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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Combined Experimental and Computational Investigation of the Elementary Reaction of Ground State Atomic Carbon (C; 3 P j ) with Pyridine (C 5 H 5 N; X 1 A 1 ) via Ring Expansion and Ring Degradation Pathways

In t his work, we explored the elementary reaction of atomic carbon (C; 3 P j ) with pyridine (C 5 H 5 N; X 1 A 1 ) at a collision energy of 34 ± 4 kJ mol-1 utilizing the crossed molecular beams technique. Forwardconvolution fitting of the data was combined with high-level electronic structure calculations and statistical (RRKM) calculations on the triplet C 6 H 5 N potential energy surface (PES). These investigations reveal that the reaction dynamics are indirect and dominated by large range reactive impact parameters leading via barrier-less addition to the nitrogen atom and to two chemically non-equivalent ‘aromatic’ carbon-carbon bonds forming three distinct collision complexes. At least two reaction pathways through atomic hydrogen loss were identified on the triplet surface. These channels involve multiple isomerization steps of the initial collision complexes via ring-opening and ring expansion forming an acyclic 1-ethynyl-3-isocyanoallyl radical (P1; 2 A”) and a hitherto unreported seven-membered 1-aza-2-dehydrocyclohepta-2,4,6-trien-4-yl radical isomer (P3; 2 A), respectively. For RRKM calculations at zero collision energy, representing conditions in cold molecular clouds, the ring expansion product P3 is formed nearly exclusively for the atomic hydrogen loss channel. Based on the computations, the molecular fragmentation channel eliminating acetylene (C 2 H 2 ) plus 3-cyano-2-propen-1-ylidene (P6; 3 A”) plays also an important role the reaction of atomic carbon with pyridine proposing a probable destruction pathway of interstellar pyridine. Lastly, these results are also discussed in light of the isoelectronic carbon – benzene (C 6 H 6 ; X 1 A 1 ) system with important implications to the rapid degradation of nitrogen-bearing polycyclic aromatic hydrocarbons (NPAHs) in the interstellar medium compared to mass growth processes of PAH counterparts through ring expansion.

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DOE OSTI2018

A Combined Experimental and Computational Study on the Reaction Dynamics of the 1-Propynyl (CH 3 CC)–Acetylene (HCCH) System and the Formation of Methyldiacetylene (CH 3 CCCCH)

We investigated the 1-propynyl (CH 3 CC; X 2 A 1 ) plus acetylene/acetylene-d 2 (HCCH/DCCD; X 1 Σg + ) under single-collision conditions using the crossed molecular beams method. The reaction was found to produce C 5 H 4 plus atomic hydrogen (H) via an indirect reaction mechanism with a reaction energy of -123 ± 18 kJ mol –1 . Using the DCCD isotopologue, we confirmed that the hydrogen atom is lost from the acetylene reactant. Our computational analysis suggests the reaction proceeds by the barrierless addition of the 1-propynyl radical to acetylene, resulting in C 5 H 5 intermediate(s) that dissociate preferentially to methyldiacetylene (CH 3 CCCCH; X 1 A 1 ) via hydrogen atom emission with a computed reaction energy of -123 ± 4 kJ mol –1 . The barrierless nature of this reaction scheme suggests the 1-propynyl radical may be a key intermediate in hydrocarbon chain growth in cold molecular clouds like TMC-1, where methyl-substituted (poly)acetylenes are known to exist.

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DOE OSTI2016

Defect Luminescence from Wurtzite CuInS 2 Nanocrystals: Combined Experimental and Theoretical Analysis

CuInS 2 nanocrystals with the wurtzite structure show promise for applications requiring efficient energy transport due to their anisotropic crystal structure. We investigate the source of photoluminescence in the near-infrared spectral region recently observed from these nanocrystals. Spectroscopic studies of both wurtzite CuInS 2 itself and samples alloyed with Cd or Zn allow the assignment of this emission to a radiative point defect within the nanocrystal structure. Further, by varying the organic passivation layer on the material, we are able to determine that the atomic species responsible for nonradiative decay paths on the nanocrystal surface are Cu- or S-based. Density functional theory calculations of defect states within the material allow identification of the likely radiative species. In conclusion, understanding both the electronic structure and optical properties of wurtzite CuInS 2 nanocrystals is necessary for their efficient integration into potential biological, photovoltaic, and photocatalytic applications.

Chemical structure↗
DOE OSTI2024

Evolution and interplay of lithium metal interphase components revealed by experimental and theoretical studies

ABSTRACT: Lithium metal batteries (LMB) have high energy densities and are crucial for clean energy solutions. The characterization of lithium metal interphase is fundamentally and practically important but technically challenging. Taking advantage of synchrotron x-ray which has the unique capability of analyzing crystalline/amorphous phases quantitative-ly with statistical significance, we study the composition and dynamics of LMB interphase for a newly developed im-portant LMB electrolyte that is based on fluorinated ether. Pair distribution function analysis revealed the sequential role of anion and solvent in interphase formation during cycling. The relative ratio between Li2O and LiF first increases and then decreases during cycling, suggesting suppressed Li2O formation in both initial and long extended cycles. Theoretical studies revealed that in initial cycles, this is due to the energy barrier in many-electron transfer. In long extended cycles, the anion decomposition product Li2O encourages solvent decomposition by facilitating solvent adsorption on Li2O which is followed by concurrent depletion of both. This work highlights the important role of Li2O in transitioning from anion-derived interphase to a solvent-derived one.

Tan, Sha↗
DOE OSTI2011

Effects of La2O3 on the Mixed Higher Alcohols Synthesis from Syngas over Co Catalysts: A Combined Theoretical and Experimental Study

The promoting role of lanthanum oxide (La{sub 2}O{sub 3}) in the catalytic synthesis of mixed higher (C{sub 2}-C{sub 6}) alcohols from syngas on Co-based catalysts was investigated using a combination of in situ and ex situ X-ray diffraction (XRD), photoelectron spectroscopy (XPS), catalyst reactivity performance studies, and ab initio molecular dynamics (AIMD) simulations. XRD measurements show that doping with La (0.5 wt %) onto activated carbon (AC) supported Co catalyst enhances the Co{sub 2}C phase formation, whereas the Co{sub 2}C phase formation is largely suppressed on alumina supported Co catalyst. A strong correlation of the selectivity toward alcohols with the ratio of Co{sub 2}C/Co particles present in the catalysts was observed. AIMD simulations suggest that on AC supports La exists as an oxide phase in the form of small clusters in the vicinity of Co particles. It was found that Co{sub 2}C formation is energetically favorable, especially for smaller Co particles because of the formation of surface carbide. Theoretical mechanistic studies indicate that oxygenated hydrocarbons can be formed on these catalysts by multiple routes involving the formation of CH{sub x}O and CH{sub x}CO species at the interface between the La{sub 2}O{sub 3} phase and Co/Co{sub 2}C. A detailed comparison with previous findings in the literature as well as discussion of the implications of these results upon the improvement of the selectivity of these catalysts toward higher alcohols is presented.

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