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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Comparison of electron and electronic temperatures in recombining nozzle flow of ionized nitrogen-hydrogen mixture. I, II.

Relaxation of the population distribution of electronic states is studied theoretically for a highly ionized nitrogen-hydrogen mixture expanding through a nozzle wherein the hydrogen content is less than 0.1%. The analysis incorporates quantum-mechanical rate coefficients, and considers the effects of wall cooling and absorption of radiation. Calculations are carried out for a condition produced experimentally. Visible and infrared line radiations from nitrogen and hydrogen were measured with a spectrograph. The geometry and stagnation conditions were those calculated theoretically. The experiment confirms quantitatively the predictions that the electronic excitation temperatures of hydrogen and (3P) core states of nitrogen are higher than the electron temperature, and that (3P) excitation temperatures exhibit maxima within the nozzle.

Park, C.↗
NASA NTRS1973

Recombination luminescence from electron-irradiated Li-diffused Si

Lithium doping has a dramatic effect on the low-temperature photoluminescence of electron-irradiated Si. In oxigen-lean Si with Li doping, a new irradiation-dependent luminescence band between 0.75 and 1.05 eV is observed, which is dominated by a zero-phonon peak at 1.045 eV. This band is believed to be due to radiative transitions involving a Li-modified divacancy. This band is present also in oxygen-rich, Li-diffused Si and is accompanied by bands previously related to the Si-G15(K) center and the divacancy. The intensities of the Li-modified divacancy and Si-G15(K) center bands are relatively weak in the oxygen-rich material, apparently due to the formation of lithium-oxygen complexes which reduce the concentration of unassociated interstitial Li and O.

Johnson, E. S.↗
NASA NTRS1974

Vibrationally excited nitrogen in stable auroral red arcs and its effect on ionospheric recombination

The time-dependent continuity equations, including diffusion, were solved for the first six energy levels of molecular nitrogen for conditions in the thermosphere corresponding to stable auroral red (SAR) arcs. The results show that molecular nitrogen is excited vibrationally to the degree that the rate constant for the ionospheric loss process, O(+) + N2 yields NO(+) + N, is increased by as much as a factor of 7.6 at F2 region altitudes. It was found that deviations from the energetically equivalent Boltzmann distribution were large, causing the rate constant to be as much as 1.6 times the rate constant calculated for the Boltzmann distribution. These results indicate that SAR arc intensities as small as 58 R can produce noticeable increases in the ionosphere ion-atom interchange reaction rate and hence in the rate of loss of ionospheric electrons. It is suggested that the observed decrease of electron density in the F2 region in SAR arcs can probably be explained by enhanced reaction rates for ion-atom interchange between O(+) and N2 caused by vibrational excitation of molecular nitrogen by electron impact.

Newton, G. P.↗
NASA NTRS1974

Rate of recombination of oxygen atoms and CO at temperatures below ambient

The measurements reported were conducted with 30.0 torr CO, 40.0 torr argon, and varying amounts of carbon dioxide from about 20 to 230 torr. Measurements were made at 277, 272, 263, and 257 K. The pseudo-first-order decay rate as a function of carbon dioxide pressure is shown in a graph. An Arrhenius plot for the rate constants obtained from the measurements is also presented. A value for the activation energy was determined on the basis of a linear least-squares fit to the data.

Inn, E. C. Y.↗
NASA NTRS1975

Influence of probe contamination on recombination of atomic hydrogen

Atomic hydrogen concentration profiles were measured through a screen-stabilized one-dimensional propane/oxygen front using a specially modified electron spin resonance (ESR) spectrometer. The ESR line occurring at 3075.5 G at 9261.2 MHz was monitored in the presence and absence of various halogenated hydrocarbons. A significant cumulative decrease in peak intensity occurred with addition of any halogenated compound. Further results suggest that the effect is due to inhibitor action on the transport tube walls followed by changes in atomic hydrogen interaction with the walls, and that hydrogen decay is nonlinear in the halogenated tube.

Collins, L. W.↗
NASA NTRS1978

Carbon recombination-line mapping of the Orion Nebula

The distribution of the C75-alpha line in the Orion Nebula has been mapped with a spatial resolution of 1.3 arcmin over a field of view of 4 by 8 arcmin. It is found that ionized carbon is more extended than the radio continuum distribution, particularly to the northeast, and possibly also beyond the ionization front in the southeast. However, the emission falls off across the ionization front northwest of the nebula. The emission is generally consistent with a model in which the line is formed in a thin sheet in the molecular cloud immediately adjacent to the H II region. However, the spatial extent of the emission does suggest that some of the emitting gas may be cooler and less dense than has previously been assumed.

Kuiper, T. B. H.↗
NASA NTRS1978

Generation of O2/c 1Sigma u -, C 3Delta u, A 3Sigma u +/ from oxygen atom recombination

The spectrum produced in the afterglow of an O2-He discharge was studied for the range 4000-8000 A. Lawrence et al. (1977) established that under the appropriate conditions the O2(c 1Sigma u - to X 3Sigma g -) system could be observed in this region. The present study has duplicated these results and has discovered three O2 band systems not previously seen in gas phase laboratory spectra. These systems are C 3Delta u-a 1Delta g, C 3Delta u-X 3Sigma g -, and c 1Sigma u - to a 1Delta g.

Slanger, T. G.↗
NASA NTRS1979

Hydrogen recombination in sealed nickel-cadmium aerospace cells

The paper presents a mechanism which offers an explanation of the observed behavior of nickel-cadmium cells during voltage reversal. Constant current reversals using aerospace Ni-Cd cells showed that at rates of C/100 and temperatures of 20 C, a steady condition of constant pressure is achieved with continuous overdischarge. Results of a test employing a battery pack of thirteen 24 Ah cells at 10 C showed that: (1) no net evolution of H occurs in Ni-Cd cells during overdischarge, (2) as H pressure increases the rate of pressure rise decreases, and (3) after attaining pressure equilibrium at a given overdischarge rate, a pressure decrease is noted when the discharge is lowered. Other tests using varying overdischarge rates were examined and have resulted in the development of a laboratory cell with a safe overdischarge capability of C/20 which is three times as great as state-of-the-art Ni-Cd cells.

Ritterman, P. F.↗
NASA NTRS1979

Analysis of the interaction of an electron beam with a solar cell. III - The effect of spacial variations of the number density of recombination centers on SEM measurements

By means of an exactly soluble model the short circuit current generated by a scanning electron microscope in a P-N junction has been determined in cases where the trap density is inhomogeneous. The diffusion length for minority carriers becomes then dependent on the spacial coordinates. It is shown that in this case the dependence of the Isc on characteristic parameters as cell thickness, distance of the beam excitation spot from ohmic contacts, etc., becomes very intricate. This fact precludes the determination of the local diffusion length in the usual manner. Although the model is somewhat simplified in order to make it amenable to exact solutions, it is nevertheless realistic enough to lead to the conclusion that SEM measurements of bulk transport parameters in inhomogeneous semiconductor material are impractical since they may lead to serious errors in the interpretation of the data by customary means.

Von Roos, O.↗
NASA NTRS1981

Non-thermal O/1D/ produced by dissociative recombination of O2/+/ - A theoretical model and observational results

Thermal and nonthermal O(1D) number density profiles are calculated. The two populations are assumed to be coupled by a thermalization cross-section which determines the loss and production in the nonthermal and thermal populations, respectively. The sources, sinks and transport of the two populations are used to model volume emission rate profiles at 6300 A. The 6300 A brightness measured by the Visible Airglow Experiment is then used to establish the presence of the nonthermal population and to determine the thermalization cross-section.

Schmitt, G. A.↗