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At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Simultaneous X-Ray and Infrared Observations of Sagittarius A*'s Variability

Emission from Sagittarius A* is highly variable at both X-ray and infrared (IR) wavelengths. Observations over the last ∼20 yr have revealed X-ray flares that rise above a quiescent thermal background about once per day, while faint X-ray flares from Sgr A* are undetectable below the constant thermal emission. In contrast, the IR emission of Sgr A* is observed to be continuously variable. Recently, simultaneous observations have indicated a rise in IR flux density around the same time as every distinct X-ray flare, while the opposite is not always true (peaks in the IR emission may not be coincident with an X-ray flare). Characterizing the behavior of these simultaneous X-ray/IR events and measuring any time lag between them can constrain models of Sgr A* ʼs accretion flow and the flare emission mechanism. Using 100+ hours of data from a coordinated campaign between the Spitzer Space Telescope and the Chandra X-ray Observatory, we present results of the longest simultaneous IR and X-ray observations of Sgr A* taken to date. The cross-correlation between the IR and X-ray light curves in this unprecedented data set, which includes four modest X-ray/IR flares, indicates that flaring in the X-ray may lead the IR by approximately 10–20 min with 68% confidence. However, the 99.7% confidence interval on the time-lag also includes zero, i.e., the flaring remains statistically consistent with simultaneity. Long-duration and simultaneous multi-wavelength observations of additional bright flares will improve our ability to constrain the flare timing characteristics and emission mechanisms, and must be a priority for Galactic Center observing campaigns.

H. Boyce↗
NASA NTRS2022

Mid-Infrared Imaging of Supernova 1987A

At a distance of 50 kpc, Supernova 1987A is an ideal target to study how a young supernova (SN) evolves in time. Its equatorial ring, filled with material expelled from the progenitor star about 20 000 yr ago, has been engulfed with SN blast waves. Shocks heat dust grains in the ring, emitting their energy at mid-infrared (IR) wavelengths We present ground-based 10–18 μm monitoring of the ring of SN 1987A from day 6067 to 12814 at a resolution of 0.5 arcsec, together with SOFIA photometry at 10–30 μm. The IR images in the 2000’s (day 6067–7242) showed that the shocks first began brightening the east side of the ring. Later, our mid-IR images from 2017 to 2022 (day 10952–12714) show that dust emission is now fading in the east, while it has brightened on the west side of the ring. Because dust grains are heated in the shocked plasma, which can emit X-rays, the IR and X-ray brightness ratio represent shock diagnostics. Until 2007 the IR to X-ray brightness ratio remained constant over time, and during this time shocks seemed to be largely influencing the east side of the ring. However, since then, the IR to X-ray ratio has been declining, due to increased X-ray brightness. Whether the declining IR brightness is because of dust grains being destroyed or being cooled in the post-shock regions will require more detailed modelling.

Mikako Matsuura↗
DOE OSTI2023

Tracing the transient reaction kinetics of adsorbed species by in situ/operando infrared spectroscopy

The dynamic reaction behavior (i.e., transient responses) of IR-observable adsorbed species and gaseous products obtained from transient kinetic studies provide valuable kinetic and mechanistic information, namely: the abundance of active intermediates and their reactivity distribution, the chemical structure of IR-observable active and spectator species, the sequence of their formation, and the kinetically significant and rate-determining step under reaction conditions of practical catalysis. We discuss the use of transient response data to elucidate the reaction mechanisms of several gas-solid reactions: CO/H 2 , CO/H 2 /C 2 H 4 , photocatalytic oxidation of ethanol, and the CO 2 -amine reaction. The IR coupled with transient kinetic techniques is especially useful for investigating the mechanisms of photocatalytic reactions because both photogenerated electrons and many adsorbed species are IR-active (exhibiting measurable IR bands), and their evolution occurs on a time scale of seconds at ambient temperature. We highlight the key features and limitations of in situ IR with transient kinetics, as well as their significance in catalyst design.

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

Materials Data on TbIr2 by Materials Project

TbIr2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Tb is bonded in a 12-coordinate geometry to twelve equivalent Ir atoms. All Tb–Ir bond lengths are 3.15 Å. Ir is bonded to six equivalent Tb and six equivalent Ir atoms to form a mixture of corner, edge, and face-sharing IrTb6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.69 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TeIr by Materials Project

IrTe crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ir is bonded in a 6-coordinate geometry to two equivalent Ir and six equivalent Te atoms. Both Ir–Ir bond lengths are 2.83 Å. All Ir–Te bond lengths are 2.76 Å. Te is bonded in a 6-coordinate geometry to six equivalent Ir atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeIr3 by Materials Project

FeIr3 is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Fe is bonded to twelve equivalent Ir atoms to form FeIr12 cuboctahedra that share corners with twelve equivalent FeIr12 cuboctahedra, edges with twenty-four equivalent IrFe4Ir8 cuboctahedra, faces with six equivalent FeIr12 cuboctahedra, and faces with twelve equivalent IrFe4Ir8 cuboctahedra. All Fe–Ir bond lengths are 2.68 Å. Ir is bonded to four equivalent Fe and eight equivalent Ir atoms to form IrFe4Ir8 cuboctahedra that share corners with twelve equivalent IrFe4Ir8 cuboctahedra, edges with eight equivalent FeIr12 cuboctahedra, edges with sixteen equivalent IrFe4Ir8 cuboctahedra, faces with four equivalent FeIr12 cuboctahedra, and faces with fourteen equivalent IrFe4Ir8 cuboctahedra. All Ir–Ir bond lengths are 2.68 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VIr3 by Materials Project

Ir3V is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. V is bonded to twelve equivalent Ir atoms to form VIr12 cuboctahedra that share corners with twelve equivalent VIr12 cuboctahedra, edges with twenty-four equivalent IrV4Ir8 cuboctahedra, faces with six equivalent VIr12 cuboctahedra, and faces with twelve equivalent IrV4Ir8 cuboctahedra. All V–Ir bond lengths are 2.71 Å. Ir is bonded to four equivalent V and eight equivalent Ir atoms to form distorted IrV4Ir8 cuboctahedra that share corners with twelve equivalent IrV4Ir8 cuboctahedra, edges with eight equivalent VIr12 cuboctahedra, edges with sixteen equivalent IrV4Ir8 cuboctahedra, faces with four equivalent VIr12 cuboctahedra, and faces with fourteen equivalent IrV4Ir8 cuboctahedra. All Ir–Ir bond lengths are 2.71 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiIr3 by Materials Project

Ir3Ti is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ti is bonded to twelve equivalent Ir atoms to form TiIr12 cuboctahedra that share corners with twelve equivalent TiIr12 cuboctahedra, edges with twenty-four equivalent IrTi4Ir8 cuboctahedra, faces with six equivalent TiIr12 cuboctahedra, and faces with twelve equivalent IrTi4Ir8 cuboctahedra. All Ti–Ir bond lengths are 2.74 Å. Ir is bonded to four equivalent Ti and eight equivalent Ir atoms to form distorted IrTi4Ir8 cuboctahedra that share corners with twelve equivalent IrTi4Ir8 cuboctahedra, edges with eight equivalent TiIr12 cuboctahedra, edges with sixteen equivalent IrTi4Ir8 cuboctahedra, faces with four equivalent TiIr12 cuboctahedra, and faces with fourteen equivalent IrTi4Ir8 cuboctahedra. All Ir–Ir bond lengths are 2.74 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoIr by Materials Project

IrMo is beta-prime cadmium gold structured and crystallizes in the orthorhombic Pmma space group. The structure is three-dimensional. Mo is bonded to four equivalent Mo and eight equivalent Ir atoms to form MoMo4Ir8 cuboctahedra that share corners with eight equivalent IrMo8Ir4 cuboctahedra, corners with ten equivalent MoMo4Ir8 cuboctahedra, edges with six equivalent MoMo4Ir8 cuboctahedra, edges with twelve equivalent IrMo8Ir4 cuboctahedra, faces with eight equivalent IrMo8Ir4 cuboctahedra, and faces with twelve equivalent MoMo4Ir8 cuboctahedra. All Mo–Mo bond lengths are 2.78 Å. There are a spread of Mo–Ir bond distances ranging from 2.73–2.81 Å. Ir is bonded to eight equivalent Mo and four equivalent Ir atoms to form IrMo8Ir4 cuboctahedra that share corners with eight equivalent MoMo4Ir8 cuboctahedra, corners with ten equivalent IrMo8Ir4 cuboctahedra, edges with six equivalent IrMo8Ir4 cuboctahedra, edges with twelve equivalent MoMo4Ir8 cuboctahedra, faces with eight equivalent MoMo4Ir8 cuboctahedra, and faces with twelve equivalent IrMo8Ir4 cuboctahedra. There are two shorter (2.78 Å) and two longer (2.80 Å) Ir–Ir bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoIr3 by Materials Project

Ir3Mo is Magnesium-derived structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Mo is bonded to twelve equivalent Ir atoms to form MoIr12 cuboctahedra that share corners with six equivalent MoIr12 cuboctahedra, corners with twelve equivalent IrMo4Ir8 cuboctahedra, edges with eighteen equivalent IrMo4Ir8 cuboctahedra, faces with eight equivalent MoIr12 cuboctahedra, and faces with twelve equivalent IrMo4Ir8 cuboctahedra. There are six shorter (2.73 Å) and six longer (2.77 Å) Mo–Ir bond lengths. Ir is bonded to four equivalent Mo and eight equivalent Ir atoms to form IrMo4Ir8 cuboctahedra that share corners with four equivalent MoIr12 cuboctahedra, corners with fourteen equivalent IrMo4Ir8 cuboctahedra, edges with six equivalent MoIr12 cuboctahedra, edges with twelve equivalent IrMo4Ir8 cuboctahedra, faces with four equivalent MoIr12 cuboctahedra, and faces with sixteen equivalent IrMo4Ir8 cuboctahedra. There are a spread of Ir–Ir bond distances ranging from 2.73–2.78 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ThIr2 by Materials Project

ThIr2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Th is bonded in a 12-coordinate geometry to twelve equivalent Ir atoms. All Th–Ir bond lengths are 3.20 Å. Ir is bonded to six equivalent Th and six equivalent Ir atoms to form a mixture of face, edge, and corner-sharing IrTh6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.73 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrIr3 by Materials Project

Ir3Cr is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Cr is bonded to twelve equivalent Ir atoms to form CrIr12 cuboctahedra that share corners with twelve equivalent CrIr12 cuboctahedra, edges with twenty-four equivalent IrCr4Ir8 cuboctahedra, faces with six equivalent CrIr12 cuboctahedra, and faces with twelve equivalent IrCr4Ir8 cuboctahedra. All Cr–Ir bond lengths are 2.70 Å. Ir is bonded to four equivalent Cr and eight equivalent Ir atoms to form distorted IrCr4Ir8 cuboctahedra that share corners with twelve equivalent IrCr4Ir8 cuboctahedra, edges with eight equivalent CrIr12 cuboctahedra, edges with sixteen equivalent IrCr4Ir8 cuboctahedra, faces with four equivalent CrIr12 cuboctahedra, and faces with fourteen equivalent IrCr4Ir8 cuboctahedra. All Ir–Ir bond lengths are 2.70 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeGe3Ir by Materials Project

CeIrGe3 crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. Ce is bonded in a 12-coordinate geometry to five equivalent Ir and twelve Ge atoms. There are one shorter (3.41 Å) and four longer (3.54 Å) Ce–Ir bond lengths. There are eight shorter (3.23 Å) and four longer (3.49 Å) Ce–Ge bond lengths. Ir is bonded in a 5-coordinate geometry to five equivalent Ce and five Ge atoms. There are one shorter (2.41 Å) and four longer (2.45 Å) Ir–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 2-coordinate geometry to four equivalent Ce, two equivalent Ir, and two equivalent Ge atoms. Both Ge–Ge bond lengths are 2.73 Å. In the second Ge site, Ge is bonded in a 1-coordinate geometry to four equivalent Ce, one Ir, and four equivalent Ge atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbIr3 by Materials Project

Ir3Nb is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Nb is bonded to twelve equivalent Ir atoms to form NbIr12 cuboctahedra that share corners with twelve equivalent NbIr12 cuboctahedra, edges with twenty-four equivalent IrNb4Ir8 cuboctahedra, faces with six equivalent NbIr12 cuboctahedra, and faces with twelve equivalent IrNb4Ir8 cuboctahedra. All Nb–Ir bond lengths are 2.78 Å. Ir is bonded to four equivalent Nb and eight equivalent Ir atoms to form distorted IrNb4Ir8 cuboctahedra that share corners with twelve equivalent IrNb4Ir8 cuboctahedra, edges with eight equivalent NbIr12 cuboctahedra, edges with sixteen equivalent IrNb4Ir8 cuboctahedra, faces with four equivalent NbIr12 cuboctahedra, and faces with fourteen equivalent IrNb4Ir8 cuboctahedra. All Ir–Ir bond lengths are 2.78 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on DyIr2 by Materials Project

DyIr2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Dy is bonded in a 12-coordinate geometry to twelve equivalent Ir atoms. All Dy–Ir bond lengths are 3.14 Å. Ir is bonded to six equivalent Dy and six equivalent Ir atoms to form a mixture of edge, face, and corner-sharing IrDy6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.68 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaIr2 by Materials Project

LaIr2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. La is bonded in a 12-coordinate geometry to twelve equivalent Ir atoms. All La–Ir bond lengths are 3.21 Å. Ir is bonded to six equivalent La and six equivalent Ir atoms to form a mixture of face, edge, and corner-sharing IrLa6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.74 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ErIr2 by Materials Project

ErIr2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Er is bonded in a 12-coordinate geometry to twelve equivalent Ir atoms. All Er–Ir bond lengths are 3.13 Å. Ir is bonded to six equivalent Er and six equivalent Ir atoms to form a mixture of corner, edge, and face-sharing IrEr6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.67 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on YbIr2 by Materials Project

YbIr2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Yb is bonded in a 12-coordinate geometry to twelve equivalent Ir atoms. All Yb–Ir bond lengths are 3.12 Å. Ir is bonded to six equivalent Yb and six equivalent Ir atoms to form a mixture of edge, face, and corner-sharing IrYb6Ir6 cuboctahedra. All Ir–Ir bond lengths are 2.66 Å.

36 MATERIALS SCIENCE↗