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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Hydrogen atom scrambling in ion-molecule reactions of methane and ethylene.

The extent of hydrogen atom exchange in the reaction, CH3(+) + CH4 yields C2H5(+) + H2, is determined by examining the product distribution for the reactions CH3(+) + CD4 and CD3(+) + CH4 as a function of relative kinetic energy from thermal energies to 10 eV. It is found that the reaction of CH4(+) with the parent neutral proceeds both via proton transfer and hydrogen abstraction accompanied by approximately 10% hydrogen atom exchange during the reaction.

Huntress, W. T., Jr.↗
NASA NTRS1993

Dynamics of flames near the rich-flammability limit of hydrogen-air mixtures

Flames near the rich-flammability limit of hydrogen-air mixtures are studied using a detailed, time-dependent, one-dimensional Lagrangian model. Results from the numerical simulations indicate that a steady burning velocity is not obtained for very rich hydrogen-air mixtures. As the amount of hydrogen is increased, a damped oscillation is observed in the flame and burning velocities, and then, with further increase in the amount of hydrogen, an undamped oscillation with a complex set of frequencies is observed. Simulations with a simplified one-step irreversible chemical reaction do not show these oscillations, suggesting that chemical kinetics plays a strong role in inducing these oscillations. Further analysis shows that the oscillations are due to a competition for H atoms between chain branching and chain-terminating reactions. Simulations of spherically expanding flames suggest that stretch effects (due to curvature) will cause the oscillations to occur in less rich mixtures than that observed for planar flames. The implications of these oscillations on the rich-flammability limit as well as the role of chemical kinetics in creating a fundamental flammability limit is discussed.

Kailasanath, K.↗
NASA NTRS1997

Kinetics of the Reactions of F((sup 2)P) and Cl((sup 2)P) with HNO3

The kinetics of the reactions of HNO3 with fluorine (k(sub 1)) and Chlorine (k(sub 2)) atoms have been studied by using a time-resolved long-path laser absorption technique to monitor the appearance of product NO3 radicals following 351-nm pulsed laser photolysis of X2/HNO3/He mixtures (X = F,Cl). Absolute rate coefficients for the F((sup 2)P) + HNO reaction have been determined over the temperature range 260-373 K. Between 260 and 320 K, the data are adequately represented by the Arrhenius expression k(sub 1)(T) = (6.0 +/- 2.6) x 10(exp -12) exp[(40 +/- 120)/T]cu cm/(molecule.s). Between 335 and 373 K, the rate coefficient is found to be (2.0 +/- 0.3) x 10(exp -11)cu cm/(molecule.s) independent of temperature. The observed temperature dependence suggests that reaction proceeds via competing direct abstraction and complex pathways. No NO3 production was observed in the experiments with X equals Cl, thus establishing that k(sub 2)(298 K) is less than 2 x 10(exp -16) cu cm/(molecule.s). The Cl((sup 2)P) + HNO reaction was also investigated by using a pulsed laser photolysis-resonance fluorescence technique to monitor the decay of Cl((sup 2)P). Upper limit values for k(sub 2) obtained from these experiments, in units of 10(exp -16)cu cm/(molecule.s), are 13 at 298 K and 10 at 400 K.

Wine, P. H.↗
NASA NTRS2001

Coarsening Experiment Being Prepared for Flight

The Coarsening in Solid-Liquid Mixtures-2 (CSLM-2) experiment is a materials science space flight experiment whose purpose is to investigate the kinetics of competitive particle growth within a liquid matrix. During coarsening, small particles shrink by losing atoms to larger particles, causing the larger particles to grow. In this experiment, solid particles of tin will grow (coarsen) within a liquid lead-tin eutectic matrix. The preceding figures show the coarsening of tin particles in a lead-tin eutectic as a function of time. By conducting this experiment in a microgravity environment, we can study a greater range of solid volume fractions, and the effects of sedimentation present in terrestrial experiments will be negligible. The CSLM-2 experiment is slated to fly onboard the International Space Station. The experiment will be run in the Microgravity Science Glovebox installed in the U.S. Laboratory module.

Hickman, J. Mark↗
NASA NTRS2003

Coarsening Experiment Prepared for Flight

The Coarsening in Solid-Liquid Mixtures-2 (CSLM-2) experiment is a materials science spaceflight experiment whose purpose is to investigate the kinetics of competitive particle growth within a liquid matrix. During coarsening, small particles shrink by losing atoms to larger particles, causing the larger particles to grow. In this experiment, solid particles of tin will grow (coarsen) within a liquid lead-tin eutectic matrix. The following figures show the coarsening of tin particles in a lead-tin (Pb-Sn) eutectic as a function of time. By conducting this experiment in a microgravity environment, we can study a greater range of solid volume fractions, and the effects of sedimentation present in terrestrial experiments will be negligible. The CSLM-2 experiment flew November 2002 on space shuttle flight STS-113 for operation on the International Space Station, but it could not be run because of problems with the Microgravity Science Glovebox in the U.S. Laboratory module. Additional samples will be sent to ISS on subsequent shuttle flights.

Hickman, J. Mark↗
NASA NTRS1994

Small UHV compatible hyperthermal oxygen atom generator

A high purity, hyperthermal, continuous beam atomic oxygen source capable of retrofitting to existing UHV systems has been developed. The instrument complements a general system capability, while its small size and simplicity of design permits tailoring the instrument for most experimental geometries. The flux level presently available is near 1 x 10 (exp 14) cm(exp -2)s(exp -1)(3P) but may be extended toward the theoretical limit of 3x10(exp 15 cm(exp -2)s(exp -1). The energy distribution of the emitted neutrals shows that the mean kinetic energy is about the same as observed for the ions or about 4 eV. The energy of the oxygen atoms may be substantially reduced for other applications by collision with a temperature controlled, non-reactive surface (with a concomitant spread in the energy distribution).

Outlaw, Ronald A.↗
NASA NTRS1979

Reaction between nitric oxide and ozone in solid nitrogen

Nitrogen dioxide, NO2, is produced when nitric oxide, NO, and ozone, O3, are suspended in a nitrogen matrix at 11-20 K. The NO2 is formed with first-order kinetics, a 12 K rate constant of (1.4 + or - 0.2) x 0.00001/sec, and an apparent activation energy of 106 + or - 10 cal/mol. Isotopic labeling, variation of concentrations, and cold shield experiments show that the growth of NO2 is due to reaction between ozone molecules and NO monomers, and that the reaction is neither infrared-induced nor does it seem to be a heavy atom tunneling process. Reaction is attributed to nearest-neighbor NO.O3 pairs probably held in a specific orientational relationship that affects the kinetic behavior. When the temperature is raised, more such reactive pairs are generated, presumably by local diffusion. Possible mechanisms are discussed.

Lucas, D.↗
NASA NTRS1990

Rate constant for reaction of atomic hydrogen with germane

Due to the interest in the chemistry of germane in the atmospheres of Jupiter and Saturn, and because previously reported kinetic reaction rate studies at 298 K gave results differing by a factor of 200, laboratory measurements were performed to determine the reaction rate constant for H + GeH4. Results of the study at 298 K, obtained via the direct technique of flash photolysis-resonance fluorescence, yield the reaction rate constant, k = (4.08 + or - 0.22) x 10(exp -12) cu cm/s.

Nava, David F.↗
NASA NTRS1983

Kinetic modeling of an IBr solar pumped laser

The possibility of using an IBr laser as a solar-energy converter is examined theoretically, and reasons for its choice are given. Broadband absorption results in dissociation with the formation of excited metastable Br atoms, some of which then lase to the ground state Br. The ground state is depopulated by three-body recombination and, more importantly, by exchange reactions which more than compensate for the high quenching in heteronuclear halogen systems. Kinetic modeling indicates lasing is possible in the pulsed mode and possibly in the steady state with a cooled gas flow system. Temperature effects are discussed. The efficiency of the laser approaches 1.2 percent at optical thicknesses large enough for complete absorption of the photons.

Harries, W. L.↗
NASA NTRS1979

Venus upper atmosphere neutral gas composition - First observations of the diurnal variations

Measurements of the composition, temperature, and diurnal variations of the major neutral constituents in the thermosphere of Venus are being made with a quadrupole mass spectrometer on the Pioneer Venus Orbiter. Concentrations of carbon dioxide, carbon monoxide, molecular nitrogen, atomic oxygen, and helium are presented, in addition to an empirical model of the data. The concentrations of the heavy gases, carbon dioxide, carbon monoxide, and molecular nitrogen, rapidly decrease from the evening terminator toward the nightside; the concentration of atomic oxygen remains nearly constant and the helium concentration increases, an indication of a nightside bulge. The kinetic temperature inferred from scale heights drops rapidly from 230 K at the terminator to 130 K at a solar zenith angle of 120 deg, and to 112 K at the antisolar point.

Niemann, H. B.↗
NASA NTRS1982

The detailed chemistry and thermodynamics of sodium in oxygen-rich flames

Measurement of sodium and OH concentrations in ten oxygen-rich H2/O2/N2 flames by respective saturated and low-power laser induced fluorescence techniques have permitted a detailed examination of the pronounced flame chemistry of sodium in such oxygen rich media. Previous interpretations have been shown to be largely incomplete or in error. The flame downstream profiles indicate that the amount of free sodium tracks the decay of H-atom and as the flame radicals decay sodium becomes increasingly bound in a molecular form. A detailed kinetic model indicates that the sodium is distributed between NaOH and NaO2 species. Concentrations of NaO are very small and NaH negligible. The actual distribution is controlled by the state of equilibrium of the flames' basic free radicals. Na, NaO2 and NaOH are all coupled to one another by fast reactions which can rapidly interconvert one to another as flame conditions vary. Above about 2000K, NaOH becomes dominant whereas NaO2 plays an increasingly important contribution at lower temperatures.

Hynes, A. J.↗
NASA NTRS1985

Scattering and stopping of hadrons in nuclear matter

It was observed, in the 180 litre xenon bubble chamber, that when hadrons with kinetic energy higher than the pion production threshold fall on a layer of nuclear matter - on an atomic nucleus in other words - in many cases they can pass through it without causing particles production but they are deflected through some deflection angles; if the energy is lower than a few GeV and the nuclear matter layer is thick enough, the hadrons can be stopped in it. The amount of the deflection at a given incident hadron energy varies with the way the hadron strikes the atomic nucleus; the probability of the occurrence of stopping depends on the incident hadron identity and energy, and on the way the hadron passed through the nucleus, as well.

Strugalski, Z.↗
NASA NTRS1980

Emission line shapes produced by dissociative excitation of atmospheric gases

The spectral line shapes of the radiation emitted from O atoms produced by the dissociative excitation of O2, CO, CO2 and NO are investigated. Doppler line shapes are derived from time-of-flight spectra of O (5S0) atoms decaying by the emission of 1356-A radiation after being produced in electron impact experiments at incident electron energies from 25 to 300 eV. It is shown that the effective line width of the radiation is large compared with the Doppler absorption widths of ambient O atoms in both photoelectron and auroral excitation, and thus the dissociatively excited component of the O I 1304-A airglow will behave as though it were optically thin, exhibiting pronounced limb brightening effects and a scale height characteristic of the initial, local source function. It is found that the average kinetic energy of the dissociation fragments inferred from O I (5S) time-of-flight spectra is in good agreement with that of O I (3S) atoms in the electron impact dissociation of CO2, although not for O2. Finally, it is suggested that although electron impact dissociation of CO and CO2 contributes to the 1304-A emission in the upper atmosphere of Venus, it cannot be the dominant source of this radiation since the absolute cross sections for the reaction are too small.

Zipf, E. C.↗
NASA NTRS1985

Transport properties for some atom-ion interactions in air

The thermal conductivity and viscosity for the N-N(+) and O-O(+) interactions have been calculated, using the kinetic theory of gases, from 500 K-20,000 K. Accurate spectroscopically determined potentials have been used for the calculations. The results are compared with previous results obtained using less accurate potentials.

Biolsi, L.↗
NASA NTRS2005

A Kinetic and Product Study of the Cl + HO2 Reaction

Absolute rate data and product branching ratios for the reactions Cl + HO2 to HCl + O2 (k1a) and Cl + HO2 to OH + ClO (k1b) have been measured from 226 to 336 K at a total pressure of 1 Torr of helium using the discharge flow resonance fluorescence technique coupled with infrared diode laser spectroscopy. For kinetic measurements, pseudo-first-order conditions were used with both reagents in excess in separate experiments. HO2 was produced by two methods: through the termolecular reaction of H atoms with O2 and also by the reaction of F atoms with H2O2. Cl atoms were produced by a microwave discharge of Cl2 in He. HO2 radicals were converted to OH radicals prior to detection by resonance fluorescence at 308 nm. Cl atoms were detected directly at 138 nm also by resonance fluorescence. Measurement of the consumption of HO2 in excess Cl yielded k1a and measurement of the consumption of Cl in excess HO2 yielded the total rate coefficient, k1. Values of k1a and k1 derived from kinetic experiments expressed in Arrhenius form are (1.6 +/- 0.2) x 10-11 exp[(249 +/- 34)/T] and (2.8 +/- 0.1) x 10-11 exp[(123 +/- 15)/T] cm3 molecule-1 s-1, respectively. As the expression for k1 is only weakly temperature dependent, we report a temperature-independent value of k1 = (4.5 +/- 0.4) x 10-11 cm3 molecule-1 s-1. Additionally, an Arrhenius expression for k1b can also be derived: k1b = (7.7 +/- 0.8) x 10-11 exp[-(708 +/- 29)/T] cm3 molecule-1 s-1. These expressions for k1a and k1b are valid for 226 K T 336 and 256 K T 296 K, respectively. The cited errors are at the level of a single standard deviation. For the product measurements, an excess of Cl was added to known concentrations of HO2 and the reaction was allowed to reach completion. HCl product concentrations were determined by IR absorption yielding the ratio k1a/k1 over the temperature range 236 K T 296 K. OH product concentrations were determined by resonance fluorescence giving rise to the ratio k1b/k1 over the temperature range 226 K T 336 K. Both of these ratios were subsequently converted to absolute numbers. Values of k1a and k1b from the product experiments expressed in Arrhenius form are (1.5 +/- 0.1) x 10-11 exp[(222 +/- 17)/T] and (10.6 +/- 1.5) x 10-11 exp[-(733 +/- 41)/T] cm3 molecule-1 s-1, respectively. These expressions for k1a and k1b are valid for 256 K T 296 and 226 K T 336 K, respectively. A combination of the kinetic and product data results in the following Arrhenius expressions for k1a and k1b of (1.4 +/- 0.3) x 10-11 exp[(269 +/- 58)/T] and (12.7 +/- 4.1) x 10-11 exp[-(801 +/- 94)/T] cm3 molecule-1 s-1, respectively. Numerical simulations were used to check for interferences from secondary chemistry in both the kinetic and product experiments and also to quantify the losses incurred during the conversion process HO2 to OH for detection purposes.

rate constants↗
NASA NTRS1973

The San Marco 3 neutral atmosphere composition experiment

The experimental instrumentation of the San Marco 3 satellite is described along with the calibration and operation. The instrumentation for the following experiments was included: an air density experiment for measuring the instantaneous drag force, and thus the neutral particle total mass density; a neutral atmosphere composition experiment for measuring the densities of helium, atomic and molecular oxygen, molecular nitrogen and argon; and a neutral atmosphere temperature experiment to determine the gas kinetic temperature by measuring molecular nitrogen density variations in an orificed spherical chamber as a function of angle of attack.

Pelz, D. T.↗
NASA NTRS1989

Making Excited Oxygen Molecules And Atoms

Oxidation of semiconductors and high-temperature superconductors achieved at lower temperatures by use of oxygen molecules or atoms raised into specific excited states. Use of excited oxygen (or other species) of interest in research on kinetics and mechanisms of chemical reactions. Used in ultra-high-vacuum chamber also equipped for such surface-analytical techniques as x-ray photoelectron spectroscopy.

Vasquez, Richard P.↗