Search NASA⌕ Search

SEARCH · Search NASA

Results for “Transfer reactions”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Ionospheric chemistry

This report deals primarily with progress in the chemistry of minor neutrals and ionized constituents of the thermosphere. Significant progress was made over the last few years in quantitative studies of many chemical processes. This success was primarily due to the advent of multiparameter multisatellite programs which permitted accurate simultaneous measurements to be made of many important parameters. In many cases studies of chemical reactions were made with laboratory-like precision. Rate coefficients have been derived as functions of temperature for a number of important reactions. New information has been acquired on nearly every major process which occurs in the thermosphere, including the recombination rates of all major molecular ions, charge transfer reactions, ion atom interchange reactions, and reactions of neutral and ionized metastable atoms and molecules.

Torr, D. G.↗
NASA NTRS1983

Electrode kinetics of oxygen reduction - A theoretical and experimental analysis of the rotating ring-disc electrode method

In order to calculate most of the rate constants for the intermediate formation of H2O2 in the electroreduction of O2 to H2O, the theoretical treatments of the rotating ring-disc electrode method by Damjanovic et al. (1966, 1967), Bagotskii et al. (1968, 1969), and Wroblowa et al. (1976) are modified. Rotating ring-disc electrode experimental data obtained for O2 reduction in Pt in 0.55 M H2SO4 are used to illustrate the calculations of rate constants according to the above theoretical treatments. A simple reaction model as proposed by the first author is consistent with the experimental data. The results indicate that O2 (97 percent) reduces to H2O in a direct four-electron transfer reaction. The adsorption of O2 is probably the rate-determining step in the potential region more negative than 0.5 V vs. reversible hydrogen electrode.

Hsueh, K.-L.↗
NASA NTRS2000

Sugars as the optimal biosynthetic carbon substrate of aqueous life throughout the universe

Our previous analysis of the energetics of metabolism showed that both the biosynthesis of amino acids and lipids from sugars, and the fermentation of organic substrates, were energetically driven by electron transfer reactions resulting in carbon redox disproportionation (Weber, 1997). Redox disproportionation--the spontaneous (energetically favorable) direction of carbon group transformation in biosynthesis--is brought about and driven by the energetically downhill transfer of electron pairs from more oxidized carbon groups (with lower half-cell reduction potentials) to more reduced carbon groups (with higher half-cell reduction potentials). In this report, we compare the redox and kinetic properties of carbon groups in order to evaluate the relative biosynthetic capability of organic substrates, and to identify the optimal biosubstrate. This analysis revealed that sugars (monocarbonyl alditols) are the optimal biosynthetic substrate because they contain the maximum number of biosynthetically useful high energy electrons/carbon atom while still containing a single carbonyl group needed to kinetically facilitate their conversion to useful biosynthetic intermediates. This conclusion applies to aqueous life throughout the Universe because it is based on invariant aqueous carbon chemistry--primarily, the universal reduction potentials of carbon groups.

NASA Center ARC↗
NASA NTRS1999

Sugars as the Optimal Biosynthetic Carbon Substrate of Aqueous Life throughout the Universe

Our previous analysis of the energetics of metabolism showed that both the biosynthesis of amino acids and lipids from sugars, and the fermentation of organic substrates, were energetically driven by electron transfer reactions resulting in carbon redox disproportionation (Weber 1997). Redox disproportionation -- the spontaneous (energetically favorable) direction of carbon group transformation in biosynthesis -- is brought about and driven by the energetically downhill transfer of electron pairs from more oxidized carbon groups (with lower half-cell reduction potentials) to more reduced carbon groups (with higher half-cell reduction potentials). In this report, we compare the redox and kinetic properties of carbon groups in order to evaluate the relative biosynthetic capability of organic substrates, and to identify the optimal biosubstrate. This analysis revealed that sugars (monocarbonyl alditols) are the optimal biosynthetic substrate because they contain the maximum number of biosynthetically useful .high energy electrons/carbon atom , while still containing a single carbonyl group needed to kinetically facilitate their conversion to useful biosynthetic intermediates. This conclusion applies to aqueous life throughout the Universe because it is based on invariant aqueous carbon chemistry -- primarily, the universal reduction potentials of carbon groups.

Weber, Arthur L.↗
NASA NTRS1997

Elucidation of the Cross-Link Structure of Nadic-End-Capped Polyimides Using NMR of C-13-Labeled Polymers

Solid NMR of C-13 isotope-labeled samples of PMR-15 was used to follow the cross-linking reaction of the nadic end cap. Some samples were labeled on one of the carbon atoms of the nadic end cap, and others on the methylene carbon atom of the methylenedianiline portion of the polymer. NMR spectra were run on these samples both before and after cross-linking. In this way, direct evidence of the major products of cross-linking under normal cure conditions is provided. The majority (approximately 85%) of the cross-linking derives from olefin polymerization through the double bond of the end cap. Approximately 15% of the products could come from a pathway involving a retro-Diels-Alder reaction. However, all of the products could be explained by a biradical intermediate without a retro-Diels-Alder reaction. Evidence is also presented that the methylene moiety in the methylenedianiline part of the polymer chain also participates in the cross-linking, albeit to a small extent, by a radical transfer reaction. Different cure conditions (higher temperatures, longer times) could change the relative distribution of the products.

Meador, Mary Ann B.↗
NASA NTRS1977

Reactions between NO/+/ and metal atoms using magnetically confined afterglows

A new method of studying thermal energy ion-neutral collision processes involving nongaseous neutral atoms is described. A long magnetic field produced by a solenoid in a vacuum chamber confines a thermal-energy plasma generated by photoionization of gas at very low pressure. As the plasma moves toward the end of the field, it is crossed by a metal atom beam. Ionic products of ion-atom reactions are trapped by the field and both the reactant and product ions move to the end of the magnetic field where they are detected by a quadrupole mass filter. The cross sections for charge transfer between NO(+) and Na, Mg, Ca, and Sr and that for rearrangement between NO(+) and Ca have been obtained. The charge-transfer reaction is found strongly dominant over the rearrangement reaction that forms metallic oxide ions.

Lo, H. H.↗
NASA NTRS1976

Electric-discharge-pumped nitrogen ion laser

The routine operation is described of an N2(+) laser oscillating on the first negative band system of N2(+) which is produced in a preionized transverse discharge device. The discharge design incorporates features which favor the efficient production of the excitation transfer reaction of He2(+) with N2. A capacitive discharge switched by means of a high-current grounded grid thyratron is used to meet the design requirement of a volumetric discharge in high-pressure gas mixtures where the electric discharge need not have an ultrafast rise time (greater than 10 nsec) but should be capable of transferring large quantities of stored electric energy to the gas. A peak power of 180 kW in an 8-nsec laser pulse was obtained with a 0.1% mixture of N2 in helium at a total pressure of 3 atm. The most intense laser oscillations were observed on the (0,1) vibrational transition at 427.8 microns.

Laudenslager, J. B.↗
NASA NTRS2003

Laboratory Studies of Thermal Energy Charge Transfer of Multiply Charged Ions in Astrophysical Plasmas

The laser ablation/ion storage facility at the UNLV Physics Department has been dedicated to the study of atomic and molecular processes in low temperature plasmas. Our program focuses on the charge transfer (electron capture) of multiply charged ions and neutrals important in astrophysics. The electron transfer reactions with atoms and molecules is crucial to the ionization condition of neutral rich photoionized plasmas. With the successful deployment of the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Chandra X-ray Observatory by NASA high resolution VUV and X-ray emission spectra fiom various astrophysical objects have been collected. These spectra will be analyzed to determine the source of the emission and the chemical and physical environment of the source. The proper interpretation of these spectra will require complete knowledge of all the atomic processes in these plasmas. In a neutral rich environment, charge transfer can be the dominant process. The rate coefficients need to be known accurately. We have also extended our charge transfer measurements to KeV region with a pulsed ion beam. The inclusion of this facility into our current program provides flexibility in extending the measurement to higher energies (KeV) if needed. This flexibility enables us to address issues of immediate interest to the astrophysical community as new observations are made by high resolution space based observatories.

Kwong, Victor H. S.↗
NASA NTRS1996

Products of Dissociative Recombination in the Ionosphere

SRI International undertook a novel experimental measurement of the product states formed by dissociative recombination (DR) of O2(+), NO(+), and N2(+) as a function of both electron energy and reactant ion vibrational level. For these measurements we used a recently developed experimental technique for measuring dissociation product distributions that allows both the branching ratios to be accurately determined and the electronic and rovibrational state composition of the reactant ions to be specified. DR is the dominant electron loss mechanism in all regions of the ionosphere. In this process, electron attachment to the molecular ion produces an unstable neutral molecule that rapidly dissociates. For a molecular ion such as O2(+), the dissociation recombination reaction is (1) O2(+) + e yields O + O + W. The atomic products of this reaction, in this case two oxygen atoms, can be produced in a variety of excited states and with a variety of kinetic energies, as represented by W in Eq. (1). These atoms are not only active in the neutral chemistry of the ionosphere, but are also especially important because their optical emissions are often used to infer in situ concentrations of the parent molecular ion and ambient electron densities. Many laboratory measurements have been made of DR reaction rates under a wide range of electron temperatures, but very little is known about the actual distributions among the final states of the atomic products. This lack of knowledge seriously limits the validity and effectiveness of efforts to model both natural and man-made ionospheric disturbances. Bates recently identified major deficiencies in the currently accepted branching ratios for O2(+) as they relate to blue and green line emission measurements in the nocturnal F-region. During our two-year effort, we partially satisfied our ambitious goals. We constructed and operated a variable pressure, electron-impact ion source and a high pressure, hollow-cathode discharge ion source for O2(+), NO(+), and N2(+) beams. Translational spectroscopy of the products of dissociative charge transfer in Cs vapor was used to accurately assay the composition of the O2(+) and NO(+) beams and to develop a methodology for the vibrationally controlled preparation of the ground state ion beams. Attempts to assay the N2(+) beam revealed a novel two-electron process in the charge transfer reactions. A coaxial electron gun for the DR measurements was constructed following an extensive numerical design of the fields. Tests of the gun, however, found substantial perturbations of the magnetic fields by the soft iron (CMI-C) assembly containing the Langmuir probe that locates the electron beam. Hydrogen annealing of the iron failed to eliminate the field perturbations, necessitating the removal of the probe assembly. During this work on the coaxial electron gun, we discovered that predissociated high Rydberg states of O2 could be produced by subjecting the molecules to a sudden perturbation by an electromagnetic field. This technique allowed a measurement of the product branching to the atomic limits for the lowest seven vibrational levels of O2(+).

Cosby, Philip↗
NASA NTRS1975

Chemical-ionization visible and ultraviolet gas lasers: A concept

Charge-transfer reactions or Penning ionization reactions are used to produce population inversions between electronic states of molecular ions which should result in stimulated emission in ultraviolet and visible regions. Such lasers could be used in study of short-lived reaction intermediates, crystal structure and scattering, and photolysis.

Laudenslager, J. B.↗
NASA NTRS1978

Artificially created holes in the ionosphere

The artificial creation of ionospheric holes by the release of highly reactive molecules into the F region is investigated. Through ion-atom interchange or charge transfer reactions, H2 or H2O reacts with O(+) to form OH(+) or H2O(+), respectively, which subsequently dissociatively recombines with electrons at a very rapid rate. The diffusion of H2 is also modified by chemical loss to the ambient atomic oxygen atmosphere. The limited spatial and temporal extent of the hole-making process allows several approximations to be made which permit three-dimensional analytic solutions of the continuity equations for the released particles, the O(+) and e(-) densities, and the intermediary molecular ions. A versatile formalism is developed whereby the hole-making capability of virtually any spatial-temporal configuration of released particles can be determined by convolving a set of destruction operators which can be viewed as Green's functions for the problem. As a specific application of the techniques developed, the modification of a winter nighttime ionosphere is described by simulating the release of 1000 kg of water vapor near a height of 300 km.

Mendillo, M.↗
NASA NTRS1979

Resonant charge transfer in He/+/-He collisions studied with the merging-beams technique

Absolute cross sections are reported for the resonant charge-transfer reaction He(+) + He yields He + He(+) at collision energies between 0.1 and 187 eV. The results, obtained using a new merging-beam apparatus are in agreement both with theory and with measurements made using other experimental techniques. The experimentally determined cross sections between 0.5 and 187 eV fall about a line given by sigma exp 1/2(sq-A) = 5.09-2.99 lnW, where W is the collision energy in eV. Considerable attention is paid to the configuration and operation of the apparatus. Tests and calculations which confirm the interpretation of the experimental data in a merging-beam experiment are discussed.

Rundel, R. D.↗
NASA NTRS1981

The optical and ultraviolet spectrum of the planetary nebula NGC 2440

New measurements of the optical and ultraviolet emission-line intensities of the high-excitation planetary nebula NGC 2440 in the wavelength range 1240-8578 A are analyzed with the aid of photoionization models. The observed O III and N II forbidden-line temperatures (13,800 K and 10,000 K, respectively) differ by more than the models predict. Inclusion of charge-transfer reactions at published rates improves agreement between calculated and observed abundances of many ions, but worsens the agreement for several highly ionized ions. Nitrogen shows a larger overabundance N(N)/N(O) approximately equal to 1.0, whereas ultraviolet lines give a carbon abundance close to the solar value. The refractory elements magnesium, calcium, and iron have similar gas-phase depletions of approximately 1.5 dex. The abundances of oxygen, neon, sodium, sulfur, chlorine, potassium, and argon are rougly solar.

Shields, G. A.↗
NASA NTRS1982

The ionization structure of the Ring Nebula. II - Ultraviolet observations

Good agreement is found for O and N abundances, and the importance of charge-transfer reactions to the ionization of Ne is confirmed, in UV observations of emission line intensities for four positions in the Ring Nebula that have been previously studied optically. It is noted that the C(2+) abundance inferred from the optical 4267 A recombination line is as much as 10 times brighter than that measured from the UV lines, and that this discrepancy is greatest near the central star. The most attractive explanation for this phenomenon is the resonance fluorescence due to light from the central star. Both Ne/O and C/H abundances are in good agreement with previously measured average values for planetary nebulae.

Barker, T.↗
NASA NTRS1985

The vibrational distribution of N2(+) in the terrestrial ionosphere

The densities and vibrational distributions of N2(+) in the X2sigma g +, A2Pi u and B2sigma u + states in the daytime terrestrial ionosphere are computed for both low and high solar activity. Altitude profiles of the relative populations of the vibrational levels of N2(+) X2sigma g + are presented. The fraction of vibrationally excited N2(+) varies from 5 percent at 100 km to 50 percent at 450 km. Several models are examined in which loss of N2(+)(v) is enhanced for v greater than 0 and in which various assumptions are made about the vibrational distributions produced in charge transfer reactions. The N2(+) densities are significantly reduced if N2(+)(v) reacts with O at rates which are near gas-kinetic. Vibrational distributions of the A2pi u and B2sigma u + states are also presented, as well as volume emission rates and integrated overhead intensities of the major bands of the Meinel and first negative systems.

Fox, J. L.↗
NASA NTRS1985

Report from the Transfer-Laser Working Group

Light absorbing molecules and lasing molecules were discussed with regard to satisfying the following criteria for blackbody transfer lasers: (1) Good absorbers of blackbody radiation at 1500-2000 K; (2) Near resonant energy transfer from the absorbing gas to the lasant, provided not too many quantum number changes are required; (3) Dipole-dipole interactions for most efficient energy transfer; (4) Exothermic forward transfer reaction; (5) Polyatomic lasant molecules with at least two fundamental vibrational modes to ensure one or more states between the upper laser level and the ground state; (6) Polyatomic lasant molecules should not be so large or so complex that fast V-V relaxation occurs; (7) Metastable upper laser level for maintaining inversion, at least with respect to radiative and V-V decay; (8) Fast V-V into the upper laser level and out of the lower laser level; and (9) Lasing wavelengths less than 10.6 microns. Possible combinations of absorbers and lasants satisfying these criteria were discussed.

Meador, W. E.↗
NASA NTRS1985

The Crab Nebula and related supernova remnants; Proceedings of the Workshop, George Mason University, Fairfax, VA, October 11, 12, 1984

Papers are presented on the Crab Nebula's composition, helium distribution, outer structure and jet, and evolution. Attention is given to line emission from supernova remnants and charge transfer reactions, a magnetohydrodynamic model of the Crab Nebula and its radiation, inferences made using data on the pulsed flux from the crab pulsar, a new interpretation of the crab pulsar X-ray interpulse radiation, and evolutionary models of the Crab Nebula's progenitor. Other topics include the evolution of the centimeter flux of 3C58 and the Crab Nebula, a search for a shock wave around the Crab Nebula, high resolution radio studies of the Crab Nebula, supernova shell structure, and the nature of the remnant 0540-693 and its implications for the study of crablike remnants. Papers are also presented on X-ray observations of: Crab-like remnants, the Crab Nebula, the Vela X region, W28, and 3C400.2. Other papers include the 50 millisecond pulsar in the Large Magellanic Cloud and the X-ray pulse emission mechanism, optical emission from the plerionic core of CTB 80, and one-arcminute resolution observations of W50.

Kafatos, M. C.↗
NASA NTRS1988

A molecular shift register based on electron transfer

An electronic shift-register memory at the molecular level is described. The memory elements are based on a chain of electron-transfer molecules and the information is shifted by photoinduced electron-transfer reactions. This device integrates designed electronic molecules onto a very large scale integrated (silicon microelectronic) substrate, providing an example of a 'molecular electronic device' that could actually be made. The design requirements for such a device and possible synthetic strategies are discussed. Devices along these lines should have lower energy usage and enhanced storage density.

Hopfield, J. J.↗