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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on HoF3 by Materials Project

HoF3 is Cementite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ho3+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of Ho–F bond distances ranging from 2.30–2.55 Å. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted trigonal planar geometry to three equivalent Ho3+ atoms. In the second F1- site, F1- is bonded in a 3-coordinate geometry to three equivalent Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Tunable Ferromagnetism in LaCoO 3 Epitaxial Thin Films

We report ferromagnetic insulators play a crucial role in the development of low-dissipation quantum magnetic devices for spintronics. Epitaxial LaCoO 3 thin film is a prominent ferromagnetic insulator, in which the robust ferromagnetic ordering emerges owing to epitaxial strain. Whereas it is evident that strong spin-lattice coupling induces ferromagnetism, the reported ferromagnetic properties of epitaxially strained LaCoO 3 thin films are highly consistent. For example, even under largely modulated degree of strain, the reported Curie temperatures of epitaxially strained LaCoO 3 thin films lie in a narrow range of 80–85 K, without much deviation. In this study, substantial enhancement (≈18%) in the Curie temperature of epitaxial LaCoO 3 thin films is demonstrated via crystallographic orientation dependence. By changing the crystallographic orientation of the films from (111) to (110), the crystal-field energy is reduced and the charge transfer between the Co and O orbitals is enhanced. These modifications lead to a considerable enhancement of the ferromagnetic properties (including the Curie temperature and magnetization), despite the identical nominal degree of epitaxial strain. The findings of this study provide insights into facile tunability of ferromagnetic properties via structural symmetry control in LaCoO 3 .

36 MATERIALS SCIENCE↗
NASA NTRS1992

Venus lower thermosphere studies

Studies undertaken in this project have sought to understand lower thermospheric structure and dynamics (less than or equal to 145 km), particularly the processes responsible. This is a region just below the reach of in-situ instruments onboard PVO (Pioneer Venus Orbiter) during the first few diurnal cycles. PVO remote airglow observations (nitric oxide, O2, visible, O 1304A) have been coupled with ground-based observations (CO densities, winds, temperatures, O2 IR nightglow) to address the behavior of lower thermospheric winds and chemistry over 95 to 150 km. This interpretation of PVO and related data is accomplished by using the NCAR Venus thermospheric general circulation model (VTGCM) (Bougher et al., 1988; 1990). This model has been modified over the last two years to improve its ability to calculate O, CO, and O2 densities, temperatures, nightglow, and subsolar-to-antisolar and zonal winds over 95 to 150 km (Bougher and Borucki, 1992). Our VTGCM studies show that: (1) O2 visible and IR nightglow distributions can be used to trace lower thermosphere / upper mesosphere winds over 100-130 km. Typically, weak zonal winds (less than or equal to 25 m/sec) and nightglow maximum patches near 0100 LT prevail. Occasionally, strong zonal winds (30-60 m/sec) and airglow patches peaking near 0300 LT characterize the Venus lower thermosphere. (2) It is clear that the dynamics of the Venus 90-130 km region is highly variable on time scales as short as an hour. This is most likely due to the time variable nature of upward propagating gravity waves, which grow in amplitude and eventually break. The resulting turbulence gives rise to local time variable eddy diffusion and momentum drag, both of which strongly impact global density and nightglow distributions. (3) The oxygen chemistry (O, O2, etc.) over 90-120 km is strongly dependent on HO(x) and CLO(x) tracer species that must be properly included in any coupled chemical dynamical model. (4) The density profiles of light species (O, CO, N, He) are strongly affected by large-scale transport by the winds. Strong eddy diffusion is not a suitable model parameterization for approximating these light species, especially for extrapolation into the region below 140 km where PVO in-situ data is lacking. Instead, the fully coupled chemical dynamical VTGCM model should be used to improve estimates of densities within the VTS3 empirical model (Hedin et al., 1983) below 140 km.

Bougher, Stephen W.↗
NASA NTRS1994

The radical amplifier

The radical amplifier as a method for measuring radical concentrations in the atmosphere has received renewed attention lately. In principle, it can measure the total concentration of HO(x) and RO(x) radicals by reacting ambient air with high concentrations of CO (3-10 percent) and NO (2-6 ppmv), and measuring the NO2 produced.

Hastie, D. R.↗
NASA NTRS2004

TRACE-P OH and HO2 Measurements with the Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) on the DC-8

The Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) measures OH and HO2 from the NASA DC-8. This instrument detects OH by laser induced fluorescence (LIF) in detection chambers at low pressure and detects HO2 by chemical conversion with NO followed by LIF detection. The demonstrated detection limit (S/N=2, 5 min.) for OH is about 0.005 pptv (1x10(exp 6)/cu cm at 2 km altitude) and for HO2 is 0.05 pptv (1x10(exp 6)/cu cm at 2 km altitude). We will use ATHOS to measure OH, HO2, and HO2/OH during TRACE- P, analyze these results by comparing them against fundamental relationships and computer models, and publish the analyses. TRACE-P HO(x), measurements will help develop a clearer picture of the atmospheric oxidation and 0 3 production that occur as Asian pollution spreads across the Pacific Ocean.

Brune, William H.↗
DOE OSTI2020

Materials Data on Ho11Te16ClO48 by Materials Project

Ho11Te16O48Cl crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are six inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.23–2.54 Å. In the second Ho3+ site, Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.22–2.75 Å. In the third Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.25–2.57 Å. In the fourth Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.25–2.54 Å. In the fifth Ho3+ site, Ho3+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of Ho–O bond distances ranging from 2.22–2.37 Å. In the sixth Ho3+ site, Ho3+ is bonded in a distorted pentagonal bipyramidal geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.24–2.45 Å. There are eight inequivalent Te4+ sites. In the first Te4+ site, Te4+ is bonded in a 3-coordinate geometry to three O2- atoms. There are a spread of Te–O bond distances ranging from 1.90–1.97 Å. In the second Te4+ site, Te4+ is bonded in a distorted T-shaped geometry to three O2- atoms. There are a spread of Te–O bond distances ranging from 1.88–1.95 Å. In the third Te4+ site, Te4+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Te–O bond distances ranging from 1.89–2.62 Å. In the fourth Te4+ site, Te4+ is bonded in a 5-coordinate geometry to four O2- and one Cl1- atom. There are a spread of Te–O bond distances ranging from 1.92–2.37 Å. The Te–Cl bond length is 2.89 Å. In the fifth Te4+ site, Te4+ is bonded in a 3-coordinate geometry to three O2- atoms. All Te–O bond lengths are 1.91 Å. In the sixth Te4+ site, Te4+ is bonded in a 3-coordinate geometry to three O2- atoms. There is two shorter (1.91 Å) and one longer (1.93 Å) Te–O bond length. In the seventh Te4+ site, Te4+ is bonded in a 3-coordinate geometry to three O2- atoms. There are a spread of Te–O bond distances ranging from 1.90–1.93 Å. In the eighth Te4+ site, Te4+ is bonded in a see-saw-like geometry to four O2- atoms. There are a spread of Te–O bond distances ranging from 1.89–2.18 Å. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ho3+ and two Te4+ atoms. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and one Te4+ atom. In the third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ho3+ and one Te4+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ho3+ and one Te4+ atom. In the fifth O2- site, O2- is bonded in a trigonal planar geometry to two Ho3+ and one Te4+ atom. In the sixth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ho3+ and one Te4+ atom. In the seventh O2- site, O2- is bonded in a trigonal planar geometry to two Ho3+ and one Te4+ atom. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to two Ho3+ and two Te4+ atoms. In the ninth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Te4+ atom. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to two Ho3+ and one Te4+ atom. In the eleventh O2- site, O2- is bonded in a 1-coordinate geometry to two Ho3+ and one Te4+ atom. In the twelfth O2- site, O2- is bonded in a distorted water-like geometry to two Te4+ atoms. In the thirteenth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Te4+ atom. In the fourteenth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Te4+ atom. In the fifteenth O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and one Te4+ atom. In the sixteenth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ho3+ and one Te4+ atom. In the seventeenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and one Te4+ atom. In the eighteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and one Te4+ atom. In the nineteenth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Te4+ atom. In the twentieth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Te4+ atom. In the twenty-first O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ho3+ and one Te4+ atom. In the twenty-second O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Te4+ atom. In the twenty-third O2- site, O2- is bonded in a 2-coordinate geometry to one Ho3+ and one Te4+ atom. In the twenty-fourth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Te4+ atom. Cl1- is bonded in a linear geometry to two equivalent Te4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2(SO4)3 by Materials Project

Ho2(SO4)3 crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Ho3+ is bonded to six O2- atoms to form HoO6 octahedra that share corners with six SO4 tetrahedra. There are a spread of Ho–O bond distances ranging from 2.22–2.25 Å. There are two inequivalent S6+ sites. In the first S6+ site, S6+ is bonded to four O2- atoms to form SO4 tetrahedra that share corners with four equivalent HoO6 octahedra. The corner-sharing octahedra tilt angles range from 15–26°. All S–O bond lengths are 1.48 Å. In the second S6+ site, S6+ is bonded to four O2- atoms to form SO4 tetrahedra that share corners with four equivalent HoO6 octahedra. The corner-sharing octahedra tilt angles range from 3–35°. All S–O bond lengths are 1.48 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to one Ho3+ and one S6+ atom. In the second O2- site, O2- is bonded in a distorted linear geometry to one Ho3+ and one S6+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and one S6+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and one S6+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and one S6+ atom. In the sixth O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and one S6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2(SeO3)3 by Materials Project

Ho2(SeO3)3 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a pentagonal bipyramidal geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.21–2.46 Å. In the second Ho3+ site, Ho3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ho–O bond distances ranging from 2.27–2.61 Å. There are three inequivalent Se4+ sites. In the first Se4+ site, Se4+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There are a spread of Se–O bond distances ranging from 1.69–1.76 Å. In the second Se4+ site, Se4+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There is one shorter (1.71 Å) and two longer (1.75 Å) Se–O bond length. In the third Se4+ site, Se4+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There is one shorter (1.70 Å) and two longer (1.74 Å) Se–O bond length. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and one Se4+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Ho3+ and one Se4+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Se4+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ho3+ and one Se4+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Se4+ atom. In the sixth O2- site, O2- is bonded in a 2-coordinate geometry to two Ho3+ and one Se4+ atom. In the seventh O2- site, O2- is bonded in a bent 120 degrees geometry to one Ho3+ and one Se4+ atom. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to two Ho3+ and one Se4+ atom. In the ninth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Ho3+ and one Se4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Low- and intermediate-temperature oxidation of dimethyl ether up to 100 atm in a supercritical pressure jet-stirred reactor

Understanding the low- and intermediate-temperature oxidation chemistry of oxygenated fuels like dimethyl ether (DME) at high pressure is paramount to the development of advanced engines with low carbon emissions. The supercritical pressure jet-stirred reactor (SP-JSR) recently developed at Princeton provides a new platform for conducting kinetic studies at low and intermediate temperatures at extremely high pressures with a uniform temperature distribution and a short flow residence time. This paper uses the SP-JSR to investigate DME oxidation at equivalence ratios of 0.175, 1.0, and 1.72, for pressures of 10 and 100 atm, and temperatures ranging from 400 to 900 K. The results demonstrate weakened NTC behavior at 100 atm relative to 10 atm due to increased flux through QOOH + O 2 = O 2 QOOH relative to QOOH = 2 CH 2 O + OH at 100 atm. Furthermore, the intermediate-temperature oxidation window is shifted to lower temperatures at 100 atm. The experimental data are compared with several chemical kinetic models from the literature. The existing models are seen to agree quite well with the experimental data at 10 atm. However, the models fail to properly capture the NTC behavior at 100 atm. Reaction pathway analyses indicate that both the low- and intermediate-temperature chemistries are controlled by RO 2 consumption pathways. The reaction rates for several of the important reactions, such as DME + OH = CH 3 OCH 2 + H 2 O, H 2 O 2 (+M) = 2 OH (+M), and 2 HO 2 = 2 OH + O 2 are updated in this work. Furthermore, the updated model improves the predictability for all key species compared to the original model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Ab initio description of bcc iron with correlation matrix renormalization theory

We applied the ab initio spin-polarized correlation matrix renormalization theory to the ferromagnetic state of the bulk bcc iron. We showed that it was capable of reproducing the equilibrium physical properties and the pressure-volume curve in good comparison with experiments. We then focused on the analysis of its local electronic correlations. By exploiting different local fluctuation-related physical quantities as measures of electronic correlation within target orbits, we elucidated the different roles of t 2g and e g states in both spin channels and presented compelling evidence to showcase this distinction in their electronic correlation.

3-dimensional systems↗
DOE OSTI2020

Crystal structures and comparisons of potassium rare-earth molybdates KRE(MoO 4 ) 2 (RE = Tb, Dy, Ho, Er, Yb, and Lu)

Six potassium rare-earth molybdates KRE(MoO 4 ) 2 (RE = Tb, Dy, Ho, Er, Yb, and Lu) were synthesized by flux-assisted growth in K 2 Mo 3 O 10 . The crystal structures were determined using single-crystal X-ray diffraction data. The synthesized molybdates crystallize with the orthorhombic Pbcn space group (No. 60). Trendlines for unit-cell parameters were calculated using data from the current study. The unit-cell parameters a and c increase linearly whereas b decreases with larger RE cations, based on crystal radii. The unit-cell volumes increase linearly and the densities decrease linearly with larger RE cations. The average distances between the RE cations and the nearest O atoms increase with larger cations whereas the average distances of Mo—O and K—O do not show specific trends.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho8Sb3O8 by Materials Project

Ho8Sb3O8 crystallizes in the monoclinic C2 space group. The structure is three-dimensional. there are four inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded in a 3-coordinate geometry to four Sb+2.67- and three O2- atoms. There are a spread of Ho–Sb bond distances ranging from 3.26–3.46 Å. There are a spread of Ho–O bond distances ranging from 2.21–2.23 Å. In the second Ho3+ site, Ho3+ is bonded in a distorted see-saw-like geometry to two equivalent Sb+2.67- and four O2- atoms. Both Ho–Sb bond lengths are 3.21 Å. There are a spread of Ho–O bond distances ranging from 2.22–2.43 Å. In the third Ho3+ site, Ho3+ is bonded in a distorted see-saw-like geometry to two equivalent Sb+2.67- and four O2- atoms. Both Ho–Sb bond lengths are 3.25 Å. There are three shorter (2.21 Å) and one longer (2.31 Å) Ho–O bond lengths. In the fourth Ho3+ site, Ho3+ is bonded in a 4-coordinate geometry to four Sb+2.67- and four O2- atoms. There are a spread of Ho–Sb bond distances ranging from 3.30–3.50 Å. There are a spread of Ho–O bond distances ranging from 2.20–2.32 Å. There are two inequivalent Sb+2.67- sites. In the first Sb+2.67- site, Sb+2.67- is bonded in a body-centered cubic geometry to eight Ho3+ atoms. In the second Sb+2.67- site, Sb+2.67- is bonded in a body-centered cubic geometry to eight Ho3+ atoms. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to four Ho3+ atoms to form a mixture of edge and corner-sharing OHo4 tetrahedra. In the second O2- site, O2- is bonded to four Ho3+ atoms to form a mixture of edge and corner-sharing OHo4 tetrahedra. In the third O2- site, O2- is bonded to four Ho3+ atoms to form a mixture of edge and corner-sharing OHo4 trigonal pyramids. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Ho3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho4MgS7 by Materials Project

MgHo4S7 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. Mg2+ is bonded to six S2- atoms to form MgS6 octahedra that share corners with three HoS6 octahedra, corners with six HoS7 pentagonal bipyramids, edges with two equivalent MgS6 octahedra, edges with three equivalent HoS6 octahedra, and an edgeedge with one HoS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 3–55°. There are a spread of Mg–S bond distances ranging from 2.55–2.69 Å. There are four inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to seven S2- atoms to form distorted HoS7 pentagonal bipyramids that share corners with four equivalent MgS6 octahedra, corners with four HoS6 octahedra, an edgeedge with one MgS6 octahedra, edges with three equivalent HoS6 octahedra, edges with two equivalent HoS7 pentagonal bipyramids, and faces with two equivalent HoS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 19–74°. There are a spread of Ho–S bond distances ranging from 2.70–3.06 Å. In the second Ho3+ site, Ho3+ is bonded to seven S2- atoms to form distorted HoS7 pentagonal bipyramids that share corners with two equivalent MgS6 octahedra, corners with six HoS6 octahedra, edges with four HoS6 octahedra, edges with two equivalent HoS7 pentagonal bipyramids, and faces with two equivalent HoS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 22–68°. There are a spread of Ho–S bond distances ranging from 2.69–2.98 Å. In the third Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share a cornercorner with one MgS6 octahedra, a cornercorner with one HoS6 octahedra, corners with four HoS7 pentagonal bipyramids, edges with two equivalent HoS6 octahedra, and edges with six HoS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 53–55°. There are a spread of Ho–S bond distances ranging from 2.65–2.72 Å. In the fourth Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share a cornercorner with one HoS6 octahedra, corners with two equivalent MgS6 octahedra, corners with six HoS7 pentagonal bipyramids, edges with two equivalent HoS6 octahedra, edges with three equivalent MgS6 octahedra, and an edgeedge with one HoS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 3–53°. There are a spread of Ho–S bond distances ranging from 2.66–2.77 Å. There are seven inequivalent S2- sites. In the first S2- site, S2- is bonded to one Mg2+ and four Ho3+ atoms to form distorted SHo4Mg trigonal bipyramids that share corners with five SHo3Mg tetrahedra, corners with four SHo5 trigonal bipyramids, an edgeedge with one SHo4 tetrahedra, and edges with five SHo4Mg trigonal bipyramids. In the second S2- site, S2- is bonded to two equivalent Mg2+ and three Ho3+ atoms to form distorted SHo3Mg2 trigonal bipyramids that share corners with five SHo3Mg tetrahedra, corners with four SHo5 trigonal bipyramids, an edgeedge with one SHo3Mg tetrahedra, and edges with five SHo4Mg trigonal bipyramids. In the third S2- site, S2- is bonded to five Ho3+ atoms to form distorted SHo5 trigonal bipyramids that share corners with four equivalent SHo3Mg tetrahedra, corners with six SHo4Mg trigonal bipyramids, edges with three SHo3Mg tetrahedra, and edges with six SHo3Mg2 trigonal bipyramids. In the fourth S2- site, S2- is bonded to five Ho3+ atoms to form distorted SHo5 trigonal bipyramids that share corners with four equivalent SHo4 tetrahedra, corners with six SHo4Mg trigonal bipyramids, edges with three SHo3Mg tetrahedra, and edges with six SHo4Mg trigonal bipyramids. In the fifth S2- site, S2- is bonded to one Mg2+ and three Ho3+ atoms to form distorted SHo3Mg tetrahedra that share corners with three SHo3Mg tetrahedra, corners with nine SHo4Mg trigonal bipyramids, and edges with four SHo3Mg2 trigonal bipyramids. In the sixth S2- site, S2- is bonded to four Ho3+ atoms to form distorted SHo4 tetrahedra that share corners with three SHo3Mg tetrahedra, corners with nine SHo4Mg trigonal bipyramids, and edges with four SHo4Mg trigonal bipyramids. In the seventh S2- site, S2- is bonded in a rectangular see-saw-like geometry to two equivalent Mg2+ and two equivalent Ho3+ atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1972

The reaction of OH with NO2

NO2 was photolyzed with 2288A radiation at 300 and 423 K in the presence of H2O, CO, and in some cases excess He. The photolysis produces O(1D) atoms which react with H2O to give HO radicals or are deactivated by CO to O(3P) atoms. The ratio k sub 5/k sub 3 is temperature dependent, being 0.33 at 300 K and 0.60 at 423 K. From these two points the Arrhenius expression is estimated to be k sub 5/k sub 3 = 2.6 exp(-1200/RT) where R is in calories/mole - K. The OH radical is either removed by NO2 or reacts with CO.

Simonaitis, R.↗
NASA NTRS1994

(abstract) Odd Hydrogen in the Atmospheres of Earth and Mars

The Martian atmosphere has many features in common with the terrestrial mesosphere. Both share similar pressure and temperature ranges, and much of the same chemistry operates in each. For example, the radical species H, OH, and H(sub 2)O, which comprise the odd hydrogen family, are of central importance in the catalytic destruction of CO and O(sub 3) in both atmospheres. The inclusion of recent chemical kinetics data, specifically temperature dependent CO(sub 2) absorption cross-sections, into our one dimensional photochemical model of the Martial atmosphere shows that oxidation of CO by odd hydrogen is too efficient. The incorporation of smaller cross sections for CO(sub 2) leads to an enhanced photolysis rate of water vapor, increasing odd hydrogen to the point where the predicted mixing ratio of CO in our model is substantially less than the observed value of 6.5 x 10(sup -4). Interestingly, most photochemical models of the terrestrial mesosphere underestimate the CO and O(sub 3) densities using currently accepted photodissociation and kinetic rate coefficients. This has also been attributed to an overabundance of odd hydrogen in the models. We shall show that agreement between models and observations of CO in the Martian atmosphere as well as of CO and O(sub 3) in the terrestrial mesosphere can be achieved by revising the rate constants for the reactions OH + HO(sub 2) and CO + OH within their published uncertainties. The fact that similar revisions alleviate discrepancies in both the terrestrial and Martian atmospheres warrants a re-evaluation of these key rate constants at the appropriate temperatures and pressures.

dioxide ozone odd hydrogen family pressure tempera↗