Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “RADICALS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Free radical propulsion concept

A free radical propulsion concept utilizing the recombination energy of dissociated low molecular weight gases to produce thrust was examined. The concept offered promise of a propulsion system operating at a theoretical impulse, with hydrogen, as high as 2200 seconds at high thrust to power ratio, thus filling the gas existing between chemical and electrostatic propulsion capabilities. Microwave energy used to dissociate a continuously flowing gas was transferred to the propellant via three body recombination for conversion to propellant kinetic energy. Power absorption by the microwave plasma discharge was in excess of 90 percent over a broad range of pressures. Gas temperatures inferred from gas dynamic equations showed much higher temperatures from microwave heating than from electrothermal heating. Spectroscopic analysis appeared to corroborate the inferred temperatures of one of the gases tested.

Hawkins, C. E.↗
NASA NTRS1981

Chlorine monoxide radical, ozone, and hydrogen peroxide - Stratospheric measurements by microwave limb sounding

Profiles of stratospheric ozone and chlorine monoxide radical (ClO) have been obtained from balloon measurements of atmospheric limb thermal emission at millimeter wavelengths. The ClO measurements, important for assessing the predicted depletion of stratospheric ozone by chlorine from industrial sources, are in close agreement with present theory. The predicted decrease of ClO at sunset was measured. A tentative value for the stratospheric abundance of hydrogen peroxide was also determined.

Waters, J. W.↗
NASA NTRS1981

Reactions of ethynyl radicals - Rate constants with CH4, C2H6, and C2D6

An experiment to measure ethynyl radical reactivity with other simple molecules is described. Flash photolysis of CF3C2H, a C2H precursor, was kinetically and spectroscopically analyzed for C2H reactions with CH4, C2H6, and C2D6 and rate constants for the abstraction reaction at room temperature were determined. The experimental apparatus is described, and the acetylene feedstock purification procedures are outlined. Rate constants are provided, and additional examination of the effects of added helium showed no alterations over the pressure range 20-700 torr.

Laufer, A. H.↗
NASA NTRS1982

The temperature dependence of the rate constant for the reaction of hydroxyl radicals with nitric acid

The rate constant for the reaction of hydroxyl radicals with nitric acid in the 225-443 K temperature range has been measured by means of the flash photolysis resonance fluorescence technique. Above 300 K, the rate constant levels off in a way that can only be explained by the occurrence of two reaction channels, of which one, operative at low temperatures, proceeds through the formation of an adduct intermediate. The implications of these rate constant values for stratospheric reaction constants is discussed.

Kurylo, M. J.↗
NASA NTRS1982

The far-infrared spectrum of the OH radical

It is thought likely that the study of spectral lines in the far-infrared might provide at least as much information about the physics and chemistry of the interstellar environment as radioastronomy. However, by comparison with the microwave region, the far-infrared is largely unexplored. There is a pressing need for good laboratory data to aid searches and assignments of spectra from the interstellar clouds and nebulae. Brown et al. (1981) have conducted a study of the laser magnetic resonance (LMR) spectrum of the OH radical in its ground state at far-infrared wavelengths. The present investigation is concerned with the computation of the frequencies of individual hyperfine transitions involving all rotational levels up to J = 4 1/2. The results of the calculation are presented in a table. The results are summarized in a diagram which shows the low-lying energy levels of OH. The frequencies of transitions between levels studied directly in the LMR spectrum are quite reliable.

Brown, J. M.↗
NASA NTRS1982

Kinetics of the reaction of hydroxyl radicals with nitric acid

An extensive study was made of the reaction of hydroxyl radicals with nitric acid in a laser photolysis-resonance fluorescence system. A 266 nm laser was used to photolyze HNO3 in the temperature range 225-415 K at pressures of 20-300 torr. A temperature dependence was detected below room temperature, with a leveling off at 298 K and a wide spread in the rate constants. A pressure dependence was observed over the entire range and was more pronounced at lower temperatures. The results are noted to be in agreement with those of previous investigations. However, the wide range of rate constants are suggested to be a problem for stratospheric HO(x) modeling for anthropogenic effects. No explanation could be given of the varying results obtained by other investigators regarding the kinetics of the reactions.

Margitan, J. J.↗
NASA NTRS1983

Balloon borne LIDAR measurements of stratospheric hydroxyl radical

A balloon-borne laser radar (LIDAR) system for determining the stratospheric hydroxyl radical concentration constructed and flown by the Goddard Space Flight Center is discussed. The system measured hydroxyl in the altitude range of 34-37 km during an afternoon and early evening, producing the first post-sunset hydroxyl determination ever obtained. Daytime values (approximately 5 x 10 to the 6th/cu cm) are somewhat lower than previous measurements using in situ resonance fluorescence. Nighttime values (approximately 7 x 10 to the 5th/cu cm at 2100 CDT) are found to be higher than predicted by current one-dimensional models. Possible sources of these discrepancies, together with improvements possible in future systems, are outlined.

Heaps, W. S.↗
NASA NTRS1983

New technological developments for the remote detection of atmospheric hydroxyl radicals

New developments in the areas of narrowband tunable excimer lasers, high-resolution high-rejection optical filters, and wavelength measurement devices are considered for application to the remote sensing of atmospheric hydroxyl radicals. The conclusion is that an increase in the SNR of 10,000 could readily be gained through the use of these new devices. Also, considerable reductions in size and electrical energy consumption could be realized.

Mcdermid, I. S.↗
NASA NTRS1984

The role of surface generated radicals in catalytic combustion

The role of surface generated OH radicals in determining the catalytic ignition characteristics for propane oxidation on platinum were studied. The experiments were conducted in a stacked-plate, catalyst bed. Transient measurements, during catalytic ignition, of the catalyst's axial temperature profile were made and the effect of equivalence ratio, inlet temperature and inlet velocity was investigated. These measurements will provide insights which will be useful in planning and interpreting to OH measurements. Attempts to measure OH concentration in the catalyst bed using resonance absorption spectroscopy were unsuccessful, indicating that OH concentrations are below 10 to the 16th power/cc but still possibly above equilibrium values. Measurements are currently underway using forward scatter laser induced fluorescence which should extend the OH detection limits several orders of magnitude below the equilibrium concentrations.

Santavicca, D. A.↗
NASA NTRS1983

Laboratory detection of the C3N an C4H free radicals

The millimeter-wave spectra of the linear carbon chain free radicals C3N and C4H, first identified in IRC + 10216 and hitherto observed only in a few astronomical sources, have been detected with a Zeeman-modulated spectrometer in laboratory glow discharges through low pressure flowing mixtures of N2 + HC3N and He + HCCH, respectively. Four successive rotational transitions between 168 and 198 GHz have been measured for C3N, and five rotational transitions between 143 and 200 GHz for C4H; each is a well-resolved spin doublet owing to the unpaired electron present in both species. Precise values for the rotational, centrifugal distortion, and spin doubling constants have been obtained, which, with hyperfine constants derived from observations of the lower rotational transitions in the astronomical source TMC 1, allow all the rotational transitions of C3N and C4H at frequencies less than 300 GHz to be calculated to an absolute accuracy exceeding 1 ppm.

Gottlieb, C. A.↗
NASA NTRS1985

A measurement of the vibrational band strength for the upsilon sub 3 band of the HO2 radical

The HO2 radicals generated in a discharge-flow system were observed with tunable diode laser absorption in the P-branch of the nu(3) vibrationall band at 1080/cm. The observed line positions agree with those calculated from the molecular constants for the nu(3) bland obtained from a previous study using laser magnetic resonance spectroscopy. The band strength was determined by observing line center absoptions when HO2 is produced in the reaction F + H2O2 yields HO2 + HF (k1) with a measured concentration of atomic fluorine and excess hydrogen peroxide. F-atom concentrations are measured by diode laser absorption of the spin-orbit transition at 404/cm. The analysis accounts for HO2 losses due to the reactions of HO2 + HO2 yields H2O2 + O2 (k3) and F + HO2 yields HF + O2 (k4). The line strength for the 6(15) 7(16) F(1) transition is 2.9 x 10 to the 21st power sq cm/molecule/cm which corresponds to a nu(3) band strength of 34 +/- 9 sq/cm(STP atm). This value is a factor of 6 lower than previous ab initio calculations. These results will be useful in assessing the feasibility of atmospheric measurements of HO2 using infrared absorption techniques.

Zahniser, M. S.↗
NASA NTRS1984

The far-infrared laser magnetic resonance spectrum of the SiH radical and determination of ground state parameters

The far-infrared laser magnetic resonance spectrum of the SiH radical in the v = O level of its X2Pi state has been recorded. The signals are rather weak. The molecules were generated in the reaction between fluorine atoms and SiH4. Rotational transitions have been detected in both 2Pi1/2 and 2Pi3/2 spin components but no fine structure transitions between the spin components were observed. Proton hyperfine splittings were resolved on some lines. The measurements have been analyzed, subjected to a least-squares fit using an effective Hamiltonian, and the appropriate molecular parameters determined. The weakness of the spectrum and the failure of attempts to power saturate favorable lines are both consistent with a small value for the electric dipole moment for SiH.

Brown, J. M.↗
NASA NTRS1984

Temperature and pressure dependence of the absolute rate constant for the reactions of NH2 radicals with acetylene and ethylene

The absolute rate constants for the reaction between the NH2 free radical and acetylene and ethylene is measured experimentally using a flash photolysis technique. The constant is considered to be a function of temperature and pressure. At each temperature level of the experiment, the observed pseudo-first-order rate constants were assumed to be independent of flash intensity. The results of the experiment indicate that the bimolecular rate constant for the NH2 + C2H2 reaction increases with pressure at 373 K and 459 K but not at lower temperatures. Results near the pressure limit conform to an Arrhenius expression of 1.11 (+ or -) 0.36 x 10 to the -13th over the temperature range from 241 to 459 K. For the reaction NH2 + C2H4, a smaller rate of increase in the bimolecular rate constant was observed over the temperature range 250-465 K. The implications of these results for current theoretical models of NH2 + C2H2 (or H4) reactions in the atmospheres of Jupiter and Saturn are discussed.

Bosco, S. R.↗
NASA NTRS1984

The CN radical in diffuse interstellar clouds

A survey of 15 lines of sight for the CN B2Sigma(+) X2Sigma(+) interstellar absorption lines shows that the CN column density in diffuse interstellar clouds follows the relation log N(CN) is proportional to m log N(H2), where m is approximately equal to 3. This result is reproduced by a reaction network in which CN is produced primarily from C2 by the neutral-neutral reaction C2 + N yields CN + C, and photodissociation is the main destruction pathway for the neutral molecules CH, C2, and CN. The CN radical is the first molecular species observed in diffuse clouds that requires a neutral-neutral reaction for its formation in the gas phase. The network also reproduces the observed ratio N(CN)/N(H2).

Federman, S. R.↗
NASA NTRS1985

A potential-energy surface study of the 2A1 and low-lying dissociative states of the methoxy radical

Accurate, ab initio quantum chemical techniques are applied in the present study of low lying bound and dissociative states of the methoxy radical at C3nu conformations, using a double zeta quality basis set that is augmented with polarization and diffuse functions. Excitation energy estimates are obtained for vertical excitation, vertical deexcitation, and system origin. The rate of methoxy photolysis is estimated to be too small to warrant its inclusion in atmospheric models.

Jackels, C. F.↗
NASA NTRS1985

Observations of the SiC2 radical toward IRC + 10216 at 1.27 centimeters

The first centimeter-wave transition of the recently identified SiC2 radical has been observed in the envelope of the evolved carbon star IRC + 10216. The excellent agreement between the measured astronomical rest frequency and the predicted frequency, and the measured line intensity support the SiC2 identification. The high-resolution line profile and mapping data are used to estimate the size of the IRC + 10216 SiC2 envelope and the abundance of SiC2 relative to H2.

Snyder, L. E.↗
NASA NTRS1985

Direct measurement of the fundamental rotational transitions of the OH radical by laser sideband spectroscopy

The direct (zero-field) spectra of the fundamental rotational transitions of the OH radical in its Omega = 3/2 and 1/2 states at 2509.9 and 1834.7 GHz are obtained using a recently developed far-infrared laser sideband spectrometer. These measurements have verified and refined the predictions of previous laser magnetic resonance work, thereby confirming the far-infrared detection of interstellar OH. The increased accuracy of these direct measurements will be useful to future astronomical and atmospheric studies of these important transitions.

Farhoomand, J.↗