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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Ambient pressure XPS and IRRAS investigation of ethanol steam reforming on Ni–CeO 2 (111) catalysts: An in situ study of C–C and O–H bond scission

Ambient-Pressure X-ray Photoelectron Spectroscopy (AP-XPS) and Infrared Reflection Absorption Spectroscopy (AP-IRRAS) have been used to elucidate the active sites and mechanistic steps associated with the ethanol steam reforming reaction (ESR) over Ni–CeO 2 (111) model catalysts. Our results reveal that surface layers of the ceria substrate are both highly reduced and hydroxylated under reaction conditions while the small supported Ni nanoparticles are present as Ni 0 /NixC. A multifunctional, synergistic role is highlighted in which Ni, CeO x and the interface provide an ensemble effect in the active chemistry that leads to H 2 . Ni 0 is the active phase leading to both C–C and C–H bond cleavage in ethanol and it is also responsible for carbon accumulation. On the other hand, CeO x is important for the deprotonation of ethanol/water to ethoxy and OH intermediates. The active state of CeO x is a Ce 3+ (OH) x compound that results from extensive reduction by ethanol and the efficient dissociation of water. Additionally, we gain an important insight into the stability and selectivity of the catalyst by its effective water dissociation, where the accumulation of surface carbon can be mitigated by the increased presence of surface OH groups. As a result, the co-existence and cooperative interplay of Ni 0 and Ce 3+ (OH) x through a metal–support interaction facilitate oxygen transfer, activation of ethanol/water as well as the removal of coke.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Ethylene glycol reforming on Pt(111): first-principles microkinetic modeling in vapor and aqueous phases

First-principles, periodic density functional theory (DFT) calculations and mean-field microkinetic modeling have been used to investigate the decomposition of ethylene glycol for hydrogen production on Pt(111) in vapor and aqueous phases. All dehydrogenated species derived from ethylene glycol (C 2 H x O 2 , x = 0–6) and methanol (CH y O, y = 0–4), and all elementary C–C, C–H, and O–H bond breaking steps are included in the microkinetic model. Reaction path analysis in vapor phase indicates that both initial C–H and O–H dehydrogenation steps are kinetically relevant at all temperatures (470–530 K). Initial O–H bond cleavage is reversible at low temperatures but accounts for an increasingly dominant fraction of the total reaction flux at higher temperatures. C–C bond scission is observed only after significant dehydrogenation (x ≤ 3) and is more likely to happen in surface intermediates where one of the cleavage products is CO. Here, the process is highly selective to the production of H2 compared to methanol. For aqueous-phase model development, free energies of solvation were computed for all surface intermediates and transition states using a continuum solvation approach. Our aqueous-phase microkinetic model predicts a 0.4 eV lower apparent activation energy and an order of magnitude larger turnover frequencies. Initial C–H bond cleavage becomes more important but the general trends are similar to the vapor phase, suggesting that the reaction chemistry is similar in both vapor and aqueous phases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Mechanistic insights into the conversion of polyalcohols over Brønsted acid sites

Multi-layered plastic (MLP) films provide excellent properties for food packaging; however, because of the complicated chemistry of the hydrophobic substrates and tightly laminated hydrophilic layers, it is challenging to recycle the MLP films. The selective conversion of polar functional groups in hydrophilic layers with a minimal destruction of the carbon backbone of constituted polymers is considered a promising approach to improve the recyclability of MLP films. Here, in this study, we combine computational and experimental studies to investigate the acid-catalyzed conversion of functional groups in polyalcohols, through which we report potential reaction pathways involved in the conversion of ethylene vinyl alcohol (EVOH), a common copolymer used in MLP films as an oxygen barrier. Using 2,4-pentanediol as a model compound, we show that its conversion proceeds primarily through the dehydration of a hydroxyl group via either a stepwise or a concerted mechanism to form an unsaturated alcohol that can be further converted into a conjugated diene or a saturated ketone; this secondary reaction determines the product selectivity. The rate determining intermediates and transition states are identified, and the activation barriers are calculated, in agreement with experimentally observed product selectivities. This study thus provides insights for the selective conversion of EVOH.

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

Benchmarking nitrous oxide adsorption and activation in metal–organic frameworks bearing coordinatively unsaturated metal centers

Anthropogenic emissions of N 2 O, the third most abundant greenhouse gas after CO 2 and CH 4 , are contributing to global climate change. Although metal–organic frameworks (MOFs) have been widely studied as adsorbents for CO 2 and CH 4 , less effort has focused on the use of MOFs to remove N 2 O from emission streams or from air. Further, N 2 O activation would enable its use as an inexpensive oxidant for fine chemical synthesis. Here, in this paper, we identify features that contribute to strong binding and high uptake of N 2 O at coordinatively unsaturated metal sites in the M 2 Cl 2 (btdd) (M = Mn, Co, Ni, Cu; btdd 2– = bis(1,2,3-triazolo[4,5-b],[4',5'-i])dibenzo[1,4]dioxin) and M 2 (dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn; dobdc 4– = 2,5-dioxido-1,4-benzenedicarboxylate) series of MOFs. Combined experimental and computational studies suggest that N 2 O adsorption at open-metal-sites is primarily based on electrostatic interactions, rather than π-backbonding, causing MOFs with more Lewis acidic metal centers to be superior N 2 O adsorbents. As a result, Mg 2 (dobdc) demonstrates strong binding and record-setting N 2 O uptake (8.75 mmol g –1 at 1 bar and 298 K). Using density functional theory (DFT) to characterize reactive intermediates and transition states, we demonstrate that N 2 O activation to form a M(IV)–oxo species and N 2 is thermodynamically favorable in Mn 2 (dobdc) and Fe 2 (dobdc) but appears to be kinetically limited in Mn 2 (dobdc). Our work lays a foundation for understanding N 2 O adsorption and activation in MOFs, paving the way for the design of promising next-generation materials for N 2 O capture and utilization.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Leveraging chiral induced spin selectivity to improve the efficiency and selectivity of electrocatalytic reduction

Energy production is a fundamental pillar of modern society, but it remains heavily reliant on fossil fuel combustion, which leads to environmental degradation and resource depletion. Electrocatalytic reduction reactions (ERRs) offer a cleaner alternative by functioning under mild conditions, eliminating the need for high temperatures or pressures. However, their widespread adoption is hindered by challenges such as low efficiency, inadequate selectivity, and sluggish kinetics. Here, the introduction of chiral-induced spin selectivity (CISS) offers a promising strategy to address these limitations by reducing energy barriers in reactions involving spin-sensitive intermediates or transition states. By leveraging CISS, ERR pathways can be manipulated to favor desired reactions, enhance product yield, and suppress unwanted byproducts, improving selectivity. Beyond reducing the impact of competing side reactions, CISS also enhances the kinetics of ERRs by accelerating reaction rates and lowering the energy barriers associated with multi-electron transfer steps. Thanks to its straightforward and versatile application, CISS shows significant potential in optimizing well-studied ERRs, such as the hydrogen evolution reaction (HER) and carbon dioxide reduction reaction (CO2RR), facilitating the future transition of these technologies from research laboratories to commercial energy plants worldwide.

14 SOLAR ENERGY↗
DOE OSTI2010

Electric dipole moment of light nuclei

We examine the sensitivity of the deuteron Electric Dipole Moment (EDM) to variation in the nucleon-nucleon interaction. In particular, we write the EDM as a sum of two terms, one depends on the target wave function, the second on intermediate multiple scattering states in the {sup 3}P{sub 1} channel. This second contribution is sensitive to off-shell behavior of the {sup 3}P{sub 1} amplitude.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Energy-weighted sum rules connecting ΔZ = 2 nuclei within the SO(8) model

Energy-weighted sum rules associated with ΔZ = 2 nuclei are obtained for the Fermi and the Gamow-Teller operators within the SO(8) model. It is found that there is a dominance of contribution of a single state of the intermediate nucleus to the sum rule. The results confirm founding obtained within the SO(5) model that the energy-weighted sum rules of ΔZ = 2 nuclei are governed by the residual interactions of nuclear Hamiltonian. A short discussion concerning some aspects of energy weighted sum rules in the case of realistic nuclei is included.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

All-optical depletion of dark excitons from a semiconductor quantum dot

Semiconductor quantum dots are considered to be the leading venue for fabricating on-demand sources of single photons. However, the generation of long-lived dark excitons imposes significant limits on the efficiency of these sources. We demonstrate a technique that optically pumps the dark exciton population and converts it to a bright exciton population, using intermediate excited biexciton states. We show experimentally that our method considerably reduces the dark exciton population while doubling the triggered bright exciton emission, approaching thereby near-unit fidelity of quantum dot depletion.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Investigating resonances above and below the threshold in nuclear reactions of astrophysical interest and beyond

Resonances in nuclear cross sections dramatically change their trends. Therefore, the presence of unexpected resonances might lead to unpredicted consequences on astrophysics and nuclear physics. In nuclear physics, resonances allow one to study states in the intermediate compound systems, to evaluate their cluster structure, for instance, especially in the energy regions approaching particle decay thresholds. In astrophysics, resonances might lead to changes in the nucleosynthesis flow, determining different isotopic compositions of the nuclear burning ashes. For these reasons, the Trojan Horse method has been modified to investigate resonant reactions. Thanks to this novel approach, for the first time normalization to direct data might be avoided. Moreover, in the case of sub threshold resonances, the Trojan Horse method modified to investigate resonances allows one to deduce the asymptotic normalization coefficient, showing the close connection between the two indirect approaches.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Exploring mechanisms of a tropospheric archetype: CH{sub 3}O{sub 2} + NO

Methylperoxy radical (CH{sub 3}O{sub 2}) and nitric oxide (NO) contribute to the propagation of photochemical smog in the troposphere via the production of methoxy radical (CH{sub 3}O) and nitrogen dioxide (NO{sub 2}). This reaction system also furnishes trace quantities of methyl nitrate (CH{sub 3}ONO{sub 2}), a sink for reactive NO{sub x} species. Here, the CH{sub 3}O{sub 2} + NO reaction is examined with highly reliable coupled-cluster methods. Specifically, equilibrium geometries for the reactants, products, intermediates, and transition states of the ground-state potential energy surface are characterized. Relative reaction enthalpies at 0 K (ΔH{sub 0K}) are reported; these values are comprised of electronic energies extrapolated to the complete basis set limit of CCSDT(Q) and zero-point vibrational energies computed at CCSD(T)/cc-pVTZ. A two-part mechanism involving CH{sub 3}O and NO{sub 2} production followed by radical recombination to CH{sub 3}ONO{sub 2} is determined to be the primary channel for formation of CH{sub 3}ONO{sub 2} under tropospheric conditions. Constrained optimizations of the reaction paths at CCSD(T)/cc-pVTZ suggest that the homolytic bond dissociations involved in this reaction path are barrierless.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Prediction of variation in d-orbital occupancy in strain induced tetragonal phase of BiFeO{sub 3} thin film

A theoretical study of the possible variation of d-orbital occupancy while going from the rhombohedral bulk phase to the strain induced tetragonal phase of BiFeO{sub 3} thin film has been carried out. A possible existence of an intermediate spin (IS) state, S=3/2 and a low spin (LS) state, S=1/2 in the tetragonal phase has been predicted, thereby clearly establishing the role of strain behind the d-orbital occupancy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Two-photon-absorption line strengths for nitric oxide: Comparison of theory and sub-Doppler, laser-induced fluorescence measurements

In this paper, we discuss the results of high-resolution, sub-Doppler two-photon-absorption laser-induced fluorescence (TPALIF) spectroscopy of nitric oxide at low pressure and room temperature. The measurements were performed using the single-longitudinal mode output of a diode-laser-seeded optical parametric generator (OPG) system with a measured frequency bandwidth of 220 MHz. The measurements were performed using a counter-propagating pump beam geometry, resulting in sub-Doppler TPALIF spectra of NO for various rotational transitions in the (0,0) vibrational band of the A 2 Σ + - X 2 Π electronic transition. The experimental results are compared with the results of a perturbative treatment of the rotational line strengths for the 20 different rotational branches of the X 2 Π(v" = 0) → A 2 Σ + (v' = 0) two-photon absorption band. In the derivation of the expressions for the two-photon transition absorption strength, the closure relation is used for rotational states in the intermediate levels of the two-photon transition in analogy with the Placzek treatment of Raman transitions. The theoretical treatment of the effect of angular momentum coupling on the two-photon rotational line strengths features the use of irreducible spherical tensors and 3j symbols. The final results are expressed in terms of the Hund’s case (a) coupling coefficients aJ and bJ for the X 2 Π(v" = 0) rotational level wavefunctions, which are intermediate between Hund’s case (a) and case (b). Considerable physical insight is provided by this final form of the equations for the rotational line strengths. Corrections to the two-photon absorption rotational line strength for higher order effects such as centrifugal stretching can be included in a straightforward fashion in the analysis by incorporating higher order terms in these coupling coefficients a J and b J , although these corrections are essentially negligible for J < 50. The theoretical calculations of relative line intensities are in good agreement both with our experiment and with published experimental results. Furthermore, the calculated line shapes and relative intensities for closely spaced main branch and satellite transitions are in excellent agreement with our experimental measurements

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

AN ONLINE CATALOG OF CATACLYSMIC VARIABLE SPECTRA FROM THE FAR-ULTRAVIOLET SPECTROSCOPIC EXPLORER

We present an online catalog containing spectra and supporting information for cataclysmic variables that have been observed with the Far-Ultraviolet Spectroscopic Explorer (FUSE). For each object in the catalog we list some of the basic system parameters such as (R.A., decl.), period, inclination, and white dwarf mass, as well as information on the available FUSE spectra: data ID, observation date and time, and exposure time. In addition, we provide parameters needed for the analysis of the FUSE spectra such as the reddening E(B - V), distance, and state (high, low, intermediate) of the system at the time it was observed. For some of these spectra we have carried out model fits to the continuum with synthetic stellar and/or disk spectra using the codes TLUSTY and SYNSPEC. We provide the parameters obtained from these model fits; this includes the white dwarf temperature, gravity, projected rotational velocity, and elemental abundances of C, Si, S, and N, together with the disk mass accretion rate, the resulting inclination, and model-derived distance (when unknown). For each object one or more figures are provided (as gif files) with line identification and model fit(s) when available. The FUSE spectra and the synthetic spectra are directly available for download as ASCII tables. References are provided for each object, as well as for the model fits. In this article we present 36 objects, and additional ones will be added to the online catalog in the future. In addition to cataclysmic variables, we also include a few related objects, such as a wind-accreting white dwarf, a pre-cataclysmic variable, and some symbiotics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Effective field theory and keV lines from dark matter

We survey operators that can lead to a keV photon line from dark matter decay or annihilation. We are motivated in part by recent claims of an unexplained 3.5 keV line in galaxy clusters and in Andromeda, but our results could apply to any hypothetical line observed in this energy range. We find that given the amount of flux that is observable, explanations in terms of decay are more plausible than annihilation, at least if the annihilation is directly to Standard Model states rather than intermediate particles. The decay case can be explained by a scalar or pseudoscalar field coupling to photons suppressed by a scale not far below the reduced Planck mass, which can be taken as a tantalizing hint of high-scale physics. The scalar case is particularly interesting from the effective field theory viewpoint, and we discuss it at some length. Because of a quartically divergent mass correction, naturalness strongly suggests the theory should be cut off at or below the 1000 TeV scale. The most plausible such natural UV completion would involve supersymmetry. These bottom-up arguments reproduce expectations from top-down considerations of the physics of moduli. A keV line could also arise from the decay of a sterile neutrino, in which case a renormalizable UV completion exists and no direct inference about high-scale physics is possible.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Magnetic field dependence of singlet fission in solutions of diphenyl tetracene

Magnetic field effects provide a convenient and specific probe of singlet exciton fission within optoelectronic devices. Here, we demonstrate that this tool may also be applied to screen potential fission material candidates in solution. We characterize the phenomenon in diphenyl tetracene (DPT), which shows strong fluorescence modulation and the expected field dependence in its transient decay as a function of concentration. Furthermore, solution measurements may also be used to test for the presence of an intermediate charge transfer state, but we observe no changes to the field dependence of DPT singlet exciton fission in toluene relative to chloroform.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Coupling between positronium formation and elastic positron-scattering channels in the rare gases

Measurements of elastic-scattering cross sections are presented for positron collisions with helium, neon, argon, krypton, and xenon around the threshold energy for positronium (Ps) formation. The elastic cross section falls slowly with increasing energy above the Ps formation threshold in helium and neon, whereas in argon, krypton, and xenon it exhibits an increase, which appears both more prominent and more sustained as the atomic number of the gas increases. It is proposed that this coupling is a result of an intermediate virtual Ps state that enhances branching into the (atom plus positron) final state.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Time-resolved Compton scattering for a model fermion-boson system

We study the scattering of a boson with a fermion with full spatial and temporal resolution based on the one-dimensional Yukawa Hamiltonian. In quantum field theory this interaction is described by the annihilation and creation of bosons with intermediate virtual particle states. We show that this process can be modeled in the center-of-mass frame by a scattering potential, permitting us to interpret the absorption and re-emission processes in quantum mechanical terms of a characteristic force. This Compton force between the fermion and boson is repulsive for large distances and attractive for shorter spacings. We also examine the periodic dynamics of a fermion and a boson that are spatially confined to a ring cavity in which they counterpropagate, enabling us to study interactions independent of the transients that characterize the (one-time) scattering event of two wave packets.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Suppression of ionization probability due to Rabi oscillations in the resonance two-photon ionization of He by EUV free-electron lasers

The two-photon resonance ionization probability of atoms in strong extreme-ultraviolet free-electron laser (EUV FEL) pulses has been investigated by the model of time-dependent wave packet propagation of a light-coupled multilevel atom. Under the simulation within the model assuming single-mode FEL pulses, the ionization probability P{sub ion} has shown characteristic dependences on the scaled coupling parameter U{sub gi} between two levels of the ground (g) and intermediate (i) resonance states, namely, P{sub ion}{proportional_to}(U{sub gi}){sup n}, with n being equal to {approx}2, less than 1, and {approx}1 for the small, medium, and large U{sub gi} regimes, respectively. This power dependence of the ionization probability has been interpreted due to Rabi oscillations between g and i states. To compare with recent experimental results on the same condition, the multimode nature of self-amplitude spontaneous emission (SASE) FEL pulses has been managed in the simulation. Then, the recent experimental laser-power dependence of the two-photon resonance ionization of He [Sato et al., J. Phys. B 44, 161001 (2011)] has been well described by that for the large U{sub gi} regime of the simulation, i.e., n{approx} 1. Thus, the observed linear laser-power dependence has been rationalized as being caused by the strong Rabi oscillations between the (2p)-(1s) states.

74 ATOMIC AND MOLECULAR PHYSICS↗