Search NASA⌕ Search

SEARCH · Search NASA

Results for “Vibrational spectra”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Vibrational spectroscopy of shock compressed condensed phase nitrous oxide: Frequency shifts in the ν 1 mode

Over many years, we have published vibrational spectra of molecular materials at extreme pressure and temperature obtained using shock compression and coherent Raman spectroscopy methods. For diatomic molecules, we were able to extract vibrational temperatures from the intensities of spectrally resolved vibrational hot bands. Larger molecules in the condensed phase suffer band broadening effects that obscure the vibrational hot bands as the anharmonicities are typically smaller than the widths of the bands. This inability to resolve the hot bands inhibits the extraction of vibrational temperature and the measurement of the vibrational frequency of the fundamental. Here, we use a hot band model based on gas-phase anharmonic coupling coefficients to fit coherent anti-Stokes Raman spectra of the ν 1 vibrational mode of shock compressed condensed phase N 2 O with shock pressures and temperatures estimated from literature equations of state and compare to fits from a model using a single Gaussian peak. We report the resulting vibrational frequency shifts with shock pressure.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Isomer-specific, Cryogenic Ion Vibrational Spectroscopy Investigation of D2-and N2- Tagged, Protonated Formic Acid Complexes Using Two Color, IR-IR Photobleaching

Here we analyze cryogenic ion vibrational spectra of tagged protonated formic acid (PFA) with electronic structure and anharmonic vibrational calculations to establish the isomers generated by electrospray ionization (ESI) followed by buffer gas cooling to ~25 K. Two isomers are identified (the trans form (E,Z) and the cis form (E,E)) and generated in comparable abundance despite the fact that the calculated E,E structure lies 6.40 kJ mol-1 above the E,Z form. A large (~60 kJ mol-1) barrier separates them such that the E,E form can be kinetically trapped upon cooling in the ion trap. The anticooperativity between the H-bonds of the OH groups is explored by measuring the shift in the D2-bound OH fundamental when a second D2 is attached. Both isomers are observed in the N2-tagged counterparts, displaying the expected red-shifted OH bands. These results indicate that ESI generates both isomers and both must be considered when analyzing cluster spectra based on the PFA core ion.

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

Microsolvation in V + (H 2 O) n Clusters Studied with Selected-Ion Infrared Spectroscopy

Gas phase ion-molecule clusters of the form V + (H 2 O) n (n = 1-30) are produced by laser vaporization in a supersonic expansion. These ions are analyzed and mass-selected with a time-of-flight mass spectrometer and investigated with infrared laser photodissociation spectroscopy. The small clusters (n ≤ 7) are studied with argon tagging, while the larger clusters are studied via the elimination of water molecules. The vibrational spectra for the small clusters include only free O-H stretching vibrations, while larger clusters exhibit red-shifted hydrogen bonding vibrations. The spectral patterns reveal that the coordination around V + ions is completed with four water molecules. A symmetric square-planar structure forms for the n = 4 ion, and this becomes the core ion in larger structures. Clusters up to n = 8 have mostly two-dimensional structures, but hydrogen bonding networks evolve to three-dimensional structures in larger clusters. The free O-H vibration of AAD (acceptor-acceptor-donor) coordinated surface molecules converges to a frequency near that of bulk water by the cluster size of n = 30. However, the splitting of this vibration for AAD- versus AD-coordinated molecules is still different compared to other singly-charged or doubly-charged cation-water clusters. Finally, this indicates that cation identity and charge-site location in the cluster can produce discernible spectral differences for clusters in this size range.

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

In-operando surface-sensitive probing of electrochemical reactions on nanoparticle electrocatalysts: Spectroscopic characterization of reaction intermediates and elementary steps of oxygen reduction reaction on Pt

In this paper we present an in-operando spectroscopic study of the reaction intermediates involved in ORR on electrified Pt nanoparticle electrocatalysts. To accomplish this, we have synthesized Ag-Pt core–shell nanoparticles, that contain a thin shell of Pt (~1 nm) uniformly deposited on a larger Ag core (~60 nm). We show that these nanostructures are ideal platforms for in-operando Plasmon Enhanced Raman Spectroscopy (PERS) of ORR on Pt. We combined these PERS studies with DFT calculations to assign the measured vibrational spectra to relevant surface intermediates as a function of electrocatalyst potential. Overall, these vibrational assignments were further verified and validated by performing PERS measurements using de-oxygenated and heavy oxygen (O 2 -18) saturated electrolyte. These studies allowed us to identity the presence of critical reaction intermediates (OH, O 2 , OOH, and H 2 O) as the function of operating voltage on the Pt surface and derive voltage-dependent elementary step mechanisms of the reaction.

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

Machine learning-based discovery of vibrationally stable materials

The identification of the ground state phases of a chemical space in the convex hull analysis is a key determinant of the synthesizability of materials. Online material databases have been instrumental in exploring one aspect of the synthesizability of many materials, namely thermodynamic stability. However, the vibrational stability, which is another aspect of synthesizability, of new materials is not known. Applying first principles approaches to calculate the vibrational spectra of materials in online material databases is computationally intractable. Here, a dataset of vibrational stability for ~3100 materials is used to train a machine learning classifier that can accurately distinguish between vibrationally stable and unstable materials. This classifier has the potential to be further developed as an essential filtering tool for online material databases that can inform the material science community of the vibrational stability or instability of the materials queried in convex hulls.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Harmonic Infrared and Raman Spectra in Molecular Environments Using the Polarizable Embedding Model

We present a fully analytic approach to calculate infrared (IR) and Raman spectra of molecules embedded in complex molecular environments modeled using the fragment-based polarizable embedding (PE) model. We provide the theory for the calculation of analytic second-order geometric derivatives of molecular energies and first-order geometric derivatives of electric dipole moments and dipole–dipole polarizabilities within the PE model. The derivatives are implemented using a general open-ended response theory framework, thus allowing for an extension to higher-order derivatives. The embedding-potential parameters used to describe the environment in the PE model are derived through first-principles calculations, thus allowing a wide variety of systems to be modeled, including solvents, proteins, and other large and complex molecular environments. Here, we present proof-of-principle calculations of IR and Raman spectra of acetone in different solvents. This work is an important step toward calculating accurate vibrational spectra of molecules embedded in realistic environments.

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

Phonon-mediated lipid raft formation in biological membranes

Short-wavelength collective molecular motions, also known as phonons, have recently attracted much interest in revealing dynamic properties of biological membranes through the use of neutron and x-ray scattering, infrared and Raman spectroscopies, and molecular dynamics simulations. Experimentally detecting unique vibrational patterns such as, shear phonon excitations, viscoelastic crossovers, transverse acoustic phonon gaps, and continuous and truncated optical phonon modes in cellular membranes, to name a few, has proven non-trivial. Here, we review recent advances in liquid thermodynamics that have resulted in the development of the phonon theory of 1 liquids. The theory has important predictions regarding the shear vibrational spectra of fluids, namely the emergence of viscoelastic crossovers and transverse acoustic phonon gaps. Furthermore, we show that these vibrational patterns are common in soft (non-crystalline) materials, including, but not limited to liquids, colloids, liquid crystals (mesogens), block copolymers, and biological membranes. The existence of viscoelastic crossovers and acoustic phonon gaps define the self-diffusion properties of cellular membranes and provide a molecular picture of the transient nature of lipid rafts.1 Importantly, the timescales (picoseconds) for the formation and dissolution of transient lipid rafts match the lifetime of the formation and breakdown of interfacial water hydrogen bonds. Apart from acoustic propagating phonon modes, biological membranes can also support more energetic non-propagating optical phonon excitations, also known as standing waves or breathing modes. Importantly, optical phonons can be truncated due to the existence of finite size nanodomains made up of strongly correlated lipid-cholesterol molecular pairs. These strongly coupled molecular pairs can serve as nucleation centers for the formation of stable rafts at larger length scales, due to correlations of spontaneous fluctuations (Onsager’s regression hypothesis). Finally and importantly, molecular level viscoelastic crossovers, acoustic phonon gaps, and continuous and truncated optical phonon modes may offer insights as to how lipid-lipid and lipid-protein interactions enable biological function.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Prospects for detecting UF6 hydrolysis intermediates by mass spectrometry, resonance Raman, and NQR spectroscopy

Simulations are performed to consider several spectrometric and spectroscopic candidates for elucidating the mechanism of the hydrolysis of uranium hexafluoride (UF6). This study is among the first to benchmark the def-mTZVP basis sets for actinide-containing molecules, and it is shown to be a suitable basis set for surveying geometrical structures and vibrational spectra when used in conjunction with density functional theory. An experiment is proposed coupling mass spectrometric ion selection with vibrational spectroscopy, and supporting infrared and Raman spectral simulations demonstrate that ionization blue-shifts bands and can change their qualitative features. Ultraviolet resonance Raman is shown to have good prospects for discriminating U–O–U bridged intermediates, evidence for which was observed recently [L. E. McNamara et al., J. Phys. Chem. A 130, 775–786 (2026)]. As a more speculative approach, we also consider the prospect of addressing 233U or 235U nuclei by quadrupole resonance (NQR) spectroscopy for assigning early stage intermediate complexes. In doing so, we provide a first order-of-magnitude estimate for the collision-induced NQR signal for the UF6 dimer, which is of interest for the interpretation of a fast decoherence time observed in liquid-phase nuclear magnetic resonance. Having provided critical insights into the formation and stability of UF6 hydrolysis intermediates in previous studies, this computational spectroscopy survey is expected to help guide and expedite future laboratory campaigns.

Lutz, Jesse J. [Center for Computing Research, San↗
DOE OSTI2024

First-principles investigation of elastic, vibrational, and thermodynamic properties of kagome metals CsM 3 Te 5 (M = Ti, Zr, Hf)

Kagome metals are a unique class of quantum materials characterized by their distinct atomic lattice arrangement, featuring interlocking triangles and expansive hexagonal voids. These lattice structures impart exotic properties, including superconductivity, interaction-driven topological many-body phenomena, and magnetism, among others. The kagome metal CsM 3 ⁢Te 5 (where M = Ti, Zr, or Hf) exhibits both superconductivity and nontrivial topological electronic properties, offering a promising platform for exploring topological superconductivity. This study employs first-principles density functional theory calculations to systematically analyze the elastic, mechanical, vibrational, thermodynamic, and electronic properties of CsM 3 ⁢Te 5 (M = Ti, Zr, Hf). Our calculations reveal that the studied compounds—CsTi 3 ⁢Te 5 , CsZr 3 ⁢Te 5 , and CsHf 3 ⁢Te 5 —are ductile metals with elastic properties akin to the hexagonal Bi and Sb, with average elastic constants, including a bulk modulus of 27 GPa, a shear modulus of 11 GPa, and Young's modulus of 29 GPa. We observe peculiar dispersionless, flat, phonon branches in the vibrational spectra of these metals. Additionally, we thoroughly analyze the symmetries of the zone-center phonon eigenvectors and predict vibrational fingerprints of the Raman- and infrared-active phonon modes. The analysis of thermodynamic properties reveals the Einstein temperature for CsTi 3 ⁢Te 5 , CsZr 3 ⁢Te 5 , and CsHf 3 ⁢Te 5 to be 66, 54, and 53 K, respectively. Our orbital-decomposed electronic structure calculations reveal significant in-plane steric interactions and multiple Dirac band crossings near the Fermi level. We further investigate the role of spin-orbit coupling effect on the studied properties. Furthermore, this theoretical investigation sheds light on the intriguing quantum behavior of kagome metals.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The Activation of Hydrogen by First-Row Transition-Metal Complexes. Final Report

We have assigned the vibrational spectra of Os 1 and Os 2 complexes of propene, butene, and acetylene, and have used them for the assignment of the vibrational frequencies of surface alkenes and alkynes. We have measured the rates of H• transfer from (C 5 R 5 )Cr(CO) 3 H to olefins of many structural types, and have learned that even one substituent on the carbon to which the H• is transferred slows down the reaction considerably. We have shown that these Cr hydrides are useful catalysts for chain transfer during radical polymerization reactions. We have determined the strengths of several M–H bonds (in particular Cr–H ones), and have confirmed that the hydrides of first-row transition metals are particularly useful for generating radicals. We have used H• transfer to terminal methylenes to generate radicals that cyclize. We have shown that (C 5 R 5 )Cr(CO) 3 H can be regenerated under H 2 and is therefore catalytic, but that (P–P)V(CO) 4 H cannot be regenerated from H 2 and therefore can only be used stoichiometrically for radical generation. (The V-H bonds are weaker than the Cr–H ones, and the H• transfer to an olefin is therefore faster.) We have found that, under five atm of H 2 pressure, cobaloximes catalyze H• transfer; they efficiently remove an H• from cyclized radicals, and therefore can be used to catalyze the cycloisomerization of some olefins. We have explored the one- and two-electron oxidation of (Ph 3 P) 6 Cu 6 H 6 . One-electron oxidation (which is reversible) generates a cation radical, whereas two-electron oxidation generates loss of a hydride (i.e., two electrons and a proton). We have found that the hydricity of (Ph 3 P) 6 Cu 6 H 6 is between 36 and 50 kcal/mol. We have shown that uncongested organic radicals (i.e., TEMPO) can catalyze H• transfer from (C 5 R 5 )Cr(CO) 3 H to congested radicals like Ar 3 C•. We have examined the one-electron oxidation of [CpV(CO 3 H] – , and have inferred from the results that the reduction of alkyl iodides with [CpV(CO 3 H] – occurs by one-electron transfer. We have been able to use that reagent to catalyze radical cyclizations from H 2 and appropriate alkyl iodides.

08 HYDROGEN↗
DOE OSTI2022

Use of vibrational spectroscopy to identify the formation of neptunyl–neptunyl interactions: a paired density functional theory and Raman spectroscopy study

Actinyl–Actinyl interactions (AAIs) occur in pentavalent actinide systems, particularly for neptunium (Np), and lead to complex vibrational signals that are challenging to analyze and interpret. Previous studies have focused on neptunyl–neptunyl dimeric species, but trimers and tetramers have been identified as the primary motif for extended topologies observed in solid-state materials. Our hypothesis is that trimeric and tetrameric AAIs lead to the additional signals in the vibrational spectra, but this has yet to be explored systematically. Herein, we investigate three different neptunyl–neptunyl subunits (dimeric, trimeric, tetrameric) and determine the vibrational frequencies of the O=Np=O stretches using both computational and experimental approaches. Density Functional Theory (DFT) was used to identify distinct vibrational motions related to specific neptunyl oligomers and compared to previous literature precedent from Np(V) in HClO 4 and HCl systems. The vibrational behavior of Np(V) in HNO 3 was then evaluated via Raman spectroscopy. As the solution evaporated signals were linked to trimeric and tetrameric models. Solid phases produced in the evaporation include (NpO 2 ) 2 (NO 3 ) 2 (H 2 O) 5 and newly identified crystalline phase, Na(NpO 2 )(NO 3 ) 2 ·4H 2 O (NpNa). Furthermore, the combined computational studies and vibrational analysis provide evidence for unique observable vibrational bands for each polymerized subunit, allowing us to assign spectral features to trimeric and tetrameric models within three different simple anionic systems.

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

Computational insights into the structure of anhydrous Pu(III) oxalate

Despite the plutonium oxalate method's wide use in plutonium reprocessing, the method's mechanistic details remain unclear, particularly the identity of the plutonium oxidation state during conversion from an oxalate hydrate to the oxide. Recently, the optical vibrational spectra of Pu(III) oxalate during calcination were measured, providing an experimental reference for computational studies aimed at elucidating the oxalate structure. Here, in this work, we compare the vibrational and electronic properties of two candidate anhydrous Pu(III) oxalate structures calculated using density functional theory with recent experiments. We find that both structures are plausible and may coexist at experimental temperatures, providing insights into the broad features measured in the Raman and infrared spectra.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

High-temperature Raman spectroscopy of K 2 Ca(CO 3 ) 2 bütschliite and Na 2 Ca 2 (CO 3 ) 3 shortite

Raman spectra of Na 2 Ca 2 (CO 3 ) 3 shortite and K 2 Ca(CO 3 ) 2 bütschliite were measured to 715°C and 740°C respectively, under vacuum. The vibrational spectra demonstrate that shortite converts to nyerereite (Na 2 Ca(CO 3 ) 2 ) and calcite at 535°C. This assemblage is stable to ~700°C, where nyerereite begins to decompose. Bütschliite converts to the isochemical phase fairchildite at 570°C, which is stable to 665°C, where it decomposes to an assemblage of K 2 CO 3 and CaO. The variation of anharmonicity between different vibrational modes of each of the low temperature phases is assessed, and these yield insights into inter-carbonate group couplings. In conclusion, both fairchildite and nyerereite exhibit spectral features consistent with extensive disordering.

58 GEOSCIENCES↗
DOE OSTI2022

Localized Phonon Densities of States at Grain Boundaries in Silicon

Since it is now possible to record vibrational spectra at nanometer scales in the electron microscope, it is of interest to explore whether extended defects in crystals such as dislocations or grain boundaries will result in measurable changes of the phonon densities of states (dos) that are reflected in the spectra. Phonon densities of states were calculated for a set of high angle grain boundaries in silicon. The boundaries are modeled by supercells with up to 160 atoms, and the vibrational densities of states were calculated by taking the Fourier transform of the velocity–velocity autocorrelation function from molecular dynamics simulations with larger supercells doubled in all three directions. In selected cases, the results were checked on the original supercells by comparison with the densities of states obtained by diagonalizing the dynamical matrix calculated using density functional theory. Near the core of the grain boundary, the height of the optic phonon peak in the dos at 60 meV was suppressed relative to features due to acoustic phonons that are largely unchanged relative to their bulk values. This can be attributed to the variation in the strength of bonds in grain boundary core regions where there is a range of bond lengths.

Materials Science↗
DOE OSTI2022

Computational insights into the lattice dynamics of Pu(IV) oxalates

Despite its use in PuO 2 production, the structure of anhydrous Pu(C 2 O 4 ) 2 is still not completely understood. Recently, two candidate structures for Pu(C 2 O 4 ) 2 were proposed via density functional theory (DFT), after which the first experimental optical vibrational spectra were reported. Here, in this study, we calculated the lattice dynamics of the candidate structures using DFT and found that the primary difference between them is the presence of a vibrational mode near 1380 cm -1 in one structure. The frequency and optical activity of this mode agree well with the published experimental results, providing strong support for this calculated structure as that of anhydrous Pu(C 2 O 4 ) 2 .

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Thermal conductivity and its relation to atomic structure for symmetrical tilt grain boundaries in silicon

We perform a systematic study of thermal resistance and conductance of tilt grain boundaries (GBs) in Si using classical molecular dynamics. The GBs studied are naturally divided into three groups according to the structural units forming the GB core. In this work we find that, within each group, the GB thermal conductivity strongly correlates with the excess GB energy. All three groups predict nearly the same GB conductivity extrapolated to the high-energy limit. This limiting value is close to the thermal conductivity of amorphous Si, suggesting similar heat transport mechanisms. While the lattice thermal conductivity decreases with temperature, the GB conductivity slightly increases. However, at high temperatures it turns over and starts decreasing if the GB structure undergoes a premelting transformation. Analysis of vibrational spectra of GBs resolved along different directions sheds light on the mechanisms of their thermal resistance. The existence of alternating tensile and compressive atomic environments in the GB core gives rise to localized vibrational modes, frequency gaps creating acoustic mismatch with lattice phonons, and anharmonic vibrations of loosely bound atoms residing in open atomic environments.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Coexistence of vitreous and crystalline phases of H 2 O at ambient temperature

Formation of vitreous ice during rapid compression of water at room temperature is important for biology and the study of biological systems. Here, we show that Raman spectra of rapidly compressed water at greater than 1 GPa at room temperature exhibits the signature of high-density amorphous ice, whereas the X-ray diffraction (XRD) pattern is dominated by crystalline ice VI. To resolve this apparent contradiction, we used molecular dynamics simulations to calculate full vibrational spectra and diffraction patterns of mixtures of vitreous ice and ice VI, including embedded interfaces between the two phases. We show quantitatively that Raman spectra, which probe the local polarizability with respect to atomic displacements, are dominated by the vitreous phase, whereas a small amount of the crystalline component is readily apparent by XRD. The results of our combined experimental and theoretical studies have implications for detecting vitreous phases of water, survival of biological systems under extreme conditions, and biological imaging. The results provide additional insight into the stable and metastable phases of H 2 O as a function of pressure and temperature, as well as of other materials undergoing pressure-induced amorphization and other metastable transitions.

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

The impact of the electric field of metal ions on the vibrations and internal hydrogen bond strength in alkali metal ion di- and triglycine complexes

Using infrared predissociation spectroscopy of cryogenic ions, we revisit the vibrational spectra of alkali metal ion (Li+, Na+, K+) di- and triglycine complexes. We assign their most stable conformation, which involves metal ion coordination to all C=O groups and an internal NH⋯NH2 hydrogen bond in the peptide backbone. An analysis of the spectral shifts of the OH and C=O stretching vibrations across the different metal ions and peptide chain lengths shows that these are largely caused by the electric field of the metal ion, which varies in strength as a function of the square of the distance. The metal ion–peptide interaction also remotely modulates the strength of internal hydrogen bonding in the peptide backbone via the weakening of the amide C=O bond, resulting in a decrease in internal hydrogen bond strength from Li+ > Na+ > K+.

Chemistry↗