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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Mapping wave packet bifurcation at a conical intersection in CH 3 I by attosecond XUV transient absorption spectroscopy

Extreme ultraviolet (XUV) transient absorption spectroscopy has emerged as a sensitive tool for mapping the real-time structural and electronic evolution of molecules. Here, attosecond XUV transient absorption is used to track dynamics in the A-band of methyl iodide (CH 3 I). Gaseous CH 3 I molecules are excited to the A-band by a UV pump (277 nm, ~20 fs) and probed by attosecond XUV pulses targeting iodine I(4d) core-to-valence transitions. Owing to the excellent temporal resolution of the technique, passage through a conical intersection is mapped through spectral signatures of nonadiabatic wave packet bifurcation observed to occur at 15 ± 4 fs following UV photoexcitation. The observed XUV signatures and time dynamics are in agreement with previous simulations [H. Wang, M. Odelius, and D. Prendergast, J. Chem. Phys. 151, 124106 (2019)]. Furthermore, due to the short duration of the UV pump pulse, coherent vibrational motion in the CH 3 I ground state along the C-I stretch mode (538 ± 7 cm -1 ) launched by resonant impulsive stimulated Raman scattering and dynamics in multiphoton excited states of CH 3 I are also detected.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Probing C–I bond fission in the UV photochemistry of 2-iodothiophene with core-to-valence transient absorption spectroscopy

The UV photochemistry of small heteroaromatic molecules serves as a testbed for understanding fundamental photo-induced chemical transformations in moderately complex compounds, including isomerization, ring-opening, and molecular dissociation. Here, a combined experimental-theoretical study of 268 nm UV light-induced dynamics in 2-iodothiophene (C 4 H 3 IS) is performed. The dynamics are experimentally monitored with a femtosecond extreme ultraviolet (XUV) probe that measures iodine N-edge 4d core-to-valence transitions. Experiments are complemented by density functional theory calculations of both the pump-pulse induced valence excitations and the XUV probe-induced core-to-valence transitions. Possible intramolecular relaxation dynamics are investigated by ab initio molecular dynamics simulations. Furthermore, gradual absorption changes up to ~0.5 to 1 ps after excitation are observed for both the parent molecular species and emerging iodine fragments, with the latter appearing with a characteristic rise time of 160 ± 30 fs. Comparison of spectral intensities and energies with the calculations identifies an iodine dissociation pathway initiated by a predominant π → π* excitation. In contrast, initial excitation to a nearby n ⟂ → σ* state appears unlikely based on a significantly smaller oscillator strength and the absence of any corresponding XUV absorption signatures. Excitation to the π → π* state is followed by contraction of the C–I bond, enabling a nonadiabatic transition to a dissociative π→σ C-I * state. For the subsequent fragmentation, a relatively narrow bond-length region along the C–I stretch coordinate between 230 and 280 pm is identified, where the transition between the parent molecule and the thienyl radical + iodine atom products becomes prominent in the XUV spectrum due to rapid localization of two singly occupied molecular orbitals on the two fragments.

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

Direct momentum imaging of charge transfer following site-selective ionization

We study ultrafast charge rearrangement in dissociating 2-iodopropane (2-C 3 H 7 I) using site-selective core-ionization at the iodine atom. Clear signatures of electron transfer between the neutral propyl fragment and multiply charged iodine ions are observed in the recorded delay-dependent ion momentum distributions. The detected charge transfer pathway is only favorable within a small (few angstrom), charge-state-dependent spatial window located at C-I distances longer than that of the neutral ground-state molecule. Lastly, these results offer new insights into the physics underpinning charge transfer in isolated molecules and pave the way for a new class of time-resolved studies.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Survey of Gravitationally lensed Objects in HSC Imaging (SuGOHI) – V. Group-to-cluster scale lens search from the HSC–SSP Survey

ABSTRACT We report the largest sample of candidate strong gravitational lenses belonging to the Survey of Gravitationally lensed Objects in HSC Imaging for group-to-cluster scale (SuGOHI-c) systems. These candidates are compiled from the S18A data release of the Hyper Suprime-Cam Subaru Strategic Program (HSC–SSP) Survey. We visually inspect ∼39 500 galaxy clusters, selected from several catalogues, overlapping with the Wide, Deep, and UltraDeep fields, spanning the cluster redshift range of 0.05 < zcl < 1.38. We discover 641 candidate lens systems, of which 536 are new. From the full sample, 47 are almost certainly bona fide lenses, 181 of them are highly probable lenses, and 413 are possible lens systems. Additionally, we present 131 lens candidates at galaxy scale serendipitously discovered during the inspection. We obtained spectroscopic follow-up of 10 candidates using the X-shooter. With this follow-up, we confirm eight systems as strong gravitational lenses. Of the remaining two, one of the sources is too faint to detect any emission, and the other has a tentative redshift close to the lens redshift, but additional arcs in this system are yet to be observed spectroscopically. Since the HSC–SSP is an ongoing survey, we expect to find ∼600 definite or probable lenses using this procedure and even more if combined with other lens finding methods.

Jaelani, Anton T.↗
DOE OSTI2021

Characterizing the magnetic fields of nearby molecular clouds using submillimeter polarization observations

Of all the factors that influence star formation, magnetic fields are perhaps the least well understood. The goal of this paper is to characterize the 3D magnetic field properties of nearby molecular clouds through various methods of statistically analysing maps of polarized dust emission. Our study focuses on nine clouds, with data taken from the Planck Sky Survey as well as data from the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry observations of Vela C. We compare the distributions of polarization fraction (p), dispersion in polarization angles ($\mathcal {S}$), and hydrogen column density (N H ) for each of our targeted clouds. To broaden the scope of our analysis, we compare the distributions of our clouds’ polarization observables with measurements from synthetic polarization maps generated from numerical simulations. We also use the distribution of polarization fraction measurements to estimate the inclination angle of each cloud’s cloud-scale magnetic field. We obtain a range of inclination angles associated with our clouds, varying from 16° to 69°. We establish inverse correlations between p and both $\mathcal {S}$ and NH in almost every cloud, but we are unable to establish a statistically robust $\mathcal {S}$ versus NH trend. By comparing the results of these different statistical analysis techniques, we are able to propose a more comprehensive view of each cloud’s 3D magnetic field properties. These detailed cloud analyses will be useful in the continued studies of cloud-scale magnetic fields and the ways in which they affect star formation within these molecular clouds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

The Davis–Chandrasekhar–Fermi method revisited

ABSTRACT Despite the rich observational results on interstellar magnetic fields in star-forming regions, it is still unclear how dynamically significant the magnetic fields are at varying physical scales, because direct measurement of the field strength is observationally difficult. The Davis–Chandrasekhar–Fermi (DCF) method has been the most commonly used method to estimate the magnetic field strength from polarization data. It is based on the assumption that gas turbulent motion is the driving source of field distortion via linear Alfvén waves. In this work, using MHD simulations of star-forming clouds, we test the validity of the assumption underlying the DCF method by examining its accuracy in the real 3D space. Our results suggest that the DCF relation between turbulent kinetic energy and magnetic energy fluctuation should be treated as a statistical result instead of a local property. We then develop and investigate several modifications to the original DCF method using synthetic observations, and propose new recipes to improve the accuracy of DCF-derived magnetic field strength. We further note that the biggest uncertainty in the DCF analysis may come from the linewidth measurement instead of the polarization observation, especially since the line-of-sight gas velocity can be used to estimate the gas volume density, another critical parameter in the DCF method.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Survey of Gravitationally lensed objects in HSC Imaging (SuGOHI). VIII. New galaxy-scale lenses from the HSC SSP

Abstract We conduct a search for galaxy-scale strong gravitational lens systems in Data Release 4 of the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP), consisting of data taken up to the S21A semester. We select 103191 luminous red galaxies from the Baryon Oscillation Spectroscopic Survey (BOSS) sample that have deep multiband imaging from the HSC SSP and use the YattaLens algorithm to identify lens candidates with blue arc-like features automatically. The candidates are visually inspected and graded based on their likelihood of being a lens. We find eight definite lenses, 28 probable lenses, and 138 possible lenses. The new lens candidates generally have lens redshifts in the range 0.3 ≲ zL ≲ 0.9, a key intermediate redshift range to study the evolution of galaxy structure. Follow-up spectroscopy will confirm these new lenses and measure source redshifts to enable detailed lens modeling.

Astronomy & Astrophysics↗
DOE OSTI2020

Materials Data on Y2C by Materials Project

Y2C is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Y2C sheets oriented in the (0, 0, 1) direction. Y is bonded in a distorted T-shaped geometry to three equivalent C atoms. All Y–C bond lengths are 2.48 Å. C is bonded to six equivalent Y atoms to form edge-sharing CY6 octahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y2C3 by Materials Project

Y2C3 is Plutonium carbide structured and crystallizes in the cubic I-43d space group. The structure is three-dimensional. Y3+ is bonded in a 9-coordinate geometry to nine equivalent C2- atoms. There are a spread of Y–C bond distances ranging from 2.52–2.83 Å. C2- is bonded to six equivalent Y3+ and one C2- atom to form a mixture of distorted edge, face, and corner-sharing CY6C trigonal bipyramids. The C–C bond length is 1.34 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CI4 by Materials Project

CI4 is Iron carbide-like structured and crystallizes in the tetragonal I-42m space group. The structure is zero-dimensional and consists of two periodomethane molecules. C4+ is bonded in a tetrahedral geometry to four equivalent I1- atoms. All C–I bond lengths are 2.18 Å. I1- is bonded in a single-bond geometry to one C4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on YC2 by Materials Project

YC2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Y is bonded in a distorted q4 geometry to ten equivalent C atoms. There are two shorter (2.45 Å) and eight longer (2.69 Å) Y–C bond lengths. C is bonded in a 6-coordinate geometry to five equivalent Y and one C atom. The C–C bond length is 1.30 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y4C5 by Materials Project

Y4C5 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are two inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to five C+2.40- atoms to form YC5 trigonal bipyramids that share corners with two equivalent CY5C octahedra, corners with four equivalent YC5 trigonal bipyramids, and edges with two equivalent YC5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 36–48°. There are a spread of Y–C bond distances ranging from 2.42–2.70 Å. In the second Y3+ site, Y3+ is bonded in a 7-coordinate geometry to nine C+2.40- atoms. There are a spread of Y–C bond distances ranging from 2.45–2.90 Å. There are three inequivalent C+2.40- sites. In the first C+2.40- site, C+2.40- is bonded to six Y3+ atoms to form CY6 octahedra that share corners with four equivalent CY5C octahedra and edges with six CY6 octahedra. The corner-sharing octahedral tilt angles are 61°. In the second C+2.40- site, C+2.40- is bonded to five Y3+ and one C+2.40- atom to form CY5C octahedra that share corners with six CY6 octahedra, corners with two equivalent YC5 trigonal bipyramids, and edges with six CY6 octahedra. The corner-sharing octahedra tilt angles range from 29–61°. The C–C bond length is 1.33 Å. In the third C+2.40- site, C+2.40- is bonded in a 5-coordinate geometry to six Y3+ and one C+2.40- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y4C7 by Materials Project

Y4C7 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to seven C+1.71- atoms to form distorted YC7 octahedra that share corners with two equivalent YC7 octahedra, a cornercorner with one CY4C trigonal bipyramid, and edges with five equivalent YC7 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Y–C bond distances ranging from 2.50–3.01 Å. In the second Y3+ site, Y3+ is bonded in a 9-coordinate geometry to nine C+1.71- atoms. There are a spread of Y–C bond distances ranging from 2.44–2.85 Å. There are four inequivalent C+1.71- sites. In the first C+1.71- site, C+1.71- is bonded to six Y3+ atoms to form CY6 octahedra that share corners with two equivalent CY4C trigonal bipyramids, edges with two equivalent CY6 octahedra, and edges with four equivalent CY4C trigonal bipyramids. In the second C+1.71- site, C+1.71- is bonded to four Y3+ and one C+1.71- atom to form distorted CY4C trigonal bipyramids that share a cornercorner with one YC7 octahedra, a cornercorner with one CY6 octahedra, corners with six equivalent CY4C trigonal bipyramids, and edges with two equivalent CY6 octahedra. The corner-sharing octahedra tilt angles range from 33–61°. The C–C bond length is 1.33 Å. In the third C+1.71- site, C+1.71- is bonded in a 6-coordinate geometry to four Y3+ and two C+1.71- atoms. The C–C bond length is 1.33 Å. In the fourth C+1.71- site, C+1.71- is bonded in a 5-coordinate geometry to five Y3+ and one C+1.71- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on YC by Materials Project

YC is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Y3+ is bonded to six equivalent C3- atoms to form a mixture of corner and edge-sharing YC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Y–C bond lengths are 2.55 Å. C3- is bonded to six equivalent Y3+ atoms to form a mixture of corner and edge-sharing CY6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on YC by Materials Project

YC is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Y3+ is bonded to four equivalent C3- atoms to form corner-sharing YC4 tetrahedra. All Y–C bond lengths are 2.37 Å. C3- is bonded to four equivalent Y3+ atoms to form corner-sharing CY4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on YC by Materials Project

YC is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Y3+ is bonded in a body-centered cubic geometry to eight equivalent C3- atoms. All Y–C bond lengths are 2.69 Å. C3- is bonded in a body-centered cubic geometry to eight equivalent Y3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y3C4 by Materials Project

Y3C4 crystallizes in the tetragonal P4/mnc space group. The structure is three-dimensional. there are four inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to six C+2.25- atoms to form YC6 octahedra that share corners with two equivalent YC6 octahedra, corners with four equivalent YC7 pentagonal bipyramids, and edges with four equivalent YC7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.51 Å) and four longer (2.62 Å) Y–C bond lengths. In the second Y3+ site, Y3+ is bonded to six C+2.25- atoms to form YC6 octahedra that share a cornercorner with one YC6 octahedra and edges with four equivalent YC7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 0°. There are a spread of Y–C bond distances ranging from 2.36–2.64 Å. In the third Y3+ site, Y3+ is bonded to seven C+2.25- atoms to form distorted YC7 pentagonal bipyramids that share a cornercorner with one YC6 octahedra, corners with two equivalent YC7 pentagonal bipyramids, edges with three YC6 octahedra, edges with two equivalent YC7 pentagonal bipyramids, and faces with two equivalent YC7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 1°. There are a spread of Y–C bond distances ranging from 2.50–2.78 Å. In the fourth Y3+ site, Y3+ is bonded in a 7-coordinate geometry to seven C+2.25- atoms. There are a spread of Y–C bond distances ranging from 2.36–2.86 Å. There are seven inequivalent C+2.25- sites. In the first C+2.25- site, C+2.25- is bonded to six Y3+ atoms to form CY6 octahedra that share corners with nine CY6 octahedra and edges with eight CY5C octahedra. The corner-sharing octahedra tilt angles range from 0–85°. In the second C+2.25- site, C+2.25- is bonded to six Y3+ atoms to form a mixture of corner and edge-sharing CY6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the third C+2.25- site, C+2.25- is bonded to six Y3+ atoms to form a mixture of corner and edge-sharing CY6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. Both C–Y bond lengths are 2.36 Å. In the fourth C+2.25- site, C+2.25- is bonded to six Y3+ atoms to form a mixture of corner and edge-sharing CY6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. There are a spread of C–Y bond distances ranging from 2.36–2.64 Å. In the fifth C+2.25- site, C+2.25- is bonded to five Y3+ and one C+2.25- atom to form a mixture of corner and edge-sharing CY5C octahedra. The corner-sharing octahedra tilt angles range from 3–85°. The C–C bond length is 1.35 Å. In the sixth C+2.25- site, C+2.25- is bonded in a 2-coordinate geometry to four equivalent Y3+ and two equivalent C+2.25- atoms. In the seventh C+2.25- site, C+2.25- is bonded in a 6-coordinate geometry to five Y3+ and one C+2.25- atom. The C–C bond length is 1.30 Å.

36 MATERIALS SCIENCE↗