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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 379 records · Page 21
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NASA NTRS1976

Carbon recombination line observations of the sharpless 140 region

Carbon recombination-line emission has been detected at two frequencies from a dark cloud contiguous with the small H II region Sharpless 140. The observations show the dark cloud to be of unusually low temperature and to have a markedly inhomogeneous density distribution, with localized region of high density surrounding one or more embedded stars. The carbon is probably ionized by photons from both the exciting star of S140 and the embedded stars. The dark cloud and S140 apparently represent two stages of star formation which have occurred over a period of at least 500,000 years in adjacent regions of the same dark cloud.

Knapp, G. R.↗
NASA NTRS1976

Storage and recombination of atomic H in solid H2

A phenomenological rate process theory is developed for the storage and rapid recombination of atomic hydrogen free radicals in a crystalline molecular hydrogen solid at temperatures in the range of about 0.1-4 K. It is shown that such a theory can account quantitatively for the recently observed dependence of the storage time on the storage temperature, for the maximum concentration of trapped H atoms, and for the time duration of the energy release in the tritium decay experiments of Webeler. The theory predicts that maximum atomic hydrogen concentrations of the order 10 to the 20th per cu cm are realizable for storage temperatures in the vicinity of 0.14 K.

Rosen, G.↗
NASA NTRS1977

The yield of N/2D/ atoms in the dissociative recombination of NO/+/

The quantum yield or branching ratio of N(2D) atoms formed in the reaction e + NO(+) yields N + O was measured to be 76% plus or minus 6%. Photoionization of buffered nitric oxide by a flash lamp was studied using time-resolved atomic absorption. Atoms were produced both by direct photodissociation and by dissociative recombination, and these two effects were separated by means of SF6 as an electron scavenger.

Kley, D.↗
NASA NTRS1978

The recombination velocity at III-V compound heterojunctions with applications to Al (x) Ga(1-x)As-GaAs(1-y)Sb(y)

Interface recombination velocity in AlxGa1-xAs-GaAs and A10.85 Ga0.15As-GaAs1-ySby heterojunction systems was studied as a function of lattice mismatch. The results are applied to the design of highly efficient III-V heterojunction solar cells. A horizontal liquid-phase epitaxial growth system was used to prepare p-p-p and p-p-n double heterojunction test samples with specified values of x and y. Samples were grown at each composition, with different GaAs and GaAsSb layer thicknesses. A method was developed to obtain the lattice mismatch and lattice constants in mixed single crystals grown on (100) and (111)B oriented GaAs substrates.

Kim, J. S.↗
NASA NTRS1977

Auroral recombination of N and O - A possible source for emission in the gamma and delta bands of NO

Radiative recombination of N and O provides a significant source for auroral emission in the gamma and delta bands of NO with selective population of vibrational levels in the A 2 Sigma(+) and C 2 Pi states. This mechanism may account for emissions detected near 2150 A. Models are derived for the auroral ionosphere and include estimates for the concentrations of N and NO. The concentration of NO is estimated to have a value of about 100 million per cu cm near 140 km in an IBC III aurora. The corresponding density for N is about 50 million per cu cm, and the concentration ratio NO(+)/O2(+) has a value of about 5.5.

Wofsy, S. C.↗
NASA NTRS1978

Exact results on the temperature dependence of the specific equilibrium recombination rate coefficient

Two theorems based on Laplace transforms are used to relate threshold and high energy behavior to a temperature dependent variable. A recombination reaction involving electrically neutral species is presented to illustrate the dynamics of the activation energy and the associated rate coefficient. The distribution functions are shown to correspond with those predicted by Boltzmann's equations.

Mickens, R. E.↗
NASA NTRS1978

The effect of N2/+/ recombination on the aeronomic determination of the charge exchange rate coefficient of O/+//2D/ with N2

The Atmosphere Explorer (AE) data are reexamined in the light of new laboratory measurements of the N2(+) recombination rate coefficient alpha. The new measurements support earlier measurements which yielded values of alpha significantly lower than the AE values. It is found that the values for alpha determined from the satellite data can be reconciled with the laboratory measurements, if the charge exchange rate coefficient for O(+)(2D) with N2 is less than one-quarter of that derived in the laboratory by Rutherford and Vroom (1971).

Torr, D. G.↗
NASA NTRS1978

H109-alpha recombination line observations of S187 and of S298

The H109-alpha recombination line has been detected in S187 and S298. These observations and previously reported 6-cm continuum observations have been used to derive the large-scale properties of the core-envelope-type structure of these nebulae. An electron temperature of 9750 K and a core-to-envelope electron density ratio of 4 are derived for S298. In S187 an electron temperature of 6200 K and a core-to-envelope electron density ratio of greater than 10 are found. The relationship of the common centrally condensed structure of H II regions to the morphology of dark cloud complexes is considered.

Rossano, G. S.↗
NASA NTRS1979

The importance of surface recombination and energy-bandgap narrowing in p-n-junction silicon solar cells

Experimental data demonstrating the sensitivity of open-circuit voltage to front-surface conditions are presented for a variety of p-n-junction silicon solar cells. Analytical models accounting for the data are defined and supported by additional experiments. The models and the data imply that a) surface recombination significantly limits the open-circuit voltage (and the short-circuit current) of typical silicon cells, and b) energy-bandgap narrowing is important in the manifestation of these limitations. The models suggest modifications in both the structural design and the fabrication processing of the cells that would result in substantial improvements in cell performance. The benefits of one such modification - the addition of a thin thermal silicon-dioxide layer on the front surface - are indicated experimentally.

Fossum, J. G.↗
NASA NTRS1980

Electron-temperature dependence of dissociative recombination of electrons with CO(+)-(CO)n-series ions

A microwave afterglow mass spectrometer apparatus is used to determine the dependence on electron temperature T sub e of the recombination coefficients alpha sub n of the dimer and trimer ions of the series CO+.(CO) sub n. It is found that alpha sub 1 = (1.3 + or - 0.3)x 0.000001 (T sub e(K)/300) to the -0.34; and alpha sub 2 = (1.9 + or - 0.4)x 0.000001 (T sub e(K)/300) to the -0.33 cu cm/sec. These dependences on T sub e are quite different from those obtained previously for polar-cluster ions of the hydronium and ammonium series but are similar to that for simple diatomic ions.

Whitaker, M.↗
NASA NTRS1980

A continuum and recombination line study of the Cep IV star formation region

The Cep IV star formation region consists of the Cep IV OB association, the H II regions W 1 and NGC 7822, and an extensive fragmented dust cloud complex. Six- and nine-cm radio continuum observations and 6-cm hydrogen recombination line observations show that all of the emission nebulosity in this region, which includes a large loop-type structure suggested by Herbst and Assousa (1977) to be a supernova remnant, has a thermal spectrum. The two components of W 1 have been detected at H 110 alpha and are found to be kinematically distinct.

Rosano, G. S.↗
NASA NTRS1980

Recombination spectrum and reddening in NGC 1068

Measurements of the emission-line intensities of NGC 1068 have been made over the wavelength range extending from rest wavelengths equal to 1216 A to 1.875 micron. The data, plus other available emission-line data, can be explained in terms of a simple model where the emission lines are formed in an H II region, and the line ratios are consistent with those predicted by standard radiative recombination theory and reddening corresponding to 0.4 mag. The continuum flux is seen to consist of a galaxy component plus a nonstellar component which dominates the observed flux in the ultraviolet. The observed ultraviolet continuum does not show an absorption dip caused by the intertellar 2200 A feature nor does it contain enough energy to power the observed infrared flux.

Neugebauer, G.↗
NASA NTRS1981

On the role of vibrational excitation in dissociative recombination

An improved physical model of dissociative recombination is presented and applied to experimental data on the temperature dependence of rate coefficients for the rare-gas and atmospheric-gas ions. It is shown that in the charge neutralisation of the rare-gas dimer ions, autoionisation plays an important role (at least in comparison with the atmospheric-gas ions) and contributes to the fast fall-off in the rate coefficient with vibrational excitation observed in shock tube studies. Numerical estimates of the observed fall-off in rate coefficient with increasing vibrational excitation are also presented.

Cunningham, A. J.↗
NASA NTRS1981

Space Shuttle laminar heating with finite-rate catalytic recombination

Temperature-dependent catalytic recombination coefficients are used to calculate the heat flux to the Space Shuttle Orbiter. With variable entropy boundary-layer edge properties obtained from a reacting inviscid flow-field calculation, the reacting boundary-layer equations are solved along the forward 50 percent of the windward centerline using the boundary-layer integral matrix procedure. The results are compared with fully catalytic and noncatalytic reacting solutions, with equilibrium solutions, and with the Orbiter-design heating rates. The fully catalytic heat fluxes are about equal to the equilibrium predictions; whereas, the finite catalytic results are about 12 to 27 percent lower than the fully catalytic results (approaching the noncatalytic results downstream) and as much as 30 to 50 percent lower than design predictions away from the nose area.

Scott, C. D.↗
NASA NTRS1981

Exact random walk definition of the collisional-radiative ionization and recombination coefficients

The collisional-radiative ionization and recombination coefficients are shown to be expressible in terms of the 'total probability', from initial level i to final level j, which excludes intermediate returns to the initial level. Applications are made to three-level and four-level systems to illustrate the method of calculation and compare with an approximation currently used.

Kastner, S. O.↗
NASA NTRS1981

A spectroscopic experimental and computer-assisted empirical model for the production and energetics of excited oxygen molecules formed by atom recombination on shuttle tile surfaces

A visible emission spectroscopic method was developed. The amounts of excited singlet and triplet oxygen molecules produced by recombination on the Space Shuttle Orbiter thermal protective tiles at elevated temperatures are determined. Rate constants and energetics of the extremely exothermic reaction are evaluated in terms of a chemical and mathematical model. Implications for potential contribution to Shuttle surface reentry heating fluxes are outlined.

Owan, D. A.↗
NASA NTRS1981

The dissociative recombination of O2/+/ in the ionosphere

Aeronomical determinations of the dissociative recombination reaction rate coefficient for O2(+) and alpha depend directly on a knowledge of the rate coefficient for the charge exchange of O(+) with O2 and k. The aeronomical determination of alpha is reevaluated using Atmosphere Explorer satellite data in light of a subsequent laboratory measurement of k (Chen et al., 1978). The results are found to be in good agreement with laboratory determinations of the coefficient for night-time conditions. For data obtained under sunlit conditions, however, the results differed significantly with those of the laboratory measurements. These results imply that the state of the O2(+) molecule major thermospheric processes needs to be examined in greater detail.

Torr, M. R.↗
NASA NTRS1983

Measuring Diffusion and Recombination in Polycrystalline Silicon

Light-beam-induced currents yield information about solar cell material. Apparatus measures short-circuit current generated when spot of concentrated light is scanned across grains and grain boundaries in material under test. Technique used to evaluate SOC samples for diffusion and recombination effects of cell processing and chemical and structural defects.

Zook, J. D.↗