Interaction Of Atomic Oxygen Research Articles

Cluster model approach to chemisorption on aluminum: Surface relaxation effects on the interaction of atomic oxygen with the Al(111) surface

The chemisorption of atomic oxygen on Al clusters, sections of the Al(111) surface containing up to 49 Al atoms, has been investigated by means of a modified version of the INDO method. The study has shown that the bonding between oxygen and the Al(111) surface is very strong and of basically local nature. The interaction proceeds through three steps: the formation of a chemisorbed overlayer, the overcoming of an energy barrier, and the incorporation of the oxygen atom in cavities below the surface. The reconstruction of the metal surface occurring when oxygen penetrates the top layer of the cluster greatly reduces the energy barrier to surface penetration.

Surface mediated radical recombination luminescence: O+NO+Ni

Results of an experimental investigation of the chemiluminescence produced by the interaction of atomic oxygen and nitric oxide on a nickel foil surface are reported. Visible luminescence which depends linearly on the atomic oxygen and nitric oxide fluxes, on the substrate temperature, and on the substrate temperature history has been observed under conditions for which the three-body gas-phase reaction of O and NO is negligible. The intensity of the luminescence is greater than can be accounted for by the gas-phase two-body radiative recombination reaction of O and NO. The time, flux, and temperature dependences, along with the intensity of the emission support strongly the notion that the observed luminescence stems from excited species, most probably electronically excited NO2, formed in a surface mediated reaction.

Results of apparent atomic oxygen reactions with spacecraft materials during Shuttle flight STS-41G

The effect of atomic oxygen interaction experienced by polymeric-based spacecraft materials is described. An experimental package (ACOMEX) flown on shuttle mission STS-41G carried out the investigation of advanced composite specimens such as carbon-epoxy and Kevlar-epoxy both with and without protective coatings added to thermal protective paints and films. Information on the exposure environment of the specimens was provided by a carbon coated atomic oxygen fluence monitor together with a photographic record. Mass loss measurements and photomicrographs made possible the analysis of the effect of interaction. After a total of about 38 hours of equivalent normal exposure at 225 km altitude the results showed that unprotected exposed surfaces exhibited severe erosion and mass loss with the possibility of seriously degrading structural and thermal performance. However, the specimens with a thin fluorocarbon overcoat showed promise of providing a protective barrier to the attack without altering the base properties of the material.

Molecular beam study of the interaction of atomic and molecular oxygen with methane

Absolute integral cross sections for collisions of CH4 with O2 molecules and of O2 molecules and O(3Pj) atoms with CH4 are measured as a function of velocity at thermal energies in a molecular beam apparatus. For the O2–CH4 interaction the glory structure observed allows an analysis in terms of an isotropic potential model and meaningful potential parameter values are obtained. For the O(3Pj)–CH4 interaction the anisotropy due to the O(3Pj) atoms causes a partial quenching of the glory amplitude. Nevertheless a realistic isotropic potential can be extracted from the glory extrema position. The present potential parameters for the O2–CH4 and the O–CH4 interactions can be used to predict realistic parameters for more complicated interactions involving O2 molecules and O atoms with other species of interest also in combustion.

Interaction of atomic oxygen with copper clusters

The chemisorption of atomic oxygen on Cu(001) is treated using a many-electron embedding theory in which the copper lattice is modeled as a 25-atom cluster. Of the three high symmetry sites investigated—fourfold, bridge, and atop-atom—the fourfold site is found to be most stable, with a dissociation energy of ∼6.1 eV (r⊥=0.7 Å), while the atop-atom configuration corresponds to the least stable site for atomic oxygen adsorption. The atop-atom site yields a radical-like state, ‘‘O−’’, whereas the open sites involve an oxide-like state, ‘O2−’, for oxygen. The principal valence ionization from oxygen is found to occur ∼8–10 eV below the vacuum level. The results of calculations on smaller clusters, CunO, n=2–5, are found to be in qualitative agreement with the results for Cu25O.

A consideration of atomic oxygen interactions with the Space Station

A computer model is developed in order to calculate fluence for a generalized spacecraft in orbital flight based on mass spectrometer and incoherent scatter (MSIS) measurements of ambient density. The calculations are used to identify criteria for the selection of materials for the construction of an LEO Space Station. The model is generalized such that the surfaces for study can be oriented in any direction with respect to: a body coordinate system fixed to the spacecraft (E surfaces); and a solar inertial coordinate system. A parametric study was performed in order to evaluate the effects of altitude, inclination, and solar activity on atomic oxygen fluence. Values are obtained for samples of Mylar, Kevlar, Kapton, Tedlar, Teflon and sulfone, as well as for some ethylene polymers. The range of values for material reactivities is from 360 microns for ram-facing surfaces to 200 microns for solar power surfaces during each cycle of solar activity. The possibility of improving reactivity by employing certain chemical coatings is also discussed.

Study of the interactions of atomic and molecular oxygen with O2 and N2 by scattering data

Absolute total scattering cross sections for the O2–O2, O2–N2, O–N2, and O–O2 systems are measured in the thermal energy range. A glory structure is present for O2–O2, O2–N2, and O–N2. For O–N2 this structure appears to be partially quenched due to the anisotropy of the 3P oxygen atom. For O–O2 the structure is almost completely quenched because of the presence of a manifold of interactions. From the analysis of the cross section data, information about the interaction potential of all these systems of atmospheric interest is obtained. For O2–O2 a potential able to reproduce also the spectroscopic and thermophysical data is proposed.

Study of the interaction of atomic oxygen and nitrogen with ruthenium by the bond interaction method

The heats of atomically adsorbed oxygen and nitrogen on Ru(0001) and Ru(1010) planes have been calculated by the semiempirical bond interaction method. The calculations show that oxygen is strongly adsorbed on ruthenium, while molecular nitrogen cannot be chemisorbed on ruthenium.

Role of gas-surface interactions in the reduction of Ogo 6 neutral particle mass spectrometer data

The gas-surface interaction effects observed by the quadrupole mass spectrometer are described, and the technique developed to account for them in determining ambient neutral densities is summarized. The total ion current and the ion currents for ions with molecular weights 2, 4, 16, 28, and 32 are sampled for 1.125 sec once every 9.216 sec, for 258 sec out of a 368 sec cycle. An equation is given for the number density of any constituent in the ion source region, and source density data are discussed. The mass 28 background gas is considered to be CO rather than N2, and a CO model is developed. A quasi-equilibrium model of the atomic oxygen interactions is constructed, and a set of surface parameters is determined which provides a reasonable fit to the mass 16 and 32 source densities consistent with the predicted ambient atomic oxygen.

Interaction of atomic oxygen with molybdenum bisulfide and certain preparates based on this compound

Interaction of atomic oxygen with molybdenum bisulfide and certain preparates based on this compound

Interaction of Atomic Oxygen with Various Surfaces

A pulsed atomic-oxygen beam is used to investigate the interaction of atomic oxygen with various surfaces at a pressure of 10−7 torr. The probability that an atom after striking a surface will return to the gas phase as an atom is measured for Pyrex, stainless steel, Teflon, gold, and titanium and is found to lie between 45% and 60% for all of these materials at room temperature. This reflection probability β is strongly temperature dependent for metals, dropping below 10% at 450°C, but less so for Pyrex, dropping only to 33% at the same temperature. The atoms which are not reflected apparently stick to the surfaces. In particular there is no evidence that at 10−7 torr they recombine to form O2 or are emitted as parts of oxygen-containing molecules such as CO2 or N2O. Qualitative experiments indicate that recombination does take place at pressures near 1 torr.

Electron–Ion and Ion–Ion Dissociative Recombination of Oxygen. I. Electron–Ion Recombination

The rate coefficient for electron–molecular-oxygen-ion recombination is calculated quantum mechanically. The quantum treatment due to Warke is presented in detail. A simple one-electron model is used. The positive molecular ion is approximated by a rotating dumbbell consisting of O(3P) and O+(4S), and the electron–atomic oxygen interaction is treated as the perturbation for the recombination process. In the one-electron approximation, only six final continuum states are possible. By assuming that one of them, the repulsive Σg+1 of O + O, crosses at the ground vibrational state of O2+, the overlap integrals are then carried out. The calculated rate coefficient, α = (2.8 ± 0.2) × 10−7cm3 / sec at T = 300°K, is close to the experimental results αexptl = (2.2 ± 0.4) × 10−7cm3 / sec.

Interaction of atomic oxygen, produced in the gas phase, with solid hydrocarbons: Reactions of the atomic oxygen with solid propylene at temperatures of 77 °-67 °K

Interaction of atomic oxygen, produced in the gas phase, with solid hydrocarbons: Reactions of the atomic oxygen with solid propylene at temperatures of 77 °-67 °K

Untersuchung von oberflächenreaktionen mittels beugung langsamer elektronen (LEED): I. Wechselwirkung von O 2 und N 2O mit (110)-, (111)- und (100)-Kupfer-Oberflächen

The interaction of molecular and (by decomposition of N 2O) atomic oxygen with atomically clean (110)-, (111)-, and (100)-copper surfaces has been studied by low energy electron diffraction (LEED). There is a great difference in the reactivity of the different surfaces. On each of the studied surfaces several structures — dependent of the experimental conditions — could be observed: The (110) plane reacts with very little amounts of O 2 at room temperature to produce a 1 × 2-structure. N 2O causes the same structure, thus indicating the dissociative adsorption of O 2. This structure changes reversibly by oxygen exposures > 10 −4 Torr-min into a new structure with a surface net described by 3 × √(10.25)−62°. On the (111) plane at room temperature only a disordered adsorption takes place, which causes a strong increase in background intensity. At 350 °C a part of the adsorbed oxygen desorbs. At 400 °C a complicated structure is produced with a sevenfold lattice constant, which changes at 450 °C into a 4 × 4- and at last at 500 °C into a 2 × 2-structure. N 2O causes the same stable 2 × 2-structure. The (111) surface can be reduced by H 2 at 450 °C. The interaction of a (100) surface with molecular oxygen produces two types of structures with rectangular unit cells as observed by Lee and Farnsworth 1). Interaction of N 2O at 500 °C causes the appearance of two other structures with the (111) symmetry of the epitaxial Cu 2O. The first has a lattice constant of approximately 1.06 a, and is characterized by groups of diffraction spots which are close together and which are ascribed to multiple scattering. This structure can be reduced by H 2 at 400 °C. The second structure has a lattice constant of a√3 and is more stable than the first one. This structure can be reduced at 450 °C. Larger amounts of oxygen cause the appearance of facets. In no case the formation of the true oxide could be observed.

Interaction of atomic oxygen generated in the gaseous phase with solid hydrocarbons: Reaction of atomic oxygen with solid ethylene at temperatures of 65 °–69 °K

The Fe/CaO catalysts with different Fe contents were prepared and used for fast pyrolysis of sawdust by Py-GC/MS experiments. The effects of Fe contents of the Fe/CaO catalysts on the yields and compositions of pyrolytic products were studied. It was found that when Fe contents changed from 5% to 15% (wt.), more Ca2Fe2O5 phases were formed on the Fe/CaO catalysts, and all the catalysts were effective in upgrading the bio-oils, but the catalytic activities were gradually inhibited with the increase of Fe contents. Among the three catalysts, the 5Fe/CaO catalyst displayed the best activity in reducing the oxygenated compounds, which is beneficial for the improvement of the properties of bio-oils used as liquid fuels.

Rate constant and mechanism of the reaction of atomic oxygen with 1, 2-dichlorethane

1. Absolute values of the rate constant for the reaction of atomic oxygen with 1, 2-dichlorethane in the temperature range 353–473° K and at pressures of 2 and 4.3mm Hg were measured. The activation energy of the reaction was determined. 2. In a study of the mechanism of the interaction of atomic oxygen with 1, 2-dichlorethane it was shown lhat the main reaction products were HC1 and CO, formed in the primary act, resulting in cleavage of the C-C bond.

Rate constant and mechanism of the reaction of atomic oxygen with methyl alcohol

1. The mechanism of the reaction of atomic oxygen with methyl alcohol in a jet has been studied. The principal carbon containing reaction product was formaldehyde, formed in the initial act of the interaction of atomic oxygen with alcohol. 2. The absolute values of the rate constant of the reaction of atomic oxygen with methyl alcohol at temperatures in the region 347–506°K and pressures 2 to 14 mm. were measured. The energy of activation of the reaction was determined. 3. Reaction of atomic oxygen with methyl alcohol proceeds by a bimolecular mechanism without participation of third particles.