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Results for “IONIZATION POTENTIAL”

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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Estimating ionization states and continuum lowering from ab initio path integral Monte Carlo simulations for warm dense hydrogen

Warm dense matter (WDM) is an active field of research, with applications ranging from astrophysics to inertial confinement fusion. Ionization degree and continuum lowering are important quantities to understand how materials behave under these conditions, but can be difficult to diagnose since experimental campaigns are limited and often require model-dependent analysis. This is especially true for hydrogen, which has a comparably low scattering cross section, making high-quality data particularly difficult to obtain. Consequently, building equation of state tables often relies on simulations in combination with untested approximations to extract properties from experiments. Here, we investigate an approach for extracting the ionization potential depression and ionization degree—quantities which are otherwise not directly accessible from the physical model—from first-principles path integral Monte Carlo (PIMC) simulations utilizing a chemical model. In contrast to experimental measurements, where noise and nonequilibrium effects add to the uncertainty of the inferred parameters, PIMC simulations provide a clean signal with well-defined thermodynamic conditions. Comparisons against commonly used models show a qualitative agreement, but we find deviations primarily for the high-density and high-temperature cases. We also demonstrate the decreasing sensitivity of the dynamic structure factor with respect to both ionization and continuum lowering for increasing scattering angles in x-ray Thomson scattering experiments. Our work has important implications for the design of future experiments, but also offers qualitative understanding of structure factors and the imaginary-time correlation function obtained from first-principles quantum Monte Carlo simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

CLASS: Coronal Line Activity Spectroscopic Survey

We conduct the first systematic survey of a comprehensive set of the twenty optical coronal lines in the spectra of nearly 1 million galaxies observed by the Sloan Digital Sky Survey (SDSS) Data Release 8 catalog. This includes often overlooked high ionization potential lines such as [Ar x] λ5533, [S XII ] λ7609, [Fe XI ] λ7892, and [Fe XIV ] λ5303. We find that, given the limited sensitivity of SDSS, strong coronal line emission is extremely rare, with only ~0.03% of the sample showing at least one coronal line, significantly lower than the fraction of galaxies showing optical narrow line ratios (~17%) or mid-infrared colors (~2%) indicative of nuclear activity. The coronal line luminosities exhibit a large dynamic range, with values ranging from ~10 34 to 10 42 erg s –1 . We find that a vast majority (~80%) of coronal line emitters in dwarf galaxies (M $\star$ < 9.6 × 10 9 M ⊙ ) do not display optical narrow line ratios indicative of nuclear activity, in contrast to higher mass galaxies (~17%). Moreover, we find that the highest ionization potential lines are preferentially found in lower mass galaxies. These findings are consistent with the theory that lower mass black holes found in lower mass galaxies produce a hotter accretion disk, which in turn enhances the higher ionization coronal line spectrum. Future coronal line searches with 30 m class telescopes or JWST may provide a pathway into uncovering the intermediate mass black hole population.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Laser resonance ionization spectroscopy of thorium

High-lying Rydberg and autoionizing (AI) states of thorium (Th) have been studied via resonance laser ionization spectroscopy at both TRIUMF Canada’s particle accelerator center and Oak Ridge National Lab (ORNL). Multiple Rydberg series converging to the ionization potential (IP) were observed via different stepwise laser excitation schemes and were assigned to be the 6d 2 7s ( 4 F 3/2 ) np, nd, and nf series. Analysis of these series enabled the determination of the IP to be 50 868.735(54) cm −1 , which improved the precision by two orders of magnitude over the current adopted NIST value of 50 867(2) cm −1 . Additionally, four AI Rydberg series were identified and assigned to nf and nd series converging to the 6d 2 7s 4 F 5/2 and 6d7s 2 2 D 3/2 metastable states of Th + . In conclusion, the measured energies of the Rydberg and AI Rydberg states are reported, and observed perturbations within the series are discussed.

Rydberg series↗
DOE OSTI2023

Choline Fluoride-Ethylene glycol deep eutectic solvent mixture – Synthesis and physicochemical properties

A critical factor in achieving tunability in DESs is varying the type of hydrogen bond acceptors (HBAs) and donors (HBDs). Choline halides (ChX), such as ChCl and ChBr, have been studied to investigate the effect of the choline anion on DESs. However, ChF-based DESs have been underrepresented in scientific research. ChF has excellent potential, such as high electron affinity, ionization potential, and strong hydrogen bond interactions. Moreover, ChF-based DES can lead to a deeper understanding of DESs due to the NMR-active 19F nuclear spin nature. We report the first synthesis and characterization of choline fluoride-EG (1:2, ChF:EG) DES, which we named “EthalineF.” We studied this mixture using various spectroscopic techniques, including NMR, FT-IR, Raman, and UV–vis spectroscopies. Polarity, density, viscosity, and conductivity measurements were collected as well. Transient absorption spectroscopy (TAS) was used to study the solvation dynamics of EthalineF. 19F NMR indicated that some fluoride anions (~15%) are coordinated to the choline cation. In EthalineF, the new type of observed fluoride anions is proposed to be a tight-binding choline-fluoride ion pair. Further, EthalineF has a larger solvodynamic radius than Ethaline. This can explain the lower conductivity for EthalineF compared to Ethaline despite the higher fluidity and solvation dynamics for EthalineF.

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

Detection of multi-reference character imbalances enables a transfer learning approach for virtual high throughput screening with coupled cluster accuracy at DFT cost

Appropriately identifying and treating molecules and materials with significant multi-reference (MR) character is crucial for achieving high data fidelity in virtual high-throughput screening (VHTS). Despite development of numerous MR diagnostics, the extent to which a single value of such a diagnostic indicates the MR effect on a chemical property prediction is not well established. We evaluate MR diagnostics for over 10 000 transition-metal complexes (TMCs) and compare to those for organic molecules. We observe that only some MR diagnostics are transferable from one chemical space to another. By studying the influence of MR character on chemical properties (i.e., MR effect) that involve multiple potential energy surfaces (i.e., adiabatic spin splitting, ΔE H–L , and ionization potential, IP), we show that differences in MR character are more important than the cumulative degree of MR character in predicting the magnitude of an MR effect. Motivated by this observation, we build transfer learning models to predict CCSD(T)-level adiabatic ΔE H–L and IP from lower levels of theory. By combining these models with uncertainty quantification and multi-level modeling, we introduce a multi-pronged strategy that accelerates data acquisition by at least a factor of three while achieving coupled cluster accuracy (i.e., to within 1 kcal mol –1 MAE) for robust VHTS.

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

Transient methods for understanding the properties of strongly oxidizing radicals

This review discusses the properties of strongly oxidizing radicals in organic and aqueous media and highlights the challenges in obtaining accurate values of their reduction potentials. Transient redox equilibrium methods based on the use of strong photooxidants or initiated by pulse radiolysis are shown to provide versatile approaches for decoupling electron transfer reactions from follow-up reactivity of unstable radical species, resulting in accurate values of reduction potentials of very positive couples, including some solvent radical cations. Here, we also show that correlations of reduction potentials with Hammett Σσ + p parameters, as well as gas phase ionization potentials, can be used to estimate the redox properties of unknown couples within a homologous series of compounds. The effects of ion pairing and hemicolligation on redox properties of organic and inorganic radicals are also discussed.

14 SOLAR ENERGY↗
DOE OSTI2023

A Catalog of 71 Coronal Line Galaxies in MaNGA: [Ne v] Is an Effective AGN Tracer

Despite the importance of active galactic nuclei (AGNs) in galaxy evolution, accurate AGN identification is often challenging, as common AGN diagnostics can be confused by contributions from star formation and other effects (e.g., Baldwin–Phillips–Terlevich diagrams). However, one promising avenue for identifying AGNs is "coronal emission lines" ("CLs"), which are highly ionized species of gas with ionization potentials ≥100 eV. These CLs may serve as excellent signatures for the strong ionizing continuum of AGNs. To determine if CLs are in fact strong AGN tracers, we assemble and analyze the largest catalog of optical CL galaxies using the Sloan Digital Sky Survey's Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) catalog. We detect CL emission in 71 MaNGA galaxies, out of the 10,010 unique galaxies from the final MaNGA catalog, with ≥5σ confidence. In our sample, we measure [Ne v]λ3347, λ3427, [Fe vii]λ3586, λ3760, λ6086, and [Fe x]λ6374 emission and crossmatch the CL galaxies with a catalog of AGNs that were confirmed with broad-line, X-ray, IR, and radio observations. We find that [Ne v] emission, compared to [Fe vii] and [Fe x] emission, is best at identifying high-luminosity AGNs. Moreover, we find that the CL galaxies with the least dust extinction yield the most iron CL detections. We posit that the bulk of the iron CLs are destroyed by dust grains in the galaxies with the highest [O III ] luminosities in our sample, and that AGNs in the galaxies with low [O III ] luminosities are possibly too weak to be detected using traditional techniques.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Role of Transition Metals in Metal–Organic Frameworks as Nanoporous Ion Emitters for Thermal Ionization Mass Spectrometry

Thermal ionization mass spectroscopy (TIMS) is a powerful analytical technique that allows for precise determination of isotopic ratios. Analysis on low abundance samples, however, can be limited by the ionization efficiency. Following an investigation into a new type of metal-organic hybrid material devised to promote the emission of analyte ions (nano-PIES) and reduce traditional sample loading problems, this work probes the impact that changing the metal in the material has on the ionization of Uranium-238. Being derived from metal-organic frameworks (MOFs), nano-PIEs inherit the tunability of the parent MOFs; the MOF-74 series has been well studied for probing the impact various framework metals (i.e., Mg, Mn, Co, Ni, Cu, Zn, and Cd) have on material properties, and thus, a series of nano-PIEs with different metals were derived from an isoreticular MOF-74 series. In conclusion, trends in ionization efficiency were studied as a function of ionization potential, volatility, and work function of the framework metals as well as the mechanism of ionization.

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

Early-stage oxidation and subsequent damage of the used nuclear fuel extractant TODGA; electron pulse radiolysis and theoretical insights

Radiation induced damage of extractant molecules is a well-known phenomenon responsible for reducing efficiency and increasing the waste and cost of reprocessing used nuclear fuel (UNF). As such, understanding early-stage (pico- to nanoseconds) radiation-induced reaction mechanisms is essential for informing the design of next generation extractants with enhanced radiation robustness. Here, in this work, we utilized picosecond and nanosecond electron pulse radiolysis experiments to probe the early-stage radioactive environment experienced by the organic phase extractant N,N,N',N'-tetraoctyldiglycolamide (TODGA), proposed for separating highly radioactive trivalent minor actinides (specifically americium and curium) from the trivalent lanthanides. Using comparisons to the similar ionization potential (IP) solute p-xylene, this work determined the mechanism of reaction with the ionized diluent (i.e., n-dodecane radical cation, DD˙ + ) is hole transfer to produce TODGA˙ + . At high TODGA concentrations (>100 mM), the majority of this transfer occurs faster than 10 ps via the capture of DD˙ + holes prior to their solvation with a C 37 = 300 mM. The surviving solvated holes were captured with k = (2.38 ± 0.15) × 10 10 M -1 s -1 . Attempts at subsequent hole transfer to lower IP solutes found that only 10% of holes were transferred, indicating bond rupture of TODGA˙ + occurs within 2.6 ns at 200 mM TODGA. Possible reaction pathways for the rapid decomposition of TODGA˙ + were explored using a combination of experiments and density functional theory (DFT) calculations.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Nanoscale Periodic Trapping Sites for Interlayer Excitons Built by Deformable Molecular Crystal on 2D Crystal

The nanoscale moiré pattern formed at 2D transition-metal dichalcogenide crystal (TMDC) heterostructures provides periodic trapping sites for excitons, which is essential for realizing various exotic phases such as artificial exciton lattices, Bose–Einstein condensates, and exciton insulators. At organic molecule/TMDC heterostructures, similar periodic potentials can be formed via other degrees of freedom. Here, we utilize the structure deformability of a 2D molecular crystal as a degree of freedom to create a periodic nanoscale potential that can trap interlayer excitons (IXs). Specifically, two semiconducting molecules, PTCDI and PTCDA, which possess similar band gaps and ionization potentials but form different lattice structures on MoS 2 , are investigated. The PTCDI lattice on MoS 2 is distorted geometrically, which lifts the degeneracy of the two molecules within the crystal’s unit cell. The degeneracy lifting results in a spatial variation of the molecular orbital energy, with an amplitude and periodicity of ~0.2 eV and ~2 nm, respectively. On the other hand, no such energy variation is observed in PTCDA/MoS 2 , where the PTCDA lattice is much less distorted. Furthermore, the periodic variation in molecular orbital energies provides effective trapping sites for IXs. For IXs formed at PTCDI/MoS 2 , rapid spatial localization of the electron in the organic layer toward the interface is observed, which demonstrates the effectiveness of these interfacial IX traps.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Formation of the C 4 H n + ( n = 2–5) ions upon ionization of acetylene clusters in helium droplets

Infrared (IR) spectroscopy using ultracold helium nanodroplet matrices has proven to be a powerful method to interrogate encapsulated ions, molecules, and clusters. Due to the helium droplets’ high ionization potential, optical transparency, and ability to pick up dopant molecules, the droplets offer a unique modality to probe transient chemical species produced via photo- or electron impact ionization. Here, in this work, helium droplets were doped with acetylene molecules and ionized via electron impact. Ion-molecule reactions within the droplet volume yield larger carbo-cations that were studied via IR laser spectroscopy. This work is focused on cations containing four carbon atoms. The spectra of C 4 H 2 + , C 4 H 3 + , and C 4 H 5 + are dominated by diacetylene, vinylacetylene, and methylcyclopropene cations, respectively, which are the lowest energy isomers. On the other hand, the spectrum of C 4 H 4 + ions hints at the presence of several co-existing isomers, the identity of which remains to be elucidated.

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

N-type molecular doping of a semicrystalline conjugated polymer through cation exchange

Control of electrical doping is indispensable in any semiconductor device, and both efficient hole and electron doping are required for many devices. In organic semiconductors, however, electron doping has been essentially more problematic compared to hole doping because in general organic semiconductors have low electron affinities and require dopants with low ionization potentials that are often air-sensitive. Here, we adapt an efficient molecular doping method, so-called ion-exchange doping, to dope electrons in a polymeric semiconductor. We initially reduce the polymeric semiconductor using one electron transfer from molecular dopants, and then the ionized dopants in the resulting air-unstable films are replaced with secondary ions via cation exchange. Improved ambient stability and crystallinity of the doped polymeric semiconductors are achieved when a specific bulky molecular cation was chosen as the secondary ion, compared to conventional methods. The presented strategy can overcome the trade-off relationship between reducing capability and ambient stability in molecular dopants, and a wider selection of dopant ions will help to realize ambient-stable electron conductors.

36 MATERIALS SCIENCE↗
DOE OSTI2022

CLASSY III. The Properties of Starburst-driven Warm Ionized Outflows

We report the results of analyses of galactic outflows in a sample of 45 low-redshift starburst galaxies in the COS Legacy Archive Spectroscopic SurveY (CLASSY), augmented by five additional similar starbursts with Cosmic Origins Spectrograph (COS) data. The outflows are traced by blueshifted absorption lines of metals spanning a wide range of ionization potential. The high quality and broad spectral coverage of CLASSY data enable us to disentangle the absorption due to the static interstellar medium (ISM) from that due to outflows. We further use different line multiplets and doublets to determine the covering fraction, column density, and ionization state as a function of velocity for each outflow. We measure the outflow's mean velocity and velocity width, and find that both correlate in a highly significant way with the star formation rate, galaxy mass, and circular velocity over ranges of four orders of magnitude for the first two properties. We also estimate outflow rates of metals, mass, momentum, and kinetic energy. We find that, at most, only about 20% of silicon created and ejected by supernovae in the starburst is carried out in the warm phase we observe. The outflows' mass-loading factor increases steeply and inversely with both circular and outflow velocity (log–log slope ~–1.6), and reaches ~10 for dwarf galaxies. We find that the outflows typically carry about 10%–100% of the momentum injected by massive stars and about 1%–20% of the kinetic energy. We show that these results place interesting constraints on, and new insights into, models and simulations of galactic winds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Density functional theory of material design: fundamentals and applications—II

Abstract This is the second and the final part of the review on density functional theory (DFT), referred to as DFT-II. In the first review, DFT-I, we have discussed wavefunction-based methods, their complexity, and basics of density functional theory. In DFT-II, we focus on fundamentals of DFT and their implications for the betterment of the theory. We start our presentation with the exact DFT results followed by the concept of exchange-correlation (xc) or Fermi-Coulomb hole and its relationship with xc energy functional. We also provide the exact conditions for the xc-hole, xc-energy and xc-potential along with their physical interpretation. Next, we describe the extension of DFT for non-integer number of electrons, the piecewise linearity of total energy and discontinuity of chemical potential at integer particle numbers, and derivative discontinuity of the xc potential, which has consequences on fundamental gap of solids. After that, we present how one obtains more accurate xc energy functionals by going beyond the LDA. We discuss the gradient expansion approximation (GEA), generalized gradient approximation (GGA), and hybrid functional approaches to designing better xc energy functionals that give accurate total energies. However, these functionals fail to predict properties like the ionization potential and the band gap. Thus, we next describe different methods of modelling these potentials and results of their application for calculation of the band gaps of different solids to highlight accuracy of different xc potentials. Finally, we conclude with a glimpse on orbital-free density functional theory and the machine learning approach.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Analytic Gradients for Equation-of-Motion Coupled Cluster with Single, Double, and Perturbative Triple Excitations

Understanding the process of molecular photoexcitation is crucial in various fields, including drug development, materials science, photovoltaics, and more. The electronic vertical excitation energy is a critical property, for example in determining the singlet-triplet gap of chromophores. However, a full understanding of excited-state processes requires additional explorations of the excited-state potential energy surface and electronic properties, which is greatly aided by the availability of analytic energy gradients. Owing to its robust high accuracy over a wide range of chemical problems, equation-of-motion coupled-cluster with single and double excitations (EOM-CCSD) is a powerful method for predicting excited state properties, and the implementation of analytic gradients of many EOM-CCSD (excitation energies, ionization potentials, electron attachment energies, etc.) along with numerous successful applications high- lights the flexibility of the method. In specific cases where a higher level of accuracy is needed or in more complex electronic structures, the inclusion of triple excitations becomes essential, for example, in the EOM-CCSD* approach of Saeh and Stanton. In this work, we derive and implement for the first time the analytic gradients of EOMEE-CCSD*, which also provides a template for analytic gradients of related ex- cited state methods with perturbative triple excitations. Here, the capabilities of analytic EOMEE-CCSD* gradients are illustrated by several representative examples.

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

Ag Alloying in Cu 2– y Ag y Ba(Ge,Sn)Se 4 Films and Photovoltaic Devices

Trigonal Cu 2 BaGe 1–x Sn x Se 4 (CBGTSe) has recently gained interest as a potential photovoltaic absorber to target mitigation of antisite defect formation in Cu 2 ZnSn(S,Se) 4 . This study examines partial substitution of Cu by Ag as a potential approach to tune the properties of Ag-incorporated CBGTSe in the following aspects: 1) phase stability and crystal structure as a function of Ag content; 2) film morphology and grain structure; 3) charge carrier properties; 4) band positions; and 5) charge carrier kinetics and recombination. Up to 20% of Cu can be substituted by Ag in CBGTSe, while above 20% a phase mixture appears. Increasing Ag content induces larger average grain size and reduced hole carrier densities. In contrast, photoelectron spectroscopy and photoluminescence measurements reveal negligible impact of Ag substitution on ionization potential (≈5.4 eV) and electron affinity (≈3.7 eV). Also, Ag content offers negligible impact on carrier lifetimes (few ns). Consistent with these fundamental properties, solar cells based on two different Ag/(Ag + Cu) ratios (≈0% and ≈20%) show comparable power conversion efficiencies (≈2.7–2.8%). Finally, these results indicate that CBGTSe films and solar cells may be less sensitive to Ag substitution compared to Cu 2 ZnSn(S,Se) 4 , at least at the current level of absorber and device optimization.

14 SOLAR ENERGY↗
DOE OSTI2022

On the nature of droplet production in DC glows with a liquid anode: mechanisms and potential applications

The interactions between plasma and liquid solutions give rise to the formation of chemically reactive species useful for many applications, but the mass transport in the interfacial region is usually limited and not fully understood. In this work, we report on the observation and explanation of droplet ejection at the plasma–liquid interface of a one-atmosphere glow discharge with the liquid anode. The impact of droplets emission on plasma properties is also analyzed by spectroscopy. The process, which is an efficient mass and charge transport mechanism, apparently occurs during discharge operation and thus constitutes a feedback vehicle between the discharge and the liquid. Distinctive from the well-known Talyor cone droplets associated with liquid cathodes, the observed droplets originate from the bubbles due to electrolysis and solvated air which does not require strong electric field at liquid surface. Instead, the droplets are ejected by bubble cavity rupture at the plasma–liquid interface and their size, initial speed are strongly dependent on the gravity, inertia and capillarity. Further, the droplets emerge near the plasma attachment and are subsequently vaporized, emitting intense UV and visible light, which originated from excited OH radicals and sodium derived from the liquid electrolyte. Spectroscopy analysis confirmed that the bursting droplets generally reduce the gas temperature while their effects on electron density depend on the composition of the liquid anode. Results also show that droplets from NaCl solution increase the plasma electron density due to the lower ionization potential of sodium. These findings reveal a new mechanism for discharge maintenance and mass transport as well as suggest a simple approach to dispersing plasma-activated liquid into the gas phase and thus enhancing plasma–liquid interaction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Organic Molecules Mimic Alkali Metals Enabling Spontaneous Harpoon Reactions with Halogens

Abstract The harpoon mechanism has been a milestone in molecular reaction dynamics. Until now, the entity from which electron harpooning occurs has been either alkali metal atoms or non‐metallic analogs in their excited states. In this work, we demonstrate that a common organic molecule, octamethylcalix[4] pyrrole (omC4P), behaves just like alkali metal atoms, enabling the formation of charge‐separated ionic bonding complexes with halogens omC4P + ⋅ X − ( X =F−I, SCN) via the harpoon mechanism. Their electronic structures and chemical bonding were determined by cryogenic photoelectron spectroscopy of the corresponding anions and confirmed by theoretical analyses. The omC4P + ⋅ X − could be visualized to form from the reactants omC4P+ X via electron harpooning from omC4P to X at a distance defined by the energy difference between the ionization potential of omC4P and electron affinity of X .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗