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Results for “VISIBLE SPECTRA”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Methane absorption in the visible spectra of the outer planets and Titan

New spectra of Jupiter, Saturn, and Titan show weak methane bands in the region below 6000 A which have been known for many years in the spectra of Uranus and Neptune. Adopting the known abundance of methane on Jupiter, we have used a band model to determine CH4 abundances and broadening pressures for the other objects. The results indicate high values of the CH4 to H2 concentration ratio for Uranus and Neptune; for Titan, a surface pressure in excess of 1 atm is implied.

Owen, T.↗
NASA NTRS1983

Analysis of the visible spectra of concentrated chromic chloride solutions

In the development of the Redox Energy Storage System, the electrical storage efficiency is low due to the complex chemical reaction of the chromium II and III species. Several studies dealing with the processes occurring at the catalyzed carbon electrode during the charging and discharging of the system are described.

Bunch, W. D.↗
NASA NTRS1983

Visible absorbance spectra: A basis for in situ and passive remote sensing of phytoplankton concentration and community composition

The concentration and composition of phytoplankton populations are measured by an optical method which can be used either in situ or remotely. This method is based upon the in vivo light absorption characteristics of phytoplankton. To provide a data base for testing assumptions relative to the proposed method, visible absorbance spectra of pure cultures of 20 marine phytoplankton were obtained under laboratory conditions. Descriptive and analytical statistics were computed for the absorbance spectra and were used to make comparisons between members of major taxonomic groups and between groups. Spectral variation between the members of the major taxonomic groups was observed to be considerably less than the spectral variation between these groups. In several cases the differences between the mean absorbance spectra of major taxonomic groups are significant enough to be detected with passive remote sensing techniques.

Farmer, F. H.↗
NASA NTRS1981

Shock waves, atmospheric structure and mass loss in Miras

Large amplitude shock waves are observed to be present in the atmospheres of the Mira variables: spectral line doubling with Delta v 30 km/s is present in infrared spectra. Even the visible spectra contain some evidence for such shocks. These shocks are sufficiently large to clearly dominate the energy balance of the atmosphere. Mira variables also show symptoms of substantial mass loss rates: they are strong maser and infrared continuum sources and have strong circumstellar absorption features. The pulsation induced shocks which are seen to be present are obvious suspects for causing or enhancing the mass loss from these stars. The Miras thus present an ideal case for the study of dynamical effects on atmospheric structure, since both the dynamics and the results are clearly observable. The results are given of calculations of the thermalization and cooling of the shock heated material passing through shock fronts whose properties were selected to be consistent with both the isothermal models and the spectroscopic observations.

Willson, L. A.↗
NASA NTRS1995

A study of the chromospherically active, short-period binary VZ piscium

The short-period binary VZ Piscium is unusual in that it has a high space velocity, indicating that it is old, and a high mass ratio, suggesting that it is presently evolving into contact with little mass exchange having occurred between the components. In this study, we obtained IUE and visible spectra to investigate Mg II h + k and Ca II H and K emission strengths. Both features are found to be strong and variable. From the visible spectra, radial velocities were measured, and a new mass ratio of q = 0.80 was deter-mined. This mass ratio was used in a new light-curve analysis, and the system was found to be in marginal contact, with the secondary component slightly detached. A model with bright (hot) regions on the inner hemisphere of the slightly detached, less massive component was found to fit well with the variety of spectroscopic and photometric observations of the system. The masses determined for the components are compatible with normal K dwarfs.

Hrivnak, Bruce J.↗
NASA NTRS1991

Alteration of the UV-visible reflectance spectra of H2O ice by ion bombardment

Satellite in the Jovian and Saturnian system exhibit differences in reflectivity between their 'leading' and 'trailing' surfaces which can affect the local vapor pressure. Since these differences are thought to be due to differences in the flux of bombarding magnetospheric ions, the influence of ion impact on the UV-visible reflectance of water ice surfaces (20-90 K) by keV ion bombardment was studied. An observed decrease in reflectance in the UV is attributed to rearrangement processes that affect the physical microstructure and surface 'roughness'. The ratio in reflectance of bombarded to freshly deposited films is compared to the ratio of the reflectance of the leading and trailing hemispheres for Europa and Ganymede.

Sack, N. J.↗
NASA NTRS1995

The effect of simulated low earth orbit radiation on polyimides (UV degradation study)

UV degradation of polyimide films in air and vacuum were studied using UV-visible, ESR, FTIR, and XPS spectroscopies. The UV-visible spectra of polyimide films showed a blue shift in the absorption compared to Kapton. This behavior was attributed to the presence of bulky groups and kinks along the polymer chains which disrupt the formation of a charge transfer complex. The UV-visible spectra showed also that UV irradiation of polyimides result extensively in surface degradation, leaving the bulk of the polymer intact. ESR spectra of polyimides irradiated in vacuum revealed the formation of stable carbon-centered radicals which give a singlet ESR spectrum, while polyimides irradiated in air produced an asymmetric signal shifted to a lower magnetic field, with a higher g value and line width. This signal was attributed to oxygen-cenetered radicals of peroxy and/or alkoxy type. The rate of radical formation in air was two fold higher than for vacuum irradiation, and reached a plateau after a short time. This suggests a continuous depletion of radicals on the surface via an ablative degradation process. FTIR, XPS, and weight loss studies supported this postulate. An XPS study of the surface indicated a substantial increase in the surface oxidation after irradiation in air. The sharp increase in the C-O binding energy peak relative to the C-C peak was believed to be associated with an aromatic ring opening reaction.

Forsythe, John S.↗
NASA NTRS1989

Simultaneous infrared and UV-visible absorption spectra of matrix-isolated carbon vapor

Carbon molecules were suggested as possible carriers of the diffuse interstellar bands. In particular, it was proposed that the 443 nm diffuse interstellar band is due to the same molecule which gives rise to the 447 nm absorption feature in argon matrix-isolated carbon vapor. If so, then an associated C-C stretching mode should be seen in the IR. By doing spectroscopy in both the IR and UV-visible regions on the same sample, the present work provides evidence for correlating UV-visible absorption features with those found in the IR. Early data indicates no correlation between the strongest IR feature (1997/cm) and the 447 nm band. Correlation with weaker IR features is being investigated.

Kurtz, Joe↗
NASA NTRS1975

Metal-to-metal charge transfer transitions - Interpretation of visible-region spectra of the moon and lunar materials

Prominent bands in the spectral profiles of Fe-Ti phases in lunar samples have been attributed to charge-transfer transitions between Fe and Ti cations, and a model is presented for calculating charge transfer energies from energy levels computed by the SCF-X(alpha) scattered wave molecular orbital method for isolated MO6 octahedral coordination clusters containing Fe(2+), Fe(3+), Ti(3+), and Ti(4+) cations. The calculated charge transfer energy for the Fe(2+) to Ti(4+) transition correlates well with a measured spectral feature around 0.6 micron in ilmenite, and, since ilmenite is a major constituent of mare basalts and dark-mantling material, the observed darkness and blueness of the regolith in lunar black spots is attributed primarily to this transition. The Ti(3+) to Ti(4+) transition is thought to contribute to some phases.

Loeffler, B. M.↗
NASA NTRS1994

Possible spinel absorption bands in S-asteroid visible reflectance spectra

Minor absorption bands in the 0.55 to 0.7 micron wavelength range of reflectance spectra of 10 S asteroids have been found and compared with those of spinel-group minerals using the modified Gaussian model. Most of these S asteroids are consistently shown to have two absorption bands around 0.6 and 0.67 micron. Of the spinel-group minerals examined in this study, the 0.6 and 0.67 micron bands are most consistent with those seen in chromite. Recently, the existence of spinels has also been detected from the absorption-band features around 1 and 2 micron of two S-asteroid reflectance spectra, and chromite has been found in a primitive achondrite as its major phase. These new findings suggest a possible common existence of spinel-group minerals in the solar system.

Hiroi, T.↗
NASA NTRS1988

The spectral properties of interplanetary dust particles

The observed spectral and mineralogical properties of interplanetary dust particles (IDP) allows the conclusion that: (1) the majority of IDP infrared spectra are dominated by olivine, pyroxene, or layer lattice silicate minerals, (2) to the first order the emission spectra of comets Halley and Kohoutek can be matched by mixtures of these IDP infrared types, implying that comets contain mixtures of these different crystalline silicates and may vary from comet to comet and perhaps even within a single comet, (3) do not expect to observe a single 20 micron feature in cometary spectra, (4) carbonaceous materials dominate the visible spectra properties of the IDPs even though the mass in these particles consists primarily of silicates, and (5) the particle characteristics summarized need to be properly accounted for in future cometary emission models.

Sandford, Scott A.↗
NASA NTRS1988

The spectral properties of collected interplanetary dust particles

The observed spectral and mineralogical properties of interplanetary dust particles (IDP) allows the conclusion that: (1) the majority of IDP infrared spectra are dominated by olivine, pyroxene, or layer lattice silicate minerals, (2) to the first order the emission spectra of comets Halley and Kohoutek can be matched by mixtures of these IDP infrared types, implying that comets contain mixtures of these different crystalline silicates and may vary from comet to comet and perhaps even within a single comet, (3) do not expect to observe a single 20 micron feature in cometary spectra, (4) carbonaceous materials dominate the visible spectra properties of the IDPs even though the mass in these particles consists primarily of silicates, and (5) the particle characteristics summarized need to be properly accounted for in future cometary emission models.

Sandford, S. A.↗
NASA NTRS1993

New K type asteroids

Several new K type asteroids were identified during near infrared spectral observations on July 30, 1992 at NASA's infrared telescope facility (IRTF) at Mauna Kea, Hawaii. These K asteroids are 513 Centesima, 633 Zelima, 1129 Neujmina, 1416 Renauxa, 1799 Koussevitzky, and 1883 Rauma. A K asteroid is an asteroid which possesses a S type spectra in visible wavelengths and a C type spectra visible in near-infrared wavelengths. These objects are usually misclassified as S asteroids on the basis of visible spectra alone. This type was first detected by the 52 infrared color asteroid survey also conducted at the IRTF. Our observations utilized a new seven color infrared asteroid filter system which allows near-infrared data to be collected from asteroids as faint as 16th 5 magnitude.

Granahan, James C.↗