Atomic Oxygen Research Papers - Academia.edu (original) (raw)

- by
- •
- Engineering, Materials Engineering, Mechanical Engineering, Aerospace Engineering

Vapor grown carbon nanofibers (Pyrograf IIIe) with 100-300 nm diameters and $10-100 lm lengths were oxidized in 69-71 wt.% nitric acid (115°C) for various times (10 min to 24 h). These fibers were remarkably oxidation-resistant. XPS (O 1s... more

Vapor grown carbon nanofibers (Pyrograf IIIe) with 100-300 nm diameters and 10−100lmlengthswereoxidizedin69−71wt.10-100 lm lengths were oxidized in 69-71 wt.% nitric acid (115°C) for various times (10 min to 24 h). These fibers were remarkably oxidation-resistant. XPS (O 1s ) showed that the surface atomic oxygen percent increased from 6.3 to 18.3-22.5% for 10-90 min oxidations followed by a drop to 14-15% after 10-24 h oxidations. No damage was observed by TEM. Little change in surface area was observed by N 2 BET but CO 2 -DR measurements exhibited an increase from 20-25 m 2 /g to 41-73 m 2 /g after 10-90 min of oxidation followed by a decrease to 35-22 m 2 /g after 10 h, consistent with the XPS findings. Shallow ultramicropore formation could account for the surface area increase. NaOH titrations showed 10−100lmlengthswereoxidizedin69−71wt.3-fold increase in surface acidic functions ($27 to 76 lmol/g) occurring after 10 min of oxidation. Then this level remained constant through 24 h of oxidation. XPS (C 1s ), O 1s ) confirmed that carboxyl groups were removed and ester, anhydride, quinoid and phenolic hydroxyls appeared upon HNO 3 oxidation. Oxidized fibers dispersed when shaken in water, demonstrating wettability had increased. A model for this oxidation behavior is proposed.

- by hossein toghiani
- •
- Engineering, Carbon, Physical sciences, Atomic Oxygen

The effects of exposure to ultraviolet (UV) light and ozone, separately and in combination, were investigated with respect to polypropylene (PP) and poly(ethylene terephthalate) (PET) surfaces. Three combinations of UV light and ozone were studied: ozone only, UV light in air (producing ozone), and UV light in air (producing ozone) supplemented by additional ozone in the incoming air. The effect of the exposure time of the PP and PET to each treatment was studied. The samples were analyzed by X-ray photoelectron spectroscopy (XPS) to determine the surface composition, and by dynamic contact angle to determine the water wettability. The results showed that the effect of the treament was dependent on the properties of the exposed polymer, with PET being more sensitive to the UV light and PP being more sensitive to the reactive species in the gas. The exposure times studied ranged from 1 to 90 min. By monitoring the oxygen uptake levels, we were able to determine that surface modification occurred within minutes. The possible reactive species and mechanisms are discussed.

- by Mark Strobel
- •
- Mechanical Engineering, Chemical Engineering, Adhesion, Surface modification

For the first time, vertically aligned carbon nanotubes (VACNTs) have been successfully synthesized using waste chicken fat as the starting material. Chicken fat oil, which was obtained through a rendering process, was directly mixed with 5.33 wt% ferrocene as a catalyst to form the synthesis stock. A mixture of single-and multi-walled VACNTs was synthesized at a fixed temperature of 750 1C in a thermal chemical vapour deposition furnace. Field emission scanning electron microscopy, micro-Raman spectroscopy and thermogravimetric analyses showed that the produced VACNTs were of excellent quality, comparable to those obtained using conventional carbon sources, with a purity of 88.2% and tube diameters ranging from 18 to 78 nm. Based on our study, waste chicken fat is a promising carbon source for the synthesis of high-quality and high-purity VACNTs.

- by Stéphane Lucas
- •
- Engineering, Materials Engineering, Mechanical Engineering, Chemical Engineering

Plasma diagnostics of atmospheric plasmas is a key tool in helping to understand processing performance issues. This paper presents an electrical, optical and thermographic imaging study of the PlasmaStream atmospheric plasma jet system. The system was found to exhibit three operating modes; one constricted/localized plasma and two extended volume plasmas. At low power and helium flows the plasma is localized at the electrodes and has the electrical properties of a corona/filamentary discharge with electrical chaotic temporal structure. With increasing discharge power and helium flow the plasma expands into the volume of the tube, becoming regular and homogeneous in appearance. Emission spectra show evidence of atomic oxygen, nitric oxide and the hydroxyl radical production. Plasma activated gas temperature deduced from the rotational temperature of nitrogen molecules was found to be of order of 400 K: whereas thermographic imaging of the quartz tube yielded surface temperatures between 319 and 347 K.

- by Barry Twomey and +1
- •
- Chemical Engineering, Nitric oxide, Land Surface Temperature, Nitrogen

Thermodynamic calculations and Gibbs free energy minimization computer experiments strongly support the hypothesis that kerogen maturation and oil generation are inevitable consequences of oxidation/reduction disproportionation reactions caused by prograde metamorphism of hydrocarbon source rocks with increasing depth of burial.These experiments indicate that oxygen and hydrogen are conserved in the process.Accordingly, if water is stable and present in the source rock

- by Denis L. Norton
- •
- Geology, Geochemistry, Thermodynamics, Mass Transfer

The operating parameters of a miniature atmospheric pressure glow discharge torch (APGD-t) are optimized for the production of excited atomic oxygen, and the effect of the plasma jet on endothelial cells grown in Petri dishes is studied. We first demonstrate the importance of accounting for the effect of the voltage probe used to measure the electrical parameters of the torch on its ignition and operation characteristics. When operated with a main plasma gas flow rate of 1 SLM He and a power level of ~1 W, the torch shows an optimum in the production of excited atomic oxygen for a O 2 flow of ~3.5 SCCM injected downstream from the plasma-forming region through a capillary electrode (i.e., 0.35 v/v % O 2 /He). It is shown that endothelial cells are detached from the Petri dishes surface under the action of the optimized plasma jet and that this effect does not originate from heating and fluid shearing effects. It is postulated that the cell detachment is caused solely by plasma-induced biochemical processes taking place at the cell-substrate interface.

The mechanical and optical properties of the metallized Teflon ® FEP thermal control materials on the Hubble Space Telescope (HST) have degraded over the nearly seven years the telescope has been in orbit. Given the damage to the outer layer of the multilayer insulation (MLI) blanket that was apparent during the second servicing mission (SM2), the decision was made to replace the outer layer during subsequent servicing missions. A Failure Review Board was established to investigate the damage to the MLI and identify a replacement material. The replacement material had to meet the stringent thermal requirements of the spacecraft and maintain mechanical integrity for at least ten years.

- by Bruce Banks
- •
- Materials Engineering, Scanning Electron Microscopy, X Rays, Optical microscopy

Methyl, methoxy, and nitrile (cyano) functional groups were incorporated into the metal-organic pendent group of a co-polyamic acid, co-PAA[(3,4 0 -ODA/ ODPA) 0.9 (3,4 0 -ODA/{MADA-p-Zr(adsp)(Rdsp)}) 0.1 ], in various locations to investigate their effects on polymer chain interactions and film quality. Proton nuclear magnetic resonance and gel permeation chromatography (GPC) performed on solutions of these products were consistent with the expected 10% (mol) functionalized pendent polymeric structures. Thermogravimetric analysis performed on ether-precipitated samples revealed little functional group effect on imidization temperature (decreases of 5-8 C), but showed a somewhat-greater effect on decomposition temperature (decreases of 6 C for the 3-methoxy derivative to 28 C for the methyl derivative). Differential scanning calorimetry performed on imidized powder sam-ples showed that glass transition temperatures increased with the addition of the functional groups from 2 C for the methyl derivative to 19 C for the 3-methoxy derivative. Imidized films were solvent resistant, transparent, and flexible, with the nitrile derivative least susceptible to crack formation. Light scattering results revealed that the nitrile derivative had the lowest second virial coefficient of the functional groups tested and formed aggregates at room temperature in NMP with n ¼ 2, thus rationalizing its superior film forming properties. Results of contact angle measurements and atomic oxygen exposure of functionalized pendent co-PI films are included.

- by Valerie Leveille
- •
- Atmospheric Pressure, Atomic Oxygen, Reaction Mechanism

The intersystem crossing (ISC) between the lowest triplet and singlet states occurring in the reaction of atomic oxygen with ethylene was studied. The importance of spin-orbit coupling (SOC) in oxirane biradicals (CR'R"-CRR*-0) is stressed through calculations where the spin-orbit matrix elements over the full Breit-Pauli soc operator has been obtained in the singlet-triplet crossing region. The calculations are performed with a multiconfigurational linear response approach, in which the spin-orbit couplings are obtained from triplet response functions using differently correlated singlet-reference-state wave functions. Computational results confirm earlier semiempirical predictions of the spin-orbit coupling as an important mechanism behind the ring opening of oxiranes and addition of oxygen O(3P) atoms to alkenes.

- by Boris Minaev
- •
- Quantum Chemistry, Atomic Oxygen, Spin-Orbit Coupling, Cross Section

DSC, TG and TG-FT-IR, and XRPD have been used to examine the effects of supposedly inert atmospheres of argon and nitrogen on the mechanism of the thermal decomposition of copper(II) oxalate. The DSC curves in pure argon at 10 • C min −1 show a broad endotherm with onset at about 280 • C and maximum at about 295 • C. In mixtures of argon and nitrogen, as the proportion of argon gas is decreased, the endothermic character of the decomposition decreases until, when nitrogen is the main component, the decomposition exhibits a complex broad exothermic character. XRPD studies showed that, regardless of the proportions of nitrogen and argon, the DSC residues consisted of mainly copper metal with small amounts of copper(I) oxide (cuprite) and, under some conditions, traces of copper(II) oxide (tenorite). Various explanations for this behaviour are discussed and a possible answer lies in the disproportionation of CO 2 (g) to form small quantities of O 2 (g) or monatomic oxygen. The possibility exists that the exothermicity in nitrogen could be explained by reaction of the nitrogen with atomic oxygen to form N 2 O(g), but this product could not be detected using TG-FT-IR. (M.E. Brown).

- by Michael Brown
- •
- Analytical Chemistry, Copper, Nitrogen, Atomic Oxygen
- by Alice Harling and +1
- •
- Environmental Engineering, Chemical Engineering, Atomic Oxygen, Thermal Plasma

Spacecraft orbiting below about 300nm are exposed to a high flux of atomic oxygen (AO) that can severely degrade surface materials, yet some coatings used on solar cell coverglass have never been qualified in this environment. Combined effects tests comprising atomic oxygen exposure, illumination, and temperature were carried out to qualify magnesium fluoride coated coverglasses. Unexpectedly severe degradation in the form of optical transmission loss was observed upon exposure to high AO fluences. It was determined that the high intensity vacuum ultraviolet (VUV) light emitted from the AO source used acts in an unexpectedly synergistic fashion with AO to accelerate the optical degradation of these coatings. Since the excess VUV from the ground test AO source is not representative of flight conditions, its unexpected synergistic effect emphasizes the need to define proper ground test conditions when qualifying materials for AO environments.

- by Donna Speckman
- •
- Solar Cell, Magnesium, Ultraviolet, Atomic Oxygen

Progressive development of microsatellite technologies has resulted in increased demand for lightweight electrical power subsystems including solar arrays. The use of thin film photovoltaics has been recognized as a key solution to meet the power needs. The lightweight cells can generate sufficient power and still meet critical mass requirements. Commercially available solar cells produced on lightweight substrates are being studied as an option to fulfill the power needs. The commercially available solar cells are relatively inexpensive and have a high payoff potential.

- by Suraj Rawal
- •
- Engineering, Materials Science, Solar Cell, Critical Mass

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

- by Jacob Kleiman
- •
- Solar Cell, Erosion, Silica, Atomic Oxygen

Low Earth orbital (LEO) atomic oxygen cannot only erode the external surfaces of polymers on spacecraft, but can cause degradation of surfaces internal to components on the spacecraft where openings to the space environment exist. Although atomic oxygen attack on internal or interior surfaces may not have direct exposure to the LEO atomic oxygen flux, scattered impingement can have serious degradation effects where sensitive interior surfaces are present. The effects of atomic oxygen erosion of polymers interior to an aperture on a spacecraft is simulated using Monte Carlo computational techniques. A 2-dimensional model is used to provide quantitative indications of the attenuation of atomic oxygen flux as a function of distance into a parallel walled cavity. The degree of erosion relative is compared between the various interior locations and the external surface of a LEO spacecraft.

- by Bruce Banks
- •
- Monte Carlo, Atomic Oxygen

ABSTRACT Chemical bonding-scale aspects of oxygen diffusion in candidate high-k gate oxides LaAlO3 and SrTiO3 were investigated from first-principles, within density functional theory. Relaxed atomic positions, total energies and electron density maps were calculated along oxygen vacancy migration paths, for 2 2 2 supercells. Quite low activation energies were obtained (∼0.6 eV, in agreement with experiment) for both compounds. Microscopic factors involved in the diffusion process were investigated further by a topological analysis of the electron density, according to Bader’s “Atoms in Molecules” theory. At the diffusion saddle point, transitory states such as O− or atomic oxygen may explain the activation energy low values. Finally, we propose the use of energy density variation maps, as a way to identify parts of the density that contribute to increase (resp. decrease) the diffusion barrier. By extension, this type of tool may help to gain insight in phenomena such as phase transitions, and constitute the basis of an “electron density engineering” for materials design and optimization.

- by Christine Frayret and +1
- •
- Materials Engineering, Condensed Matter Physics, Computational Materials Science, High Energy Density Physics

The adsorption of both O 2 and NH 3 on Pt(410) was studied using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Molecular NH 3 desorbed from Pt(410) between 100 and 450 K, and dissociation was not observed. Radiation (X-rays, electrons) induced NH 3ad dissociation, and as a result several dissociation products (NH 2ad , NH ad , and N ad ) were observed in the N 1s core-level spectrum. NH ad is a rather stable dissociation product that starts to dehydrogenate above 350 K. The N ad and H ad formed in this process desorbed on formation (as N 2 and H 2 ). Both molecular and dissociative O 2 adsorption were observed after the surface was exposed to O 2 (g) at 100 K. Molecularly adsorbed O 2 desorbed below 200 K, whereas atomic oxygen desorbed (as O 2 ) between 600 and 900 K, in two distinct desorption peaks. In the O 1s core-level spectrum, both molecular O 2 and two different types of O ad were distinguished. NH 3ad dissociation was observed on an oxygen-presaturated surface. The NH 3ad oxy-dehydrogenation started at 150 K. NO ad and NO(g) were also observed, but only during experiments in which an excess of O ad was available. NO ad desorbed/decomposed between 400 and 500 K. For the steady-state ammonia oxidation reaction, N 2 and H 2 O were the major products at low temperatures, whereas the selectivity toward NO and H 2 O changed at higher temperatures. This selectivity change can be attributed to changes in surface composition. (C.J. Weststrate).

- by Johan Bakker
- •
- Chemical Engineering, Catalysis, PHOTOELECTRON SPECTROSCOPY, Synchrotron Radiation

The adsorption and photocleavage of chlorobenzene (CB) molecule on the anatase TiO 2 (0 0 1), (1 0 0) and surfaces are studied with semiempirical SCF MO method, MSINDO. The surfaces have been modeled with two saturated clusters Ti 21 O 58 H 32 and Ti 36 O 90 H 36 . The dissociative perpendicular adsorption of CB on TiO 2 and surfaces revealed comparable stabilities and much higher than on the (0 0 1) surface. The aromatic ring cleavage by atomic oxygen, singlet oxygen and superoxide anion molecules has been investigated computationally and relevant mechanisms are proposed. Molecular dynamics (MD) simulations have been implemented for the adsorption models and the early stages of photocleavage mechanisms. The oxygen-type chemistry is involved actively in the water mediated photocleavage step upon excitation. The O ÅÀ 2 radical anion dependant ring opening mechanism, through the dioxetane intermediate, is thermodynamically the most favourable.

- by Hilal Wahab
- •
- Engineering, Thermodynamics, Chemical Physics, Adsorption

To help provide insight into the remarkable catalytic behavior of the oxygen/silver system for heterogeneous oxidation reactions, purely sub-surface oxygen, and structures involving both on-surface and sub-surface oxygen, as well as oxide-like structures at the Ag(111) surface have been studied for a wide range of coverages and adsorption sites using density-functional theory. Adsorption on the surface in fcc sites is energetically favorable for low coverages, while for higher coverage a thin surface-oxide structure is energetically favorable. This structure has been proposed to correspond to the experimentally observed (4 × 4) phase. With increasing O concentrations, thicker oxide-like structures resembling compressed Ag2O(111) surfaces are energetically favored. Due to the relatively low thermal stability of these structures, and the very low sticking probability of O2 at Ag , their formation and observation may require the use of atomic oxygen (or ozone, O3) and low temperatures. We also investigate diffusion of O into the sub-surface region at low coverage (0.11 ML), and the effect of surface Ag vacancies in the adsorption of atomic oxygen and ozone-like species. The present studies, together with our earlier investigations of on-surface and surface-substitutional adsorption, provide a comprehensive picture of the behavior and chemical nature of the interaction of oxygen and Ag , as well as of the initial stages of oxide formation.

- by Catherine Stampfl
- •
- Surfaces and Interfaces, Heterogeneous Catalysis, Atomic Oxygen, Ozone

New ceramic materials are necessary for the design of primary heat shields for future reusable space vehicles re-entering atmospheric planet. During the re-entry phase on earth, one of the most important phenomena occurring on the heat shield is the recombination of atomic species and among them atomic oxygen. The recombination of atomic oxygen is catalyzed by the material of the heat shield.

- by O. Gerasimova and +1
- •
- Engineering, Chemical Physics, Heterogeneous Catalysis, Physical sciences

The CEDAR Optical Tomographic Imaging Facility (COTIF) consists of a midlatitude chain of meridional imaging spectrographs whose slit apertures subtend a common volume in the ionosphere. The facility provides a set of simultaneous multispectral brightness measurements that are used in a two-dimensional tomographic reconstruction (horizontal versus vertical) of auroral and airglow features in the midlatitude, subauroral ionosphere. A tomographic inversion method is summarized which regularizes the vertical (field-aligned) dimension using a nonlinear low-dimensional basis expansion. Three experimental results are presented for atomic oxygen 557.7-and 630.0-nm emissions at midlatitude. Time sequences of the reconstructed emission fields illustrate the variability in O I excitation patterns in both the diffuse aurora and SAR arcs. The results are interpreted with respect to outstanding issues associated with midlatitude aurora. Extracted vertical profiles are compared with published experimental and theoretical results.

- by Joshua Semeter
- •
- Geology, Multidisciplinary, Ionosphere, Atomic Oxygen

This paper presents a new device generating highvoltage pulsed cold atmospheric plasma jets. With these plasmas, the quantity of atomic oxygen (and, accordingly, the chemical activity) is a lot higher than that in previous researches. The main characteristic of the new device is the usage of three tubular needle-type electrodes connected in parallel. By applying highvoltage pulses (with 20-30-kV amplitude, duration of hundreds of nanoseconds, and hundreds of pulses per second), three independent discharges are formed in the discharge room. The plasma-forming gas is He, with a low quantity of oxygen introduced through the high-voltage electrodes. Each discharge has an optimal percentage of 0.5% vol. O 2 in He, which maximizes the quantity of atomic oxygen in the plasma. The plasmas of the three discharges unite to a single jet though, which contains a quantity of atomic oxygen that is a lot higher than that of the plasma of each discharge. The emission spectra of the plasma jets show the maximization of the intensity of the O I 777 nm line when a concentration of 1.5% vol. O 2 in He (three times higher than so far) is introduced in the plasma-forming gas.

- by Nicolae Georgescu
- •
- High Voltage, Atomic Oxygen, Electrical And Electronic Engineering

A 1-D collisional Monte Carlo model of Europa's atmosphere is described in which the sublimation and sputtering sources of H 2 O molecules and their molecular fragments are accounted for as well as the radiolytically produced O 2 . Dissociation and ionization of H 2 O and O 2 by magnetospheric electron, solar UV-photon and photo-electron impact, and collisional ejection from the atmosphere by the low-energy plasma are taken into account. Reactions with the surface are discussed, but only adsorption and atomic oxygen recombination are included in this model. The size of the surface-bounded oxygen atmosphere of Europa is primarily determined by a balance between atmospheric sources from irradiation of the satellite's icy surface by the high-energy magnetospheric charged particles and atmospheric losses from collisional ejection by the low-energy plasma, photo-and electron-impact dissociation, and ionization and pick-up from the surface-bounded atmosphere. A range of sources rates for O 2 to H 2 O are used with a larger oxygen-to-water ratio than suggested by laboratory measurements in order to account for differences in adsorption onto grains in the regolith. These calculations show that the atmospheric composition is determined by both the water and oxygen photochemistry in the near-surface region, escape of suprathermal oxygen and water into the jovian system, and the exchange of radiolytic water products with the porous regolith. For the electron impact ionization rates used, pick-up ionization is the dominant oxygen loss process, whereas photo-dissociation and atmospheric sputtering are the dominant sources of neutral oxygen for Europa's neutral torus. Including desorption and loss of water enhances the supply of oxygen species to the neutral torus, but hydrogen produced by radiolysis is the dominant source of neutrals for Europa's torus in these models.  2004 Elsevier Inc. All rights reserved.

- by V. Shematovich
- •
- Geochemistry, Geophysics, Monte Carlo, Low Energy Buildngs

The interaction of N 2 O with Ir(1 1 0) and the N 2 O±H 2 reaction on that surface have been studied in the temperature range from 300 up to 800 K. Decomposition of N 2 O into N 2 was observed, along with, surprisingly, N 2 O desorption or formation up to 450 K. Isothermal sustained oscillations in rate were found in the temperature range between 460 and 464 K for H 2 /N 2 O ratios close to 1. The reaction products are N 2 and H 2 O. N 2 O oscillates in anti-phase with N 2 and the maxima in H 2 O formation are``delayed'' compared to the maxima in N 2 formation during the oscillations. The period was close to 60 s. A possible explanation for the oscillations is proposed based on a built-up of atomic oxygen on the surface, produced by N 2 O decomposition, modifying the rate of N 2 O dissociation until oxygen is released in the form of water. Ó

- by Bernard Nieuwenhuys
- •
- Condensed Matter Physics, Quantum Physics, Surface Science, Nitrogen

Abstract For co-polyimides (PIs) of mellitic acid dianhydride, 1, 3-aminophenoxybenzene and 4, 4′-oxydiphthalic anhydride, Zr-pendent group content could be increased to 50%(mol) improving atomic oxygen (AO) resistance while retaining... more

Water, an important natural resource is sometimes contaminated with heavy metals which derived from acid mine drainage and from many industries, including those involving metal plating, mining, pickling and tanning. Water pollution due to the toxic metals has been a major cause of concern for environmental engineers. The industrial and domestic wastewater is responsible for causing several damages to the

- by Carmen Deleanu
- •
- Environmental Engineering, Chemistry, Acid Mine Drainage, Water Pollution

This paper describes a methodology for water vapor retrieval in the mesosphere-lower thermosphere (MLT) using 6.6 µm daytime broadband emissions measured by SABER, the limb scanning infrared radiometer on board the TIMED satellite. Particular attention is given to accounting for the non-local thermodynamic equilibrium (non-LTE) nature of the H 2 O 6.6 µm emission in the MLT. The non-LTE H 2 O(ν 2 ) vibrational level populations responsible for this emission depend on energy exchange processes within the H 2 O vibrational system as well as on interactions with vibrationally excited states of the O 2 , N 2 , and CO 2 molecules. The rate coefficients of these processes are known with large uncertainties that undermines the reliability of the H 2 O retrieval procedure. We developed a methodology of finding the optimal set of rate coefficients using the nearly coincidental solar occultation H 2 O density measurements by the ACE-FTS satellite and relying on the better signal-to-noise ratio of SABER daytime 6.6 µm measurements. From this comparison we derived an update to the rate coefficients of the three most important processes that affect the H 2 O(ν 2 ) populations in the MLT: a) the vibrational-vibrational (V-V) exchange between the H 2 O and O 2 molecules; b) the vibrationaltranslational (V-T) process of the O 2 (1) level quenching by collisions with atomic oxygen, and c) the V-T process of the H 2 O(010) level quenching by collisions with N 2 , O 2 , and O. Using the advantages of the daytime retrievals in the MLT, which are more stable and less susceptible to uncertainties Correspondence to: A. G. Feofilov (artem-feofilov@cua-nasa-gsfc.info) of the radiance coming from below, we demonstrate that applying the updated H 2 O non-LTE model to the SABER daytime radiances makes the retrieved H 2 O vertical profiles in 50-85 km region consistent with climatological data and model predictions. The H 2 O retrieval uncertainties in this approach are about 10% at and below 70 km, 20% at 80 km, and 30% at 85 km altitude. A. G. Feofilov et al.: Daytime SABER/TIMED observations of water vapor in the mesosphere 8155 Acknowledgements.

- by Artem Feofilov
- •
- Atmospheric sciences, Atomic Oxygen, Infrared, Excited states

On October 1-2, 2002, a moderate geomagnetic storm took place with the 3-hour K p index reaching 5-for 24 hours and 7 twice. Evidence from ISR, TEC, airglow, and ionosonde data indicate that a series of large-scale thermospheric atmospheric gravity waves were launched from the auroral zone, modulating the mid-latitude ionosphere over Arecibo by over 150 km and driving mid-latitude and indirectly equatorial spread-F. A

- by Sixto A González
- •
- Ionosphere, Atomic Oxygen, Wave propagation, Indexation

The main goal of this paper is to investigate the interaction of atomic oxygen with graphite surfaces, using first principles total energy calculations. Oxygen coverage, position and crystallographic orientation of the surfaces are the main parameters of this study. At the basal surface, the binding energy is given by the contribution of the in-network interaction between oxygen atoms and between oxygen and graphite. Relaxation effects are non-negligible at low and medium coverages. Zig-zag surfaces are the most reactive ones, followed by armchair and basal ones. For both surfaces, the oxidative etching process that forms the CO and CO 2 gases is also discussed on the basis of our calculations.

- by alain pasturel
- •
- Condensed Matter Physics, Quantum Physics, Surface Science, Atomic Oxygen

After 2 years of operation onboard the Spanish satellite MINISAT, EURDhas achieved an unprecedented success in the observation of the terrestrialnightglow in the EUV, covering a range of ∼ 350-1100 Å EURD hasprovided a total of more than 543 hours ofintegration in the long wavelength spectrometer and more than898 hours in the short wavelength one, allowing the achievement of the most detailed atlas of the terrestrial EUV nightglow ever obtained. We present here the spectra obtained, together with the identification of the lines, some of themdetected for the first time in the nightglow. These spectrarepresent an improvement in sensitivity of several orders of magnitude with respect to previous observations. It has beenpossible, for the first time, to identify the complete Lymanseries of atomic hydrogen, resolving up to Lyman-ε. It hasalso been possible to identify the helium Lyman-β line at 537 Å andto detect other lines of the blended Lyman series of helium, at 515 and522 Å. The spectra clearly show the presenceof the OII lines at 617, 644, 673, and 718 Å, previouslyobserved in the dayglow but seen here for the first time in thenightglow. In addition to the recombination continuum of the atomicoxygen at 911 Å, two features of OI have been detected in thenightglow: the 3s′ 3Do transition at 989 Å, previouslyobserved by Chakrabarti (1984) and the 2p34s3So transition at 1040 Å, partially overlapped with Lyman β, but clearly distinguishable from it. This feature has been seen for the first timein the terrestrial nightglow. The radiative recombination continuum of atomic oxygen at 911 Å, that wasabsent in the observations of the first year of operation of EURD,is now clearly visible. The reasons of the absence of the OIfeature during the first year of operation are still unknown.Anderson et al. (1976) also noticed a strong variation with time of this 911 Å emission.

- by Eric Korpela
- •
- Space Science, Atomic Oxygen, Spectrum, First Year

Optical emission spectroscopy was applied for the characterization of inductively coupled RF oxygen plasma at pressures between 10 and 300 Pa. The plasma was generated with an RF generator at a frequency of 27.12 MHz and output power of 300 W. Spectra were measured in the range 200-1100 nm by an optical spectrometer. At high pressure, the main spectral features observed were the wavelengths of the atomic oxygen transitions at 777.2 and 844.6 nm. Molecular oxygen band at 762 nm was observed as well. The atomic emission intensity showed a maximum when the pressure was about 75 Pa, while molecular band intensity increased monotonically as the total pressure increased. On decreasing the oxygen pressure, other atomic and molecular features appeared in spectra, such as H atomic lines, molecular OH band, and O 2 + band. The behavior of spectral features was explained by collision phenomena in the ionized gas.

- by Uroš Cvelbar
- •
- Materials Engineering, High Pressure, Plasma, Vacuum

The low Earth orbit (LEO) environment is considered hazardous to spacecraft, resulting in materials degradation. Currently, in order to evaluate the degradation of materials in LEO, a retrieval of space exposed samples is required. In this study, a novel approach is proposed to evaluate degradation of materials in LEO without the need of retrieval. The method is utilizing photovoltaic cells (PVCs), an existing component onboard of any satellite. The PVCs are coated by various materials which are sensitive to different LEO constituents, such as atomic oxygen (AO) or ultra-violet (UV) radiation. The method's acronym is ORMADD (on-ORbit MAterials Degradation Detector). The ORMADD's principle of operation is based on measuring the PVC output power which depends on the cell coating material's optical transmission. Erosion of the coating by AO or coloring due to UV radiation affects its optical transmission and, accordingly, the PVC output. The ORMADD performance was tested us...

- by Irina Gouzman and +1
- •
- Engineering, Scientific Instruments, Scientific, Ultraviolet

Study of H , O , CO adsorption and CO q O reaction on 2 2 2 ž / ž / Pt 100 , Pd 110 monocrystal surfaces Abstract Nanoscale changes in the surface morphology of Pd particles that accompany the uptake of hydrogen have been studied Ž . in situ by Field Electron Microscopy FEM . Exposure of a Pd tip to H at low temperatures led to the formation of 2 extruding PdH particles on top of the Pd tip. Growth of these particles proceeds in a ''staccato'' manner. When most of the x hydrogen have been removed from the sample by heating in vacuum, Pd crystallites remain on the surface. They are quite Ž . stable up to about 700 K, where they melt back into the bulk of the tip. A sharp low temperature H -peak 220 K appears in 2 Ž . the TD spectra as a result of decomposition of PdH hydrides on Pd 110 single crystal surface. During the O q H x 2 a d s Ž . Ž . reaction, a hydrogen-modified Pt 100 -hex surface shows an increase in the population of atomic oxygen states: three O ads Ž . states are observed by high resolution electron energy loss spectroscopy HREELS as a result of the presence of defect sites.

Binding energies and preferred adsorption sites of O, OH, and H 2 O to bimetallic clusters PtX, Pt 2 X, and PtX 2 (X ) Pt, Co, Cr, Ni) are determined using density functional theory. The second metal element in the alloy has stronger affinity for OH than the Pt sites, and it is able to adsorb up to two OH radicals per site in oxygenated clusters. The highest binding strength of atomic oxygen is found in the hollow sites of Ni 3 and Co 3 , followed by adsorption in hollow or bridge sites of Pt 2 X or PtX 2 , in all cases significantly stronger than that found in Pt 3 . H 2 O adsorbs on top sites of pure and alloy clusters with much weaker energies compared with those of OH and O; however, the H 2 O binding strength in the Co, Cr, and Ni atoms is enhanced with respect to that on the Pt site, whereas the binding strength of H 2 O on the top of Pt sites of the alloy clusters is much reduced with respect to that in the pure cluster.

- by Perla Balbuena
- •
- The, Atomic Oxygen, Binding Energy, THEORETICAL AND COMPUTATIONAL CHEMISTRY

The polarisation of the atomic oxygen red line in the Earth's thermosphere is observed in different configurations with respect to the magnetic field line at high latitude during several coordinated Incoherent Scatter radar/optical experiment campaigns. When pointing northward with a line-of-sight nearly perpendicular to the magnetic field, we show that, as expected, the polarisation is due to precipitated electrons with characteristic energies of a few hundreds of electron Volts. When pointing toward the zenith or southward with a line-of-sight more parallel to the magnetic field, we show that the polarisation practically disappears. This confirms experimentally the predictions deduced from the recent discovery of the red line polarisation. We show that the polarisation direction is parallel to the magnetic field line during geomagnetic activity intensification and that these results are in agreement with theoretical work.

- by I. McCrea
- •
- Geophysics, Magnetic field, Atmospheric sciences, Atomic Oxygen
- by Luciano Anselmo
- •
- Mechanical Engineering, Aerospace Engineering, Bias, Space

The in¯uence of gravity waves on photochemical heating in the mesopause region is studied in this paper. The results indicate that gravity waves can cause a loss of photochemical heating in the region of the mesopause. The in¯uences of the variation of background temperature and of atomic oxygen density on the loss of photochemical heating induced by gravity waves are discussed. The results indicate that, as background temperature decreases, or as the background atomic oxygen density increases, the gravity wave induced loss of photochemical heating increases and the ratio between it and the background photochemical heating rate also increases. #

- by Ying Jian
- •
- Atomic Oxygen

Spacecraft surface charging can lead to arcing and a loss of electricity generation capability in solar panels or even loss of a satellite. The charging problem may be further aggravated by atomic oxygen (AO) exposure in Low Earth orbits, which modifies the surface of materials like polyimide, Teflon, anti-reflective coatings, cover glass etc, used on satellite surfaces, affecting materials properties, such as resistivity, secondary electron emissivity and photo emission, which govern the charging behavior. These properties are crucial input parameters for spacecraft charging analysis. To study the AO exposure effect on charging governing properties, an atomic oxygen exposure facility based on laser detonation of oxygen was built. The facility produces AO with a peak velocity value around 10-12km/s and a higher flux than that existing in orbit. After exposing the polyimide test material to the equivalent of 10 years of AO fluence at an altitude of 700-800 km, surface charging properties like surface resistivity and volume resistivity were measured. The measurement was performed in a vacuum using the charge storage decay method at room temperature, which is considered the most appropriate for measuring resistivity for space applications. The results show that the surface resistivity increases and the volume resistivity remains almost the same for the AO exposure fluence of 5.4×1018 atoms cm-2.

- by Arifur Khan and +1
- •
- Atomic Oxygen, Surface Charge

Behavior of atomic oxygen, O 2 and O 3 molecules adsorbed on external surface of H-capped (5,0) singlewalled carbon nanotube is studied using density functional calculations. Geometry optimizations were carried out at B3LYP/6-31G* level of theory using Gaussian 98 suites of program. Binding energies corresponding to chemical adsorption of atomic oxygen, O 2 and O 3 molecules are obtained to be in the range 65-250 kcal/mol. An oxygen atom is found to bind to the outside surface of the nanotubes to give stable epoxide-like and ether structures. Of these, the most stable is the epoxide, with calculated adsorption energy of 68.014 kcal/mol. Calculated chemical shielding, electric filed gradient tensors and their relative orientation at the sites of carbons reveal that atomic oxygen, O 2 and O 3 adsorptions have a dramatic effect on the electronic structure of single-walled carbon nanotubes (SWCNTs). Moreover, total density of states calculations show a significant difference in the density of states at the Fermi level for the two sites of (O-CNT) system.

Abstraet--A rocket payload designed to measure mesospheric sodium, hydroxyl and oxygen nightglow emissions, in addition to electron density and temperature, was launched from the Alchntara Launch Center (2°S, 44°W), Brazil, at 23:52 LST on 31 May 1992. The height profiles of the atomic oxygen 01557.7 nm and molecular oxygen Atmospheric (0-0) band emissions showed maxima at 100 + 3 km and 98 + 3 km, respectively. The emission data are used to calculate the atomic oxygen concentration profiles. The results show the validity for the equatorial region of the empirical parameters proposed by McDade et al. (1986).

- by Paulo P Batista
- •
- Atmospheric Science, Atomic Oxygen, Electron Density

a b s t r a c t Carbon coverage, oxidation and reduction of Au, Pt, Pd, Rh, Cu, Ru, Ni and Co layers of 1.5 nm thickness on Mo have been characterized with ARPES and desorption spectroscopy upon exposure to thermal H and O radicals. We observe that only part of the carbon species is chemically eroded by atomic H exposure, yielding hydrocarbon desorption. Exposure to atomic O yields complete carbon erosion and CO 2 and H 2 O desorption. A dramatic increase in metallic and non-metallic oxide is observed for especially Ni and Co surfaces, while for Au and Cu, the sub-surface Mo layer is much more oxidized. Although volatile oxides exist for some of the d-metals, there is no indication of d-metal erosion. Subsequent atomic H exposure reduces the clean oxides to a metallic state under desorption of H 2 O. Due to its adequacy, we propose the atomic oxygen and subsequent atomic hydrogen sequence as a candidate for contamination removal in practical applications like photolithography at 13.5 nm radiation.

- by Fred Bijkerk
- •
- Condensed Matter Physics, Quantum Physics, Surface Science, ARPES

The interaction of graphite with plasmas of pure gases (O 2 , N 2 or H 2 O), air or mixtures of gases containing NO has been studied by XPS ''in situ'' analysis. Depending on the type of plasma, different species of nitrogen, oxygen and carbon have been detected on the surface of graphite. The nitrogen containing species have been attributed to pyridinic, pyrrol, quartenary and oxidized groups adsorbed on the surface. The evolution with the treatment time of the relative intensity of the different nitrogen bands for Ar + NO, N 2 + NO, air or N 2 plasmas has served to propose a model accounting for the reactions of graphite with plasmas of NO containing gases. The model explains why carbon materials (in the form of graphite, soot particles, etc.) can be very effective for the removal of the NO present in exhaust combustion gases excited by a plasma. The analysis of the C1s and O1s photoemission peaks reveals the formation of C/O adsorbed species up to a maximum concentration on the surface of around 10% atomic oxygen. A general evolution is the progressive formation of C/O species where the carbon is sp 3 hybridized. This tendency is enhanced when graphite is treated with the plasma of water.

- by Agustin R. Gonzalez-Elipe
- •
- Engineering, Carbon, Physical sciences, Nitrogen

We have studied oxygen interaction with Au crystals ͑field emitter tips͒ using time-resolved ͑atom-probe͒ field desorption mass spectrometry. The results demonstrate no adsorption to take place on clean Au facets under chosen conditions of pressures ͑p Ͻ 10 −4 mbar͒ and temperatures ͑T = 300-350 K͒. Steady electric fields of 6 V / nm do not allow dissociating the oxygen molecule. The measured O 2 + intensities rather reflect ionization of O 2 molecules at critical distances above the Au tip surface. Certain amounts of Au-O 2 complex ions can be found at the onset of Au field evaporation. Calculations by density functional theory ͑DFT͒ show weak oxygen end-on interaction with Au 10 clusters ͑⌬E = 0.023 eV͒ and comparatively stronger interaction with Au 1 /Au͑100͒ model surfaces ͑⌬E = 0.25 eV͒. No binding is found on ͕210͖ facets. Including ͑positive͒ electric fields in the DFT calculations leads to an increase of the activation energy for oxygen dissociation thus providing an explanation for the absence of atomic oxygen ions from the field desorption mass spectra.

- by Frederik Tielens
- •
- Engineering, Surfaces and Interfaces, Mass Spectrometry, Chemical Physics

Rhodium single crystals show a surprisingly wide range of reconstructions induced by light elements such as oxygen and nitrogen, as well a number of chemical reactions of fundamental chemical importance. In this review, we present and critically discuss the current state of knowledge of the interaction of oxygen, nitrogen and mixed O+N layers with such Rh surfaces, emphasising structural aspects and their impact on the surface reactivity. On the basis of the available experimental results we will elucidate some general trends, which shed light on the possible driving forces behind the diffusive and displacive reconstructions induced by adsorbed atomic oxygen and nitrogen. More attention will be paid to the reconstructive interactions on a Rh(1 1 0) surface.

- by R. Rosei
- •
- Condensed Matter Physics, Surface Science, Scanning tunneling microscopy, Ultraviolet