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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Interconversion of diborane(4) isomers

Highly correlated electronic structure computations using many-body perturbation theory and coupled-cluster gradient techniques are used to study the reaction pathway that links the two forms (C2u and D2d) of diborane(4). The results obtained indicate that a low-energy pathway exists for interconversion of the two low-lying isomers of diborane(4). The proposed mechanism consists of a single concerted but nonsynchronous rotation of the BH2 groups. The pathway first follows an idealized reaction coordinate which preserves C2 symmetry, but then bifurcates at a branch point, leading to two equivalent transition states which lack nontrivial elements of symmetry.

Stanton, John F.↗
NASA NTRS1985

NMR characterization of functional groups: 9--isomer ratios of available chloromethylstyrene mixtures

From the assignments of the 1H and 13C 11.7 tesla NMR spectra of available mixtures of m- and p-chloromethylstyrene, the proportion of the meta and para compounds are easily determined. For these materials from two common commercial sources, proportions of 72 and 28% and 68 and 32% were found. These concentrations are substantially different from the often assumed 60 and 40% for the meta and para compounds, respectively. The influence of this difference on the desired properties of copolymers made from such mixtures is discussed. An alternative quantitative procedure for determining the chloromethyl group isomer ratios is also described which employs silver trifluoroacetate in acetone displacement of chloride and 19F NMR examination of the resulting ester mixture with a 2.3 tesla spectrometer.

Polystyrenes/analysis/chemistry↗
NASA NTRS1992

Esterification of all four monoribonucleotides with acetyl-D-L-valine proceeds with a preference for the D-isomer but the D/L ratio in the products declines as a function of the hydrophobicity of the nucleotide

We recently reported that esterification of 5'-AMP with N-acetyl amino acids proceeds with a preference for D-amino acids, and the D/L ratio in products declines as the hydrophobicity of the amino acid declines. Using one amino acid, Ac-Val, we now show that esterification of all four nucleotides proceeds with a preference for the D-isomer and the preference declines as the hydrophobicity of the nucleotide declines. So, in both types of experiments, the preferences seem determined by hydrophobic interactions.

NASA Discipline Exobiology↗
NASA NTRS2019

Solid-State Isomerization and Infrared Band Strengths of Two Conformational Isomers of Cyclopropanecarboxaldehyde, A Candidate Interstellar Molecule

At least a dozen of the known interstellar molecules possess a formyl group (HCO), suggesting that other such species exist and await discovery in the interstellar medium. Here, we examine the mid-infrared (mid-IR) spectrum and selected physical properties of one such candidate, cyclopropanecarboxaldehyde, in amorphous ices. Mid-IR transmission spectra of solid cyclopropanecarboxaldehyde are presented for the first time and used to determine the cis-to-trans ratio of conformational isomers present in amorphous samples. The measured ratio is compared to one from an electron-diffraction study of the gas-phase compound. The cis-to-trans isomerization in the amorphous compound is followed, and the activation energy is determined. The first IR band strengths for solid cyclopropanecarboxaldehyde are reported. Also presented are refractive indices and densities at 15 K for amorphous forms of two related compounds, cyclopropane and cyclopropanemethanol. Two low-temperature reactions for the interstellar formation of cyclopropanecarboxaldehyde are briefly described.

band strengths↗
NASA NTRS2020

First Detections of Dichlorobenzene Isomers and Trichloromethylpropane from Organic Matter Indigenous to Mars Mudstone in Gale Crater, Mars: Results from the Sample Analysis at Mars Instrument Onboard the Curiosity Rover

Chromatographic analysis of the Cumberland mudstone in Gale crater by the Sample Analysis at Mars (SAM) instrument revealed the detection of two to three isomers of dichlorobenzene. Their individual concentrations were estimated to be in the 0.5–17 ppbw range relative to the sample mass. We also report the first detection of trichloromethylpropane and the confirmation of the detection of chlorobenzene previously reported. Supporting laboratory experiments excluded the SAM internal background as the source of those compounds, thus confirming the organic carbon and chlorine of the newly detected chlorohydrocarbons are indigenous to the mudstone sample. Laboratory experiments also demonstrated that the chlorohydrocarbons were mainly produced from chemical reactions occurring in the SAM ovens between organic molecules and oxychlorines contained in the sample. The results we obtained show that meteoritic organics and tested chemical species (a polycyclic aromatic hydrocarbon, an amino acid, and a carboxylic acid) were plausible organic precursors of the chlorinated aromatic molecules detected with SAM, thus suggesting that they could be among the organic molecules present in the mudstone. Results from this study coupled with previously reported detections of chlorinated aromatics (<300 ppbw) indigenous to the same mudstone highlight that organics can be preserved from the harsh surface conditions even at shallow depth. The detection of new chlorohydrocarbons with SAM confirms that organic molecules should have been available in an environment favorable to life forms, strengthening the habitability aspect of Gale crater. Key Words: Mars—Chlorinated organic molecules—In situ measurements—Sample Analysis at Mars— Mudstone—Gale crater. Astrobiology 20, 292–306.

Szopa, Cyril↗
NASA NTRS2005

Gas-Phase Formation Rates of Nitric Acid and Its Isomers Under Urban Conditions

Ozone formation in urban smog is controlled by a complex set of reactions which includes radical production from photochemical processes, catalytic cycles which convert NO to NO2, and termination steps that tie up reactive intermediates in long-lived reservoirs. The reaction OH + NO2 + M -4 HONO2 + M (la) is a key termination step because it transforms two short-lived reactive intermediates, OH and NO2, into relatively long-lived nitric acid. Under certain conditions (low VOC/NOx), ozone production in polluted urban airsheds can be highly sensitive to this reaction, but the rate parameters are not well constrained. This report summarizes the results of new laboratory studies of the OH + NO2 + M reaction including direct determination of the overall rate constant and branching ratio for the two reaction channels under atmospherically relevant conditions.

Air pollution↗
DOE OSTI2023

Catalytic Transformation of Positional Nitrophenol Isomers on Highly Active Ag/Linde‐Type A4 Zeolite: A Comparative Analysis

Abstract The catalytic transformation of ortho‐( o‐ NP), meta‐( m‐ NP) and para‐nitrophenols ( p‐ NP) by Ag nanoparticles (Ag‐NPs) stabilised on zeolite A4 (ZA4) is presented for the first time. The catalysts are prepared by microwave‐assisted synthesis (Ag/ZA4‐MW) or ion exchange (Ag/ZA4‐IE). The results indicate that the nitrophenol reduction rate depends on the molecule structure and the presence of low‐coordinated metallic Ag‐NPs (∼2 nm and sub nanometric species). Meanwhile, the reactivity tendency depends on the synthesis methodology ( m‐ NP> p‐ NP> o‐ NP and o‐ NP> m‐ NP> p‐ NP for Ag/ZA4‐MW and Ag/ZA4‐IE, respectively). The turnover frequency (TOF) values estimated for nitrophenols reduction are superior for Ag/ZA4‐MW catalyst by several orders of magnitude compared with those obtained for Ag/ZA4‐IE catalyst. In addition, the catalyst exhibits remarkable catalytic stability for the reduction of p‐ NP even after the fifth consecutive catalytic run. The presently prepared catalysts are characterised by superior catalytic activity for the reduction of nitroaromatic compounds than similar Ag‐based materials reported in the literature.

Horta‐Fraijo, Patricia↗
DOE OSTI2020

Branching ratio and γ -ray emission probabilities in the decay of the J π = 13 / 2 + isomer in 197Hg

Gamma rays following the decay of the 197 g Hg and 197 m Hg radionuclides were measured using chemically-purified sources and a planar HPGe detector. In the case of 197 m Hg, precise values of 94.68 (9)% and 5.32 (9)% were confirmed for the IT and EC branches, respectively, the latter discovered to differ significantly from previously published data. The half-lives of 197 g Hg and 197 m Hg were also measured as 64.81 (24) h and 23.82 (4) h.

197𝑔Hg↗