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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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14 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A Glimpse into Photodetachment Spectra of Giant and Nested Fullerene Anions

We focus on the study of the photodetachment of bare, i.e., single-cage (CN)− as well as nested (multi-cage) (CN@CM@…)− singly charged fullerene anions. We calculate the attached electron’s wavefunctions, energies, oscillator strengths and photodetachment cross sections of the C60−, C240−, C540−, (C60@C240)−, (C60@C540)−, (C240@C540)− and (C60@C240@C540)− fullerene anions, where the attached electron is captured into the ground s-state by the resultant external field provided by all fullerene cages in the anion. The goal is to gain insight into the changes in behavior ofphotodetachment of this valence electron as a function of the different geometries and potentials of the various underlying fullerenes or nested fullerenes (fullerene onions) both due to their increasing size and due to “stuffing” of a larger bare fullerene with smaller fullerenes. To meet this goal, we opt for a simple semi-empirical approximation to this problem: we approximate each individual fullerene cage by a rigid potential sphere of a certain inner radius, thickness and potential depth, as in numerous other model studies performed to date. The results reveal a number of rather significant differences in the wavefunctions, oscillator strengths and photodetachment cross sections among these fullerene anions, some of which are completely counter-intuitive. The results obtained can serve as a “zeroth-order-touchstone” for future studies of single-cage and nested fullerene anions by more rigorous theories and/or experiments to build upon this work to assess the importance of interactions omitted in the present study.

Dolmatov, Valeriy K.↗
DOE OSTI2020

Fullerene Negative Ions: Formation and Catalysis

We first explore negative-ion formation in fullerenes C 44 to C 136 through low-energy electron elastic scattering total cross sections calculations using our Regge-pole methodology. Then, the formed negative ions C 44 – to C 136 – are used to investigate the catalysis of water oxidation to peroxide and water synthesis from H 2 and O 2 . The exploited fundamental mechanism underlying negative-ion catalysis involves hydrogen bond strength-weakening/breaking in the transition state. Density Functional Theory transition state calculations found C 60 – optimal for both water and peroxide synthesis, C 100 – increases the energy barrier the most, and C 136 – the most effective catalyst in both water synthesis and oxidation to H 2 O 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Photoinduced electron transfer from zinc meso -tetraphenylporphyrin to a one-dimensional perylenediimide aggregate: Probing anion delocalization effects

Organic photovoltaics incorporating non-fullerene acceptors based on perylenediimide (PDI) now rival fullerene acceptor-based devices in performance, although the mechanisms of charge generation in PDI-based devices are not yet fully understood. Fullerene-based systems are proposed to undergo electron transfer directly from the photoexcited donor into a band of delocalized acceptor states, thus increasing charge generation efficiency. Similarly, anion delocalization has been shown to enhance the rate of electron transfer from a photoexcited donor to two electronically coupled PDI acceptors. Here we investigate how additional electron acceptors may further increase the rate of electron transfer from the donor zinc meso-tetraphenylporphyrin (ZnTPP) to an aggregate of PDI acceptors (PDI[Formula: see text]. Femtosecond transient visible and mid-infrared absorption spectroscopies show that the rate of electron transfer from 1 *ZnTPP to the PDI assembly ZnTPP 2 -PDI 3 is statistically identical to that of the previously examined ZnTPP-PDI 2 . A Marcus theory analysis indicates that the parameters governing electron transfer are nearly identical for the two molecules, suggesting that the maximum electron transfer rate enhancement has been achieved in a cofacial PDI dimer because the ZnTPP directly couples to the first two PDI acceptors whereas the coupling to the third PDI is too weak.

bio-inspired↗
NASA NTRS2019

Titan's Ionospheric Chemistry, Fullerenes, Oxygen, Galactic Cosmic Rays and the Formation of Exobiological Molecules on and within its Surfaces and Lakes

We discuss the formation of aerosols within Titan's thermosphere-ionosphere and the different chemical pathways. Negative ion measurements by the Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) give evidence for formation of unsaturated anion carbon chains, while positive ion measurements of the Cassini Ion Neutral Mass Spectrometer (INMS) indicate formation of more aromatic cation hydrocarbons. There is presently no direct observational evidence for large neutral molecule growth in Titan's thermosphere-ionosphere. The hydrocarbon cations are expected to form Polycyclic Aromatic Hydrocarbons (PAH), those with the addition of nitrogen being called PAHNs. We theorize anion carbon chains can eventually become long enough to fold into fullerene C(60,70) carbon shells, of various charge states. Based on laboratory data the fullerenes can trap incoming O(sup +) magnetospheric ions that have relatively high energy collisions with the fullerenes and, once trapped, protect the oxygen atom from Titan's reducing thermosphere-ionosphere. The fullerenes can form into larger onion fullerenes and condense into larger embryo aerosols (i.e., m/q > 10,000 amu/q anions as observed by CAPS/ELS) eventually falling onto Titan's surface and precipitating to the bottom of its hydrocarbon lakes. Molecule production composed of H, C, N is known to occur in Titan's atmosphere with energy input from the magnetosphere, solar UV, and deeppenetrating irradiation from galactic cosmic rays (GCR). Space radiation effects by GCR irradiation of Titan's surface and lakes can lead to the manufacture of exobiological molecules with oxygen as the new ingredient. We have developed a model of galactic cosmic ray irradiation of Titan's atmosphere, surface, subsurface and bottoms of Titan lakes. GCR would provide further energy for processing of the aerosols into more complex organic forms such as tholins and precursor molecules for amino acids. A second process called hydrolysis then converts the precursor molecules into amino acids. Hydrolysis is provided via meteor impacts with size > 10 km and cryovolcanism both which can produce liquid water on Titan's surface for episodic periods > several 100 to 1000 years. Our model shows that GCR secondary particles can penetrate ~ 100 m below the ice surface (including the bottom of Titan's less dense hydrocarbon lakes ~ 150 m depths) and produce chemically significant dosages over very long timescales ~ 450 Myrs. The GCR model is combined with laboratory data from experiments in which dry methyl ices were irradiated to doses producing prebiotic amino acids such as glycine. The model calculations show glycine can form to ~ 2.5 ppb levels near the surface after ~450 Myrs of GCR proton irradiation and potentially to 5 ppb if heavy-ion GCRs up through Fe are included. If such molecules were detected, this would not only confirm this model but indicate that life forms different from ours may not be required.

Edward C. Sittler Jr↗
NASA NTRS2020

Titan's Ionospheric Chemistry, Fullerenes, Oxygen, Galactic Cosmic Rays and the Formation of Exobiological Molecules on and Within Its Surfaces and Lakes

We discuss the formation of aerosols within Titan's thermosphere-ionosphere and the different chemical pathways. Negative ion measurements by the Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) give evidence for formation of unsaturated anion carbon chains, while positive ion measurements of the Cassini Ion Neutral Mass Spectrometer (INMS) indicate formation of more aromatic cation hydrocarbons. There is presently no direct observational evidence for large neutral molecule growth in Titan's thermosphere-ionosphere. The hydrocarbon cations are expected to form Polycyclic Aromatic Hydrocarbons (PAHs), those with the addition of nitrogen being called PAHNs. We theorize anion carbon chains can eventually become long enough to fold into fullerene C60,70 carbon shells, of various charge states. Based on laboratory data the fullerenes can trap incoming O+ magnetospheric ions that have relatively high energy collisions with the fullerenes and, once trapped, protect the oxygen atom from Titan's reducing thermosphere-ionosphere. The fullerenes can form into larger onion fullerenes and condense into larger embryo aerosols (i.e., m/q (mass-to-charge ratio) greater than 10,000 amu/q (atomic mass unit-to-charge ratio) anions as observed by CAPS/ELS) eventually falling onto Titan's surface and precipitating to the bottom of its hydrocarbon lakes. Molecule production composed of H, C, N is known to occur in Titan's atmosphere with energy input from the magnetosphere, solar UV (ultraviolet), and deep-penetrating irradiation from galactic cosmic rays (GCR). Space radiation effects by GCR irradiation of Titan's surface and lakes can lead to the manufacture of exobiological molecules with oxygen as the new ingredient. We have developed a model of galactic cosmic ray irradiation of Titan's atmosphere, surface, subsurface and bottoms of Titan lakes. GCR would provide further energy for processing of the aerosols into more complex organic forms such as tholins and precursor molecules for amino acids. A second process called hydrolysis then converts the precursor molecules into amino acids. Hydrolysis is provided via meteor impacts with size greater than 10 kilometers and cryovolcanism both which can produce liquid water on Titan's surface for episodic periods more than several 100 to 1000 years. Our model shows that GCR secondary particles can penetrate ~100 meters below the ice surface (including the bottom of Titan's less dense hydrocarbon lakes ~150-meter depths) and produce chemically significant dosages over very long timescales ~450 million years. The GCR model is combined with laboratory data from experiments in which dry methyl ices were irradiated to doses producing prebiotic amino acids such as glycine. The model calculations show glycine can form to ~2.5 parts-per-billion levels near the surface after ~450 million years of GCR proton irradiation and potentially to 5 parts-per-billion if heavy-ion GCRs up through Fe are included. If such molecules were detected, this would not only confirm this model but indicate that life forms different from ours may not be required.

Edward C. Sittler Jr↗
DOE OSTI2021

Negative Ion Formation in Complex Heavy Systems

The project’s primary objective is to gain a fundamental theoretical understanding of the near-threshold electron attachment mechanism in low energy electron elastic scattering from complex heavy systems through the calculation of integral and differential cross sections and extract reliable electron affinities (EAs). The complex angular momentum (CAM), also known as Regge-pole methodology wherein is fully embedded the crucial electron-electron correlations and the core polarization interaction, is used for the investigations. Regge trajectories allow us to probe electron attachment at the fundamental level near threshold, thereby uncovering new manifestations, including the mechanism of nanocatalysis, and determine reliable EAs. Low-energy electron elastic scattering total cross sections (TCSs) for the lanthanide and actinide atoms and the fullerene molecules are calculated. From the TCSs ground, metastable and excited states anionic binding energies (BEs) are extracted and compared with the available measured and/or calculated EAs. Significantly, our calculated ground state anionic BEs correspond to the theoretically challenging to calculate EAs and they are used to assess the reliability of existing EAs. Doubly charged negative ions of atoms and molecules are proposed as novel tunable catalysts and demonstrated in the oxidation of water into peroxide. Negatively charged fullerene molecules are used to catalyze water oxidation to peroxide and water synthesis from H 2 and O 2 as well. Violation of time-reversal and particle-hole symmetries in strongly correlated Fermi systems are reviewed with the collaboration involving the International Laboratory of Fermi Condensation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Supramolecular Assembly of U(IV) Clusters and Superatoms with Unconventional Countercations

Superatoms are nanometer-sized molecules or particles that form ordered lattices, mimicking their atomic counterparts. Hierarchical assembly of superatoms gives rise to emergent properties in lattices of quantum dots, p-block clusters, and fullerenes. In this report, we introduce a family of uranium-oxysulfate cluster anions whose hierarchical assembly in water is controlled by two parameters: acidity and the lanthanide or transition-metal countercation. In acid, larger Ln III (Ln = La–Ho) link hexamer (U 6 ) oxoclusters into body-centered cubic frameworks, while smaller Ln III (Ln = Er–Lu and Y) promote linking of 14 U 6 clusters into hollow superclusters (U 84 superatoms). U 84 assembles into superlattices including cubic-closest packed, body-centered cubic, and interpenetrating networks, bridged by interstitial countercations and U 6 clusters. Divalent transition metals (TM = Mn II and Zn II ) charge-balance and promote the fusion of 10 U 6 and 10 U monomers into a wheel-shaped cluster (U 70 ). Dissolution of U 70 in organic media shows (by small-angle X-ray scattering) that differing supramolecular assemblies are accessed, controlled by TM II -linking of U 70 clusters. Magnetic measurements of these assemblies reveal Curie–Weiss behavior at high temperatures, without pairing of the 5f 2 -electrons down to 2 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Doubly-Charged Negative Ions as Novel Tunable Catalysts: Graphene and Fullerene Molecules Versus Atomic Metals

The fundamental mechanism underlying negative-ion catalysis involves bond-strength breaking in the transition state (TS). Doubly-charged atomic/molecular anions are proposed as novel dynamic tunable catalysts, as demonstrated in water oxidation into peroxide. Density Functional Theory TS calculations have found a tunable energy activation barrier reduction ranging from 0.030 eV to 2.070 eV, with Si 2– , Pu 2– , Pa 2– and Sn 2– being the best catalysts; the radioactive elements usher in new application opportunities. C 60 2– significantly reduces the standard C 60 – TS energy barrier, while graphene increases it, behaving like cationic systems. According to their reaction barrier reduction efficiency, variation across charge states and systems, rank-ordered catalysts reveal their tunable and wide applications, ranging from water purification to biocompatible antiviral and antibacterial sanitation systems.

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

Direct and Inverse Photoelectron Spectroscopy Evidence for a Revised Picture of Electronic States of Negative Polarons in n‐Doped C 60

Abstract Determining the electronic levels associated with polarons, the fundamental charge carriers in organic semiconductors, is key to understanding the charge transport properties of these materials. Recent findings challenge the traditional view of these electronic levels by highlighting the importance of intra‐molecular Coulomb interactions in polarons. Experimental evidence was previously presented for a revised model of the negative polaron in the case of the polymer semiconductor poly(NDI2OD‐T 2 ); there, the addition of an excess electron was seen to lead to the emergence of a singly occupied state within the energy gap of the undoped material and an unoccupied state above the edge of the conduction states . Here, focus is on a small‐molecule semiconductor, C 60 , and spectral evidence is provided of a similar picture for the new states appearing upon polaron formation. Specifically, direct and inverse photoemission spectroscopy is used to investigate the density of states in C 60 films n‐doped with two dimeric dopants. The Coulomb interaction energy (Hubbard U ) of the C 60 anion is experimentally determined to be ≈1.1 eV, a value that aligns closely with theoretical predictions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Stepwise deprotonation of truxene: structures, metal complexation, and charge-dependent optical properties

As a planar subunit of C 60 -fullerene, truxene (C 27 H 18 ) represents a highly symmetrical rigid hydrocarbon with strong blue emission. Herein, we used truxene as a model to investigate the chemical reactivity of a fullerene fragment with alkali metals. Monoanion, dianion, and trianion products with different alkali metal counterions were crystallized and fully characterized, revealing the core curvature dependence on charge and alkali metal coordination. Moreover, a proton nuclear magnetic resonance study coupled with computational analysis demonstrated that deprotonation of the aliphatic CH 2 segments introduces aromaticity in the five-membered rings. Importantly, the UV-vis absorption and photoluminescence of truxenyl anions with different charges reveal intriguing charge-dependent optical properties, implying variation of the electronic structure based on the deprotonation process. An increase in aromaticity and π-conjugation yielded a red shift in the absorption and photoluminescent spectra; in particular, large Stokes shifts were observed in the truxenyl monoanion and dianion with high emission quantum yield and time of decay. Overall, stepwise deprotonation of truxene provides the first crystallographically characterized examples of truxenyl anions with three different charges and charge-dependent optical properties, pointing to their potential applications in carbon-based functional materials.

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

Low-Energy Electron Elastic Collisions with Actinide Atoms Am, Cm, Bk, Es, No and Lr: Negative-Ion Formation

The rigorous Regge-pole method is used to investigate negative-ion formation in actinide atoms through electron elastic total cross sections (TCSs) calculation. The TCSs are found to be characterized generally by negative-ion formations, shape resonances and Ramsauer-Townsend(R-T) minima, and they exhibit both atomic and fullerene molecular behavior near the threshold. Additionally, a polarization-induced metastable cross section with a deep R-T minimum is identified near the threshold in the Am, Cm and Bk TCSs, which flips over to a shape resonance appearing very close to the threshold in the TCSs for Es, No and Lr. We attribute these new manifestations to size effects and orbital collapse significantly impacting the polarization interaction. From the TCSs unambiguous and reliable ground, metastable and excited states negative-ion binding energies (BEs) for Am−, Cm−, Bk−, Es−, No− and Lr− anions formed during the collisions are extracted and compared with existing electron affinities (EAs) of the atoms. The novelty of the Regge-pole approach is in the extraction of the negative-ion BEs from the TCSs. We conclude that the existing theoretical EAs of the actinide atoms and the recently measured EA of Th correspond to excited anionic BEs.

Msezane, Alfred Z. (ORCID:0000000212485661)↗
DOE OSTI2024

Reaction mechanisms for electrical doping of organic semiconductors using complex dopants

Electrical doping of organic semiconductors (OSCs) can be achieved using simple one-electron reductants and oxidants as n- and p-dopants, respectively, but for such dopants, increased doping strength is accompanied by increased sensitivity to ambient moisture and/or oxygen. “Indirect” or “complex” dopants—defined here as those that generate OSC radical cations or anions via pathways more complex than a single simple electron transfer, i.e., by multistep reactions—represent a means of circumventing this problem. Further, this review highlights the importance of understanding the reaction mechanisms by which such dopants operate for: (i) ensuring a researcher knows the composition of a doped material; (ii) predicting the thermodynamic feasibility of achieving doping with related dopant:OSC combinations; and (iii) predicting whether thermodynamically feasible doping reactions are likely to be rapid or slow, or to require subsequent activation. The mechanistic information available to date for some of the wide variety of complex n- and p-dopants that have been reported is then reviewed, emphasizing that in many cases our knowledge is far from complete.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

A density functional theory based comparative study of hybrid photoemissions from Cl@C 60 , Br@C 60 and I@C 60

Photoionization from atom-C 60 hybrid levels in halogen endofullerene molecules, Cl@C 60 , Br@C 60 and I@C 60 , are calculated using a linear response density functional method. Both the ordinary electron-configuration where the open shell halogen is at the center of C 60 and the stable configuration after the atom receives an electron from C 60 to form a closed shell anion are considered. Similar ground state hybridization is found for all three systems while, in general, a slight weakening of the effect is noticed after the electron transfer. At lower photon energies, cross sections of the outer hybrid levels attain identical shapes from enhancements driven by the C 60 plasmon resonances, while the higher energy emissions remain distinguishable from the differences in atomic responses. These results further show near insensitivity to the choice of a configuration. The inner hybrid cross sections in general exhibit similar overall structures, although differ in details between molecules. Furthermore, for these states the results significantly differ before and after the electron transfer – a feature that can be useful to experimentally determine the real configuration of the molecules via photoelectron spectroscopy.

74 ATOMIC AND MOLECULAR PHYSICS↗