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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 OSTI2024

Evaluating Possible Formation Mechanisms of Criegee Intermediates during the Heterogeneous Autoxidation of Squalene

Organic molecules in the environment oxidatively degrade by a variety of free radical, microbial, and biogeochemical pathways. A significant pathway is heterogeneous autoxidation, in which degradation occurs via a network of carbon and oxygen centered free radicals. Recently, we found evidence for a new heterogeneous autoxidation mechanism of squalene that is initiated by hydroxyl (OH) radical addition to a carbon–carbon double bond and apparently propagated through pathways involving Criegee Intermediates (CI) produced from β-hydroxy peroxy radicals (β-OH-RO 2 •). It remains unclear, however, exactly how CI are formed from β-OH-RO 2 •, which could occur by a unimolecular or bimolecular pathway. Combining kinetic models and multiphase OH oxidation measurements of squalene, we evaluate the kinetic viability of three mechanistic scenarios. Scenario 1 assumes that CI are formed by the unimolecular bond scission of β-OH-RO 2 •, whereas Scenarios 2 and 3 test bimolecular pathways of β-OH-RO 2 • to yield CI. Scenario 1 best replicates the entire experimental data set, which includes effective uptake coefficients vs [OH] as well as the formation kinetics of the major products (i.e., aldehydes and secondary ozonides). Finally, although the unimolecular pathway appears to be kinetically viable, future high-level theory is needed to fully explain the mechanistic relationship between CI and β-OH-RO 2 • in the condensed phase.

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

Coupling of Lipid Peroxidation and Criegee Intermediate Mediated Autoxidation in the Heterogeneous Oxidation of Linoleic Acid Aerosols

Autoxidation is an established mechanism for the degradation of organic molecules, which is relevant in the atmosphere, combustion processes, the environment, and the rancidification of lipids (commonly known as lipid peroxidation). Autoxidation proceeds via radical chain reactions involving hydroxyl (•OH), peroxy (RO2•), and alkoxy radicals, which are also prominent oxidants in the atmosphere. Recent reports have provided evidence for an alternative autoxidation mechanism driven instead by Criegee intermediates (CIs), which are produced from the reaction of β-hydroxy peroxy radicals (β-OH-RO2•). This work evaluates the contributions of these two mechanisms in the •OH initiated heterogeneous oxidation of linoleic acid (LA) aerosols. Reaction kinetics and product distributions are monitored using a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer. To explain the observed kinetics, a kinetic model is developed that incorporates both the conventional peroxidation and alternative CI-mediated autoxidation mechanisms. We observe that the CI-mediated autoxidation pathways enhance the heterogeneous autoxidation rate, while the peroxidation reactions, although present, contributes less to the overall oxidation rate. α-Acyloxyalkyl hydroperoxides (AAHPs) are identified as key indicators for bimolecular reactions of CI with LA, highlighting the role of LA as a CI scavenger. Moreover, the measured functionalized LA products with hydroxyl or carbonyl group(s), serve as markers for the peroxidation reactions. In summary, this work presents a quantitative framework to understand the coupled reaction network of •OH, RO2•, β-OH-RO2• radicals, and CI in driving heterogeneous autoxidation, which is crucial for understanding degradation mechanisms of organic molecules in the environment and atmosphere.

Criegee intermediate↗
DOE OSTI2024

Neural network emulation of flow in heavy-ion collisions at intermediate energies

Applications of new techniques in machine learning are speeding up progress in research in various fields. In this work, we construct and evaluate a deep neural network (DNN) to be used within a Bayesian statistical framework as a faster and more reliable alternative to the Gaussian process (GP) emulator of an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model simulator of heavy-ion reactions at intermediate beam energies. We found strong evidence of the DNN being able to emulate the IBUU simulator's prediction on the strengths of protons' directed and elliptical flow very efficiently even with small training datasets and with accuracy about ten times higher than the GP. Here, limitations of our present work and future improvements are also discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Unraveling Electronic Effects that Influence the Bimolecular Chemistry of Fluorinated Criegee Intermediates

Ozonolysis is important for the removal of unsaturated volatile organic compounds emitted into the Earth's atmosphere. The alkene + ozone reaction (alkene ozonolysis) forms a carbonyl oxide – a Criegee intermediate (CI). CIs are interesting from an atmospheric chemistry perspective. They are implicated in enhancing the oxidizing capacity of the troposphere and in secondary organic aerosol formation. CIs may participate in bimolecular reactions with trace atmospheric vapors like water and methanol. Here, the chemistry of the two isomers of CFHOO and of CF 3 CHOO with water, water dimer, and methanol is explored. The present study confirms that the syn-conformer is the minimum energy structure for both CIs and that the reactions of anti-CFHOO display slightly lower activation energies cf. syn-CFHOO, thus promoting faster reaction. For both syn- and anti-CFHOO, the energy barrier in the pathway to adding water, water dimer, or methanol is lower—and the overall reaction exoergicity greater—than for the corresponding reactions involving the nonfluorinated analogue, CH 2 OO. Here, the corresponding bimolecular reaction rates are thus predicted to be faster for CFHOO than CH 2 OO. Similar reactivity trends are found when comparing the same reactions of syn-CF 3 CHOO, cf. syn-CH 3 CHOO, but not when comparing the energetics of the reactions involving anti-CF 3 CHOO cf. anti-CH 3 CHOO.

Guidry, Lily M. [University of Louisiana at Lafaye↗
DOE OSTI2024

Preparation of coenzyme F430 biosynthetic enzymes and intermediates

Methyl-coenzyme M reductase (MCR) is the key enzyme in pathways for the formation and anaerobic oxidation of methane. As methane is a potent greenhouse gas and biofuel, investigations of MCR catalysis and maturation are of interest for the development of both methanogenesis inhibitors and natural gas conversion strategies. Here, the activity of MCR is dependent on a unique, nickel-containing coenzyme F430, the most highly reduced tetrapyrrole found in nature. Coenzyme F430 is biosynthesized from sirohydrochlorin in four steps catalyzed by the CfbABCDE enzymes. Here, methods for the expression and purification of the coenzyme F430 biosynthesis enzymes are described along with conditions for the synthesis and purification of biosynthetic intermediates on the milligram scale from commercially available porphobilinogen.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Reactivity of net-zero carbon alcohol fuels and their corresponding aldehyde intermediates on PGM-based commercial oxidation catalysts for lean-burn emissions control

Alcohol net-zero carbon fuels will play a significant role in decarbonization of the hard-to-electrify transportation sectors. However, the combustion process in alcohol-fueled engines generate toxic aldehydes. For commercialization of net-zero carbon fuels on engines, compliance with the stringent U.S. EPA regulations is necessary. Here, this contribution focuses on reactivity of alcohols and aldehydes on commercial diesel oxidation catalysts (DOC) to inform selection of future net-zero carbon fuels. Alcohol (and aldehyde) light-off temperatures were measured on aged DOCs under full synthetic engine-exhaust conditions. Methanol was the most reactive, while ethanol completely oxidized at higher temperatures. Alcohols typically formed less reactive aldehyde intermediates. DRIFTS revealed strongly adsorbing surface formates and acetates during methanol and ethanol oxidation, respectively, resulting in inhibition effects. Preliminary alcohol oxidation mechanisms combining flow reactor and DRIFTS observations are presented. Aldehydes inhibited CO oxidation. Minimal N 2 O formation was observed for the alcohols investigated.

Alcohol oxidation↗
DOE OSTI2025

The ladder and readout cables of intermediate silicon strip detector for sPHENIX

A new silicon-strip-type detector was developed for precise charged-particle tracking in the central rapidity region of heavy ion collisions. A new detector and collaboration at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory is sPHENIX, which is a major upgrade of the PHENIX detector. The intermediate tracker (INTT) is part of the advanced tracking system of the sPHENIX detector complex together with a CMOS monolithic-active-pixel-sensor based silicon-pixel vertex detector, a time-projection chamber, and a micromegas-based detector. The INTT detector is barrel shaped and comprises 56 silicon ladders. Two different types of strip sensors of 78 micron pitch and 320 micron thick are mounted on each half of a silicon ladder. Each strip sensor is segmented into 8 × 2 and 5 × 2 blocks with lengths of 16 and 20 mm. Strips are read out with a silicon strip-readout (FPHX) chip. In order to transmit massive data from the FPHX to the down stream readout electronics card (ROC), a series of long and high speed readout cables were developed. This document focuses on the silicon ladder, the readout cables, and the ROC of the INTT. The radiation hardness is studied for some parts of the INTT devices in the last part of this document, since the INTT employed some materials from the technology frontier of the industry whose radiation hardness is not necessarily well known.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Beam test results of the Intermediate Silicon Tracker for sPHENIX

The Intermediate Silicon Tracker (INTT), a two-layer barrel silicon strip tracker, is a key component of the tracking system for sPHENIX at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The INTT is designed to enable the association of reconstructed tracks with individual RHIC bunch crossings. To evaluate the performance of preproduction INTT ladders and the readout chain, a beam test was conducted at the Research Center for Accelerator and Radioisotope Science, Tohoku University, Japan. This paper presents the performance of the INTT evaluated through studies of the signal-to-noise ratio, residual distribution, spatial resolution, hit-detection efficiency, and multiple track reconstruction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Dramatic Slowdown of Bimolecular Reactions of Criegee Intermediates in Organic Aerosols

Although Criegee intermediates (CIs) play a central role in driving the transformation of organic molecules, their condensed-phase reaction kinetics remains poorly understood. While CIs undergo unimolecular decomposition to produce OH radicals, stabilized CIs participate in a host of other bimolecular reactions forming larger molecular weight products, including secondary ozonides (kSOZ), alkoxyalkyl hydroperoxides (kAlAHP), and acyloxyalkyl hydroperoxides (kAcAHP). Here, we demonstrate, using prior literature and new measurements of heterogeneous organic aerosol reactions using O3 or OH radicals, that these condensed-phase bimolecular reaction rate coefficients kSOZ (10-20 cm3·molecule-1·s-1), kAlAHP, and kAcAHP (10-19 cm3·molecule-1·s-1) are 7-10 orders of magnitude slower than analogous gas-phase reactions (∼ 10-10-10-13 cm3·molecule-1·s-1). This contrasts with current evidence that the rate coefficients for unimolecular steps in the condensed phase are similar in magnitude to those in the gas phase. Kinetic models using gas-phase-like bimolecular coefficients consistently overestimate the importance of bimolecular relative to unimolecular pathways while underpredicting the aerosol reactivity by up to 30-fold. The slowing of bimolecular reactivity in aerosols is likely due to solvation effects and the increased steric hindrance of larger molecular weight CIs and their scavengers in the condensed phase. These results challenge the conventional view that the high reactant density of an organic aerosol should favor bimolecular over unimolecular reactions, underscoring the need for more accurate CI condensed-phase rate constants for reliable modeling of oxidative processes across a diverse set of atmospheric and environmental systems.

Zeng, Meirong↗
DOE OSTI2024

Infrared Fingerprint and Unimolecular Decay Dynamics of the Hydroperoxyalkyl Intermediate (•QOOH) in Cyclopentane Oxidation

A transient carbon-centered hydroperoxyalkyl intermediate (•QOOH) in the oxidation of cyclopentane is identified by IR action spectroscopy with time-resolved unimolecular decay to hydroxyl (OH) radical products that are detected by UV laser-induced fluorescence. Two nearly degenerate •QOOH isomers, β- and γ-QOOH, are generated by H atom abstraction of the cyclopentyl hydroperoxide precursor. Fundamental and first overtone OH stretch transitions and combination bands of •QOOH are observed and compared with anharmonic frequencies computed by second-order vibrational perturbation theory. An OH stretch transition is also observed for a conformer arising from torsion about a low-energy CCOO barrier. Definitive identification of the β-QOOH isomer relies on its significantly lower transition state (TS) barrier to OH products, which results in rapid unimolecular decay and near unity branching to OH products. A benchmarking approach is utilized to compute high-accuracy stationary point energies, most importantly TS barriers, for cyclopentane oxidation (C 5 H 9 O 2 ), building on higher level reference calculations for ethane oxidation (C 2 H 5 O 2 ). The experimental OH product appearance rates are compared with computed statistical microcanonical rates using RRKM theory, including heavy-atom tunneling, thereby validating the computed TS barrier. The results are extended to thermal unimolecular decay rate constants at temperatures and pressures relevant to cyclopentane combustion via master-equation modeling. Furthermore, the various torsional and ring puckering states of the wells and transition states are explicitly considered in these calculations.

Chemical calculations↗
DOE OSTI2025

Vibrational Signatures of Unrealized Phosphorus Suboxide Intermediates in White Phosphorus Oxidation Reactions

White phosphorus ignition notoriously produces the phosphoric acid anhydride P 4 O 10 , yet the intermediate oxidation steps remain undetermined. Here, we report the first geometric and vibrational characterization of two P 4 O 2 isomers, P 3 OPO and P 3 PO 2 , and substantiate a previously proposed cyclic P 4 O 2 isomer. We formally assign the infrared bands observed by Andrews and Mielke at 898 and 891 cm −1 to the antisymmetric P− O−P vibrations of P 3 OPO species. Additional bands corresponding to terminal P=O and −PO 2 stretches of P 3 OPO and P 3 PO 2 discussed herein also went unrecognized due to the peculiar bonding of P 4 O 2 species compared to oxo-bridged P 4 O x (x = 3−6) species. Sequential addition of oxygen atoms to the P 4 tetrahedron appears to form P 3 OPO and P 3 PO 2 , while cyclic P 4 O 2 is formed from P 2 O dimerization. CCSD(T) geometries, CCSD(T) + MP2[δVPT2] fundamental frequencies, and enthalpies of formation extrapolated using focal-point analysis are reported. The predicted enthalpies of formation relative to tetrahedral P 4 plus 3 Σ g − O 2 for bent-P 3 OPO, extended-P 3 OPO, P 3 PO 2 , and cyclic-P 4 O 2 are −93, −88, −85, and −63 kcal mol −1 , respectively.

Molecular structure↗
DOE OSTI2026

Nanosecond Structure of Radical Pair Intermediates from High-Frequency Quantum Oscillations: Insight into the Q A •– to Q B Electron Transfer Step in Purple Bacterial Photosynthesis

We demonstrate the validity of our approach to deduce, from the anisotropy of quantum oscillations, the geometry of short-lived radical pair intermediates in photosynthesis. A global fit of a two-dimensional W-band (94 GHz) electron paramagnetic resonance (EPR) experiment provides the same global minimum values for the geometry of the A-side radical pair P 700 •+ A 1A •− in photosystem I (PSI) as observed in a previous Q-band (34 GHz) EPR study, yet with a significantly increased convergence rate of 62%. This demonstrates that the global fit yields the correct radical pair geometry even at Q-band frequencies. With this information, we revisit our previous Q-band study of the cofactor arrangement of P 865 •+ Q A •− , the stabilized charge-separated state in purple bacterial reaction centers (RCs). Analysis of calculated two-dimensional data sets of P 865 •+ Q A •− reveals that the quantum oscillation technique is unaffected by a mirror ambiguity in disordered solids and thus can provide unambiguous solutions for all five Euler angles of the radical pair geometry. This enables us to elucidate the Q A •− to Q B electron transfer step in purple bacterial photosynthesis, the subject of controversial discussions for more than 25 years. Our results show that this electron transfer step involves a gating mechanism requiring a 60° rotation of the headgroup of Q A •− in its binding pocket.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Charge Tethering Drives Intermediate-Range Order and Slow Dynamics in Zwitterionic Liquids

We have synthesized and characterized a family of zwitterionic liquids (ZwLs) based on the poly(ethylene oxide) imidazolium cation and the alkyl sulfonate anion. To better rationalize ZwLs′ structural behavior and networkforming properties, we have computationally studied them in contrast to isostructural but chemically untethered ionic liquid (IL) analogues. Perhaps surprisingly, it is the molecular liquids and not the ILs that show the most selfassembly and intermediate-range order associated with scattering prepeaks; the ZwLs display also the slowest dynamics. This is consistent with prior work showing the importance of networks in considering the viscoelastic relaxation of liquids. We find that, because of their significantly large molecular dipoles, these zwitterions are versatile network-building blocks that result in highly viscous liquids. From a structural perspective, networks in these ZwLs sit somewhere in between what would be true chemical connectivity and the Coulombic networks observed in ionic liquids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Dynamic Activation of Single-Atom Catalysts by Reaction Intermediates: Conversion of Formic Acid on Rh/Fe 3 O 4 (001)

The stability and activity of supported single-atom catalysts (SACs) represent critical yet opposing factors limiting our ability to explore and exploit their unique properties. Here, this study demonstrates the operation of a switchable catalyst that is activated in the presence of surface intermediates and reverts back to a stable but inactive form when the reaction is completed. We employ atomically defined Rh-Fe 3 O 4 (001) catalysts to demonstrate how structurally stable Rh, bound in surface octahedral Fe sites, gets destabilized to form highly active Rh adatoms and small clusters. Conversion of formic acid, leading initially to surface formate and hydroxyl species, is employed as a model reaction to probe the dynamics of such processes. We find that surface hydroxyl recombination to water through the Mars van Krevelen mechanism reduces Rh coordination, triggering its conversion to active Rh adatoms. Since such lattice oxygen exchange is observed in many acid-base and redox chemistries, the process can be broadly applicable to controlling the activation of the range of SACs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Insights into Sustainable Nitrogen Fixation by Gas-phase Spectroscopic Measurements and Global Modeling of Reaction Intermediates in Humid Nitrogen Plasma

In this article, there is growing interest in reacting molecular nitrogen and water to sustainably synthesize fixed forms of nitrogen such as ammonia. In particular, low-temperature plasmas can activate these relatively inert feedstocks at or near room temperature without a catalyst. However, because of the enhanced reactivity and nonequilibrium chemistry, a diverse range of products is formed, and the underlying reaction mechanisms are exceedingly complex. In this work, we studied a simplified reactor consisting of a gaseous plasma containing controlled mixtures of nitrogen gas and water vapor. Densities of key chemical species such as N, H, OH, NH, and NO were measured by emission and laser-based spectroscopy as a function of the relative humidity. A global model was constructed and the reaction network was validated by comparing calculated species densities with experiments. We discover that N, a key initial intermediate for ammonia, strongly decreases in the presence of water vapor, and as a result, ammonia formation becomes limited at high relative humidity. This decrease is surprisingly not because N itself reacts, but because one of its main sources, an excited molecular nitrogen state, is reacted away. In addition, oxidation pathways for nitrogen, which lead to NO and related products, are found to be favored over reduction pathways because the corresponding reverse reactions are less significant. Together, this understanding helps explain previously reported observations of selectivity toward nitrogen oxides over ammonia, particularly at higher relative humidities.

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

Criegee Intermediates Compete Well with OH as a Cleaning Agent for Atmospheric Amides

Elucidating the chemical kinetics of stabilized Criegee intermediates (sCIs) in the atmosphere is critically important for climate modeling. Here, we report a class of very rapid bimolecular reactions of two sCIs, namely, CH 2 OO and syn-CH 3 CHOO, with amides. We used electronic structure calculations and kinetics calculations to elucidate a universal mechanism by which the oxygen atom of the carbonyl group in an amide is added to the carbon atom of the COO group in the sCI with simultaneous transfer of the amide hydrogen to the terminal oxygen atom of the carbonyl oxide of the sCI. The barriers for the mechanism are submerged below reactants by ∼9 kcal/mol, which means that the tight transition state is not the rate-determining step, and the rate constants are determined by loose free energy bottlenecks between the reactants and the precursor complexes. We calculate the rate constants due to these loose and barrierless transition states by variable-reaction-coordinate variational transition-state theory. We find that bimolecular reactions of sCIs with amides are very rapid, with rate constants 1 to 5 × 10 –10 cm 3 molecule –1 s –1 , which is a factor of 2 faster than the rate constants of carboxylic acids with sCIs and 10 2 faster than the rate constants of OH reactions with amides. This has the consequence that, under a wide range of conditions, sCIs are the major sink for atmospheric amides, in contrast to the usual assumption that OH radicals are the dominant sinks.

Amides↗
DOE OSTI2024

Neuromorphic intermediate representation: A unified instruction set for interoperable brain-inspired computing

Abstract Spiking neural networks and neuromorphic hardware platforms that simulate neuronal dynamics are getting wide attention and are being applied to many relevant problems using Machine Learning. Despite a well-established mathematical foundation for neural dynamics, there exists numerous software and hardware solutions and stacks whose variability makes it difficult to reproduce findings. Here, we establish a common reference frame for computations in digital neuromorphic systems, titled Neuromorphic Intermediate Representation (NIR). NIR defines a set of computational and composable model primitives as hybrid systems combining continuous-time dynamics and discrete events. By abstracting away assumptions around discretization and hardware constraints, NIR faithfully captures the computational model, while bridging differences between the evaluated implementation and the underlying mathematical formalism. NIR supports an unprecedented number of neuromorphic systems, which we demonstrate by reproducing three spiking neural network models of different complexity across 7 neuromorphic simulators and 4 digital hardware platforms. NIR decouples the development of neuromorphic hardware and software, enabling interoperability between platforms and improving accessibility to multiple neuromorphic technologies. We believe that NIR is a key next step in brain-inspired hardware-software co-evolution, enabling research towards the implementation of energy efficient computational principles of nervous systems. NIR is available atneuroir.org

Science & Technology - Other Topics↗
DOE OSTI2026

Can ferric-oxyl excited states explain elongated iron-oxygen bonds in heme peroxidase catalytic intermediates?

The use of X-ray structures to determine and interpret the ferryl iron-oxygen bond order in molecular oxygen-activating heme enzymes has, in the past, been controversial. This has mainly stemmed from the susceptibility of ferryl species to X-ray-induced electronic state changes. In this work we establishe using time-resolved serial femtosecond X-ray crystallography (tr-SFX) on a dye-decolourising peroxidase that the ferryl intermediate species (Compounds I and II) captured following in situ mixing of microcrystals with H 2 O 2 have single, rather than the double bond character expected. X-ray emission validated tr-SFX data with quantum refinement, time-dependent-DFT calculations and QM/MM geometry optimizations together support the concept that the single iron-oxygen bond character is not an indication of ferryl reduction or a protonated form (Fe IV -OH) but is instead attributed to the existence of accessible excited states possessing ferric-oxyl (Fe III –O •– ) character. Such states offer insight into the nature of ferryl heme.

Williams, Lewis J. [University of Essex, Colcheste↗