densities, and its dependence on temperature and the presence of other molecules is examined. The issue of whether the products of photolysis can be trapped and thus preserve a peculiar isotopic composition is discussed.

Navon, O.↗

NASA NTRS1985

Differential scattering cross sections for collisions of 0.5-, 1.5-, and 5.0-keV helium atoms with He, H2, N2, and O2

This paper reports the first results of an experimental program established to provide cross section data for use in modeling various atmospheric processes. Absolute cross sections, differential in the scattering angle, have been measured for collisions of 0.5-, 1.5-, and 5.0-keV helium atoms with He, H2, N2, and O2 at laboratory scattering angles between 0.1 deg and 5 deg. The results are the sums of cross sections for elastic and inelastic scattering of helium atoms; charged collision products are not detected. Integration of the differential cross section data yields integral cross sections consistent with measurements by other workers. The apparatus employs a position-sensitive detector for both primary and scattered particles and uses a short target cell with a large exit aperture to ensure a simple and well-defined apparatus geometry.

Newman, J. H.↗

NASA NTRS1985

Rate constants for the quenching of metastable O2 (1Sigma g +) molecules

The O2 (1Sigma g +) rates for CO2, H2, N2, Cl2, CO, O3, and 2,3 DMB-2 are determined by monitoring the 762-nm emission in a fast-flow-discharge chemiluminescence detection system (Leu, 1984; Leu and Smith, 1981). The results are presented in tables and graphs and briefly characterized. The rate constants (in cu cm/s x 10 to the -16th) are 4600 + or - 500 for CO2, 7000 + or - 300 for H2, 17 + or - 1 for N2, 4.5 + or - 0.8 for Cl2, 45 + or - 5 for CO, 220,000 + or - 30,000 for O3, and 6000 + or - 100 for 2,3 DMB-2. The temperature dependence of the CO2 and O3 quenching reactions at 245-362 K is found to be negligible.

Kwang, Y. C.↗

NASA NTRS1986

Calculated potential surfaces for the reactions: O + N2 yields NO + N and N + O2 yields NO + O

Complete Active Space SCF/Contracted CI (CASSCF/CCI) calculations, using large Gaussian basis sets, are presented for selected portions of the potential surfaces for the reactions in the Zeldovich mechanism for the conversion of N2 to NO. The N + O2 reaction is exoergic by 32 kcal/mole and is computed to have an early barrier of 10.2 kcal/mole for the (sup 2)A(sup prime) surface and 18.0 kcal/mole for the (sup 4)A(sup prime) surface. The O + N2 reaction is endoergic by 75 kcal/mole. The (sup 3)A(sup double prime) surface is calculated to have a late barrier of 0.5 kcal/mole, while the (sup 3)A(sup prime) surface is calculated to have a late barrier of 14.4 kcal/mole.

Walch, Stephen P.↗

NASA NTRS1987

The production of O(1D) from dissociative recombination of O2(+)

The results of large scale ab initio calculations of the rates for production of O(1D) by dissociative combination of O2(+) are presented for electron temperatures in the range 100 to 3000 K. A 1-delta-u state is the dominant dissociative route from v = 0 and a 3-sigma-u(-) state is the most important route from v = 1 and v = 2. The calculated total rate for O(1D) production from v = 0 is 2.21(+0.21,-0.24) x 10(-7) x (T sub e/300) exp -.46 near room temperature. The v = 1 and v = 2 rates are about 17% and 47% smaller respectively, than the v = 0 rate at 300 K.

Guberman, Steven L.↗

NASA NTRS1986

Differential cross sections for scattering of 0.5-, 1.5-, and 5.0-keV hydrogen atoms by He, H2, N2, and O2

This paper reports measurements of absolute cross sections, differential in angle, for scattering of 0.5-, 1.5-, and 5.0-keV hydrogen atoms by He, H2, N2, and O2 at laboratory scattering angles between 0.1 and 5 deg. The measured cross sections are the sums of those for elastic and inelastic collisions having a fast H atom product and are needed for calculating energy transfer to the upper atmosphere from precipitating ring current particles.

Newman, J. H.↗

NASA NTRS1986

A model of the Schumann-Runge continuum of O2

Ab initio calculations of the B3Sigma sub u(-) potential energy curve of O2 are reported together with the transition moment connecting the B3Sigma sub u(-) and the ground electronic states. Photodissociation cross sections are presented over the wavelength region 127-152 nm. Small adjustments to the potential energy curve and the transition moment lead to a model of the absorption which agrees well with the experimental cross sections and which reproduces the structural features observed on the high-energy edge. The shoulder at 135.6 nm is attributed to the lowest 3Pi sub u state and the auxiliary maxima to transitions into the B3Sigma sub u(-) state.

Allison, A. C.↗

NASA NTRS1987

Full CI benchmark calculations on N2, NO, and O2 - A comparison of methods for describing multiple bonds

Full configuration interaction (CI) calculations on the ground states of N2, NO, and O2 using a DZP Gaussian basis are compared with single-reference SDCI and coupled pair approaches (CPF), as well as with CASSCF multireference CI approaches. The CASSCF/MRCI technique is found to describe multiple bonds as well as single bonds. Although the coupled pair functional approach gave chemical accuracy (1 kcal/mol) for bonds involving hydrogen, larger errors occur in the CPF approach for the multiple bonded systems considered here. CI studies on the 1Sigma(g +) state of N2, including all single, double, triple, and quadruple excitations show that triple excitations are very important for the multiple bond case, and accounts for most of the deficiency in the coupled pair functional methods.

Bauschlicher, Charles W., Jr.↗

NASA NTRS1987

Differential cross sections for scattering of 0.5-, 1.5-, and 5.0 keV oxygen atoms by He, N2, and O2

This paper reports measurements of absolute scattering cross sections, differential in angle, for collisions of ground-state oxygen atoms with He, N2, and O2. Data are presented for scattering of 0.5-, 1.5-, and 5.0-keV oxygen-atom projectiles in the range of laboratory frame angles between 0.06 and 5 deg. These measurements provide information relevant to calculations of the aeronomic consequences of O(+) precipitation in the earth's upper atmosphere.

Schafer, D. A.↗

NASA NTRS1987

The calculation of high-temperature equilibrium and nonequilibrium specific heat data for N2, O2 and NO

Specific heat data for high-temperature air species are needed to compute the temperature and enthalpy of gas mixtures in aerothermodynamics flowfield calculations. Accurate data are known only for temperatures under 6000 K, but are required for temperatures exceeding 25,000 K. In the present study, CP data are computed for N2, O2 and NO. The calculations are based on summations over all the vibration-rotation energy levels for all known bound electronic states. Estimates are made for the error introduced by the neglect of possible additional high-lying electronic states. In addition, a scheme for the partitioning of the internal energy into vibrational, rotational and electronic contributions is presented which consistently accounts for the nonseparable nature of the various energy modes. The multitemperature specific heat data are recommended for use in nonequilibrium flowfield models.

Jaffe, Richard L.↗