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Results for “Absorption spectroscopy”

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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

On the state of the emitter of the 3.3 micron unidentified infrared band - Absorption spectroscopy of polycyclic aromatic hydrocarbon species

Results of absorption measurements indicate that the PAH species responsible for the UIR (unidentified infrared) emission probably exist in a condensed form rather than as isolated molecules. It is shown that the peak absorption of the C-H stretch feature of vapor-phase PAHs occurs at a higher frequency than that of the condensed-phase PAHs and does not match the 3.289-micron interstellar feature. The vapor-phase experiments duplicate the phenomenon of the 3.3-micron profile simplification of PAH in KBr at elevated temperature. This confirms that the change of the profile with temperature is an intrinsic molecular effect, and is not a consequence of matrix (KBr) or condensed state interactions.

Flickinger, Gregory C.↗
NASA NTRS1993

On the evaluation of air mass factors for atmospheric near-ultraviolet and visible absorption spectroscopy

The interpretation of UV-visible twilight absorption measurements of atmospheric chemical constituents is dependent on how well the optical path, or air mass factor, of light collected by the spectrometer is understood. A simple single scattering model and a Monte Carlo radiative transfer scheme have been developed to study the effects of multiple scattering, aerosol scattering, surface albedo and refraction on air mass factors for scattered light observations. At fairly short visible wavelengths (less than about 450 nm), stratospheric air mass factors are found to be relatively insensitive to multiple scattering, surface albedo and refraction, as well as aerosol scattering by background aerosols. Longer wavelengths display greater sensitivity to refraction and aerosol scattering. Tropospheric air mass factors are found to be highly dependent on aerosol scattering, surface albedo and, at long visible wavelengths (about 650 nm), refraction. Absorption measurements of NO2 and O4 are shown to support these conclusions.

Perliski, Lori M.↗
DOE OSTI2021

2p x-ray absorption spectroscopy of 3d transition metal systems

This review provides an overview of the different methods and computer codes that are used to interpret 2p x-ray absorption spectra of 3d transition metal ions. We first introduce the basic parameters and give an overview of the methods used. We start with the semi-empirical multiplet codes and compare the different codes that are available. A special chapter is devoted to the user friendly interfaces that have been written on the basis of these codes. Next we discuss the first principle codes based on band structure, including a chapter on Density Functional theory based approaches. We also give an overview of the first-principle multiplet codes that start from a cluster calculation and we discuss the wavefunction based methods, including multi-reference methods. We end the review with a discussion of the link between theory and experiment and discuss the open issues in the spectral analysis.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Multielectronic and multiatomic effects in the U O 4,5 x-ray absorption spectroscopy of uranium dioxide

In order to explain all of the spectral features observed in the U O 4,5 x-ray absorption spectrum of uranium dioxide (UO 2 ), it is necessary to include both multielectron effects and multiatomic effects. The 5d (core hole)-5f (electron) angular momentum coupling that gives rise to the giant resonance has been treated within ligand field density functional theory, and the electron scattering that generates the extended x-ray absorption fine structure has been included via the spectral simulation program FEFF: both within a UO 8 fluorite cluster picture. An atomic model is insufficient to explain all of the observed spectral features.

36 MATERIALS SCIENCE↗
NASA NTRSDate not supplied

Examination of Mars2020 Shock-Layer Conditions via Infrared Laser Absorption Spectroscopy of CO2 and CO

Amid-infrared laser absorption diagnostic was deployed to study a simulated Mars2020 shock layer in the Electric Arc Shock Tube (EAST) facility at NASA’s Ames Research Center. Rapid RF-diplexing techniques enabled quantitative temperature and number density measurements of CO2 and CO with μs-resolution over an incident shock velocity range of 1.39 – 3.75 km/s. Two interband cascade lasers were utilized at 4.17 and 4.19 μm to resolve eight CO2 asymmetric stretch fundamental band (𝜈3) transitions from two different vibrational levels: 0000 (ground state) and 0110 (first excited bending mode). The probed rotational levels span across J” = 58 to J” = 140. Results are compared to DPLR simulations of the shock layer using kinetic mechanisms of Johnston et al. and Cruden et al. At shock velocities below 3.1 km/s, the agreement between the measurements and the Johnston mechanism is typically within 5% for temperature and within 10% for number density. At shock velocities above 3.1 km/s, the CO2 measurement becomes sensitive to a thin boundary layer and corrections of this effect are presented. On test cases with enough energy to dissociate CO2, a quantum cascade laser scanned the P(2, 20), P(0, 31), and P(3, 14) transitions of the CO fundamental band at 4.98 μm. CO formation rate is measured to be close to the Johnston kinetic mechanism at low velocities, and then trending towards the Cruden kinetic mechanism at high velocities. On a few low velocity test cases, rovibrational relaxation of the Martian atmosphere is probed with μs resolution.

Laser Absorption↗
DOE OSTI2020

Interferometric two-photon-absorption spectroscopy with three entangled photons

In this work, we propose an interferometric pump-probe technique that employs three entangled photons generated by cascaded spontaneous parametric downconversion. A Mach–Zehnder interferometer made of two three-port waveguide arrays is inserted in the optical path. Two independent phases introduced to manipulate the entangled photon state serve as control parameters and can selectively excite matter pathways. Compared to two-photon-absorption of an entangled photon-pair, the three-photon signals are significantly enhanced by frequency-dispersed photon-counting detection.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Ultrafast Adsorbate Excitation Probed with Subpicosecond-Resolution X-Ray Absorption Spectroscopy

We use a pump-probe scheme to measure the time evolution of the C K-edge x-ray absorption spectrum from CO/Ru(0001) after excitation by an ultrashort high-intensity optical laser pulse. Because of the short duration of the x-ray probe pulse and precise control of the pulse delay, the excitation-induced dynamics during the first picosecond after the pump can be resolved with unprecedented time resolution. By comparing with density functional theory spectrum calculations, we find high excitation of the internal stretch and frustrated rotation modes occurring within 200 fs of laser excitation, as well as thermalization of the system in the picosecond regime. The ~100 fs initial excitation of these CO vibrational modes is not readily rationalized by traditional theories of nonadiabatic coupling of adsorbates to metal surfaces, e.g., electronic frictions based on first order electron-phonon coupling or transient population of adsorbate resonances. Finally, we suggest that coupling of the adsorbate to nonthermalized electron-hole pairs is responsible for the ultrafast initial excitation of the modes.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Plasmon Dynamics Driven by Aggregation of Tris(2,2′-bipyridine)ruthenium(II)-Functionalized Gold Nanoparticles Probed by XANES and Transient Absorption Spectroscopy

Energy conversion dynamics is critical for advancing next-generation photovoltaics, optoelectronics, and light-harvesting technologies. Noble metal plasmonic nanoparticles play a pivotal role as nanoscale electromagnetic confinement structures, driving photon-induced chemical reactions. In this study, we explore the effects of [Ru(bpy) 3 ] 2+ functionalization and aggregation on citrate-capped gold nanoparticles (AuNPs) of 40 and 100 nm diameters, focusing on molecule-plasmon interactions and their influence on electronic and energy dissipation properties. X-ray absorption near-edge spectroscopy (XANES) revealed that [Ru(bpy) 3 ] 2+ functionalization induces controlled aggregation without altering the oxidation state of gold. A more pronounced white-line intensity is observed in 40 nm AuNPs, consistent with greater s–p–d hybridization and a higher density of surface states, likely influenced by both nanoparticle size and aggregation. Transient absorption (TA) spectroscopy highlights faster electron–phonon relaxation dynamics in aggregated 40 nm nanoparticles, which is attributed to increased electron delocalization and more efficient coupling to the phonon bath. In contrast, 100 nm nanoparticles exhibit minimal changes due to a lower degree of aggregation. Interestingly, we observe that enhanced electron–phonon coupling in aggregated nanoparticles coincides with a slowing of electron–electron scattering. These observations suggest a competitive interplay between the two relaxation pathways, where enhanced energy transfer to the lattice in aggregated systems can suppress electronic thermalization. In conclusion, these findings underscore the critical role of nanoparticle size, aggregation, and molecule–surface interactions in modulating plasmonic dynamics and excited-state lifetimes and further provide valuable insights into designing tailored plasmonic systems with transformative potential for sensing, catalysis, and energy conversion.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Sulfur x-ray absorption spectroscopy data from bedrock shale, soil, and floodplain sediment from the East River, Colorado watershed

This dataset includes sulfur x-ray absorption near edge spectroscopy (XANES) data collected on solid samples as a part of the Watershed Function Scientific Focus Area (SFA) located in the Upper Colorado River Basin. The data were collected in order to investigate the speciation of sulfur and degree of shale weathering in solid samples across the watershed and their impact on riverine export of sulfate. Solid samples, including shale, hillslope soil, and floodplain sediment samples collected in 2016-2018, were analyzed by bulk XANES. Density fractions of hillslope soil, including a light fraction representing particulate organic matter and a heavy fraction representing minerals are also analyzed by bulk XANES. Micro-focused XANES on a weathered shale sample (PLM6, 2.7 m) was also performed. Sample locations are included in the 'sample meta data.csv' file, and XANES data for each sample type are included in csv files.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Insights from Femtosecond Transient Absorption Spectroscopy into the Structure–Function Relationship of Glyceline Deep Eutectic Solvents

This study aimed to determine the structure–function relationship (SFR) for ChCl–glycerol mixtures, a deep eutectic solvent (DES), by investigating their microscopic solvation dynamics and how it relates to their macroscopic properties across varying concentrations of ChCl. Femtosecond transient absorption (fs-TA) spectroscopy revealed two distinct solvation dynamics time constants: τ 1 , governed by glycerol–glycerol interactions, and τ 2 , dominated by the choline response. The τ 2 minimum at 25–30 mol % ChCl closely aligned with the eutectic composition (~33.33 mol % ChCl), where the glycerol network was the most organized and the choline ions exhibited the fastest relaxation. The viscosity decreased sharply up to ~25 mol % ChCl and then plateaued, while the conductivity increased monotonically with ChCl concentration, reflecting enhanced ionic mobility. The density decreased with both increasing ChCl concentration and temperature, indicating disrupted hydrogen bonding and reduced molecular packing. The polarity, measured using betaine-30 (B30) and the E T (30) polarity scale, increased steeply up to approximately 25 mol % ChCl before reaching a plateau. These findings identified the eutectic composition as the optimal concentration range for balancing stability, fluidity, conductivity, and enhanced dynamics within the glycerol system.

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

X-ray Absorption Spectroscopy Studies of a Molecular CO 2 -Reduction Catalyst Deposited on Graphitic Carbon Nitride

Metal-ligand complexes have been extensively explored as well-defined molecular catalysts in small molecule activation reactions such as carbon dioxide (CO 2 ) reduction. Many hybrid photocatalysts have been prepared by coupling such complexes with photoactive surfaces for use in solar CO 2 reduction. In this work, we employ X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies, density functional theory (DFT) and computational XANES modeling to interrogate the structure of a hybrid photocatalyst consisting of a macrocyclic cobalt complex deposited on graphitic carbon nitride (C 3 N 4 ). Results show that the cobalt complex binds on C 3 N 4 through surface OH or NH 2 groups. By refining the local geometry and binding sites of this well-defined molecular cobalt complex on C 3 N 4 , here we established an important benchmark for modeling a large class of molecular catalysts that can be adapted to in situ/operando studies and further enhanced by applying chemometrics-based approaches and machine learning methods of XANES data analysis.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Tunable Infrared Laser Absorption Spectroscopy of Aluminum Monoxide $A^2\Pi_i $–$X^2\Sigma^+$.

We report the details of an infrared, laser absorption diagnostic capable of quantifying aluminum monoxide temperature and column density at 100 kHz repetition rate. This novel technique employs a near infrared MEMS-VCSEL to measure rotationally resolved optical absorption spectra of aluminum monoxide $A^2\Pi_i$ - $X^2\Sigma^+$ from approximately 7400 –7900 cm -1 . Temperatures and column densities are extracted from model regressions to provide temporally resolved thermochemical information on aluminum oxidation reactions. The measurement capability is demonstrated by performing 100 kHz measurement in the plume of an exploding bridgewire with measured temperatures of 3450–3100 K and column densities of 1– 11 x 10 16 cm -2 . To the authors knowledge, this is the first use of the AlO $A^2\Pi_i$ - $X^2\Sigma^+$ transition to characterize aluminum combustion environments. Details regarding signal extraction and calibration of MEMS-VCSEL spectra are also included. Although unsuccessful, efforts to extract kinetic temperature and column density from simultaneously measured, atomic aluminum 2 P 3/2,1/2 - 2 S 1/2 transitions at 7618 cm -1 and 7602 cm -1 are also described.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Modeling Heterogeneity in UO 2 Nanoparticles Using X‐ray Absorption Spectroscopy

Abstract EXAFS provides the capability to interrogate nanoparticle (NP) structure in atomistic detail without relying on long‐range crystallinity. There is a limitation in that EXAFS provides averaged structural information, making it difficult to separate a small amount of heterogeneous structure from bulk. In this work, models were developed to extract surface‐specific information from conventional EXAFS measurements collected on UO 2 NPs of varying size. Specifically, the surface terminating species of UO 2 NPs was determined from comparison of coordination numbers with geometric models while the origin of static disorder was interrogated from user‐defined simulations. Results show that the degree of oxygenation on the NP surface does not significantly deviate from bulk surface and that static disorder is highly enhanced in NP surface layers but cannot be attributed to surface relaxation effects alone. The approach described herein has the potential to be adapted to a range of inorganic NP systems to interrogate surface structure.

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

Pressure-induced changes of valence fluctuation in β - YbAlB 4 probed by x-ray absorption spectroscopy

Here we report detailed valence fluctuation phenomena in the unique quantum-critical compound β-YbAlB 4 under pressures and at low temperatures. We directly observed the drastic change in the pressure dependence of the mean Yb valence at about 3 GPa with no pressure-induced structural transition. Below 3 GPa, the anomaly in the temperature dependences of the mean Yb valence was observed at about 55 K under ambient pressure, corresponding to a previously observed reduced Kondo coherence temperature, and this temperature rapidly decreases to 22 K at 2.2 GPa, in contrast to the monotonous decrease of the high Kondo temperature (~250K at ambient pressure). The present results reveal that this reduced Kondo coherence temperature is responsible for the unconventional quantum critical behaviors in β-YbAlB 4 . Above 3 GPa, it was found that the temperature dependence of the mean Yb valence exhibits a discontinuous change at low temperature (10.5 and 9 K under 4.8 and 5.5 GPa, respectively).

36 MATERIALS SCIENCE↗