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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 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Electronic spectroscopy and ionization potentials for YbOH and YbOCH 3

The polyatomic molecules YbOH and YbOCH 3 have been recognized as being of potential value for spectroscopic experiments that explore charge-parity and time reversal symmetry violation effects. These measurements require very high precision, which, in turn, will necessitate that the molecules be manipulated at ultra-cold temperatures. Both YbOH and YbOCH 3 have electronic transitions that appear suitable for laser cooling ($\tilde{A}$ 2 Π 1/2 -$\tilde{X}$ 2 Σ + and $\tilde{A}$2E 1/2 -$\tilde{X}$ 2 A 1 , respectively) but the currently available spectroscopic data is not sufficient to determine the extent to which population leaks may compromise the optical cooling processes. A further complication is that the quantum states of interest for these measurements will need to be selectively populated. The $\tilde{A}$-$\tilde{X}$ band systems of both YbOH and YbOCH 3 show evidence of vibronic perturbations, such that there are unassigned vibronic features at energies that are just above the origin bands. Here, in the present study we have recorded spectra for the $\tilde{A}$ 2 Π 1/2 -$\tilde{X}$ 2 Σ + transition of jet-cooled YbOD to facilitate the vibronic assignments. In addition, spectra for the $\tilde{B}$ 2 Σ + - $\tilde{X}$ 2 Σ + transition of YbOH were recorded, establishing the origin band at 20473.8 cm -1 . Previously, the reaction of Yb with CH 3 OH has been used to generate gas-phase YbOCH 3 . As this reaction also yields YbOH, there have been complications in spectroscopic studies of YbOCH 3 due to overlap of the $\tilde{A} -\tilde{X}$ band systems. To identify specific regions of overlap, resonantly enhanced two-photon ionization spectra were recorded using mass-resolved detection of the YbOH + and YbOCH 3 + ions. These data confirmed the overlap of vibronic bands near 17640 and 17680 cm -1 . Two-photon ionization spectroscopy also provided accurate ionization energies of IE(YbOH)=45788(10) and IE(YbOCH 3 )=45283(10) cm -1 . The IE for YbOH is relevant to problems encountered in previous attempts to determine the bond dissociation energy of YbOH + .

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

Pump and ionizing-probe dynamics in a simultaneous treatment of electronic and nuclear motion in LiH

The dissociative single ionization of the LiH molecule using a two-color UV-UV pump-probe scheme is simulated in ab initio calculations demonstrating how the dynamics initiated on intermediate Rydberg states of diatomic molecules can be imaged by such experiments. The theoretical treatment combines nuclear motion with highly correlated descriptions of electronic continua and bound electronic states. Nuclear dynamics on Rydberg states are only weakly reflected by changes in photoelectron energies ejected by time-delayed ionizing pulses if the Rydberg potential curves parallel those of the ion states being produced. However, coincidence measurements guided by knowledge of the photoionization amplitudes as a function of internuclear distance can still reveal intermediate-state dynamics in pump-probe experiments.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Diffusion quantum Monte Carlo approach to the polaritonic ground state

Making and using polaritonic states (i.e., hybrid electron-photon states) for chemical applications has recently become one of the most prominent and active fields that connects the communities of chemistry and quantum optics. Modeling of such polaritonic phenomena using ab initio approaches calls for new methodologies, leading to the reinvention of many commonly used electronic structure methods, such as Hartree-Fock, density functional, and coupled cluster theories. Here in this work, we explore the formally exact diffusion quantum Monte Carlo approach to obtain numerical solutions to the polaritonic ground state during the dissociation of the H 2 molecular system. Here, we examine various electron-nuclear-photon properties throughout the dissociation, such as changes to the minimum of the cavity Born-Oppenheimer surface, the localization of the electronic wave function, and the average mode occupation. Finally, we directly compare our results to that obtained with state-of-the-art, yet approximate, polaritonic coupled cluster approaches.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Attosecond x-ray free-electron lasers utilizing an optical undulator in a self-selection regime

Accelerator-based x-ray free-electron lasers (XFELs) are the latest addition to the revolutionary tools of discovery for the 21st century. The two major components of an XFEL are an accelerator-produced electron beam and a magnetic undulator, which tend to be kilometer-scale long and expensive. A proof-of-principle demonstration of free-electron lasing at 27 nm using beams from compact laser wakefield accelerators was shown recently by using a magnetic undulator. However, scaling these concepts to x-ray wavelengths is far from straightforward as the requirements on the beam quality and jitters become much more stringent. Here, we present an ultracompact scheme to produce tens of attosecond x-ray pulses with several GW peak power utilizing a novel aspect of the FEL instability using a highly chirped, prebunched, and ultrabright tens of MeV electron beam from a plasma-based accelerator interacting with an optical undulator. The FEL resonant relation between the prebunched period and the energy selects resonant electrons automatically from the highly chirped beam which leads to a stable generation of attosecond x-ray pulses. Furthermore, two-color attosecond pulses with subfemtosecond separation can be produced by adjusting the energy distribution of the electron beam so that multiple FEL resonances occur at different locations within the beam. Such a tunable coherent attosecond x-ray sources may open up a new area of attosecond science enabled by x-ray attosecond pump/probe techniques. Published by the American Physical Society 2024

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Colossal Density-Driven Resistance Response in the Negative Charge Transfer Insulator MnS 2

A reversible density driven insulator to metal to insulator transition in high-spin MnS 2 is experimentally observed, leading with a colossal electrical resistance drop of $10^8$ Omega by 12 GPa. Density functional theory simulations reveal the metallization to be unexpectedly driven by previously unoccupied $S_{2}^{-2}$ $\sigma^{*}_{3p}$ antibonding states crossing the Fermi level. This is a unique variant of the charge transfer insulator to metal transition for negative charge transfer insulators having anions with an unsaturated valence. By 36 GPa the emergence of the low-spin insulating arsenopyrite ($P2_1/c$) is confirmed, and the bulk metallicity is broken with the system returning to an insulative electronic state.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Pulse Energy and Pulse Duration Effects in the Ionization and Fragmentation of Iodomethane by Ultraintense Hard X Rays

The interaction of intense femtosecond x-ray pulses with molecules sensitively depends on the interplay between multiple photoabsorptions, Auger decay, charge rearrangement, and nuclear motion. Here, we report on a combined experimental and theoretical study of the ionization and fragmentation of iodomethane (CH 3 I) by ultraintense (~10 19 W/cm 2 ) x-ray pulses at 8.3 keV, demonstrating how these dynamics depend on the x-ray pulse energy and duration. We show that the timing of multiple ionization steps leading to a particular reaction product and, thus, the product’s final kinetic energy, is determined by the pulse duration rather than the pulse energy or intensity. While the overall degree of ionization is mainly defined by the pulse energy, our measurement reveals that the yield of the fragments with the highest charge states is enhanced for short pulse durations, in contrast to earlier observations for atoms and small molecules in the soft x-ray domain. Finally, we attribute this effect to a decreased charge transfer efficiency at larger internuclear separations, which are reached during longer pulses.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A comparative study of cerium oxides formed by pulsed laser ablation and continuous wave laser heating

Abstract The formation of Ce 2 O 3 from cerium metal requires complex reducing conditions. Alternatively, we show that different stoichiometries and structures of cerium oxides can be generated in high‐temperature laser experiments by varying the availability of oxygen and the use of either pulsed laser ablation (PLA) or continuous wave (CW) laser heating of cerium metal. X‐ray diffraction and Raman spectroscopy suggest that a low structural order Ce 2 O 3 /CeO 2 mixed structure is formed in a 1% O 2 atmosphere with PLA. For CW heating in a 1% O 2 environment, Raman measurements show the formation of crystalline A‐type Ce 2 O 3 in proximity to the point of laser impingement. These experiments were repeated in 18 O 2 and allowed us to report for the first time the corresponding Raman spectrum of Ce 2 18 O 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Perspectives on UV and x-ray photoelectron spectroscopy

Atomic photoionization using electron spectroscopy was one of the scientific topics in which Professor David A. Shirley excelled and established a research legacy. We discuss selected highlights of atomic photoionization research done by the Shirley group beginning in the 1970s. Our main topics are electron correlation satellites, photoelectron angular distributions with tunable synchrotron radiation, and developments of theory. We also discuss examples of more recent research that extends the earlier work, including double K-shell photoionization, nondipole interactions, and the pervasive role of interchannel coupling. Furthermore, we conclude with examples of current experimental and theoretical research.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2025

Multigas Adsorption with Single-Site Cooperativity in a Metal-Organic Framework

Cooperative gas adsorption in metal-organic frameworks (MOFs) is a rare phenomenon that generally involves long-range communication between multiple binding sites. We demonstrate a MOF containing cobalt(II)-methyl sites that selectively and reversibly capture two carbon monoxide (CO) molecules per site, leading to record-high adsorption capacities at ambient temperatures and pressures. Gas adsorption and structural, spectroscopic, and computational analyses support a mechanism in which binding of one CO molecule triggers a spin transition, followed by binding of a second CO molecule and migratory insertion of the first CO molecule into the cobalt-methyl bond to form an acetyl. The greater binding affinity associated with the second CO results in sigmoidal adsorption isotherms, a hallmark of cooperativity and phase-change materials, despite the absence of long-range interactions within the framework.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Perspective—Lithium Metal Nucleation and Growth on Conductive Substrates: A Multi-Scale Understanding from Atomistic, Nano-, Meso-, to Micro-Scales

Reversible lithium (Li) deposition and stripping on conductive substrates like copper is vital for long-life high-energy rechargeable Li batteries. The reversibility is believed hindered by solid electrolyte interphase (SEI) formation and Li dendritic growth. Via in situ, operando cryo-microscopy and molecular dynamics simulation, we discovered amorphous Li before a disorder-order phase transition to bcc phase. The kinetics plays a significant role in Li nucleation and morphology evolution. This perspective on Li nucleation and growth from atomistic to nano- (<20 nm), meso- (20–100 nm), and micro-scales (>100 nm) provides a practical guidance on regulating dense Li deposits reversibly for long life performance.

25 ENERGY STORAGE↗
DOE OSTI2020

Dr. Ian Hutcheon Award: Spectroscopic Fingerprinting of Vapor-Phase Uranium Species

The Dr. Ian Hutcheon Post-Doctoral Fellowship provides resources to fund a TNFapplicable research project as well as promote mentorship, career development, and relevant training for the recipient. The two-year proposal incorporated a research plan to investigate uranium chemistry relevant to post-detonation nuclear forensics and a mentorship plan to address career development for the recipient in TNF-relevant areas.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Physical Sciences Vistas: Perspectives on Excellence in Mission-Focused Science, Technology, and Engineering at Los Alamos Laboratory (Issue 1, 2020)

This is the first 2020 issue of Physical Sciences Vistas, with a focus on “excellence in mission-focused science, technology, and engineering.” Excellence in mission-focused ST&E comprises one of the four elements of the Laboratory Agenda, focusing on sustaining and enhancing LANL’s science base. This issue highlights the diverse efforts of personnel in our Physical Sciences Directorate (ALDPS) to enhance science, technology, and engineering at the Laboratory. As we reflect on work at the Laboratory, mostly from our homes due to COVID-19, it is gratifying to see the important, diverse contributions to ST&E across ALDPS.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The Opus radiative opacity code, a new implementation of the super-transition array method

This report describes the development of our new radiative opacity code Opus, submitted as part of a 2020 Level 2 milestone requirement. This code aims to incorporate the capabilities in existing but separate opacity codes previously developed at LLNL (Opal, Topaz, and Tycho). The first phase in the development, which was to implement the super-transition (STA) method of Bar-Shalom and co-workers is now completed. In this work, we describe the underlying physics, implementation, usage, and regression testing as well as providing numerical examples for the opacity tables of boron, chromium, iron, and nickel. The latter are benchmarked against the LLNL legacy STA code Tycho, with an average absolute relative difference of ~1.5 and 0.5% for Planck and Rosseland opacity means, respectively. The cases where differences are larger are well understood in terms of numerical instabilities near discontinuities of the average degree of ionization inherent to the assumed opacity/equation-of-state model.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Isomer-specific spectroscopy of aromatics and their resonance-stabilized radical intermediates

There are many circumstances in which complex gas-phase reaction mixtures must be interrogated and understood, including combustion, plasmas, atmospheres, and molecular clouds. Spectroscopic tools are essential to selective detection and characterization of the widening array of precursors and the reactive intermediates they generate. This research program has focused on the development and implementation of sensitive spectroscopic detection schemes that are isomer-specific and even conformation-specific. In particular, we used an array of laser-based and broadband microwave methods to carry out isomer-specific and conformation-specific spectroscopy on large flexible molecules and reactive intermediates formed by photolysis, pyrolysis, combustion, or electron-driven chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Dancing Droplets on a Defect Line [Poster]

Liquid crystalline (LC) phases are made up of molecules or other small units that organize into mesoscale assemblies. Their order resembles that of crystalline solids, but since the molecules have some freedom to move position and direction, these assemblies also behave like liquids. Thus, highly birefringent and responsive phases with many defect (or disclination) lines can emerge. These ever fluctuating lines indicate regions of the LC where the position of the molecules disrupt the local rotational symmetry within the phase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Actinides and Correlated Electron Materials

The Actinides and Correlated Electron Materials area of leadership spans Los Alamos National Laboratory competency in actinide materials research dating to the Manhattan Project as articulated in the Integrated Plutonium Science and Research Strategy and competency in strongly correlated electron systems dating back to at least the early 1980s. This area of leadership focuses on the goals of discovering, understanding, and controlling emergent electronic states and predictive performance of actinide materials. They are quintessentially linked by the fact that the physics of actinides—and plutonium in particular—are governed by strong electronic correlations. Not only is the electronic structure of actinides dictated by fine details of electron correlations, but chemical bonding and physical structure are as well. Hence, by addressing the first goal of this leadership area we can significantly accelerate progress on the second goal. To understand such matter requires probing the intertwined spin, charge, orbital, and lattice degrees of freedom with greater precision and developing models that accurately predict the consequences of these coupled degrees of freedom, on multiple length and time scales and including acute reactivity and effects of self-irradiation phenomena in these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Understanding Proton Movement in [Fe-Fe] Hydrogenases

Nature uses specialized metalloenzymes to carry out small molecule activation reactions, including CO 2 fixation, O 2 activation, and proton reduction, with unparalleled efficiency, rates, and selectivity. The latter reactions are performed by hydrogenases, protein metallo-complexes that interconverts H 2 to protons and electrons (H 2 oxidation) and the reverse reaction (H 2 production) with incredibly low energy input and amazingly fast kinetics. Reproducing both the activity and efficiency of metalloenzymes in sustainable anthropogenic systems remains one of the “holy grails” of inorganic chemistry. However, identifying the precise molecular components responsible for these desirable properties has been challenging in the natural metalloenzymes, hindering efforts to develop analogous processes in synthetic compounds. Considering the inherent complexity of a metalloenzyme and the many interactions, both strong and weak, that contribute to the function of an enzyme, we have elected to model natural metalloenzymes on a biochemical platform. Towards this end, we have a developed structural, functional, and mechanistic mimic of the [Ni-Fe] hydrogenases within a robust protein scaffold, rubredoxin, to understand the influence of the secondary coordination environment on the metal center. This involved preparing a series of three rubredoxin constructs containing a single point mutation at Val positions and making the NMR chemical shift assignments for the paramagnetic (nickel-substituted) and non-paramagnetic (zinc-substituted) form. These physical studies were complemented with in silico molecular dynamic studies on proteins with [Fe-S] clusters to engineer new proton channels to test in vitro . To assist our search for new natural metalloprotein scaffolds within the vast number of sequenced genomes, we created a neural network-based program to identify proteins with specific metal-binding sites. These computational and physical studies with metalloenzymes provide direct insight into the fundamental chemical principles driving the natural systems and offer design principles for developing catalysts that utilize analogous principles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗