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At least 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on HoNiGe by Materials Project

HoNiGe crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ho is bonded in a 12-coordinate geometry to six equivalent Ni and six equivalent Ge atoms. There are a spread of Ho–Ni bond distances ranging from 2.95–3.21 Å. There are a spread of Ho–Ge bond distances ranging from 2.97–3.16 Å. Ni is bonded in a 10-coordinate geometry to six equivalent Ho, one Ni, and three equivalent Ge atoms. The Ni–Ni bond length is 2.68 Å. There are two shorter (2.40 Å) and one longer (2.64 Å) Ni–Ge bond lengths. Ge is bonded in a 10-coordinate geometry to six equivalent Ho, three equivalent Ni, and one Ge atom. The Ge–Ge bond length is 2.72 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2GaOs by Materials Project

Ho2OsGa is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ho is bonded in a body-centered cubic geometry to four equivalent Os and four equivalent Ga atoms. All Ho–Os bond lengths are 3.00 Å. All Ho–Ga bond lengths are 3.00 Å. Os is bonded in a body-centered cubic geometry to eight equivalent Ho atoms. Ga is bonded in a body-centered cubic geometry to eight equivalent Ho atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoPu3 by Materials Project

Pu3Ho is Magnesium-derived structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Pu sites. In the first Pu site, Pu is bonded to eight Pu and four equivalent Ho atoms to form PuHo4Pu8 cuboctahedra that share corners with four equivalent HoPu12 cuboctahedra, corners with fourteen equivalent PuHo4Pu8 cuboctahedra, edges with six equivalent HoPu12 cuboctahedra, edges with twelve PuHo4Pu8 cuboctahedra, faces with four equivalent HoPu12 cuboctahedra, and faces with sixteen PuHo4Pu8 cuboctahedra. There are a spread of Pu–Pu bond distances ranging from 3.39–3.51 Å. There are two shorter (3.44 Å) and two longer (3.45 Å) Pu–Ho bond lengths. In the second Pu site, Pu is bonded to eight equivalent Pu and four equivalent Ho atoms to form PuHo4Pu8 cuboctahedra that share corners with four equivalent HoPu12 cuboctahedra, corners with fourteen PuHo4Pu8 cuboctahedra, edges with six equivalent HoPu12 cuboctahedra, edges with twelve equivalent PuHo4Pu8 cuboctahedra, faces with four equivalent HoPu12 cuboctahedra, and faces with sixteen PuHo4Pu8 cuboctahedra. There are two shorter (3.44 Å) and two longer (3.45 Å) Pu–Ho bond lengths. Ho is bonded to twelve Pu atoms to form HoPu12 cuboctahedra that share corners with six equivalent HoPu12 cuboctahedra, corners with twelve PuHo4Pu8 cuboctahedra, edges with eighteen PuHo4Pu8 cuboctahedra, faces with eight equivalent HoPu12 cuboctahedra, and faces with twelve PuHo4Pu8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoGePd by Materials Project

HoPdGe crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Ho is bonded in a 12-coordinate geometry to six equivalent Pd and six equivalent Ge atoms. There are a spread of Ho–Pd bond distances ranging from 3.05–3.20 Å. There are a spread of Ho–Ge bond distances ranging from 3.06–3.25 Å. Pd is bonded in a 10-coordinate geometry to six equivalent Ho, one Pd, and three equivalent Ge atoms. The Pd–Pd bond length is 2.83 Å. There are two shorter (2.53 Å) and one longer (2.78 Å) Pd–Ge bond lengths. Ge is bonded in a 10-coordinate geometry to six equivalent Ho, three equivalent Pd, and one Ge atom. The Ge–Ge bond length is 2.59 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba3Ho by Materials Project

Ba3Ho is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Ba sites. In the first Ba site, Ba is bonded to eight Ba and four equivalent Ho atoms to form BaBa8Ho4 cuboctahedra that share corners with twelve equivalent BaBa8Ho4 cuboctahedra, edges with eight equivalent HoBa12 cuboctahedra, edges with sixteen BaBa8Ho4 cuboctahedra, faces with four equivalent HoBa12 cuboctahedra, and faces with fourteen BaBa8Ho4 cuboctahedra. There are four shorter (4.17 Å) and four longer (4.19 Å) Ba–Ba bond lengths. All Ba–Ho bond lengths are 4.19 Å. In the second Ba site, Ba is bonded to eight equivalent Ba and four equivalent Ho atoms to form BaBa8Ho4 cuboctahedra that share corners with four equivalent BaBa8Ho4 cuboctahedra, corners with eight equivalent HoBa12 cuboctahedra, edges with twenty-four BaBa8Ho4 cuboctahedra, faces with six equivalent HoBa12 cuboctahedra, and faces with twelve BaBa8Ho4 cuboctahedra. All Ba–Ho bond lengths are 4.17 Å. Ho is bonded to twelve Ba atoms to form HoBa12 cuboctahedra that share corners with four equivalent HoBa12 cuboctahedra, corners with eight equivalent BaBa8Ho4 cuboctahedra, edges with eight equivalent HoBa12 cuboctahedra, edges with sixteen equivalent BaBa8Ho4 cuboctahedra, faces with four equivalent HoBa12 cuboctahedra, and faces with fourteen BaBa8Ho4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2CdHg by Materials Project

Ho2HgCd is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ho is bonded in a body-centered cubic geometry to four equivalent Hg and four equivalent Cd atoms. All Ho–Hg bond lengths are 3.22 Å. All Ho–Cd bond lengths are 3.22 Å. Hg is bonded in a body-centered cubic geometry to eight equivalent Ho atoms. Cd is bonded in a body-centered cubic geometry to eight equivalent Ho atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho3(GaNi3)2 by Materials Project

Ho3(Ni3Ga)2 crystallizes in the cubic Im-3m space group. The structure is three-dimensional. Ho is bonded in a 12-coordinate geometry to eight equivalent Ni and four equivalent Ga atoms. There are four shorter (2.74 Å) and four longer (3.03 Å) Ho–Ni bond lengths. All Ho–Ga bond lengths are 3.15 Å. Ni is bonded in a 12-coordinate geometry to four equivalent Ho, six equivalent Ni, and two equivalent Ga atoms. There are four shorter (2.56 Å) and two longer (2.85 Å) Ni–Ni bond lengths. Both Ni–Ga bond lengths are 2.48 Å. Ga is bonded to six equivalent Ho and six equivalent Ni atoms to form a mixture of face and corner-sharing GaHo6Ni6 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ho2AgHg by Materials Project

Ho2AgHg is Heusler structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ho is bonded in a body-centered cubic geometry to four equivalent Ag and four equivalent Hg atoms. All Ho–Ag bond lengths are 3.17 Å. All Ho–Hg bond lengths are 3.17 Å. Ag is bonded in a body-centered cubic geometry to eight equivalent Ho atoms. Hg is bonded in a body-centered cubic geometry to eight equivalent Ho atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoU3 by Materials Project

U3Ho is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent U sites. In the first U site, U is bonded to eight U and four equivalent Ho atoms to form UHo4U8 cuboctahedra that share corners with twelve equivalent UHo4U8 cuboctahedra, edges with eight equivalent HoU12 cuboctahedra, edges with sixteen UHo4U8 cuboctahedra, faces with four equivalent HoU12 cuboctahedra, and faces with fourteen UHo4U8 cuboctahedra. There are four shorter (3.09 Å) and four longer (3.23 Å) U–U bond lengths. All U–Ho bond lengths are 3.23 Å. In the second U site, U is bonded to eight equivalent U and four equivalent Ho atoms to form distorted UHo4U8 cuboctahedra that share corners with four equivalent UHo4U8 cuboctahedra, corners with eight equivalent HoU12 cuboctahedra, edges with twenty-four UHo4U8 cuboctahedra, faces with six equivalent HoU12 cuboctahedra, and faces with twelve UHo4U8 cuboctahedra. All U–Ho bond lengths are 3.09 Å. Ho is bonded to twelve U atoms to form HoU12 cuboctahedra that share corners with four equivalent HoU12 cuboctahedra, corners with eight equivalent UHo4U8 cuboctahedra, edges with eight equivalent HoU12 cuboctahedra, edges with sixteen equivalent UHo4U8 cuboctahedra, faces with four equivalent HoU12 cuboctahedra, and faces with fourteen UHo4U8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoNiAs by Materials Project

HoNiAs is hexagonal omega structure-derived structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Ho is bonded to six equivalent Ni and six equivalent As atoms to form a mixture of edge and face-sharing HoNi6As6 cuboctahedra. All Ho–Ni bond lengths are 3.02 Å. All Ho–As bond lengths are 3.02 Å. Ni is bonded in a 3-coordinate geometry to six equivalent Ho and three equivalent As atoms. All Ni–As bond lengths are 2.34 Å. As is bonded in a 3-coordinate geometry to six equivalent Ho and three equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NaHo9(Si3O13)2 by Materials Project

NaHo9(SiO4)6O2 crystallizes in the trigonal P3 space group. The structure is three-dimensional. Na1+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Na–O bond distances ranging from 2.39–2.91 Å. There are five 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 2.20–2.82 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 2.22–2.69 Å. In the third Ho3+ site, Ho3+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Ho–O bond distances ranging from 2.30–2.76 Å. In the fourth Ho3+ site, Ho3+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Ho–O bond distances ranging from 2.30–2.78 Å. In the fifth Ho3+ site, Ho3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are three shorter (2.28 Å) and three longer (2.39 Å) Ho–O bond lengths. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Si–O bond distances ranging from 1.63–1.65 Å. In the second Si4+ site, Si4+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Si–O bond distances ranging from 1.60–1.66 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to three Ho3+ and one Si4+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to three Ho3+ and one Si4+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, two Ho3+, and one Si4+ atom. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to three equivalent Ho3+ atoms. In the fifth O2- site, O2- is bonded in a trigonal planar geometry to three equivalent Ho3+ atoms. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to three Ho3+ and one Si4+ atom. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, two Ho3+, and one Si4+ atom. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to three Ho3+ and one Si4+ atom. In the ninth O2- site, O2- is bonded in a 1-coordinate geometry to one Na1+, two Ho3+, and one Si4+ atom. In the tenth O2- site, O2- is bonded in a 1-coordinate geometry to two Ho3+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HoCoRu by Materials Project

HoRuCo crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. Ho is bonded in a 12-coordinate geometry to six equivalent Ru and six equivalent Co atoms. There are four shorter (3.03 Å) and two longer (3.05 Å) Ho–Ru bond lengths. There are four shorter (3.03 Å) and two longer (3.06 Å) Ho–Co bond lengths. Ru is bonded to six equivalent Ho, two equivalent Ru, and four equivalent Co atoms to form RuHo6Co4Ru2 cuboctahedra that share corners with eight equivalent CoHo6Co2Ru4 cuboctahedra, corners with ten equivalent RuHo6Co4Ru2 cuboctahedra, edges with six equivalent RuHo6Co4Ru2 cuboctahedra, faces with six equivalent RuHo6Co4Ru2 cuboctahedra, and faces with twelve equivalent CoHo6Co2Ru4 cuboctahedra. Both Ru–Ru bond lengths are 2.58 Å. All Ru–Co bond lengths are 2.60 Å. Co is bonded to six equivalent Ho, four equivalent Ru, and two equivalent Co atoms to form CoHo6Co2Ru4 cuboctahedra that share corners with eight equivalent RuHo6Co4Ru2 cuboctahedra, corners with ten equivalent CoHo6Co2Ru4 cuboctahedra, edges with six equivalent CoHo6Co2Ru4 cuboctahedra, faces with six equivalent CoHo6Co2Ru4 cuboctahedra, and faces with twelve equivalent RuHo6Co4Ru2 cuboctahedra. Both Co–Co bond lengths are 2.57 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Experimental and modeling study of the autoignition behavior of a saturated heterocycle: Pyrrolidine

Experiments are conducted in both rapid compression machine (RCM) and shock tube (ST) to better quantify autoignition behavior (e.g., ignition delay, heat release) and understand heteroatomic effects in heterocyclic compounds, which are important reference components for the combustion of biomass-derived liquid fuels. These tests focus on the nitrogen-containing, five-membered saturated ring, pyrrolidine, at diluted conditions covering pressures of 20 and 50 bar, temperatures of 720–1450 K and a range of stoichiometries (ϕ = 0.5–2). A chemical kinetic model is developed and coupled to an existing combustion kinetics framework describing key nitrogen containing intermediates (e.g. pyrrole, ammonia and NOx). H-abstraction reactions by OH, H, CH 3 and HO 2 , are determined using ab-initio transition state theory methods, while analogies to cyclopentane are adopted for many other reactions, such as ring-opening. Here, the autoignition measurements reveal the lack of negative temperature coefficient (NTC) behavior and low-temperature chemistry for pyrrolidine, as opposed to its saturated hydrocarbon analogue, cyclopentane. Interestingly, at the lowest temperatures (T < 750 K), the reactivity of cyclopentane is greater than pyrrolidine, while at higher temperatures, pyrrolidine becomes more reactive. Agreement between the experimental measurements and the model is good, and it is found that H-abstraction reactions by HO 2 and ensuing chemistry play key roles in controlling the reactivity of this cyclic amine. Most of the fluxes, i.e., >70 %, are predicted to move through 1- or 2-pyrroline (C 4 H 7 N) and then the cyclic C 4 H 6 N radical, at both lower and higher temperatures, to form either CH 2 CHCHCHNH via ring-opening or pyrrole via β-scission. It appears that the ring opens more easily at lower temperature whereas the C–H β-scission dominates at higher temperature and lower pressure, such that the reaction of the fuel radical intermediate carrying an unpaired electron on the nitrogen atom with HO 2 is the next most notable in promoting oxidation. When comparing pyrrolidine and cyclopentane, which exhibits distinct pathways in different temperature regimes, the pyrrolidine pathways and sensitivity analysis align more closely to the high temperature case of cyclopentane where the important role of HO 2 radicals is seen to provide chain branching through HO 2 reaction with the fuel, accompanied by H 2 O 2 formation and decomposition to OH. The formation of 5-membered diene rings and ring opening reactions are also found to be highly relevant. Of particular note, it is found that there is little influence of small molecule nitrogen-chemistry, e.g., NH 2 , HCN, NO/NO 2 on the reactivity of the pyrrolidine mixtures investigated here where no recirculated combustion gases are included.

Autoignition↗
DOE OSTI2025

Impact of gasoline composition on the effects of nitric oxide on autoignition and knock in a DISI engine

Modern spark-ignition engines use exhaust gas recirculation (EGR) to dilute the charge and suppress knock, enabling the use of higher compression ratios and/or more optimum combustion phasing for higher efficiency. The effectiveness of EGR is affected by the composition of the fuel and its chemical-kinetic interactions with combustion products. Among those, nitric oxide (NO) has been shown to strongly affect autoignition reactivity. However, the impact of fuel composition of the effect of NO on reactivity is not well-understood. Here, in this study, engine experiments were conducted to assess the impact of NO seeded to the intake on knock-limited operation of two gasoline fuels (high cycloalkane content, or HCA, and high olefin content, or HO). Results showed that compositionally-different fuels responded differently to NO. HCA, which was less knock-limited than HO for NO < 200 ppm, became more knock-limited for NO > 200 ppm. Moreover, it was found that differences in knock between fuels were caused by differences in autoignition chemistry and not in the sequential autoignition process of the end gas that occurs due to thermal stratification. Chemical kinetic simulations were performed to better understand the experimental results. For HCA, intermediate-temperature heat release had a greater impact on autoignition reactivity than low-temperature heat release, while the opposite was observed for HO. For both fuels, NO enhances the magnitude of low-temperature heat release via NO + HO 2 → NO 2 + OH. The effect of NO on reactivity was stronger for HCA because OH produced from NO helped to overcome the OH quenching effect of cyclopentane, a main species in HCA. In contrast, HO had relatively strong inherent low-temperature chemistry arising from iso-octane, which reduced the impact of NO on reactivity. For the range of NO mole fractions tested in this study, in-cylinder NO increased fuel’s knock propensity, especially for fuels with mild low-temperature chemistry.

Autoignition↗
DOE OSTI2021

Magnetic structure of magnetoelectric multiferroic HoFeWO 6

The polar magnetic oxide, HoFeWO6, is synthesized, and its crystal structure, magnetic structure, and thermodynamic properties are investigated. HoFeWO 6 forms the polar crystal structure (space group Pna2 1 (#33)) due to the cation ordering of W 6+ and Fe 3+ . An antiferromagnetic transition at T N = 17 K is accompanied by a significant change in magnetic entropy with a value of ≈ 5 J kg -1 K-1 in a 70 kOe applied field. Temperature dependent neutron diffraction and magnetization data indicate that the Fe sublattice orders in a strongly non-collinear and non-coplanar arrangement below T N . The Fe ordering initially leads to induced ordering of the Ho spins such that the Ho spins also show behavior of long-range ordering that is evident from the neutron diffraction measurements. Below T ≈ 4 K, the Ho spins order independently and pull the Fe spins toward the direction of Ho spins. A comparison with the magnetic structures and corresponding ferroelectric properties of other members of RMWO 6 (R = Y, Sm-Tm, M = Cr, Fe, V) family indicate that the spontaneous polarization is due to the magnetic structure specific to the Fe sublattice through magnetoelectric coupling whereas the polarization is independent of the Ho sublattice.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Active Sites in the Dealuminated Beta Zeolite-Supported Cobalt Catalyst for Non-Oxidative Ethane Dehydrogenation

Dispersed metal species in siliceous zeolites have been actively studied for non-oxidative dehydrogenation of ethane (NDE). Fundamental insights into the dynamics of metal species in zeolites under reaction conditions have rarely been explored. Herein, we report an atomic level understanding of the dynamics and activity of cobalt (Co) sites in dealuminated Beta zeolite (DeAl-BEA) for NDE during induction and reaction conditions with extensive characterization techniques such as diffuse reflectance UV–vis, solid state nuclear magnetic resonance and X-ray photoelectron, X-ray diffraction along with in situ Fourier transform infrared and X-ray absorption spectroscopy. For a catalyst with 0.5 mass % Co loading, tetrahedral Co 2+ mononuclear sites, di-coordinated to the zeolite framework and with two silanol groups in vicinity (i.e., (≡SiO) 2 Co(HO–Si≡) 2 ), form upon exposure to hydrogen during induction and persist through the NDE reaction. Increasing the Co loading to 3.0 mass % yielded Co sites with similar electronic and coordination structures but slightly elongated Co–O bonds. Upon cooling to room temperature, the Co sites persisted in the same coordination environment, though the disappearance of a feature in the Co K-edge near-edge region revealed changes in the active site’s electronic structure coinciding with modest shifts in bond lengths. The electronic structure and activity of (≡SiO) 2 Co(HO–Si≡) 2 sites were studied comparatively to a few other hypothetical Co 2+ coordination structures, using electronic structure calculations and microkinetic simulations. The simulations showed that NDE is controlled by β-hydride elimination following C–H bond activation and that Co-sites possessing flexibility because of neighboring silanol defects are more active. Interestingly, dinuclear Co–O–Co sites (i.e., (≡SiO)Co(HO–Si≡) 2 –O–(HO–Si≡) 2 Co(≡SiO)) were more active than the mononuclear (≡SiO) 2 Co(HO–Si≡) 2 sites because of favorable hydrogen bonding with the vicinal silanol groups. In conclusion, the present study bridges the gap between the knowledge acquired by ex-situ characterizations and the active sites under the reaction conditions in alkane dehydrogenation chemistry.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Assessment of Hydroxyl Radical Reactivity in Sulfur-Containing Amino Acid Models Under Acidic pH

Methionine residues in proteins and peptides are frequently oxidized by losing one electron. The presence of nearby amide groups is crucial for this process, enabling methionine to participate in long-range electron transfer. Hydroxyl radical (HO•) plays an important role being generated in aerobic organisms by cellular metabolisms as well as by exogenous sources such as ionizing radiations. The reaction of HO• with methionine mainly affords the one-electron oxidation of the thioether moiety through two consecutive steps (HO• addition to the sulfur followed by HO− elimination). We recently investigated the reaction of HO• with model peptides mimicking methionine and its cysteine-methylated counterpart, i.e., CH3C(O)NHCHXC(O)NHCH3, where X = CH2CH2SCH3 or CH2SCH3 at pH 7. The reaction mechanism varied depending on the distance between the sulfur atom and the peptide backbone, but, for a better understanding of various suggested equilibria, the analysis of the flux of protons is required. We extended the previous study to the present work at pH 4 using pulse radiolysis techniques with conductivity and optical detection of transient species, as well as analysis of final products by LC-MS and high-resolution MS/MS following γ-radiolysis. Comparing all the data provided a better understanding of how the presence of nearby amide groups influences the one-electron oxidation mechanism.

Biochemistry & Molecular Biology↗
NASA NTRS1986

Tunable-diode laser absorption spectrometry

Tunable-diode laser absorption spectrometry (TDLAS) affords a number of advantages for atmospheric measurements. It is a universal method, applicable, in principle, to all gases of atmospheric interest. Because of its extremely high spectral resolution it provides unequivocal identification of the target species, with no interferences from other gases. It provides real-time, in situ measurements with time resolutions better than 1 minute. The sensitivity of the current TDLAS system is marginally capable of measuring HO2. This species exists in the troposphere at concentrations which are up to 2 orders of magnitude higher than those of HO and, in addition, is much less susceptible to removal by the surfaces of the instrument and its sampling system. HO2 is an important HO sub x species in its own right but can also give direct information on the HO concentration by virtue of the rapid partitioning between these two species. The addition of the high-frequency modulation technique to the TDLAS system would ensure its ability to measure HO2 under most atmospheric conditions. The ability of the TDLAS to measure hydrogen peroxide (H2O2) in the ambient atmosphere was also demonstrated. H2O2 measurements give a clear indication of HO sub x mixing ratios and are also important as a photolytic source of HO and as an important oxidant for other atmospheric consitituents such as SO2.

Schiff, H. I.↗