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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Restricted Partition Function Semiclassical Transition State Theory (RPF-SCTST): Applications to Reactions Involving Hydrogen Cyanide, Hydrogen Peroxide, and Formaldehyde Oxide

We demonstrate the efficiency of the numerical calculation of thermal semiclassical transition state theory (SCTST) rates across several representative chemical reactions using the restricted partition function (RPF)─viz a function that depends only on the imaginary action associated with a reaction. Here, we treat the potential energy surfaces (PESs) through fourth order expansions around the saddle point and integrate the Hamiltonian up to second order in employing vibrational perturbation theory. We apply this formalism to uni- and bimolecular reactions with different─though relatively high─barrier heights to uncover the influence of the barrier properties, minimal energies, and separability of the rotational motion on rate constants and tunneling corrections. Although all modes are coupled within the RPF, we found in our numerical examples that the rotational component in the absence of significant rotational distortions can be separated from the vibrational contributions. Moreover, a classical treatment of the rotational contribution is adequate over the temperature range from approximately 100 to 1000 K. We also found that the choice of DFT basis set can lead to variations in rate constants of up to an order of magnitude. Lastly, different schemes for counting eligible energy levels result in rate constants that differ by no more than a factor of 2, with the remaining discrepancies attributed to the treatment of near-convergent levels in perturbation theory.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Deciphering the Mechanism of Base-Triggered Conversion of Ammonia to Molecular Nitrogen and Methylamine to Cyanide

Here we report an in-depth investigation into the ammonia oxidation mechanism by the catalyst [Ru III (tpy)(dmabpy)NH 3 ] 3 + ([Ru(NH 3 )] 3 + ). Stoichiometric reactions of [Ru(NH 3 )] 3 + were carried out with exogenous noncoordinating bases to trigger a proposed redox disproportionation reaction, which was followed using variable-temperature NMR spectroscopy. An intermediate species was identified as a dinitrogen-bridged complex using 15 N NMR and Raman spectroscopy on isotopically labeled complexes. This intermediate is proposed to derive from coupling of nitridyl species formed upon sequential redox disproportion reactions. Acetonitrile displaces the dinitrogen bridge to yield free N 2 . DFT calculations support this lower-energy pathway versus that previously reported for ammonia oxidation by the parent [Ru III (tpy)(bpy)NH 3 ] 3 + complex. These experimental and computational results are consistent with the interpretation of redox disproportionation involving sequential hydrogen atom transfer reactions by an amide/aminyl intermediate, [Ru(NH 2 ) – ] + $\Leftrightarrow$ [Ru(NH 2 ) • ] + , formed upon deprotonation of the parent complex. Control experiments employing a large excess of ammonia as a base indicate this new proposed lower-energy pathway contributes to the oxidation of ammonia to dinitrogen in conditions relevant to electrocatalysis. In addition, analogous methylamine complexes, [Ru(NH 2 CH 3 )] 2 + /3 + , were prepared to further test the proposed mechanism. Treating [Ru(NH 2 CH 3 )] 3 + with a base cleanly yields two products [Ru(NH 2 CH 3 )] 2 + and [Ru(CN)] + in an ~3:1 ratio, fully consistent with the proposed cascade of hydrogen atom transfer reactions by an intermediate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Giant Negative Linear Compressibility in Orthorhombic Copper Cyanide

Most reported negative linear compressibility (NLC) materials exhibit either a small NLC over a large pressure range or a high NLC over a very small pressure range. Here, we report the remarkable discovery of giant NLC in the low-temperature form of CuCN (LT-CuCN) over an unusually large pressure range. High- pressure XRD studies on LT-CuCN observed the NLC of –20.5 TPa –1 along the a axis at zero pressure, and the ambient orthorhombic phase remained stable up to 9.8 GPa. Pressure- and temperature-dependent Raman studies identified the phonon vibrations responsible for NLC and negative thermal expansion (NTE).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Observations of the Hydrogen Cyanide in Comet 46P/Wirtanen at a 3.4 mm Wavelength

We searched for rotational lines of H{sup 12}C{sup 14}N in comet 46P/Wirtanen, using the Purple Mountain Observatory 13.7 m radio telescope. The J = 1–0 lines of HCN (3.4 mm wavelength) were unambiguously detected in 46P during the 2018 December 14–15 period, with a beam resolution of 62.″2 and a velocity resolution of ∼0.21 km s{sup −1} per channel. The molecular production rates were computed. The mean HCN(1–0) production rate of 46P was (6.45 ± 1.31) × 10{sup 24} molec s{sup −1} in the above two days. We found possible indications of time variation in the outgassing activity. The average HCN abundance relative to water Q {sub [HCN]}/Q{sub [H{sub 2O]}} of 46P was (0.09 ± 0.01)%. The HCN line shapes gave primary information on the kinematics of the cometary atmosphere. The HCN linewidths provided a direct determination of the coma expansion velocity, which was about 0.5 ± 0.05 km s{sup −1} at post-perihelion (1.056 au).

79 ASTRONOMY AND ASTROPHYSICS↗