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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Optimizing minimum free-energy crossing points in solution: Linear-response free energy/spin-flip density functional theory approach

Examining photochemical processes in solution requires understanding the solvent effects on the potential energy profiles near conical intersections (CIs). For that purpose, the CI point in solution is determined as the crossing between nonequilibrium free energy surfaces. In this work, the nonequilibrium free energy is described using the combined method of linear-response free energy and collinear spin-flip time-dependent density functional theory. The proposed approach reveals the solvent effects on the CI geometries of stilbene in an acetonitrile solution and those of thymine in water. Polar acetonitrile decreases the energy difference between the twisted minimum and twisted-pyramidalized CI of stilbene. For thymine in water, the hydrogen bond formation stabilizes significantly the CI puckered at the carbonyl carbon atom. The result is consistent with the recent simulation showing that the reaction path via this geometry is open in water. Therefore, the present method is a promising way of identifying the free-energy crossing points that play an essential role in photochemistry of solvated molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Direct production of OH radicals upon CH overtone activation of (CH{sub 3}){sub 2}COO Criegee intermediates

Ozonolysis of alkenes, a principle non-photolytic source of atmospheric OH radicals, proceeds through unimolecular decay of energized carbonyl oxide intermediates, known as Criegee intermediates. In this work, cold dimethyl-substituted Criegee intermediates are vibrationally activated in the CH stretch overtone region to drive the 1,4 hydrogen transfer reaction that leads to OH radical products. IR excitation of (CH{sub 3}){sub 2}COO reveals the vibrational states with sufficient oscillator strength, coupling to the reaction coordinate, and energy to surmount the effective barrier (≤ 16.0 kcal mol{sup −1}) to reaction. Insight on the dissociation dynamics is gleaned from homogeneous broadening of the spectral features, indicative of rapid intramolecular vibrational energy redistribution and/or reaction, as well as the quantum state distribution of the OH X{sup 2}Π (v = 0) products. The experimental results are compared with complementary electronic structure calculations, which provide the IR absorption spectrum and geometric changes along the intrinsic reaction coordinate. Additional theoretical analysis reveals the vibrational modes and couplings that permit (CH{sub 3}){sub 2}COO to access to the transition state region for reaction. The experimental and theoretical results are compared with an analogous recent study of the IR activation of syn-CH{sub 3}CHOO and its unimolecular decay to OH products [F. Liu, J. M. Beames, A. S. Petit, A. B. McCoy, and M. I. Lester, Science 345, 1596 (2014)].

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Experimental evidence for an optical interference model for vibrational sum frequency generation on multilayer organic thin film systems. I. Electric dipole approximation

In the field of vibrational sum frequency generation spectroscopy (VSFG) applied to organic thin film systems, a significant challenge to data analysis is in the accurate description of optical interference effects. Herein, we provide experimental evidence that a model recently developed in our lab provides an accurate description of this phenomenon. We studied the organic small molecule N,N′-dioctyl-3,4,9,10-perylenedicarboximide vapor deposited as a thickness gradient on silicon wafer substrates with two oxide thicknesses and two surface preps. VSFG data were obtained using the ssp and the sps polarization combinations in the imide carbonyl stretching region as a function of organic thickness. In this first of two reports, the data are modeled and interpreted within the ubiquitous electric dipole approximation for VSFG. The intrinsic sample responses are parameterized during the fitting routines while optical interference effects are simply calculated from the model using known refractive indices, thin film thicknesses, and beam angles. The results indicate that the thin film model provides a good description of optical interferences, indicating that interfacial terms are significant. Inconsistencies between the fitting results within the bounds of the electric dipole response motivate deliberation for additional effects to be considered in the second report.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Identification of luminescent surface defect in SiC quantum dots

The surface defect that results in the usually observed blue luminescence in the SiC quantum dots (QDs) remains unclear. We experimentally identify that the surface defect C=O (in COO) is responsible for this constant blue luminescence. The HO···C=O [n{sub (OH)} → π*{sub (CO)}] interaction between the hydroxyl and carbonyl groups changes the energy levels of C=O and makes the light absorption/emission arise at around 326/438 nm. Another surface defect (Si–Si) is identified and its light absorption contributes to both C=O-related luminescence and quantum-confinement luminescence of the SiC QDs.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Diffusion studies on permeable nitroxyl spin probes through bilayer lipid membranes: A low frequency ESR study

Electron spin resonance (ESR) studies were carried out for permeable 2mM {sup 14}N-labeled deutrated 3 Methoxy carbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL) in pure water and 1mM, 2mM, 3mM, 4mM concentration of 14N-labeled deutrated MC-PROXYL in 400mM concentration of liposomal solution by using a 300 MHz ESR spectrometer. The ESR parameters such as linewidth, hyperfine coupling constant, g-factor, partition parameter and permeability were reported for these samples. The line broadening was observed for the nitroxyl spin probe in the liposomal solution. The line broadening indicates that the high viscous nature of the liposomal solution. The partition parameter and permeability values indicate the maximum diffusion of nitroxyl spin probes in the bilayer lipid membranes at 2 mM concentration of nitroxyl radical. This study illustrates that ESR can be used to differentiate between the intra and extra- membrane water by loading the liposome vesicles with a lipid-permeable nitroxyl spin probe. From the ESR results, the spin probe concentration was optimized as 2mM in liposomal solution for ESR phantom studies/imaging, invivo and invitro experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The geometrical change and intramolecular energy transfer upon S{sub 1}←S{sub 0} excitation in cyclopentanone

The ultrafast dynamics in vibrationally hot S{sub 1} electronic excited state in cyclopentanone molecule was discovered with time resolved spectroscopy. Investigation of the geometry change upon the S{sub 1}←S{sub 0} excitation and D{sub 0}←S{sub 1} ionization has shown that the dihedral angle between the C=O bond and the plane given by the carbonyl and the α-carbons is 180° either in S{sub 0} or D{sub 0} state and is reduced to 145.8° by out-out-plane deformation of the oxygen in S{sub 1} state according to the theoretical calculation. The time domain experiments with femtosecond resolution have given rich insights into the energy transfer of the cyclopentanone molecule. The molecules are excited to the vibrationally hot S{sub 1} (n, π{sup ∗}) state following absorption of one 267-nm photon. It is found that the population of the S{sub 1} (n, π{sup ∗}) state undergoes ultrafast internal conversion to the highly vibrationally hot S{sub 0} state within 80 fs and nonradiative deactivation by intersystem crossing to triplet T{sub 1} (n, π{sup *}) state occurring in 3.14 ps. Several Rydberg states have worked as stepping stones during the ionization. The available energy was distributed in the symmetric methylene group wagging and the symmetric skeletal ring breathing modes in D{sub 0} state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Making sense of the conflicting magic numbers in WSi{sub n} clusters

First principles studies on the geometric structure, stability, and electronic structure of WSi{sub n} clusters, n = 6-16, have been carried out to show that the observed differing “magic sizes” for WSi{sub n} clusters are associated with the nature of the growth processes. The WSi{sub 12} cluster, observed as a magic species in experiments reacting transition metal ions with silane, is not stable due to a filled shell of 18 electrons, as previously proposed, but due to its atomic structure that arrests further growth because of an endohedral transition metal site. In fact, it is found that all of these clusters, n = 6-16, have filled 5d shells except for WSi{sub 12}, which has a 5d{sup 8} configuration that is caused by crystal field splitting. The stability of WSi{sub 15}{sup +}, observed as highly stable in clusters generated by vaporizing silicon and metal carbonyls, is shown to be associated with a combination of geometric and electronic features. The findings are compared with previous results on CrSi{sub n} clusters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Conductivity study and fourier transform infrared (FTIR) characterization of methyl cellulose solid polymer electrolyte with sodium iodide conducting ion

Sodium ion (Na{sup +}) based solid polymer electrolyte (SPE) has been prepared using solution cast technique with distilled water as solvent and Methylcellulose (MC) as a polymer host. Methylcellulose polymer was chosen as the polymer host due to the abundance of lone pair electrons in the carbonyl and C-O-C constituents, which in turn provide multiple hopping sites for the Na{sup +} conducting ions. Variable compositions of sodium iodide (NaI) salt were prepared to investigate the optimum MC-NaI weight ratio. Results from Electrical Impedance Spectroscopy (EIS) technique show that pure methylcellulose has a low conductivity of 3.61 × 10{sup −11} S/cm.The conductivity increases as NaI content increases up to optimum NaIcomposition of 40 wt%, which yields an average conductivity of 2.70 × 10{sup −5} S/cm.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Molecular hydrogen messengers can lead to structural infidelity: A cautionary tale of protonated glycine

The effects of tagging protonated glycine with either He or between 1 and 14 H{sub 2} molecules on the infrared photodissociation spectra and the ion structure were investigated. Differences in the IR spectra with either a single He atom or H{sub 2} molecule attached indicate that even a single H{sub 2} molecule can affect the frequencies of some vibrational bands of this simple ion. The protonation site is the preferred location of the tag with He and with up to two H{sub 2} molecules, but evidence for H{sub 2} attachment to the hydrogen atom of the uncharged carboxylic acid is observed for ions tagged with three or more H{sub 2} molecules. This results in a 55 cm{sup −1} red shift in the carboxylic acid OH stretch, and evidence for some structural isomers where the hydrogen bond between the protonated nitrogen and the carbonyl oxygen is partially broken; as a result H{sub 2} molecules attached to this site are observed. These results are supported by theory, which indicates that H{sub 2} molecules can effectively break this weak hydrogen bond with three or more H{sub 2} molecules. These results indicate that large spectral shifts as a result of H{sub 2} molecules attaching to sites remote from the charge can occur and affect stretching frequencies as a result of charge transfer, and that tagging with multiple H{sub 2} molecules can change the structure of the ion itself.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Photodissociation dynamics of CH{sub 3}C(O)SH in argon matrix: A QM/MM nonadiabatic dynamics simulation

In this work, we have first employed the combined quantum mechanics/molecular mechanics (QM/MM) method to study the photodissociation mechanism of thioacetic acid CH{sub 3}C(O)SH in the S{sub 1}, T{sub 1}, and S{sub 0} states in argon matrix. CH{sub 3}C(O)SH is treated quantum mechanically using the complete active space self-consistent field and complete active space second-order perturbation theory methods; argon matrix is described classically using Lennard-Jones potentials. We find that the C-S bond fission is predominant due to its small barriers of ca. 3.0 and 1.0 kcal/mol in the S{sub 1} and T{sub 1} states. It completely suppresses the nearby C—C bond fission. After the bond fission, the S{sub 1} radical pair of CH{sub 3}CO and SH can decay to the S{sub 0} and T{sub 1} states via internal conversion and intersystem crossing, respectively. In the S{sub 0} state, the radical pair can either recombine to form CH{sub 3}C(O)SH or proceed to form molecular products of CH{sub 2}CO and H{sub 2}S. We have further employed our recently developed QM/MM generalized trajectory-based surface-hopping method to simulate the photodissociation dynamics of CH{sub 3}C(O)SH. In 1 ps dynamics simulation, 56% trajectories stay at the Franck-Condon region; the S{sub 1} C—S bond fission takes place in the remaining 44% trajectories. Among all nonadiabatic transitions, the S{sub 1} → S{sub 0} internal conversion is major (55%) but the S{sub 1} → T{sub 1} intersystem crossing is still comparable and cannot be ignored, which accounts for 28%. Finally, we have found a radical channel generating the molecular products of CH{sub 2}CO and H{sub 2}S, which is complementary to the concerted molecular channel. The present work sets the stage for simulating photodissociation dynamics of similar thio-carbonyl systems in matrix.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Luminescent single-ion magnets from Lanthanoid(III) complexes with monodentate ketone ligands

We synthesized [Ln{sup III}(hfac){sub 3}(H{sub 2}O)(L)] (abbreviated as Ln-L; Ln = Gd, Tb, Eu; L = DTBK (di-t-butyl ketone), BP (benzophenone)), in which the carbonyl oxygen atom was coordinated to the Ln ion center, despite of such bulky substituents. Their crystal structures were determined by means of X-ray diffraction study. Gd-DTBK is completely isomorphous to the di-t-butyl nitroxide derivative and accordingly can be regarded as a model with the ligand spin masked. The ac magnetic susceptibility measurements on Tb-DTBK and -BP showed frequency dependence, characteristic of single-ion magnets. They also displayed photoluminescence in the solid state at room temperature. The quantum yields of the luminescence of Tb-DTBK and -BP (λ{sub ex} = 360 nm) were improved to 57 and 35%, respectively, from that of the starting material [TbI{sup III}(hfac){sub 3}(H{sub 2}O){sub 2}] (28% at λ{sub ex} = 370 nm). Similarly, the quantum yields for Eu-DTBK and -BP were 8 and 15%, respectively, with λ{sub ex} = 400 nm, while that of the starting material [EuI{sup III}(hfac){sub 3}(H{sub 2}O){sub 2}] was 4% at λ{sub ex}=400 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Electron paramagnetic resonance spectral study of [Mn(acs){sub 2}(2–pic){sub 2}(H{sub 2}O){sub 2}] single crystals

Acesulfame potassium salt is a synthetic and non-caloric sweetener. It is also important chemically for its capability of being ligand in coordination compounds, because it can bind over Nitrogen and Oxygen atoms of carbonyl and sulfonyl groups and ring oxygen. Some acesulfame containing transition metal ion complexes with mixed ligands exhibit solvato and thermo chromic properties and these properties make them physically important. In this work single crystals of Mn{sup +2} ion complex with mixed ligand, [Mn(acs){sub 2}(2-pic){sub 2}(H{sub 2}O){sub 2}], was studied with electron paramagnetic resonance (EPR) spectroscopy. EPR parameters were determined. Zero field splitting parameters indicated that the complex was highly symmetric. Variable temperature studies showed no detectable chance in spectra.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Lead titanate/cyclic carbonate dependence on ionic conductivity of ferro/acrylate blend polymer composites

Impedance, XRD, DSC and FTIR studies had been carried out for PVdF-co-HFP/LIBETI based system for three plasticizer (EC/DMC) – filler (PbTiO3) weight ratios. The enhanced conductivity 4.18 × 10{sup −5} Scm{sup −1} was noted for 57.5 wt% −7.5 wt% plasticizer – filler. while blending PEMA to PVdF-co-HFP respectively 7.5: 22.5 wt % (3/7), 15 wt%: 15 wt % (5/5) and 22.5wt %: 7.5 wt % (7/3), the improved conductivity was noted for 3/7 ratio 1.22 × 10{sup −5} S cm{sup −1} and its temperature dependence abide Arrhenius behavior. The intensity of peaks in XRD diffractogram registered dominance of lead titanate, from 2θ = 10° to 80° and absence of VdF crystallites (α+β phase) was noted. In DSC studies, the presence of the exotherm events, filler effect was distinctively seen exhibiting recrystallization of VdF crystallites. In blending PEMA, however, no trace of exotherms was found suggestive of PEMA better inhibiting recrystallization. FTIR study confirmed molecular interactions of various constituents in the vibrational band 500 – 1000 cm{sup −1} both in pristine PVdF-co-HFP and PEMA blended composites with reference to C-F stretching, C-H stretching and C=O carbonyl bands.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The physical chemistry of Criegee intermediates in the gas phase

Here, carbonyl oxides, also known as Criegee intermediates, are key intermediates in both gas phase ozonolysis of unsaturated hydrocarbons in the troposphere and solution phase organic synthesis via ozonolysis. Although the study of Criegee intermediates in both arenas has a long history, direct studies in the gas phase have only recently become possible through new methods of generating stabilised Criegee intermediates in sufficient quantities. This advance has catalysed a large number of new experimental and theoretical investigations of Criegee intermediate chemistry. In this article we review the physical chemistry of Criegee intermediates, focusing on their molecular structure, spectroscopy, unimolecular and bimolecular reactions. These recent results have overturned conclusions from some previous studies, while confirming others, and have clarified areas of investigation that will be critical targets for future studies. In addition to expanding our fundamental understanding of Criegee intermediates, the rapidly expanding knowledge base will support increasingly predictive models of their impacts on society.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

THE ORIGIN OF THE 3.4 {mu}m FEATURE IN WILD 2 COMETARY PARTICLES AND IN ULTRACARBONACEOUS INTERPLANETARY DUST PARTICLES

We analyzed two ultracarbonaceous interplanetary dust particles (IDPs) and two cometary Wild 2 particles with infrared spectroscopy. We characterized the carrier of the 3.4 {mu}m band in these samples and compared its profile and the CH{sub 2}/CH{sub 3} ratios to the 3.4 {mu}m band in the diffuse interstellar medium (DISM), in the insoluble organic matter from three primitive meteorites, in asteroid 24 Themis, and in the coma of comet 103P/Hartley 2. We found that the 3.4 {mu}m band in both Wild 2 and IDPs is similar, but different from all of the other astrophysical environments that we compared it to. The 3.4 {mu}m band in the IDPs and Wild 2 particles is dominated by CH{sub 2} groups, the peaks are narrower and stronger than in the meteorites, asteroid Themis, and the DISM. Also, the presence of the carbonyl group C=O at {approx}1700 cm{sup -1} (5.8 {mu}m) in most of the spectra of our samples indicates that these aliphatic chains have O bonded to them, which is quite different from astronomical spectra of the DISM. Based on all of these observations, we conclude that the origin of the carrier of the 3.4 {mu}m band in the IDPs and Wild 2 samples is not interstellar; instead, we suggest that the origin lies in the outermost parts of the solar nebula.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Structure of a HAp/TiO{sub y} Nanocomposite Studied by Vibrational Spectroscopy Techniques

A hydroxyapatite/TiO{sub y} nanocomposite material has been studied by X-ray diffraction, infrared spectroscopy, and Raman spectroscopy. The results demonstrate that annealing at 400°C changes the valence state of the titanium and leads to the formation of [Ti(OH){sub 2}]{sup 2+} and [TiHPO{sub 4}]{sup 2+} surface groups and terminal carbonyls and partial heterovalent cation substitutions of Ti{sup 3+} and Ti{sup 4+} for Ca{sup 2+}. As the annealing temperature is raised to 600°C, surface groups disappear. The amount of inflowing oxygen is insufficient for the complete oxidation of TiO{sub 0.92} to TiO{sub 2} in hydroxyapatite/TiO{sub 0.92}. The result is the formation of an intermediate nanophase with the composition Ti{sub 4.5}O{sub 5}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Molecular and crystal structures of p-heptyloxyphenyl p-hexyloxybenzoate and p-butyloxyphenyl p-heptyloxybenzoate: Mesophase design

Two aromatic esters with the formulas C{sub 6}H{sub 13}-O-C{sub 6}H{sub 4}-C(O)O-C{sub 6}H{sub 4}-O-C{sub 7}H{sub 15} (1) and C{sub 7}H{sub 15}-O-C{sub 6}H{sub 4}-C(O)O-C{sub 6}H{sub 4}-O-C{sub 4}H{sub 9} (2) belonging to nematic liquid-crystal compounds were studied by X-ray diffraction. Compound 1 crystallizes in two modifications: monoclinic (1-m) and triclinic (1-tr). The crystal packing of 1 and 2 is built from alternating loosely packed aliphatic regions and closely packed aromatic regions. In crystal structures 1-m and 2, the aromatic regions are linked into chains by hydrogen bonds with the participation of the carbonyl oxygen atom of the ester group and the C-H fragment of the benzene ring, but these hydrogen bonds in 1-m are much weaker than in 2. In 1-m there are {pi}-stacking interactions between the molecules, resulting in the formation of centrosymmetric dimers with an interplanar distance of 3.45 A. In 1-tr, the aromatic fragments form a herringbone packing motif favorable for a two-dimensional network of directional C-H...{pi}-system interactions.

36 MATERIALS SCIENCE↗