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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

On the inclusion of the hydrogen dimer in the analysis of Voyager IRIS spectra

Empirical formulas are fitted to existing theoretical absorption spectra of H2-H2 pairs in the far-infrared allowing the inclusion of dimer absorption, parameterized with the height dependence of the para-hydrogen profile, in the calculations. Comparison between synthetic and Voyager IRIS spectra shows that once the dimer absorption is included it is now possible to reproduce the hydrogen portion of the IRIS spectrum to within the precision of the measurements.

Carlson, Barbara E.↗
DOE OSTI2021

Tolyporphins A–R, unusual tetrapyrrole macrocycles in a cyanobacterium from Micronesia, assessed quantitatively from the culture HT-58-2

The ‘pigments of life’ family has been enlarged by the discovery of the tetrapyrrole macrocycles dubbed tolyporphins, which are present in a cyanobacterial culture (HT-58-2). Of the 18 known tolyporphins, fourteen (A–J and L–O) are dioxobacteriochlorins, three (K, Q and R) are oxochlorins, and one (P) is a porphyrin. The members with a given chromophore absorb similarly but not identically with each other, presenting the problem of absorption spectral aliasing. Tolyporphins G and H are isomers, as are tolyporphins L–O, given the nature of the peripheral ( C -glycoside, –OH, or –OAc) substituents, presenting the (isobaric) problem of mass spectrometric analysis. The distribution of tolyporphin members is known to change over time and under different growth conditions, however, the complexity of the tolyporphins mixture presents challenges toward characterization of the underlying factors that alter such distributions. Liquid chromatography-mass spectrometry with dynamic multiple reaction monitoring (LC-MS-dMRM) was employed to characterize the distribution of tolyporphins under distinct growth media, using two semisynthetic standards, tolyporphin A O,O -dibutyrate and tolyporphin D O,O,O,O -tetrabutyrate. Growth in media containing both ammonium and nitrate salts versus nitrate alone affords increased production of tolyporphins. The absorption spectra of tolyporphins A–R have been reevaluated with regards to molar absorption coefficients, are compared with those of selected tetrapyrrole macrocycles to better understand the effects of chromophores and substituents, and are made available here in print and digital forms for comparison with isolated tolyporphins and mixtures thereof. Together, the work provides the foundation for quantitative assessment of these unusual natural products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2010

Carbon Dioxide (CO2) Retrievals from Atmospheric Chemistry Experiment (ACE) Solar Occultation Measurements

The Atmospheric Chemistry Experiment ACE satellite (SCISAT-1) was launched into an inclined orbit on 12 August 2003 and is now recording high signal-to-noise 0.02 per centimeter resolution solar absorption spectra covering 750-4400 per centimeter (2.3-13 micrometers). A procedure has been developed for retrieving average dry air CO2 mole fractions (X(sub CO2)) in the altitude range 7-10 kilometers from the SCISAT-1 spectra. Using the N2 continuum absorption in a window region near 2500 per centimeter, altitude shifts are applied to the tangent heights retrieved in version 2.2 SCISAT-1 processing, while cloudy or aerosol-impacted measurements are eliminated. Monthly-mean XCO2 covering 60 S to 60 N latitude for February 2004 to March 2008 has been analyzed with consistent trends inferred in both hemispheres. The ACE XCO2 time series have been compared with previously-reported surface network measurements, predictions based on upper tropospheric aircraft measurements, and space-based measurements. The retrieved X(sub CO2) from the ACE-FTS spectra are higher on average by a factor of 1.07 plus or minus 0.025 in the northern hemisphere and by a factor of 1.09 plus or minus 0.019 on average in the southern hemisphere compared to surface station measurements covering the same time span. The ACE derived trend is approximately 0.2% per year higher than measured at surface stations during the same observation period.

Rinsland, Curtis P.↗
NASA NTRS1975

Conversion of laser energy to gas kinetic energy

Techniques for the gas phase absorption of laser radiation for conversion to gas kinetic energy are discussed. Absorption by inverse Bremsstrahlung, in which laser energy is converted at a gas kinetic rate in a spectrally continuous process, is briefly described, and absorption by molecular vibrational rotation bands is discussed at length. High pressure absorption is proposed as a means of minimizing gas bleaching and dissociation, the major disadvantages of the molecular absorption process. A band model is presented for predicting the molecular absorption spectra in the high pressure absorption region and is applied to the CO molecule. Use of a rare gas seeded with Fe(CO)5 for converting vibrational modes to translation modes is described.

Caledonia, G. E.↗
NASA NTRS2006

Measurements and Theoretical Calculations of N2-broadening and N2-shift Coefficients in the v2 band of CH3D

In this paper, we report measured Lorentz N2-broadening and N2-induced pressure-shift coefficients of CH3D in the v2 fundamental band using a multispectrum fitting technique. These measurements were made by analyzing 11 laboratory absorption spectra recorded at 0.0056 cm(exp -1) resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 10.2 and 25 cm. The total sample pressures ranged from 0.98 to 402.25 Torr with CH3D volume mixing ratios of 0.01 in nitrogen. We have been able to determine the N2 pressure- broadening coefficients of 368 v2 transitions with quantum numbers as high as J"= 20 and K = 16, where K" = K' equivalent to K (for a parallel band). The measured N2-broadening coefficients range from 0.0248 to 0.0742 cm(exp -1) atm(exp -1) at 296 K. All the measured pressure-shifts are negative. The reported N2-induced pressure-shift coefficients vary from about 0.0003 to 0.0094 cm(exp -1) atm(exp -1). We have examined the dependence of the measured broadening and shift parameters on the J", and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = -J", J", and J" + 1 in the (sup Q)P-, (sup Q)Q-, and (sup Q)R-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.7%. The N2-broadening and pressureshift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom atom Lennard-Jones potential. The theoretical results of the broadening coefficients are in good overall agreement with the experimental data (8.7%). The N2-pressure shifts whose vibrational contribution is derived from parameters fitted in the (sup Q)Q-branch of self-induced shifts of CH3D, are also in reasonable agreement with the scattered experimental data (20% in most cases).

Predoi-Cross, A.↗
NASA NTRS1988

Laboratory simulation of dust spectra

Laboratory studies of the IR spectra of interstellar dust are reviewed. Studies of the absorption spectra of dense molecular clouds are discussed, including methods to produce interstellar ice analogues, simulations of astronomical spectra, and IR absorption features caused by ices. Comparisons are made between observational and experimental results of interstellar dust studies. Also, the interstellar emission features associated with dusty regions exposed to UV radiation are examined, including bands related to PAHs and PAH-related materials. It is shown that interstellar spectra are more consistant with emission from free PAHs than with emission from particles.

Allamandola, L. J.↗
NASA NTRS1992

Vibronic spectra of Cu(2+) in ZnTe

Infrared-absorption spectra of substitutional Cu(2+) ions in ZnTe have been measured at 4.6 K. Several distinct absorption peaks are observed between 800 and 2000/cm. Absorption peaks at 1002 and 1069/cm are identified as zero-phonon lines arising from 2T2-2E transitions. Between 1069 and 2000/cm, several sets of sharp absorption lines are seen to recur regularly at an interval of 210/cm, corresponding to the LO phonon energy. Within each set distinct vibronic sidebands that cannot be identified with critical-point energies of TA, LA, TO or LO phonon modes are observed. A dynamic Jahn-Teller effect, involving coupling between a single-phonon mode and the electronic states of the 2E level, is proposed to account for the observed spectra.

Volz, M. P.↗
DOE OSTI2025

Database of low‐temperature absorption and fluorescence spectra of native photosynthetic tetrapyrrole macrocycles

Low-temperature (77 K) absorption and fluorescence spectra of 12 naturally occurring photosynthetic tetrapyrrole macrocycles have been recorded in a frozen glass (2-methyltetrahydrofuran). The compounds encompass distinct chromophore classes: porphyrin, chlorophyll c 2 ; chlorin, chlorophylls a, b, d, f and bacteriochlorophylls c, d, e, f; and bacteriochlorin, bacteriochlorophylls a, b, g. The spectra are compared with those of the same pigment in liquid solution (predominantly 2-methyltetrahydrofuran) at room temperature (293 K). The measured Stokes shifts at 77 K across the 12 macrocycles range from ~30 to 300 cm −1 . The spectral data in digital form are made available as part of the PhotochemCAD databases. Literature searches have revealed extensive published data for Chl a (often in biological matrices) but at best rather limited data for less common macrocycles. The availability of a systematic collection of curated spectral data collected at low temperature should be useful for a variety of assessments, including reconstruction of absorption spectra of (bacterio)chlorophyll-containing protein complexes, vibrational analysis of absorption and fluorescence spectra, and calculations where knowledge of energy levels is important.

Niedzwiedzki, Dariusz M. [Washington University in↗
DOE OSTI2019

Spectroscopic and mechanical studies of lithium aluminoborate glasses doped with chromium ions

Aluminoborate glasses, doped with chromium ions, were prepared using melt quenching technique. Spectroscopic and mechanical tools were utilized to study the impact of B{sub 2}O{sub 3} substitution with Al{sub 2}O{sub 3} on the structure of the glass system. Infrared spectra uncovered that substitution of B{sub 2}O{sub 3} with Al{sub 2}O{sub 3} causes concealment of non-bridging oxygen NBOs and creation of inflexible AlO{sub 4} tetrahedral. The UV–Vis absorption spectra demonstrated a blue-shift of the optical absorption edge with increasing Al{sub 2}O{sub 3} content. The optical band gap was found to increase, while the refractive index diminished with addition of Al{sub 2}O{sub 3} content. The calculated crystalline field Dq, Racah parameters (B and C) and Dq/B indicated the diminishment in inter-electron repulsion with increasing the covalency. In particular, a value of Dq/B larger than 2.3 assures that chromium ions are in strong ligand field sites. The elastic moduli increase with increasing Al{sub 2}O{sub 3} content, due to the reduction NBOs and, consequently, the increased average bond connectivity.

36 MATERIALS SCIENCE↗
NASA NTRS2002

Submillimeter Spectra of Low Temperature Gases and Mixtures

Submillimeter absorption spectra of nitrogen, nitrogen-argon mixtures, and methane have been measured using temperatures and pressures near to those found in the atmospheres of Titan and Saturn. The experiments show the spectral signature of dimers which will likely appear in far-infrared spectra of Titan that will be obtained by the Composite Infrared Spectrometer (CIS) onboard the Cassini spacecraft. The recent CIRS spectrum of Jupiter shows far-infrared spectral lines of methane and the corresponding lines are observed in the laboratory. We are extending this work to lower frequencies using a new differential Michelson interferometer that operates over the frequency region 3-30 1/cm..

Wishnow, E. H.↗
NASA NTRS1982

The vacuum ultraviolet spectra of HCN, C2N2, and CH3CN

Quantitative vacuum ultraviolet absorption spectra for HCN, C2N2, and CH3CN have been obtained over the wavelength range 60-160 nm. Where comparison is possible, the measurements of the absorption coefficients for HCN and C2N2 are consistent with previous studies. Because of the superior resolution of this work (0.05 nm), vibrational assignments in the valence and Rydberg transitions of HCN have been extended while higher members of the Rydberg series in CH3CN have been identified.

Nuth, J. A.↗
DOE OSTI2022

Poly(cyclosilane) Connectivity Tunes Optical Absorbance

We report herein the influence of skeletal connectivity on the conformation-dependent optical properties of cyclosilane homo- and copolymers. 1,3-Linked cyclosilanes were bathochromically shifted by 20 nm in solution relative to 1,4-linked cyclosilanes, an effect reproduced by quantum chemical calculations on oligomeric model systems. Polysilane optical properties are conformation-dependent, and 1,3-linked cyclosilanes were hypothesized to adopt a favorable conformation unavailable to 1,4-linked cyclosilanes constrained to an endocyclic gauche conformation. Copolymerization of the isomeric cyclosilanes 1,3Si 6 and 1,4Si 6 afforded linear statistical copolymers, as characterized by 1 H and 29 Si NMR spectroscopies. The distinct connectivity of each comonomer was found to give rise to tunable absorption spectra, where the position of the absorption band systematically increased with the increased corporation of 1,3Si 6 . Computational studies pointed to conformation-dependent changes in orbital symmetry in shifting the most intense transition from the low-energy highest occupied molecular orbital (HOMO) → lowest unoccupied molecular orbital (LUMO) transition to a higher-energy HOMO → LUMO + n transition. Here, the results of these studies demonstrate for the first time the role of silicon skeletal connectivity in controlling conformation and optoelectronic properties and provide new insight into the structure-based design of solution-processable silicon-based polymeric materials.

36 MATERIALS SCIENCE↗
NASA NTRS1977

Infrared heterodyne spectroscopy of atmospheric ozone

The absorption spectrum of atmospheric ozone is measured within a 1/cm region at 1100/cm, using an IR heterodyne detector (spectrometer with CO2 local oscillator) developed for astronomical work. Absorption spectra obtained by passing radiation from the tunable diode laser through an absorption cell, heterodyne spectra of atmospheric ozone, and a predicted atmospheric spectrum are compared. Water vapor absorbing in the region of interest (1100/cm) is also considered. Preliminary results encourage the use of diode laser local oscillators in tunable heterodyne detector systems for spectroscopy of atmospheric ozone and remote high-resolution spectroscopy of atmospheric constituents and pollutants.

Frerking, M. A.↗