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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Molecular parameters of the O2 molecule.

By analyzing all existing frequency data of the oxygen molecule in microwave, submillimeter, and infrared spectroscopy, a new set of molecular parameters is obtained. The parameters are tabulated and compared with values obtained by other authors. Observed and calculated frequencies of oxygen lines are also given.

Welch, W. M.↗
NASA NTRS2006

MEMS-Based Force-Detected Nuclear Magnetic Resonance (FDNMR) Spectrometer

Nuclear Magnetic Resonance (NMR) spectroscopy allows assignment of molecular structure by acquiring the energy spectrum of nuclear spins in a molecule, and by interpreting the symmetry and positions of resonance lines in the spectrum. As such, NMR has become one of the most versatile and ubiquitous spectroscopic methods. Despite these tremendous successes, NMR experiments suffer from inherent low sensitivity due to the relatively low energy of photons in the radio frequency (rt) region of the electromagnetic spectrum. Here, we describe a high-resolution spectroscopy in samples with diameters in the micron range and below. We have reported design and fabrication of force-detected nuclear magnetic resonance (FDNMR).

force detected nuclear magnetic resonance (FDNMR)↗
NASA NTRS2010

Selective Functionalization of Carbon Nanotubes: Part II

An alternative method of low-temperature plasma functionalization of carbon nanotubes provides for the simultaneous attachment of molecular groups of multiple (typically two or three) different species or different mixtures of species to carbon nanotubes at different locations within the same apparatus. This method is based on similar principles, and involves the use of mostly the same basic apparatus, as those of the methods described in "Low-Temperature Plasma Functionalization of Carbon Nanotubes" (ARC-14661-1), NASA Tech Briefs, Vol. 28, No. 5 (May 2004), page 45. The figure schematically depicts the basic apparatus used in the aforementioned method, with emphasis on features that distinguish the present alternative method from the other. In this method, one exploits the fact that the composition of the deposition plasma changes as the plasma flows from its source in the precursor chamber toward the nanotubes in the target chamber. As a result, carbon nanotubes mounted in the target chamber at different flow distances (d1, d2, d3 . . .) from the precursor chamber become functionalized with different species or different mixtures of species. In one series of experiments to demonstrate this method, N2 was used as the precursor gas. After the functionalization process, the carbon nanotubes from three different positions in the target chamber were examined by Fourier-transform infrared spectroscopy to identify the molecular groups that had become attached. On carbon nanotubes from d1 = 1 cm, the attached molecular groups were found to be predominantly C-N and C=N. On carbon nanotubes from d2 = 2.5 cm, the attached molecular groups were found to be predominantly C-(NH)2 and/or C=NH2. (The H2 was believed to originate as residual hydrogen present in the nanotubes.) On carbon nanotubes from d3 = 7 cm no functionalization could be detected - perhaps, it was conjectured, because this distance is downstream of the plasma source, all of the free ions and free radicals of the plasma had recombined into molecules.

Meyyappan, Meyya↗
NASA NTRS1994

Alpha-helical hydrophobic polypeptides form proton-selective channels in lipid bilayers

Proton translocation is important in membrane-mediated processes such as ATP-dependent proton pumps, ATP synthesis, bacteriorhodopsin, and cytochrome oxidase function. The fundamental mechanism, however, is poorly understood. To test the theoretical possibility that bundles of hydrophobic alpha-helices could provide a low energy pathway for ion translocation through the lipid bilayer, polyamino acids were incorporated into extruded liposomes and planar lipid membranes, and proton translocation was measured. Liposomes with incorporated long-chain poly-L-alanine or poly-L-leucine were found to have proton permeability coefficients 5 to 7 times greater than control liposomes, whereas short-chain polyamino acids had relatively little effect. Potassium permeability was not increased markedly by any of the polyamino acids tested. Analytical thin layer chromatography measurements of lipid content and a fluorescamine assay for amino acids showed that there were approximately 135 polyleucine or 65 polyalanine molecules associated with each liposome. Fourier transform infrared spectroscopy indicated that a major fraction of the long-chain hydrophobic peptides existed in an alpha-helical conformation. Single-channel recording in both 0.1 N HCl and 0.1 M KCl was also used to determine whether proton-conducting channels formed in planar lipid membranes (phosphatidylcholine/phosphatidylethanolamine, 1:1). Poly-L-leucine and poly-L-alanine in HCl caused a 10- to 30-fold increase in frequency of conductive events compared to that seen in KCl or by the other polyamino acids in either solution. This finding correlates well with the liposome observations in which these two polyamino acids caused the largest increase in membrane proton permeability but had little effect on potassium permeability. Poly-L-leucine was considerably more conductive than poly-L-alanine due primarily to larger event amplitudes and, to a lesser extent, a higher event frequency. Poly-L-leucine caused two populations of conductive events, one in the 0.1-0.5 pA range, and one in the 1.0-5.0 pA range, whereas nearly all events caused by poly-L-alanine were in the 0.1-0.5 pA range at an applied voltage of +60 mV. The channel-like activity appeared to switch between conductive and nonconductive states, with most open-times in the range of 50-200 ms. We conclude that hydrophobic polyamino acids produce proton-conducting defects in lipid bilayers that may be used to model functional proton channels in biological membranes.

NASA Discipline Exobiology↗
NASA NTRS1964

The structure of c2b5h7

Microwave spectroscopic methods for molecular structure determination of 2,4-dicarbaheptaborane

MOLECULAR STRUCTURE↗
NASA NTRS1977

Molecular clouds

An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.

Thaddeus, P.↗
NASA NTRS1984

The 1.5 - 3.5 Micron Spectroscopy of the Orion H2 Source

A synopsis of current research with near infrared airborne spectroscopy of the Orion molecular hydrogen emission line source is presented. It is suggested that (H2) is the most abundant molecular species in the interstellar medium and is of paramount importance to understand its behavior and distribution in that medium. The H2 has no permanent electric dipole moment which precludes dipole transitions. It is, however, detected in absorption against background starlight by UV electronic transitions and in the IR through electric quadrupole rotation/vibration and pure rotation emission lines. The physical parameters of this region, in the context of their relationships to other members of the complex family of Orion objects, molecular clouds, compact IR sources, H 2 regions, and shock fronts are described.

Davis, D. S.↗
NASA NTRS1985

Time dependent chemistry in dense molecular clouds. I - Grain surface reactions, gas/grain interactions and infrared spectroscopy

For the fist time, a time-dependent model is described which includes the role of grains in the production of molecules in dense clouds including ion-molecule gas phase chemistry. The approach provides information regarding the coupling between the two phases. Although the coupling between the two chemistries is extremely strong, the two domains maintain their own identities. While H2O, CH4, and NH3 are made efficiently, with a high production rate on grains and released back to the gas phase, the gas phase is essentially responsible for the formation of CO, a very stable molecule which may or may not react on grains with atomic oxygen and may or may not form CO2.

Dhendecourt, L. B.↗
NASA NTRS1987

Infrared emission from interstellar PAHs

The mid-IR absorption and Raman spectra of polycyclic aromatic hydrocarbons (PAHs) and the mechanisms determining them are reviewed, and the implications for observations of similar emission spectra in interstellar clouds are considered. Topics addressed include the relationship between PAHs and amorphous C, the vibrational spectroscopy of PAHs, the molecular emission process, molecular anharmonicity, and the vibrational quasi-continuum. Extensive graphs, diagrams, and sample spectra are provided, and the interstellar emission bands are attributed to PAHs with 20-30 C atoms on the basis of the observed 3.3/3.4-micron intensity ratios.

Allamandola, L. J.↗
NASA NTRS1991

Oxygen desorption from YBa2Cu3O(7-x) and Bi2CaSr2Cu2O(8 + delta) superconductors

Oxygen desorption experiments from YBa2Cu3O(7-x) (YBCO) and Bi2CaSr2Cu2O(8 + delta) (BSCCO) superconductors were carried out using a quadrupole mass spectrometer for monitoring the desorbing species and X-ray photoemission spectroscopy for surface characterization. Molecular oxygen was found to desorb from both superconductors following photoirradiation with ultraviolet/optical radiation and subsequent heating at over 150 C. Both YBCO and BSCCO were found to have similar oxygen desorption rates and similar activation energies. The desorption data as well as the X-ray photoemission data indicate that the oxygen desorption is not intrinsic to the superconductors but rather due to molecular oxygen entrapped in the material.

Mesarwi, A.↗
NASA NTRS2004

Precise Laboratory Measurement of LINR Frequencies Useful to Studies of Star and Planet Formation

In March 2002, we began a program in laboratory spectroscopy to provide accurate molecular line frequencies essential to studies of the motions and abundances in star-froming dense cores and planet-forming circumstellar disks. The CN radical is one of the most important tracers of dynamical motions in protoplanetary disks around low mass pre-main sequence stars. The millimeter-wave spectrum of CN consists of rotational transitions every 113 GHz which are split into many resolved hyperfine components. Very narrow and fairly bright lines of SiO in the ground vibrational state have been observed in regions where protostellar outflows interact with the cold ambient gas. In support of future astronomical observations in these regions, 10 successive rotational lines in the ground vibrational state of Si0 between 86 and 500 GHz, and two lines near 800 GHz were measured in the laboratory to an accuracy of a few kHz. A negative glow discharge spectrometer that will allow the determination of accurate line frequencies of molecular ions has been constructed. We are presently modifying the method for cooling the magnetic field enhanced (negative glow) discharge cell to 77 K.

Myers, Philip C.↗
NASA NTRS2005

Precise Laboratory Measurement of Line Frequencies Useful to Studies of Star and Planet Formation

In March 2002, we began a program in laboratory spectroscopy to provide accurate molecular line frequencies essential to studies of the motions and abundance in star-forming dense cores and planet-forming circumstellar disks. Summarized here is the progress that has been made in Year 3 of this grant. Work included measurement of 10 successive rotational lines in the ground vibrational state of SiO between 86 and 500 GHz, and two lines near 800 GHz to an accuracy of a few kHz; conducting pilot experiments on molecular ions in collision-free supersonic beams, including HCO+, N2H+, and H2D+; measurement of 22 lines of CN between 113 and 340 GHz; and setting up an experiment that would allow us to refine earlier measurements of the neutral species such as C3H2, CCS, H2CS, and SO by observing the very narrow sub-Doppler (Lamb dip) features in the millimeter-wave spectra of these species.

Myers, Philip C.↗
NASA NTRS1973

A comment on the measurement of atmospheric density by absorption of Lyman-alpha.

It is shown that the absorption cross section for molecular oxygen at Lyman alpha is about 0.8 times 10 to the minus twentieth power sq cm. It is pointed out that, for application of absorption spectroscopy to the measurement of molecular oxygen density in the atmosphere, no correction for the variation of cross section with wavelength is necessary.

Smith, L. G.↗