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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
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Diels-Alder Trapping of Photochemically Generated o-Xylenols: Application in the Synthesis of Novel Organic Molecules and Polymers

Bis(o-xylenol) equivalents are useful synthetic intermediates in the construction of polymers and hydroxyl substituted organic molecules which can organize by hydrogen bonded self-assembly into unique supramolecular structures. These polymers and supramolecular materials have potential use as coatings and thin films in aerospace, electronic and biomedical applications.

Meador, Michael A.↗
NASA NTRS2003

Bisadducts from the Diels-Alder Trapping of Bis(o-Xylenols) Photochemically Generated from 2,5-Dibenzoyl-p-xylene

Photolysis of 2,5-dibenzoyl-p-xylene produces two discrete o-xylenols which undergo Diels-Alder cycloadditions with standard dienophiles, such as methyl acrylate, to produce 1,5-dihydroxy-1,5-diphenyl-l,2,3,4,5,6,7,8-octahydroanthracenes, 2a, in good yield (greater than 80%). The anti bisadduct crystallizes into hydrogen bonded stacks. Conversion of both syn- and anti-bisadducts to the corresponding anthracenes was achieved through the use of standard dehydration and aromatization chemistry.

Meador, Michael A.↗
NASA NTRS1990

Photochemical cycloaddition reactions of cyanoacetylene and dicyanoacetylene

Photolysis of cyanoacetylene with 185- or 206-nm light yields 1,3,5-tricyanobenzene while 254-nm radiation yields a mixture of tetracyanocyclooctatetraenes, 1,2,4- and 1,3,5-tricyanobenzene. A polymer of cyanoacetylene is the major photoproduct. 1,3,5-Tricarbomethoxybenzene was the only photoproduct identified from the irradiation of methyl propiolate at 254 nm. Mono-, di-, and tricyanobenzenes are formed by irradiation of mixtures of acetylene and cyanoacetylene at 185, 206, and 254 nm along with trace amounts of cyclooctatetraenes. No photoadducts were detected on photolysis of mixtures of cyanoacetylene and CO or HCN. The tetracyanocyclooctatetraene structures were established by UV, MS, and NMR analyses. The 1H NMR of the product mixture exhibited a singlet at delta 7.028 consistent with either 1 or 2 and two singlets at delta 6.85 and 6.91 assigned to 3. Photolysis of mixtures of dicyanoacetylene and acetylene with either 185- or 206-nm light yielded 1,2-dicyanobenzene and (E,Z)-1-buten-3-yne-1,4-dicarbonitrile. These products were also obtained using 254-nm light along with a mixture of tetracyanocyclooctatetraenes. The same three singlets were observed in this product mixture as were observed in the tetracyanocyclooctatetraenes obtained from cyanoacetylene. From this observation it was concluded that the delta 7.02 signal is due to 2 and not 1. The photolysis of cyanoacetylene and dicyanoacetylene in the presence of ethylene with 185-nm light yields 1-cyanocylobutene and 1,2-dicyanocyclobutene, respectively. 2-Cyanobutadiene and 2,3-dicyanobutadiene are the photoproducts with 254-nm light. Reaction pathways are proposed to explain these findings.

NASA Discipline Exobiology↗
NASA NTRS2000

Deuterium enrichment of polycyclic aromatic hydrocarbons by photochemically induced exchange with deuterium-rich cosmic ices

The polycyclic aromatic hydrocarbon (PAH) coronene (C24H12) frozen in D2O ice in a ratio of less than 1 part in 500 rapidly exchanges its hydrogen atoms with the deuterium in the ice at interstellar temperatures and pressures when exposed to ultraviolet radiation. Exchange occurs via three different chemical processes: D atom addition, D atom exchange at oxidized edge sites, and D atom exchange at aromatic edge sites. Observed exchange rates for coronene (C24H12)-D2O and d12-coronene (C24D12)-H2O isotopic substitution experiments show that PAHs in interstellar ices could easily attain the D/H levels observed in meteorites. These results may have important consequences for the abundance of deuterium observed in aromatic materials in the interstellar medium and in meteorites. These exchange mechanisms produce deuteration in characteristic molecular locations on the PAHs that may distinguish them from previously postulated processes for D enrichment of PAHs.

NASA Center ARC↗
NASA NTRS1990

[Chemistry of alpha-aminonitriles. Aziridine-2-carbonitrile: photochemical formation from 2-aminopropenenitrile]

2-Aminopropenenitrile in solvents such as MeCN, MeOH, or H2O is photoisomerized by UV light to racemic aziridine-2-carbonitrile (rac-2); the larger part of the starting material, however, fragments to HCN and MeCN. The observed photocyclization constitutes a structural connection within an ensemble of C3H4N2 compounds considered to be potentially relevant to prebiotic chemistry.

NASA Program Exobiology↗
NASA NTRS2003

Tropospheric Modeling Studies of TRACE-P Data: Investigations of the HO(x)/NO(x)/O3 Photochemical System and Its Coupling to Sulfur/Aerosol Species

During the duration of the NASA Grant NCC1-01-24, members of research team consisted of: D. Davis, G. Chen, S. Liu, C. Song, B. DiNunno, J. Nowak, and X. Gong. The major goal of our group effort was that of analyzing data from several NASA field studies and then preparing manuscripts for publication reflecting these analyses. Many of the papers so published were initiated by members of the Davis group; however, for a great many others one or more group members assisted other PI'S in writing their manuscripts. Both types of manuscripts are listed below as representing the final product from this grant.

Davis, Douglas D.↗
NASA NTRS2005

Photochemically Etched Construction Technology Developed for Digital Xenon Feed Systems

Electric propulsion systems are quickly emerging as attractive options for primary propulsion in low Earth orbit, in geosynchronous orbit, and on interplanetary spacecraft. The driving force behind the acceptance of these systems is the substantial reduction in the propellant mass that can be realized. Unfortunately, system designers are often forced to utilize components designed for chemical propellants in their electric systems. Although functionally acceptable, these relatively large, heavy components are designed for the higher pressures and mass flow rates required by chemical systems. To fully realize the benefits of electric propulsion, researchers must develop components that are optimized for the low flow rates, critical leakage needs, low pressures, and limited budgets of these emerging systems.

Otsap, Ben↗
NASA NTRS1978

Photochemical preparation of olefin addition catalysts

Novel polymer supported catalysts are prepared by photo-irradiation of low valent transition metal compounds such as Co.sub.2 (CO).sub.8, Rh.sub.4 (CO).sub.12 or Ru.sub.3 (CO).sub.12 in the presence of solid polymers containing amine ligands such as polyvinyl pyridine. Hydroformylation of olefins to aldehydes at ambient conditions has been demonstrated.

Gray, Harry B.↗
NASA NTRS2010

Methane on Mars: Thermodynamic Equilibrium and Photochemical Calculations

The detection of methane (CH4) in the atmosphere of Mars by Mars Express and Earth-based spectroscopy is very surprising, very puzzling, and very intriguing. On Earth, about 90% of atmospheric ozone is produced by living systems. A major question concerning methane on Mars is its origin - biological or geological. Thermodynamic equilibrium calculations indicated that methane cannot be produced by atmospheric chemical/photochemical reactions. Thermodynamic equilibrium calculations for three gases, methane, ammonia (NH3) and nitrous oxide (N2O) in the Earth s atmosphere are summarized in Table 1. The calculations indicate that these three gases should not exist in the Earth s atmosphere. Yet they do, with methane, ammonia and nitrous oxide enhanced 139, 50 and 12 orders of magnitude above their calculated thermodynamic equilibrium concentration due to the impact of life! Thermodynamic equilibrium calculations have been performed for the same three gases in the atmosphere of Mars based on the assumed composition of the Mars atmosphere shown in Table 2. The calculated thermodynamic equilibrium concentrations of the same three gases in the atmosphere of Mars is shown in Table 3. Clearly, based on thermodynamic equilibrium calculations, methane should not be present in the atmosphere of Mars, but it is in concentrations approaching 30 ppbv from three distinct regions on Mars.

Levine, J. S.↗
NASA NTRS2021

Photochemical and Microbial Degradation of Chromophoric Dissolved Organic Matter Exported from Tidal Marshes

Wetlands export chromophoric dissolved organic matter (CDOM) to estuaries, where CDOM is removed and transformed through biotic and abiotic process, subsequently impacting nutrient cycling, light availability, ecosystem metabolism, and phytoplankton activity. We examined the bioavailability and photoreactivity of CDOM exported from four Chesapeake Bay tidal marshes across three seasons and along an estuarine salinity gradient using three incubation treatments: 14-day microbial (MD), 7-day combined photochemical/microbial (PB+MD), and 7-day microbial incubation after photobleaching (MD after PB). CDOM absorption at 300 nm (aCDOM300) and dissolved organic carbon (DOC) concentrations showed strong seasonality, with minima in winter, but CDOM quality (absorption spectral slopes, fluorescence component ratios) was less variable seasonally. PB+MD over 7 days decreased aCDOM300 (–56.0%), humic-like fluorescence (–67.6%), and DOC (–17.8%), but increased the spectral slope ratio SR (=S275-295/S300-350) (+94.8%), suggesting a decrease in CDOM molecular weight. Photochemistry dominated the PB+MD treatment. Photoreactivity was greater during the winter and in marsh/watershed versus down-estuary sites, likely due to less previous light exposure. Prior photobleaching increased the bioavailability of marsh-exported CDOM, resulting in a greater loss of aCDOM300 and DOC, and a greater increase in humic-like fluorescence (–6.0%, –5.9%, and +18.4% change, respectively, over 7-day MD after PB incubations, versus –2.8%, –5.5%, and +2.6% change, respectively, over 14-day MD incubations). CDOM exported from a marsh downstream of a major wastewater treatment plant showed the greatest photoreactivity and bioavailability. This highlights the significance of human activity on estuarine CDOM quality and biogeochemical cycles.

Dissolved organic matter↗
NASA NTRS2020

Impact of Hydrogen Sulfide on Photochemical Haze Formation in Methane/Nitrogen Atmospheres

The chemistry of trace sulfur gases in planetary organic haze formation is poorly understood, though both are ubiquitous in planetary atmospheres. Here, we perform laboratory studies to explore how the addition of trace amounts of H2S (0.5–5 ppmv) affects organic aerosol produced from ultraviolet photochemistry of CH4 in N2. We analyze the aerosol product composition and size in real time. Inclusion of trace amounts of H2S in the precursor mixture significantly enhances the formation of organic aerosol mass and the particle effective density, both of which increase as a function of initial H2S concentration and in the absence of an additional carbon source. We further present evidence that the addition of trace H2S to the precursor mixtures leads to the formation of organosulfur compounds. Their inclusion in the aerosol-phase contributes to the organic aerosol mass enhancement. Thiyl-alkene chemistry is proposed as a possible organosulfur formation mechanism. In contrast to previous assumptions that sulfur and carbon chemistry occur largely independently of each other, these results suggest a coupling between the two chemistries. This coupling has potential impacts on organic haze and atmospheric sulfur chemistry in planetary atmospheres.

Nathan W Reed↗