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DOE OSTI2020

Materials Data on US2 by Materials Project

US2 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are two inequivalent U4+ sites. In the first U4+ site, U4+ is bonded in a 9-coordinate geometry to nine S2- atoms. There are three shorter (2.73 Å) and six longer (2.95 Å) U–S bond lengths. In the second U4+ site, U4+ is bonded in a 9-coordinate geometry to nine S2- atoms. There are six shorter (2.71 Å) and three longer (2.96 Å) U–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to five U4+ atoms. In the second S2- site, S2- is bonded to four U4+ atoms to form a mixture of distorted corner and edge-sharing SU4 tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on US2 by Materials Project

US2 is Cotunnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. U4+ is bonded in a 9-coordinate geometry to nine S2- atoms. There are a spread of U–S bond distances ranging from 2.71–3.12 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to four equivalent U4+ atoms to form a mixture of distorted edge and corner-sharing SU4 tetrahedra. In the second S2- site, S2- is bonded in a 5-coordinate geometry to five equivalent U4+ atoms.

36 MATERIALS SCIENCE↗

NASA NTRS1987

Coordinated ultraviolet and radio observations of selected nearby stars

All of the US2 shifts assigned were successfully completed with simultaneous International Ultraviolet Explorer (IUE) and the Very Large Array (VLA) observations of the proposed target stars. The target stars included dwarf M flare stars and RS CVn stars. The combined ultraviolet (IUE) and microwave (VLA) observations have provided important new insights to the radiation mechanisms at these two widely-separated regions of the electromagnetic spectrum. The VLA results included the discovery of narrow-band microwave radiation and rapid time variations in the microwave radiation of dwarf M flare stars. The results indicate that conventional radiation mechanisms cannot explain the microwave emission from these stars. In general, ultraviolet variations and bursts occur when no similar variations are detected at microwave wavelengths and vice versa. Although these is some overlap, the variations in these two spectral regions are usually uncorrelated, suggesting that there is little interaction between the activity centers at the two associated atmospheric levels.

Lang, Kenneth R.↗

NASA NTRS1988

Ultraviolet observations of selected astronomical sources

The results of the 9th and 10th IUE episode programs listed are summarized. Observations and basic data reductions were completed for 4 extragalactic programs which were allocated a total of 9 US1 shifts, and 2 stellar investigations which used 10 US2 shifts. Use was made of the Goddard RDAF to obtain better signal to noise ratio spectra using the Gaussian extraction routines. Highlights include the first IUE observations of H1821+643, the second brightest quasar in the sky, and the discovery of accretion disk emission line profiles in the elliptical Seyfert galaxy Arp 102B. Both of these observations were accompanied by nearly simultaneous optical spectrophotometry. As a result of the stellar programs, large amplitude variability associated with the rotation period of the Ap stars 78 Vir and 53 Cam was found.

Halpern, Jules P.↗