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8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on IrC4 by Materials Project

IrC4 crystallizes in the trigonal P3_121 space group. The structure is three-dimensional. Ir4+ is bonded in a 8-coordinate geometry to eight C1- atoms. There are a spread of Ir–C bond distances ranging from 2.11–2.27 Å. There are three inequivalent C1- sites. In the first C1- site, C1- is bonded to two equivalent Ir4+ and two C1- atoms to form a mixture of corner and edge-sharing CIr2C2 tetrahedra. There is one shorter (1.50 Å) and one longer (1.51 Å) C–C bond length. In the second C1- site, C1- is bonded to two equivalent Ir4+ and two equivalent C1- atoms to form a mixture of distorted corner and edge-sharing CIr2C2 tetrahedra. In the third C1- site, C1- is bonded to two equivalent Ir4+ and two equivalent C1- atoms to form a mixture of corner and edge-sharing CIr2C2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on IrC4 by Materials Project

IrC4 is lead oxide-like structured and crystallizes in the orthorhombic Ccce space group. The structure is three-dimensional. Ir4+ is bonded in a distorted rectangular see-saw-like geometry to four equivalent C1- atoms. All Ir–C bond lengths are 2.19 Å. C1- is bonded to one Ir4+ and three equivalent C1- atoms to form distorted corner-sharing CIrC3 tetrahedra. There is one shorter (1.42 Å) and two longer (1.47 Å) C–C bond length.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on IrC4 by Materials Project

IrC4 is Hausmannite-like structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ir4+ is bonded to six C1- atoms to form distorted IrC6 octahedra that share corners with four equivalent IrC6 octahedra and corners with fourteen CIr2C2 tetrahedra. The corner-sharing octahedral tilt angles are 75°. There are a spread of Ir–C bond distances ranging from 2.08–2.46 Å. There are two inequivalent C1- sites. In the first C1- site, C1- is bonded to two equivalent Ir4+ and two equivalent C1- atoms to form CIr2C2 tetrahedra that share corners with two equivalent IrC6 octahedra and corners with fourteen CIr2C2 tetrahedra. The corner-sharing octahedra tilt angles range from 79–83°. There is one shorter (1.47 Å) and one longer (1.48 Å) C–C bond length. In the second C1- site, C1- is bonded to one Ir4+ and three C1- atoms to form CIrC3 tetrahedra that share corners with five equivalent IrC6 octahedra and corners with nine CIr2C2 tetrahedra. The corner-sharing octahedra tilt angles range from 59–77°. The C–C bond length is 1.46 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on IrC4 by Materials Project

IrC4 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Ir4+ is bonded in a 1-coordinate geometry to sixteen equivalent C1- atoms. All Ir–C bond lengths are 2.88 Å. C1- is bonded in a 3-coordinate geometry to four equivalent Ir4+ and three equivalent C1- atoms. There is one shorter (1.39 Å) and two longer (1.45 Å) C–C bond length.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on IrC4 by Materials Project

IrC(C)3 crystallizes in the orthorhombic Cmcm space group. The structure is two-dimensional and consists of two C sheets oriented in the (0, 0, 1) direction and two IrC sheets oriented in the (0, 0, 1) direction. In each C sheet, C1- is bonded in a trigonal planar geometry to three equivalent C1- atoms. All C–C bond lengths are 1.41 Å. In each IrC sheet, there are two inequivalent Ir4+ sites. In the first Ir4+ site, Ir4+ is bonded in a distorted hexagonal planar geometry to six equivalent C1- atoms. There are four shorter (2.53 Å) and two longer (2.56 Å) Ir–C bond lengths. In the second Ir4+ site, Ir4+ is bonded in a distorted hexagonal planar geometry to six equivalent C1- atoms. There are two shorter (2.53 Å) and four longer (2.54 Å) Ir–C bond lengths. C1- is bonded in a distorted single-bond geometry to six Ir4+ and one C1- atom. The C–C bond length is 1.34 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on IrC by Materials Project

IrC is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Ir4+ is bonded to four equivalent C4- atoms to form corner-sharing IrC4 tetrahedra. All Ir–C bond lengths are 2.01 Å. C4- is bonded to four equivalent Ir4+ atoms to form corner-sharing CIr4 tetrahedra.

36 MATERIALS SCIENCE↗
NASA NTRS1998

NICMOS Narrow-band Images of OMC-1

We present images of a 90in. x 90in. field centered on BN in OMC-1, taken with the Near-Infrared Camera and MultiObject Spectrograph (NICMOS) aboard the Hubble Space Telescope. The observed lines are H2 1-0 S(l), Pa, [FeII] 1.64 pm, and the adjacent continua. The region is rich in interesting structures. The most remarkable are the streamers or "fingers" of H2 emission which extend from 15in. to 50in. from IRc2, seen here in unprecedented detail. Unlike the northern H2 fingers, the inner fingers do not exhibit significant [FeII] emission at theirdips, which we suggest is due to lower excitation. These observations also show that the general morphology of the Pa and [FeII] emission (both imaged for the first time in this region) bears a striking resemblance to that of the Ha and [SII] emission previously observed with WFPC2. This implies that these IR and optical lines are produced by radiative excitation on the surface of the molecular cloud. The Pa morphology of HH 202 is also very similar to its H a and [OIII] emission, again suggesting that the Pa in this object is photo-excited by the Trapezium, as has been suggested for the optical emission. We find evidence of shock-excited [FeII] in HH 208, where it again closely follows the morphology of [SII]. There is also H2 coincident with the [SII] and [FeII] emission, which may be associated with HH 208. Finally, we note some interesting continuum features: diffuse "tails" trailing from IRc3 and IRc4, more extensive observations of the "crescent" found by Stolovy, et al. (1998), and new observations of a similar oval object nearby. We also find a "V"-shaped region which may be the boundary of a cavity being cleared by IRc2.

Schultz, Angela S. B.↗
NASA NTRS2006

Hubble Space Telescope NICMOS Polarization Measurements of OMC-1

We present 2 micrometer polarization measurements of positions in the BN region of the Orion Molecular Cloud (OMC-1) made with NICMOS Camera 2 (0.2" resolution) on Hubble Space Telescope. Our goals are to seek the sources of heating for IRc2, 3, 4, and 7, identify possible young stellar objects (YSOs), and characterize the grain alignment in the dust clouds along the lines-of-sight to the stars. Our results are as follows: BN is approximately 29% polarized by dichroic absorption and appears to be the illuminating source for most of the nebulosity to its north and up to approximately 5" to its south. Although the stars are probably all polarized by dichroic absorption, there are a number of compact, but non-point-source, objects that could be polarized by a combination of both dichroic absorption and local scattering of star light. We identify several candidate YSOs, including an approximately edge-on bipolar YSO 8.7" east of BN, and a deeply-embedded IRc7, all of which are obviously self-luminous at mid-infrared wavelengths and may be YSOs. None of these is a reflection nebula illuminated by a star located near radio source I, as was previously suggested. Other IRc sources are clearly reflection nebulae: IRc3 appears to be illuminated by IRc2-B or a combination of the IRc2 sources, and IRc4 and IRc5 appear to be illuminated by an unseen star in the vicinity of radio source I, or by Star n or IRc2-A. Trends in the magnetic field direction are inferred from the polarization of the 26 stars that are bright enough to be seen as NICMOS point sources. Their polarization ranges from N less than or equal to 1% (all stars with this low polarization are optically visible) to greater than 40%. The most polarized star has a polarization position angle different from its neighbors by approximately 40 degrees, but in agreement with the grain alignment inferred from millimeter polarization measurements of the cold dust cloud in the southern part of OMC-1. The polarization position angle of another highly-polarized, probable star also requires a grain alignment and magnetic field orientation substantially different from the general magnetic field orientation of OMC-1.

Simpson, Janet P.↗