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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Cometary atmospheres: Modeling the spatial distribution of observed neutral radicals

Progress on modeling the spatial distributions of cometary radicals is described. The Monte Carlo particle-trajectory model was generalized to include the full time dependencies of initial comet expansion velocities, nucleus vaporization rates, photochemical lifetimes and photon emission rates which enter the problem through the comet's changing heliocentric distance and velocity. The effect of multiple collisions in the transition zone from collisional coupling to true free flow were also included. Currently available observations of the spatial distributions of the neutral radicals, as well as the latest available photochemical data were re-evaluated. Preliminary exploratory model results testing the effects of various processes on observable spatial distributions are also discussed.

Combi, M. R.↗
NASA NTRS1985

The internal state distribution of CN radicals produced in the photolysis of HC2CN and CH3CN

The energy partitioning in CN radicals produced by the vacuum ultraviolet photodissociation of HC2CN and CH3CN is studied by means of laser-induced fluorescence of the B-X transition. Experiments are performed in two collision regimes: (1) in the low-collision number regime, the energy partitioning in CN(X) is measured; (2) in the high-collision number regime, the formation of CN(A) is monitored. It is shown that photodissociation of HC2CN in its linear predissociative 1Sigma(+) state produces predominantly ground-state CN in rotationally and vibrationally excited states. The vibrational population ratios and the temperatures computed from a Boltzmann fit of the rotational levels are given in a table. The excitation of CH3CN produces CN radicals almost entirely in the first excited A-state with vibrational excitation.

Cody, R. J.↗
NASA NTRS1984

Radical molecule and ion-molecule mechanisms in the polymerization of hydrocarbons and chlorosilanes in R.F. plasmas at low pressures (below 1.0 Torr)

The ion-molecule and the radical-molecule mechanisms are responsible for the dissociation of hydrocarbons, and chlorosilane monomers and the formation of polymerized species, respectively, in the plasma state of a RF discharge. In the plasma, of a mixture of monomer with Ar, the rate determining step for both dissociation and polymerization is governed by an ion-molecular type interaction. Additions of H2 or NH3 to the monomer Ar(+) mixture transforms the rate determining step from an ion-molecular interaction to a radical-molecule type interaction for both monomer dissociation and polymerization processes.

Avni, R.↗
NASA NTRS1986

The rotational spectrum of the C3H radical

The rotational spectrum of the recently discovered C3H radical in both fine-structure ladders of its electronic ground state (X2Pi) with lambda doubling and hyperfine structure has been determined to high accuracy, and the strongest transitions at frequencies less than 376 GHz are tabulated. Recently published spectroscopic constants derived from astronomical and laboratory data (Gottlieb et al., 1985) allowed calculation of the spectrum to a radial velocity of 0.4 km/s at frequencies less than 200 GHz, the uncertainties above being somewhat larger. The hyperfine constants of the sequence of four hydrocarbon radicals CH, C2H, C3H, and C4H are briefly described.

Gottlieb, C. A.↗
NASA NTRS1986

Peroxy radical detection by chemical amplification (PERCA)

Important reactions of atmospheric free radicals are the chain oxidation of NO and CO. Thus: H2O + NO yields OH + NO2; OH + CO yields H + CO2; H + O2 + M yields HO2 + M. In most models, the need to know the free radical concentration could also be described as the need to know the rate of the above oxidation chain in the atmosphere. It is the total rate of this chain (also carried by RO2 and RO) which was measured using the PERCA. The PERCA is thus essentially a RO sub X meter. The PERCA works by adding excess CO (10%) and NO (5ppm) to a stream of air and measuring the NO2 produced after 3s of reaction time. Since other processes produce NO2, the chain reaction is modulated by switching the CO for N2. The chain length is limited by the reaction OH + NO yields HONO and is modeled to be somewhat over 1000. Measured chain lengths agree with the modeled numbers.

Stedman, D. H.↗
NASA NTRS1986

Radiocarbon tracer measurements of atmospheric hydroxyl radical concentrations

The usefulness of the C-14 tracer in measurements of atmospheric hydroxyl radical concentration is discussed. The apparatus and the experimental conditions of three variations of a radiochemical method of atmosphere analysis are described and analyzed: the Teflon bag static reactor, the flow reactor (used in the Wallops Island tests), and the aircraft OH titration reactor. The procedure for reduction of the aircraft reactor instrument data is outlined. The problems connected with the measurement of hydroxyl radicals are discussed. It is suggested that the gas-phase radioisotope methods have considerable potential in measuring tropospheric impurities present in very low concentrations.

Campbell, M. J.↗
NASA NTRS1987

Photodissociation lifetimes of CH and CD radicals in comets

The rates of photodissociation of the CH radical from absorption of solar radiation are calculated to lie between 0.00416 and 0.0267/sec for heliocentric velocities between -42 and 42 km/sec at 1 AU from the Sun. For CD, the corresponding rates lie between 0.00433 and 0.0131/sec. The v'=0 level of the C2 sigma(+) is the main channel of CH as well as CD dissociation and, in each case, contributes over 77 percent of the total dissociation. The CH and CD radicals may be detectable in comets through absorption lines of the C2 sigma(+) - X2Di(r) electronic bands near 3143.2 and 3142.1 A, respectively.

Singh, P. D.↗
NASA NTRS1987

Atmospheric trends in methylchloroform and the global average for the hydroxyl radical

ALE-GAGE (Atmospheric Lifetime Experiment-Global Atmospheric Gases Experiment) data obtained over the seven-year period from July 1978 to June 1985 are presented and interpreted. The data, combined with knowledge of industrial emissions, are used in an optimal estimation inversion scheme to deduce a globally average methylchloroform atmospheric lifetime of 6.3(+ 1.2, - 0.9) years (1 sigma uncertainty) and a globally averaged tropospheric hydroxyl radical concentration of (7.7 + or - 1.4) x 10 to the 5th radicals/cu cm (1 sigma uncertainty). These results provide the most accurate estimates yet of the trends and lifetime of methylchloroform and of the global average for tropospheric hydroxyl radical levels.

Prinn, R.↗
NASA NTRS1988

Measurements of the ClO radical vibrational band intensity and the ClO + ClO + M reaction product

There is considerable interest in the kinetics and concentrations of free radicals in the stratosphere. Chlorine monoxide is a critically important radical because of its role in catalytic cycles for ozone depletion. Depletion occurs under a wide variety of conditions including the Antarctic spring when unusual mechanisms such as the BrO sub x/ClO sub x, ClO dimer (Cl sub 2 O sub 2), and ClO sub x/HO sub x cycles are suggested to operate. Infrared spectroscopy is one of the methods used to measure ClO in the stratosphere (Menzies 1979 and 1983; Mumma et al., 1983). To aid the quantification of such infrared measurements, researchers measured the ClO ground state fundamental band intensity.

Burkholder, James B.↗
NASA NTRS1989

Spectroscopic study of combustion diagnostics on hydroxyl radicals

Experimental observations of propane/air flames have been carried out. Measurements of hydroxyl (OH) radical concentration have been made using resonance line absorption techniques. A microwave-pumped low pressure discharge in argon and water vapor is employed to produce strong OH radical band radiation in the 308 nm region. This radiation is transmitted through the plume and absorption data is taken at various radial positions using an optical multichannel analyzer. This absorption data is used to compute OH number density using a model for the absorption band characteristics as a function of temperature based on an atlas of line strengths. A numerical computation of flow fields, temperature profile, OH number density and water vapor mass fraction profiles was carried out by using a technique of computational fluid dynamics (CFD). The results of CFD computation are compared with experimental observation with a good agreement.

Eskridge, Richard↗
NASA NTRS1989

Infrared line intensity measurements in the v = 0-1 band of the ClO radical

Integrated line intensity measurements in the ClO-radical fundamental vibrational v = 0-1 band were carried out using a high-resolution Fourier transform spectrometer coupled to a long-path-length absorption cell. The results of a series of measurements designed to minimize systematic errors, yielded a value of the fundamental IR band intensity of the ClO-radical equal to 9.68 + or - 1.45/sq cm per atm at 296 K. This result is consistent with all the earlier published results, with the exception of measurements reported by Kostiuk et al. (1986) and Lang et al. (1988).

Burkholder, James B.↗
NASA NTRS1990

The microwave spectrum of the AlO radical

The rotational spectrum of the aluminum monoxide radical in the ground electronic state X 2Sigma(+) was observed in the millimeter- and submillimeter-wave region. Aluminum monoxide radicals were generated directly in a flow reactor absorption cell by the reaction of N2O with aluminum vaporized from a high-temperature crucible. The observed spectrum was analyzed to yield molecular constants including the rotational constant, centrifugal distortion constant, spin-rotation interaction constant, magnetic hyperfine interaction constants, and nuclear quadrupole coupling constant.

Yamada, Chikashi↗
NASA NTRS1991

Innovative techniques for the production of energetic radicals for lunar materials processing including photogeneration via concentrated solar energy

A technique for photo generation of radicals is discussed that can be used in the recovery of oxygen and metals from extraterrestrial resources. The concept behind this work was to examine methods whereby radicals can be generated and used in the processing of refractory materials. In that regard, the focus is on the use of sunlight. Sunlight provides useful energy for processing in the forms of both thermal and quantum energy. A number of experiments were conducted in the chlorination of metals with and without the aid of UV and near UV light. The results of some of those experiments are discussed.

Osborn, D. E.↗
NASA NTRS1991

Photodissociation of the hydroxyl radical (OH) at 157 nm

The photodissociation of the OH radical was studied at 157 nm via the detection of the product H atoms with the resonance fluorescence technique. OH radicals were produced in a fast-flow cell from the reaction between H and NO2 and subsequently photodissociated by an excimer laser operating on the F2 emission. The quantum yield for photodissociation of OH was measured to be 1.10 + or - 0.28. The photodissociation cross section was calculated to be 6.6 x 10 to the -18th sq cm (+ or - 25 percent).

Cody, R. J.↗
NASA NTRS1993

OH-radical imaging and velocity field measurements in a gaseous hydrogen/oxygen rocket

Detailed measurements of the OH-radical and velocity fields for a shear coaxial unielement rocket chamber burning gaseous hydrogen and gaseous oxygen propellants are reported. The velocity measurements indicate that a highly unsteady flowfield results from the turbulent combustion of the coaxial jets. The core of the oxygen stream is observed to remain intact well downstream of the injector face while the maximum turbulent intensities in the shear layer region between the hydrogen and oxygen flows were measured to be about 25 percent. Both 1D and 2D laser-induced fluorescence studies of the OH-radical are reported and provide information on the evolving flame structure under rocketlike conditions. Both single and multiple laser pulse images indicate that the structure of the unsteady flowfield is directly reflected in the combustion zone flame structure. Preliminary results regarding analysis approaches and interpretation of the data are also presented.

Moser, M. D.↗
NASA NTRS1994

Method of making a membrane having hydrophilic and hydrophobic surfaces for adhering cells or antibodies by using atomic oxygen or hydroxyl radicals

A portion of an organic polymer article such as a membrane is made hydrophilic by exposing a hydrophobic surface of the article to a depth of about 50 to about 5000 angstroms to atomic oxygen or hydroxyl radicals at a temperature below 100C., preferably below 40 C, to form a hydrophilic uniform surface layer of hydrophilic hydroxyl groups. The atomic oxygen and hydroxyl radicals are generated by a flowing afterglow microwave discharge, and the surface is outside of a plasma produced by the discharge. A membrane having both hydrophilic and hydrophobic surfaces can be used in an immunoassay by adhering antibodies to the hydrophobic surface. In another embodiment, the membrane is used in cell culturing where cells adhere to the hydrophilic surface. Prior to adhering cells, the hydrophilic surface may be grafted with a compatibilizing compound. A plurality of hydrophilic regions bounded by adjacent hydrophobic regions can be produced such that a maximum of one cell per each hydrophilic region adheres.

Koontz, Steven L.↗
NASA NTRS1994

The millimeter and submillimeter rotational spectrum of the MgCN radical (X (sup 2) Sigma(+))

The pure rotational spectrum of the MgCN radical has been recorded in the laboratory using millimeter/submillimeter direct absorption spectroscopy. Twenty-seven rotational transitions of the species were observed in the range 101-376 GHz and indicate that the molecule is linear with a (sup 2)Sigma(+) ground electronic state, as predicted by theory. Spin rotation interactions were resolved in the spectra, but no hyperfine splittings were observed, which would originate with the nitrogen nuclear spin. The rotational and fine-structure constants were determined for this radical from a nonlinear least-squares fit to the data using a (sup 2)Sigma Hamiltonian. MgCN is of astrophysical interest because it is the metastable isomer of MgNC, which recently has been detected toward IRC +10216

Anderson, M. A.↗
NASA NTRS1994

Millimeter and submillimeter rest frequencies for the MgF radical

The pure rotational spectrum of the MgF radical in its ground X(sup 2) Sigma(+) electronic state has been observed in the laboratory using millimeter/submillimeter direct absorption spectroscopy. Rotational transitions arising from the v = 0, 1, 2, and 3 vibrational modes of the main magnesium isotopic species, (24)MgF, have been recorded, as well as those arising from the v = 0 state of the Mg-25 and Mg-26 isotopomers. Rotational and fine-structure constants have been determined for these molecules, as well as hyperfine parameters for both the F-19 (I = 1/2) and Mg-25 (I = 5/2) nuclei. The rest frequencies presented here for MgF have an estimated accuracy of +/- 200 kHz, and will enable astronomical searches to be carried out for this fluoride radical. Magnesium fluoride may be present in the late-type carbon star IRC +10216, where AlF appears to be abundant.

Anderson, M. A.↗