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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Time-resolved measurements of HO 2 radical in a heated plasma flow reactor

Time-resolved, absolute HO 2 number density in diluted H 2 –O 2 –Ar, CH 4 –O 2 -Ar, and C 2 H 4 –O 2 –Ar mixtures excited by a repetitive ns pulse discharge in a heated plasma flow reactor is measured by Cavity Ringdown Spectroscopy (CRDS). The experimental results are obtained at $\textit{T}$ = 300-600 K and $\textit{P}$ = 130 Torr, both during the discharge pulse burst and in the afterglow. In this work, the HO 2 number density is inferred from the CRDS data using a spectral model exhibiting good agreement with previous measurements of absolute HO 2 absorption cross sections. In the room-temperature H 2 –O 2 mixture, as well as in CH 4 –O 2 and C 2 H 4 –O 2 mixtures over the entire temperature range studied, HO2 is generated only during the discharge burst and decays in the afterglow. However, in the H 2 –O 2 mixture at elevated temperatures, $\textit{T}$ = 400-600 K, HO 2 persists in the afterglow up to 10 ms after the discharge burst, comparable with the flow residence time in the reactor. Comparison with kinetic modeling shows that the sustained reactivity after the source of radicals is turned off is due to a chain propagation / hydrogen oxidation process, which dominates the radical recombination reactions. The kinetic modeling predictions are in good agreement with the relative HO 2 number density measured in all three mixtures, although the model underpredicts the absolute number densities in H 2 –O 2 at $\textit{T}$ = 400-600 K by up to a factor of two. Detection of the sustained low-temperature reactivity in H 2 –O 2 , initiated by the radical generation in the plasma, suggests that the plasma excitation may also affect kinetics of oxidation and reforming of fuels exhibiting low-temperature chemistry below hot ignition point.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Local site behavior of the 5$d$ and 4$f$ ions in the frustrated pyrochlore Ho 2 Os 2 O 7

The pyrochlore osmate Ho 2 Os 2 O 7 is a candidate material for a fragile J=0 local singlet ground state, however little is known regarding the single-ion behavior of either the Os or Ho ions. To address this we present polarized neutron powder diffraction (PNPD) and resonant inelastic x-ray scattering (RIXS) measurements that separately probe the local site behavior of the Os and Ho ions. The PNPD results are dominated by Ho 3+ scattering and the analysis reveals local site susceptibility behavior consistent with spin ice materials. Complimentary unpolarized neutron powder diffraction show an ordered spin ice ground state in an applied magnetic field. To isolate the Os 4+ single-ion behavior we present resonant inelastic x-ray scattering (RIXS) measurements at the osmium L-edge. Analysis of the RIXS spectra parameterize the spin-orbit coupling (0.35 eV), Hund’s coupling (0.27 eV) and trigonal distortion (-0.17 eV). Here, the results are considered within the context of a J=0 model and possible departures from this through structural distortions, excitonic interactions and 5d-4f interactions between the Os ion and the surrounding Ho lattice. The experimental methodology employed highlights the complimentary information available in rare earth based 5d pyrochlores from distinct neutron and x-ray scattering techniques that allow for the isolation and determination of the behavior of the different ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Materials Data on Ho(MnSn)6 by Materials Project

HoMn6Sn6 crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. Ho is bonded to eight Sn atoms to form distorted edge-sharing HoSn8 hexagonal bipyramids. There are two shorter (3.00 Å) and six longer (3.15 Å) Ho–Sn bond lengths. Mn is bonded in a 12-coordinate geometry to six Sn atoms. There are a spread of Mn–Sn bond distances ranging from 2.73–2.83 Å. There are three inequivalent Sn sites. In the first Sn site, Sn is bonded in a 8-coordinate geometry to one Ho, six equivalent Mn, and one Sn atom. The Sn–Sn bond length is 3.00 Å. In the second Sn site, Sn is bonded in a 6-coordinate geometry to six equivalent Mn atoms. In the third Sn site, Sn is bonded in a 12-coordinate geometry to three equivalent Ho and six equivalent Mn atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(CuS)2 by Materials Project

Ho(CuS)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ho is bonded to six equivalent S atoms to form distorted HoS6 octahedra that share corners with twelve equivalent CuS4 tetrahedra, edges with six equivalent HoS6 octahedra, and edges with six equivalent CuS4 tetrahedra. All Ho–S bond lengths are 2.82 Å. Cu is bonded to four equivalent S atoms to form distorted CuS4 tetrahedra that share corners with six equivalent HoS6 octahedra, corners with six equivalent CuS4 tetrahedra, edges with three equivalent HoS6 octahedra, and edges with three equivalent CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 24–54°. There are three shorter (2.33 Å) and one longer (2.49 Å) Cu–S bond lengths. S is bonded in a 7-coordinate geometry to three equivalent Ho and four equivalent Cu atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(Ni2As)2 by Materials Project

Ho(Ni2As)2 crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Ho is bonded to six equivalent As atoms to form a mixture of distorted corner and edge-sharing HoAs6 octahedra. The corner-sharing octahedral tilt angles are 40°. There are two shorter (2.89 Å) and four longer (2.91 Å) Ho–As bond lengths. Ni is bonded in a 3-coordinate geometry to three equivalent As atoms. All Ni–As bond lengths are 2.40 Å. As is bonded in a 9-coordinate geometry to three equivalent Ho and six equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(Ni2P)2 by Materials Project

Ho(Ni2P)2 crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Ho is bonded in a 6-coordinate geometry to six equivalent P atoms. There are two shorter (2.79 Å) and four longer (2.83 Å) Ho–P bond lengths. Ni is bonded in a 3-coordinate geometry to three equivalent P atoms. There are two shorter (2.30 Å) and one longer (2.31 Å) Ni–P bond lengths. P is bonded in a 9-coordinate geometry to three equivalent Ho and six equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

On the Rate Constant for NH 2 +HO 2 and Third-Body Collision Efficiencies for NH 2 +H(+M) and NH 2 +NH 2 (+M)

In low-temperature flash photolysis of NH 3 /O 2 /N 2 mixtures, the NH 2 consumption rate and the product distribution is controlled by the reactions NH 2 + HO 2 → products (R1), NH 2 + H (+M) → NH 3 (+M) (R2), and NH 2 + NH 2 (+M) → N 2 H 4 (+M) (R3). In the present work, published flash photolysis experiments by, among others, Cheskis and co-workers, are re-interpreted using recent direct measurements of NH 2 + H (+N 2 ) and NH 2 + NH 2 (+N 2 ) from Altinay and Macdonald. To facilitate analysis of the FP data, relative third-body collision efficiencies compared to N 2 for R2 and R3 were calculated for O 2 and NH 3 as well as for other selected molecules. We report results were in good agreement with the limited experimental data. Based on reported NH 2 decay rates in flash photolysis of NH 3 /O 2 /N 2 , a rate constant for NH 2 + HO 2 → NH 3 + O 2 (R1a) of $k_{1\text{a}}$ = 1.5(±0.5) × 10 14 cm 3 mol –1 s –1 at 295 K was derived. This value is higher than earlier determinations based on the FP results but in good agreement with recent theoretical work. Kinetic modeling of reported N 2 O yields indicates that NH 2 + HO 2 → H 2 NO + O (R1c) is competing with R1a, but perturbation experiments with addition of CH4 indicate that it is not a dominating channel. Measured HNO profiles indicate that this component is formed directly by NH 2 + HO 2 → HNO + H 2 O (R1b), but theoretical work indicates that R1b is only a minor channel. Based on this analysis, we estimate $k_{1\text{c}}$ = 2.5 × 10 13 cm 3 mol –1 s –1 and $k_{1\text{b}}$ = 2.5 × 10 12 cm 3 mol –1 s –1 at 295 K, with significant uncertainty margins.

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

Materials Data on Ho(AlCl4)3 by Materials Project

Ho(AlCl4)3 crystallizes in the trigonal P3_112 space group. The structure is one-dimensional and consists of one Ho(AlCl4)3 ribbon oriented in the (0, 0, 1) direction. Ho3+ is bonded in a 8-coordinate geometry to eight Cl1- atoms. There are a spread of Ho–Cl bond distances ranging from 2.72–2.92 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded in a tetrahedral geometry to four Cl1- atoms. There are two shorter (2.16 Å) and two longer (2.17 Å) Al–Cl bond lengths. In the second Al3+ site, Al3+ is bonded in a tetrahedral geometry to four Cl1- atoms. There are a spread of Al–Cl bond distances ranging from 2.10–2.24 Å. There are six inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a distorted L-shaped geometry to one Ho3+ and one Al3+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Al3+ atom. In the third Cl1- site, Cl1- is bonded in a single-bond geometry to one Al3+ atom. In the fourth Cl1- site, Cl1- is bonded in a distorted L-shaped geometry to one Ho3+ and one Al3+ atom. In the fifth Cl1- site, Cl1- is bonded in a distorted L-shaped geometry to one Ho3+ and one Al3+ atom. In the sixth Cl1- site, Cl1- is bonded in an L-shaped geometry to one Ho3+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(MnGe)2 by Materials Project

HoMn2Ge2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ho is bonded in a 8-coordinate geometry to eight equivalent Ge atoms. All Ho–Ge bond lengths are 3.06 Å. Mn is bonded to four equivalent Ge atoms to form a mixture of corner and edge-sharing MnGe4 tetrahedra. All Mn–Ge bond lengths are 2.43 Å. Ge is bonded in a 9-coordinate geometry to four equivalent Ho, four equivalent Mn, and one Ge atom. The Ge–Ge bond length is 2.57 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(NO3)3 by Materials Project

Ho(NO3)3 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of one Ho(NO3)3 sheet oriented in the (0, 0, 1) direction. Ho3+ is bonded in a 10-coordinate geometry to ten O2- atoms. There are a spread of Ho–O bond distances ranging from 2.34–2.68 Å. There are three inequivalent N5+ sites. In the first N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.26–1.28 Å. In the second N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.26 Å) and two longer (1.27 Å) N–O bond length. In the third N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.24–1.31 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Ho3+ and one N5+ atom. In the second O2- site, O2- is bonded in a distorted L-shaped geometry to one Ho3+ and one N5+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two equivalent Ho3+ and one N5+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to one Ho3+ and one N5+ atom. In the fifth O2- site, O2- is bonded in a distorted L-shaped geometry to one Ho3+ and one N5+ atom. In the sixth O2- site, O2- is bonded in a single-bond geometry to one Ho3+ and one N5+ atom. In the seventh O2- site, O2- is bonded in a distorted single-bond geometry to one Ho3+ and one N5+ atom. In the eighth O2- site, O2- is bonded in a 2-coordinate geometry to one Ho3+ and one N5+ atom. In the ninth O2- site, O2- is bonded in a distorted L-shaped geometry to one Ho3+ and one N5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(CuS)3 by Materials Project

Ho(CuS)3 crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of one Ho(CuS)3 sheet oriented in the (0, 0, 1) direction. Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with nine CuS4 tetrahedra, edges with six equivalent HoS6 octahedra, and edges with six CuS4 tetrahedra. There are three shorter (2.72 Å) and three longer (2.84 Å) Ho–S bond lengths. There are three inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded to four equivalent S2- atoms to form CuS4 tetrahedra that share corners with six equivalent HoS6 octahedra, corners with six equivalent CuS4 tetrahedra, edges with three equivalent HoS6 octahedra, and edges with three equivalent CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 22–52°. There are three shorter (2.34 Å) and one longer (2.48 Å) Cu–S bond lengths. In the second Cu1+ site, Cu1+ is bonded in a trigonal planar geometry to three equivalent S2- atoms. All Cu–S bond lengths are 2.25 Å. In the third Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share corners with three equivalent HoS6 octahedra, corners with six equivalent CuS4 tetrahedra, and edges with three equivalent HoS6 octahedra. The corner-sharing octahedral tilt angles are 12°. There are one shorter (2.27 Å) and three longer (2.43 Å) Cu–S bond lengths. There are three inequivalent S2- sites. In the first S2- site, S2- is bonded to three equivalent Ho3+ and four equivalent Cu1+ atoms to form distorted SHo3Cu4 pentagonal bipyramids that share corners with three equivalent SHo3Cu3 octahedra, edges with three equivalent SHo3Cu3 octahedra, and edges with nine equivalent SHo3Cu4 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 3°. In the second S2- site, S2- is bonded to three equivalent Ho3+ and three equivalent Cu1+ atoms to form distorted SHo3Cu3 octahedra that share corners with three equivalent SHo3Cu4 pentagonal bipyramids, corners with three equivalent SCu4 trigonal pyramids, edges with six equivalent SHo3Cu3 octahedra, and edges with three equivalent SHo3Cu4 pentagonal bipyramids. In the third S2- site, S2- is bonded to four Cu1+ atoms to form SCu4 trigonal pyramids that share corners with three equivalent SHo3Cu3 octahedra and corners with six equivalent SCu4 trigonal pyramids. The corner-sharing octahedral tilt angles are 68°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(AsO)2 by Materials Project

Ho(AsO)2 crystallizes in the tetragonal I4_1/amd space group. The structure is zero-dimensional and consists of eight Ho(AsO)2 clusters. Ho3+ is bonded in a linear geometry to two equivalent O2- atoms. Both Ho–O bond lengths are 2.11 Å. As+0.50+ is bonded in a single-bond geometry to one O2- atom. The As–O bond length is 1.78 Å. O2- is bonded in a distorted linear geometry to one Ho3+ and one As+0.50+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho(PO)2 by Materials Project

Ho(PO)2 crystallizes in the tetragonal I4_1/amd space group. The structure is zero-dimensional and consists of eight Ho(PO)2 clusters. Ho3+ is bonded in a linear geometry to two equivalent O2- atoms. Both Ho–O bond lengths are 2.20 Å. P+0.50+ is bonded in a single-bond geometry to one O2- atom. The P–O bond length is 1.58 Å. O2- is bonded in a water-like geometry to one Ho3+ and one P+0.50+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlZn2Sb(HO)12 by Materials Project

Zn2Al(OH)6Sb(HO)6 crystallizes in the trigonal P-3 space group. The structure is two-dimensional and consists of one Sb(HO)6 cluster and one Zn2Al(OH)6 sheet oriented in the (0, 0, 1) direction. In the Sb(HO)6 cluster, Sb5+ is bonded in an octahedral geometry to six equivalent O2- atoms. All Sb–O bond lengths are 2.01 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. O2- is bonded in a distorted single-bond geometry to one Sb5+ and one H1+ atom. In the Zn2Al(OH)6 sheet, Zn2+ is bonded to six equivalent O2- atoms to form ZnO6 octahedra that share edges with three equivalent ZnO6 octahedra and edges with three equivalent AlO6 octahedra. There are three shorter (2.13 Å) and three longer (2.17 Å) Zn–O bond lengths. Al3+ is bonded to six equivalent O2- atoms to form AlO6 octahedra that share edges with six equivalent ZnO6 octahedra. All Al–O bond lengths are 1.93 Å. H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. O2- is bonded in a 1-coordinate geometry to two equivalent Zn2+, one Al3+, and one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Kinetic study of reaction C 2 H 5 + HO 2 in a photolysis reactor with time-resolved Faraday rotation spectroscopy

The rate constant and branching ratios of ethyl reaction with hydroperoxyl radical, C 2 H 5 + HO 2 (1), a key radical-radical reaction for intermediate temperature combustion chemistry, were measured in situ for the first time in a photolysis Herriott cell by using mid-IR Faraday rotation spectroscopy (FRS) and UV-IR direct absorption spectroscopy (DAS). The microsecond time-resolved diagnostic technique in this work enabled the direct rate measurements of the target reaction at 40 and 80 mbar and reduced the experimental uncertainty considerably. C 2 H 5 and HO 2 radicals were generated by the photolysis of (COCl) 2 /C 2 H 5 I/CH 3 OH/O 2 /He mixture at 266 nm. By direct measurements of the transient profiles of C 2 H 5 , HO 2 and OH concentrations, the overall rate constant for this reaction at 297 K was determined as k 1 (40 mbar) = (3.8 ± 0.8) × 10 –11 cm 3 molecule –1 s –1 and k 1 (80 mbar) = (4.1 ± 1.0) × 10 –11 cm 3 molecule –1 s –1 . As a result, the direct observation of hydroxyl radical (OH) indicated that OH formation channel was the major channel with a branching ratio of 0.8 ± 0.1.

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

High-Temperature Reaction Kinetics of the e aq – and HO 2 • Radicals with Iron(II) Ions in Aqueous Solutions

Pulsed electron radiolysis was used to determine the chemical reaction kinetics and Arrhenius parameters for iron(II) reactions in aqueous solutions under irradiation. The second-order Fe 2+ reactions with the hydrated electron (e aq – ) and the perhydroxyl radical (HO 2 • ), arising from water radiolysis, were measured to high temperatures using custom-built flow-through cells with a multichannel optical detection system. The reaction with the HO 2 • radical was found to proceed via the formation of a metal-ion adduct species, Fe 2+ –HO 2 • . Additionally, the adduct’s molar extinction coefficient and its first-order decay rate coefficients are reported.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

2D photofragmentation LIF imaging of H 2 O 2 and HO 2 in the effluent of an atmospheric-pressure plasma jet: effects of solid and liquid interfaces

Two-dimensional (2D) absolute measurements of hydrogen peroxide (H 2 O 2 ) and approximations of the hydroperoxyl radical (HO 2 ) in the effluent of a COST Reference Microplasma Jet operated with a He/H 2 O feed gas are presented. Gas-phase densities are mapped using photofragmentation laser-induced fluorescence (PF-LIF) under three boundary conditions: open effluent, a solid target, and a liquid target. A novel method is presented for separating PF-LIF signals from H 2 O 2 and HO 2 using comparative measurements in oxygen-rich and oxygen-free environments to exploit the preferential formation of HO 2 in the presence of molecular oxygen. This separation strategy is supported by results from a plug-flow plasma chemistry model. Measured densities agree closely with model predictions in both magnitude and trend, while the 2D experimental distributions provide additional insight into the spatial dependencies of these species. In particular, the results show distinct differences in species transport depending on the target type: solid surfaces induce lateral deflection and reduced centerline densities, whereas liquid interfaces promote axial accumulation and higher near-axis concentrations.

atmospheric-pressure plasma jet (APPJ)↗
DOE OSTI2020

Isomeric and beta-decay spectroscopy of 173,174 Ho

β-decay spectroscopy of 173,174 Ho (Z = 67, N = 106,107) was conducted at Radioactive Isotope Beam Factory at RIKEN by using in-flight fission of a 345-MeV/u 238 U primary beam. A previously unreported isomeric state at 405 keV with half-life of 3.7(12) μs and a spin and parity of (3/2 + ) is identified in 173 Ho. Moreover, a new state with a spin and parity of 9 - was discovered in 174 Er. The experimental log ft values of 5.84(20) and 5.25(18) suggest an allowed-hindered β decay from the ground state of 174 Ho to the K π = 8 - isomeric state in 174 Er. Configuration-constrained potential energy surface (PES) calculations were performed and the predictions are in reasonable agreement with the experimental results.

150 ≤ A ≤ 189↗