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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Optical vibrational spectra and proposed crystal structure of ε-UO 3

ε-UO 3 is an exotic polymorph in the uranium trioxide system with an undetermined crystal structure and limited optical vibrational spectroscopic data. To improve understanding of this compound, we synthesize and investigate the crystal structure and optical vibrational spectra of ε-UO 3 . Infrared spectra collected for ε-UO 3 are in good agreement with previously published results, and our studies extend the available data into the low-energy (600–100 cm –1 ) regime. For the first time, Raman spectra are presented for ε-UO 3 using both 785 and 532 nm excitation wavelengths. Previous reports suggest an impurity phase may be present in ε-UO 3 produced by calcination of U 3 O 8 ; however, spectral center-of-mass calculations, principal component analyses, and Raman spectroscopic mapping employed to investigate this possibility indicate that the product of U 3 O 8 calcined in O 3 (g) in this work is likely phase-pure. A possible novel structure solution for ε-UO 3 is determined via Rietveld refinement of powder X-ray diffraction data and is triclinic, P-1, with a = 4.01 Å, b = 3.85 Å, c = 4.18 Å, and α = 98.26°, β = 90.41°, γ = 120.46° (R wp = 8.30%). The asymmetric unit of ε-UO 3 consists of U(VI) in hexagonal bipyramidal coordination with displaced equatorial oxygen. Further analysis reveals that the structure of ε-UO3 is best described by a 2 × 1 × 2 supercell structure in P-1 with a = 8.03 Å, b = 3.86 Å, c = 8.37 Å with α = 98.26°, β = 90.41°, and γ = 120.46°, although a higher-symmetry structure is possible. Optical vibrational spectroscopic and structural measurements of ε-UO 3 presented here furthers our understanding of this complex uranium oxide and clarifies the origin of reported structural similarity to U 3 O 8 .

-UO3↗
NASA NTRS1997

Electronic and Vibrational Spectra of InP Quantum Dots Formed by Sequential Ion Implantation

We have performed sequential ion implantation of indium and phosphorus into silica combined with controlled thermal annealing to fabricate InP quantum dots in a dielectric host. Electronic and vibrational spectra were measured for the as-implanted and annealed samples. The annealed samples show a peak in the infrared spectra near 320/cm which is attributed to a surface phonon mode and is in good agreement with the value calculated from Frolich's theory of surface phonon polaritons. The electronic spectra show the development of a band near 390 nm that is attributed to quantum confined InP.

Hall, C.↗
DOE OSTI2026

A foundation model for non-destructive defect identification from vibrational spectra

Defects are ubiquitous in solids and strongly influence materials’ functional properties. However, non-destructive characterization and quantification of defects, especially when multiple types coexist, remain a long-standing challenge. Here, we introduce DefectNet, a foundation machine learning model that predicts the chemical identity and concentration of substitutional point defects with multiple coexisting elements directly from vibrational spectra, specifically phonon density-of-states (PDoS). Trained on over 16,000 simulated spectra from 2,000 semiconductors, DefectNet employs a tailored attention mechanism to identify up to six distinct defect elements at concentrations ranging from 0.2% to 25%. The model generalizes well to unseen crystals across 56 elements and can be fine-tuned on experimental data. Validation using inelastic scattering measurements of SiGe alloys and MgB 2 superconductor demonstrates its accuracy and transferability. Furthermore, our work establishes vibrational spectroscopy as a viable, non-destructive probe for bulk point defect quantification, and highlights the promise of foundation models in data-driven defect engineering.

artificial intelligence↗
DOE OSTI2021

Influence of heterocyclic N-donors on the structural topologies and vibrational spectra of uranyl selenate phases

Uranyl (U(VI)O 2 2+ ) selenate compounds represent a well-studied family of structures with diverse structural arrays. Differences in the overall topology and bonding with the uranyl cation combined with additional intermolecular interactions can lead to variation in the resulting spectroscopic signals. Here, in the current study, we evaluated the structural chemistry and vibrational spectroscopy for uranyl selenates crystallized with heterocyclic N-donors. Five compounds ((C 4 H 12 N 2 )[(UO 2 )(SeO 4 ) 2 (H 2 O)]·H 2 O (USe_pip), (C 4 H 5 N 2 ) 2 [(UO 2 )(SeO 4 ) 2 (H 2 O)] (USe_pyrdz), (C 5 H 5 N) 2 [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] ∙ 3H 2 O (USe_pyrmd), (H 3 O) 2 (C 4 H 5 N 2 ) 2 [(UO 2 ) 3 (SeO 4 ) 5 (H 2 O)]·H 2 O (USe_pyrz), and (C 5 H 6 N) 2 [(UO 2 ) 2 (SeO 4 ) 3 (H 2 O)] ∙ 3H 2 O (USe_pyr)) were characterized using X-ray diffraction (single-crystal and powder) and vibrational (Raman and IR) spectroscopy. Two one-dimensional (1-D) chain and three two-dimensional sheet (2-D) topologies were identified and classified based upon previous graphical representations. Overall, the arrangement of the heteroatoms could be linked to the hydrogen bonding network associated with the heterocycles and selenate anions. Vibrational spectra of the solid-state compounds were complex, with multiple bands associated with the uranyl cation, selenate anion, and heteroatoms. The ν 1 symmetric stretching band of the uranyl was relatively consistent across all compounds, whereas differences were observed for the ν 3 asymmetric band between the 1-D and 2-D structural topologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1974

Rotationsal and vibrational spectra of molecular ions: Feasibility of laboratory and astrophysical observation

The rotational spectra of a number of small molecular ions should be detectable in the microwave or millimeter wave regions in laboratory experiments using currently available techniques. The dipole moments and absorption coefficients of polar diatomics CO(+) and NO(+) as well as asymmetric isotopically enriched species, like O-18O-16(+), NE-20NE-22(+), and OC-18 O-16(+) are calculated to be sufficiently large to allow observation of their spectra. In addition to the detailed molecular structure information which such spectral data would provide, precise knowledge of the transition frequencies would render likely the detection of certain of these ions in the interstellar sources or in planetary atmospheres. All of these ions also possess vibrational spectra which should be detectable in the infrared region in laboratory or astrophysical sources.

Woods, R. C.↗
DOE OSTI2022

Periodic Trends within Actinyl(VI) Nitrates and Their Structures, Vibrational Spectra, and Electronic Properties

In this work, a series of actinyl(VI) nitrate salts of the form MAnO 2 (NO 3 ) 3 , where M = NH 4 + K + , Rb + , Cs + , and Me 4 N + and AnO 2 2+ = U, Np, Pu, and AnO 2 (NO 3 ) 2 (H 2 O) 2 ·H 2 O, and the uranyl tetranitrates M 2 UO 2 (NO 3 ) 4 have been synthesized from aqueous solution and their structures determined using single-crystal X-ray diffraction. Together, these complexes represent an isostructural series of actinide complexes among the salts crystallized with the same charge-compensating cation and have been studied using vibrational spectroscopy including Raman and Fourier-transform infrared. Periodic trends in both the structural properties of these complexes and their vibrational spectra are presented and discussed, in particular the invariant nature of the O≡An≡O asymmetric stretching frequencies observed across the actinyl series. Electronic structure calculations were performed at a variety of levels of theory to aid in the interpretation of the vibrational data and to correlate trends in the data with the underlying electronic properties of these molecules.

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

Unexpected features in the optical vibrational spectra of δ-UO 3

Uranium trioxide displays a complex chemical phase space, with at least six structurally distinct polymorphs accessible via different synthetic routes. Remarkably, despite its technological importance, full structural and electronic characterization of these polymorphs remains an open area of study. δ-UO 3 in particular has attracted significant theoretical attention due to its high point group and space group symmetries, having U (VI) in octahedral coordination with polyhedra interconnected through corner-sharing to build a 3-D cubic lattice with space group symmetry Pm-3m and Z = 1. Critical experimental information, such as its optical vibrational spectra, are not known. Here, we study the Raman and infrared (IR) spectra of δ-UO 3 together with the support of density functional theory (DFT) calculations for spectral interpretation. A symmetry analysis of the DFT-predicted phonon eigenmodes indicates that δ-UO 3 should have two IR active modes and no Raman active modes. Experimental results, however, indicate significant Raman scattering from δ-UO 3 . We therefore propose four potential explanations for this apparent contradiction: a possible tetragonal distortion to the cubic cell, the existence of a surface impurity layer, vacancy scattering, and structural activation of Raman signal. We use powder X-ray diffraction and confocal Raman spectroscopy with depth profiling to investigate these possibilities and suggest future experiments to explore this phenomenon in more detail. Understanding the lattice dynamics of δ-UO 3 is important for identification of technogenic U phases via Raman and infrared spectroscopy and our results indicate that the simple understanding of δ-UO 3 as a high-symmetry cubic structure should be reconsidered.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2025

A systematic exploration of the hydrolysis products of the uranium trioxide polymorphs and their optical vibrational spectra

Study of the uranium trioxide (UO 3 )-water system is complex with inconclusive results and limited details in the literature. The UO 3 system is home to at least seven structural polymorphs and an amorphous phase. The proposed hydrolysis products of UO 3 are just as numerous, yet investigations of these alteration products are sporadic and generally antiquated, thus requiring systematic investigations. Recent developments in the understanding of UO 3 phase space, aided by improvements in analytical and computational techniques, necessitate more modern investigations into the uranyl hydroxide family and their naturally occurring mineral counterparts. We present findings from a systematic investigation of the products formed via hydrothermal reactions of common UO 3 polymorphs and discuss how the equatorial coordination of the uranyl/uranyl-like ions within the UO 3 precursors leads to differences in the optical vibrational spectra of the resulting hydrolysis products. The hypo-stochiometric nature of α-UO 2 (OH) 2 allows for the formation of multiple unique uranyl sites and a distortion of the unit cell to a lower symmetry. This study provides, for the first time, an analysis of β-UO 2 (OH) 2 using modern techniques and instrumentation (Raman/infrared spectroscopy and powder x-ray diffraction) and lays a foundation for future time-dependent investigations into the structural dependence of the hydrolysis kinetics of the UO 3 phases. In conclusion, given the prevalence of UO 3 at both ends of the nuclear fuel cycle, an understanding of its behavior with water has applications ranging from nuclear forensics to waste management and environmental transport.

Uranium trioxide↗
DOE OSTI2021

Vibronic coupling in energy transfer dynamics and two-dimensional electronic–vibrational spectra

We introduce a heterodimer model in which multiple mechanisms of vibronic coupling and their impact on energy transfer can be explicitly studied. We consider vibronic coupling that arises through either Franck-Condon activity in which each site in the heterodimer has a local electron-phonon coupling or Herzberg-Teller activity in which the transition dipole moment coupling the sites has an explicit vibrational mode-dependence. We have computed two-dimensional electronic-vibrational (2DEV) spectra for this model while varying the magnitude of these two effects and find that 2DEV spectra contain static and dynamic signatures of both types of vibronic coupling. Franck-Condon activity emerges through a change in the observed excitonic structure, while Herzberg-Teller activity is evident in the appearance of significant side-band transitions that mimic the lower-energy excitonic structure. A comparison of quantum beating patterns obtained from analysis of the simulated 2DEV spectra shows that this technique can report on the mechanism of energy transfer, elucidating a means of experimentally determining the role of specific vibronic coupling mechanisms in such processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRSDate not supplied

Using Anharmonic PAH Vibrational Spectra to Simulate Fully Anharmonic Cascade Emission Spectra

In recent years, we have developed vibrational second-order perturbation theory (VPT2) approaches that can be applied to very large molecules, such as polycyclic aromatic hydrocarbon (PAH) molecules. One of the main difficulties in applying standard VPT2 methods to PAHs is the large number of Fermi resonances that occur, especially in the C-H stretching region of the infrared spectrum. In order to properly account for these resonances, it is necessary to set up resonance polyads for each irreducible representation of the symmetry point group to which the molecule belongs, and for specific wavenumber regions, such as the C-H stretching region. Diagonalization of the polyads allows us to determine vibrational band positions, the intensity sharing due to the resonances, and hence there will be many more vibrational bands present than there are C-H bonds. Using these data, a library of fully anharmonic temperature-dependent spectra, with proper treatment of polyad resonances, can be determined and subsequently used to model the cascade emission spectra of PAH molecules – the type of spectra directly observed by astronomers. The theoretical approach will be described, with comparison to experiment where possible, and the latest fully anharmonic PAH cascade emission spectra will be discussed.

Timothy J Lee↗
NASA NTRS1993

Electronic and vibrational spectra of matrix isolated anthracene radical cations - Experimental and theoretical aspects

The IR vibrational and visible/UV electronic absorption spectra of the anthracene cation, An(+), were studied experimentally, in argon matrices at 12 K, as well as theoretically, using ab initio calculations for the vibrational modes and enhanced semiempirical methods with configuration interaction for the electronic spectra. It was found that both approaches predicted well the observed photoelectron spectrum. The theoretical IR intensities showed some remarkable differences between neutral and ionized species (for example, the CH in-plane bending modes and CC in-plane stretching vibrations were predicted to increase by several orders of magnitude upon ionization). Likewise, estimated experimental IR intensities showed a significant increase in the cation band intensities over the neutrals. The implication of these findings for the hypothesis that polycyclic aromatic hydrocarbon cations are responsible for the unidentified IR emission bands from interstellar space is discussed.

Szczepanski, Jan↗
DOE OSTI2022

Optical vibrational spectra of β -U 3 O 8

Technogenic uranium oxides are ubiquitous in the nuclear fuel cycle. Identifying the chemical composition of these oxides is frequently done with optical vibrational spectroscopy (infrared and Raman spectroscopy). The α phase of U 3 O 8 is the most stable and common uranium oxide, but a β phase of U 3 O 8 can be produced via very slow cooling of the α phase from elevated temperatures or the application of small shear forces. However, optical spectra of this compound have not been reported. In this work, we use high-resolution attenuated total reflection infrared spectroscopy and Raman spectroscopy to collect the optical vibrational spectra. Despite similarities in the crystal structure of α and β – U 3 O 8 , the optical spectra of these compounds differ substantially, with additional Raman active modes in β – U 3 O 8 that are likely originating from differences in the U–O coordination units. Measurements presented here provide spectral characterization that can be used for chemical identification in future studies of uranium oxides.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Vibrational spectra and structure of azomethane and azomethane-d6.

The infrared and Raman spectra of azomethane and azomethane-d(6) were examined in detail. Vibrational data provided definitive verification of a trans-structure with C(2h) symmetry. A vibrational assignment is proposed for the 24 fundamental modes based upon the observed contours, isotopic shift ratios, and group frequency correlations. Spectra of the polycrystalline samples indicate that there are at least four molecules per unit cell, since a number of the bands were observed to be split into doublets. The crystal also appeared to have a center of symmetry, since mutual exclusion was clearly operative.

Durig, J. R.↗
NASA NTRS2019

Computing Rotational, Rovibrational, and Vibrational Spectra for Astronomical Observations: High Accuracy Line Lists for High Temperatures, Limited Line Lists for Biosignature Molecules, and PAH Emission Spectra

Over the last several years, our group has been involved in developing approaches to compute highly accurate spectroscopic constants and vibrational frequencies for small transient molecules that may be used in the interpretation and assignment of high-resolution laboratory experiments as well as high-resolution astronomical spectra. Additionally, we have used the computed spectroscopic constants to simulate purely rotational and rovibrational spectra so that these may be compared directly with high- resolution astronomical observations, and we have worked on developing approaches that can be applied to much larger molecules, such as PAHs, where we can explicitly determine an harmonic corrections to vibrational modes as well as take into account intensity sharing due to resonances. Another part of our work in spectroscopic signatures involves computing highly accurate line lists for common molecules, such as CO2, SO2, and NH3, which occur in many astrophysical environments, including the atmospheres of exoplanets, and often need to have their lines identified in high- resolution observations in order to determine which lines are due to other molecules. In order to characterize the atmospheres of hot exoplanets, these line lists need to be very accurate and extend to very high energies. I will discuss our latest work in these areas of astrochemical spectroscopy research.

Lee, Timothy J.↗
DOE OSTI2026

Isolating the Vibrational Spectra of the Red Chlorophylls in Photosystem I with Multispectral Two-Dimensional Spectroscopy

Photosystem I (PSI) uses an antenna of chlorophyll (Chl) molecules to create a charge separated state with high quantum efficiency. Understanding the charge separation mechanism is currently hindered by spectral overlap between the antenna and reaction center (RC) Chls and the fact that energy transfer and electron transfer occur with similar time scales. Here, we characterize the antenna excited states by applying two-dimensional electronic (2DES) and two-dimensional electronic-vibrational (2DEV) spectroscopy to PSI complexes with closed RCs. Comparison of the 2DES and 2DEV spectra, which evolve with the same kinetics, enabled characterization of the vibrational modes of the antenna during energy equilibration between spectrally distinct Chls. Through global analysis, we learn how energy transfer between the Bulk and Red Chls presents in the 2DEV spectra and we definitively identify vibrations of the cationic components of the mixed exciton and intermolecular charge transfer states associated with the Red Chls. This work enables future studies of the initial charge separation mechanism of PSI by 2DEV spectroscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1971

Vibrational spectra and structure of dimethylaminodichlorophosphine.

Evaluation of the infrared spectra of dimethylaminodichlorophosphine and dimethylaminodichlorophosphine-d sub 6 recorded from 4000 to 33 per cm in the gas and solid phases. The Raman spectra of the liquid and solid phases for both compounds were also recorded. The spectra were consistent with the presence of only one isomer over the range of phases and temperatures studied. Available experimental data were discussed in connection with the spectra, and it is concluded that the molecule exists in the gauche conformer with the PNC2 portion of the molecule planar. A vibrational assignment is proposed for the molecule.

Durig, J. R.↗