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Contains fundamental spectroscopic results regarding atomic oxygen. Data represent basic science contributions and are not associated with an application or defense article.
Nightglow emission from atomic oxygen caused by dissociative recombination in F region
A predictive tool was developed to estimate the low Earth orbit (LEO) atomic oxygen erosion yield of polymers based on the results of the Polymer Erosion and Contamination Experiment (PEACE) Polymers experiment flown as part of the Materials International Space Station Experiment 2 (MISSE 2). The MISSE 2 PEACE experiment accurately measured the erosion yield of a wide variety of polymers and pyrolytic graphite. The 40 different materials tested were selected specifically to represent a variety of polymers used in space as well as a wide variety of polymer chemical structures. The resulting erosion yield data was used to develop a predictive tool which utilizes chemical structure and physical properties of polymers that can be measured in ground laboratory testing to predict the in-space atomic oxygen erosion yield of a polymer. The properties include chemical structure, bonding information, density and ash content. The resulting predictive tool has a correlation coefficient of 0.914 when compared with actual MISSE 2 space data for 38 polymers and pyrolytic graphite. The intent of the predictive tool is to be able to make estimates of atomic oxygen erosion yields for new polymers without requiring expensive and time consumptive in-space testing.
An atomic oxygen beam apparatus that produces flux levels and atomic kinetic energy similar to that encountered by spacecraft in low Earth orbit (LEO) is described. The beam apparatus consists of an electric discharge ion source, mass filter, decelerator, and neutralizer. Specific design goals include a 1.3 cm beam diameter, a 5 eV beam energy, and a flux density on the order of 10(15) cm(-2) s(-1). The total fluence will be on the order of 10(19) cm(-2) for an 8 hour test. The neutral oxygen beam will expose various materials contained within a large target chamber. Within the chamber will be a rather complex suite of instrumentation that will allow real-time studies of material mass loss and reactant species spatial distribution. In addition, a UV solar simulator will aid in the understanding of various synergistic effects.
Using data obtained by an ultraviolet spectrometer on the Pioneer-Venus Orbiter, energy and altitude distribution of nonthermal oxygen atoms in the Venus atmosphere for typical daytime and nighttime conditions are calculated using two different numerical methods. Agreement is found between results obtained by the two-stream transport method and the diffusion equation technique. Dissociative recombination of molecular oxygen ions and charge exchange of atomic oxygen ions with the neutral hydrogen and oxygen gas are the source terms, and calculations show that the dissociative recombination term is the dominant one. It is shown that measured hot atom concentrations exceed estimates of the thermal hydrogen atom concentrations derived from Brinton et al. (1980) over most of the daytime exosphere, and the calculated concentrations do so to an even greater extent. It is concluded that hot oxygen atoms are an important component of the dayside exosphere of Venus, their most important effect being the absorption of solar wind.
Total absorption cross section of atomic oxygen, using microwave discharge in He-O2 mixture
The University of Nebraska is currently evaluating Low Earth Orbit (LEO) simulation techniques as well as a variety of thin film protective coatings to withstand atomic oxygen (AO) degradation. Both oxygen plasma ashers and an electron cyclotron resonance (ECR) source are being used for LEO simulation. Thin film coatings are characterized by optical techniques including Variable Angle Spectroscopic Ellipsometry, Optical spectrophotometry, and laser light scatterometry. Atomic Force Microscopy (AFM) is also used to characterize surface morphology. Results on diamondlike carbon (DLC) films show that DLC degrades with simulated AO exposure at a rate comparable to Kapton polyimide. Since DLC is not as susceptible to environmental factors such as moisture absorption, it could potentially provide more accurate measurements of AO fluence on short space flights.
The rate constant for the reaction of atomic oxygen with phosphine has been measured at 298 K using flash photolysis combined with time-resolved detection of O(3P) via resonance fluorescence. Atomic oxygen was produced by flash photolysis of N2O or NO highly diluted in argon. The results were shown to be independent of (PH3), (O), total pressure and the source of O(3P). The mean value of all the experiments is k1 = (3.6 + or -0.8) x 10 to the -11th cu cm/s (1 sigma). Two previous measurements of k1 differed by more than an order of magnitude, and the results support the higher value obtained in a discharge flow-mass spectrometry study. A comparison with rate data for other atomic and free radical reactions with phosphine is presented, and the role of these reactions in the aeronomy or photochemistry of Jupiter and Saturn is briefly considered.
Report describes experimental study of chemical reactions of atomic oxygen in ground state {O(3P)} with polybutadienes and related polymers. Attention focused on such reactions because of adverse effects of environmental atomic oxygen on polymeric materials in low orbits around Earth.
An organic black thermal blanket material was coated with indium tin oxide (ITO) to prevent blanket degradation in the low Earth orbit (LEO) atomic oxygen environment. The blankets were designed for the Galileo spacecraft. Galileo was initially intended for space shuttle launch and would, therefore, have been exposed to atomic oxygen in LEO for between 10 and 25 hours. Two processes for depositing ITO are described. Thermooptical, electrical, and chemical properties of the ITO film are presented as a function of the deposition process. Results of exposure of the ITO film to atomic oxygen (from a shuttle flight) and radiation exposure (simulated Jovian environment) are also presented. It is shown that the ITO-protected thermal blankets would resist the anticipated LEO oxygen and Jovian radiation yet provide adequate thermooptical and electrical resistance. Reference is made to the ESA Ulysses spacecraft, which also used ITO protection on thermal control surfaces.
A pulsed high-flux source of nearly monoenergetic atomic oxygen was developed to perform accelerated erosion testing of spacecraft materials in a simulated low-earth orbit (LEO) environment. Molecular oxygen is introduced into an evacuated conical expansion nozzle at several atmospheres pressure through a pulsed molecular beam valve. A laser-induced breakdown is generated in the nozzle throat by a pulsed CO2 TEA laser. The resulting plasma is heated by the ensuing laser-supported detonation wave, and then it rapidly expands and cools. An atomic oxygen beam is generated with fluxes above 10 to the 18th atoms per pulse at 8 + or - 1.6 km/s with an ion content below 1 percent for LEO testing. Materials testing yielded the same surface oxygen enrichment in polyethylene samples as observed on the STS mission, and scanning electron micrographs of the irradiated polymer surfaces showed an erosion morphology similar to that obtained on low earth orbit.
Mass spectrometric investigation of oxygen atoms reacting with methane
Experimental and analytical analysis of the atomic oxygen erosion of pyrolytic graphite as well as Monte Carlo computational modeling of the erosion of Kapton H (DuPont, Wilmington, DE) polyimide was performed to determine the hyperthermal energy of low frequency (30 to 35 kHz) plasma ashers operating on air. It was concluded that hyperthermal energies in the range of 0.3 to 0.9 eV are produced in the low frequency air plasmas which results in texturing similar to that in low Earth orbit (LEO). Monte Carlo computational modeling also indicated that such low energy directed ions are fully capable of producing the experimentally observed textured surfaces in low frequency plasmas.
The experimental investigation of the atomic oxygen response of an open-source mass spectrometer conducted in a high-velocity molecular-beam facility is described, and its results are evaluated. These preliminary results illustrate the value of studies of this type and tentatively support the thesis that in rocket flights of open-source mass spectrometers atomic oxygen loss is not a serious problem.
Various polymers were exposed to atomic oxygen O(3P) and comparisons made of their stability. The rates of reaction and mass removal for polyphosphazenes exposed to atomic oxygen were found to be significantly lower than for other polymers evaluated in this study. Surface analysis of polyphosphazene films indicated that O(3P) induces rearrangements in the phosphorus-nitrogen backbone of the polymer, resulting in cross-linking and cleavage of some pendant groups that are then replaced by oxygen.
In this work, we describe a joint experimental and theoretical investigation on oxygen double photoionization—the emission of two electrons from atomic oxygen following single photon absorption. High-resolution experimental measurements were performed at the Advanced Light Source, revealing sharp resonance structure superimposed on the more familiar Wannier-like, nearly-linear background. These resonance features are attributed to ionization-plus-excitation Feshbach resonances embedded in the double ionization continuum, doubly-excited states that lie above the double-ionization threshold. Such features are absent in the double photoionization cross section of He, or other quasi-two-electron systems, for which the doubly-ionized atomic core remains inert. For a corresponding theoretical analysis, the R-matrix with pseudostates (RMPS) method was invoked by calculating final-state, two-electron resonances-plus-continua wavefunctions and corresponding single-photon absorption cross sections. Overall agreement is found in the direct, background double photoionization cross section. However, the RMPS method, using a small basis due to practical computational limitations, was unable to reproduce quantitatively the smooth background or the sharper resonance features observed in the measurements, showing instead large-scale oscillations about the experimental background, and characteristic pseudoresonance jitter, associated with an insufficient convergence of the pseudostate representation to the true two-electron infinite series of Feshbach resonances embedded in the two-electron continuum. The prominent resonance structure observed highlights the need to consider multiple excitation processes in atoms more complex than He or quasi-two-electron systems.
The oxidation of nickel by atomic oxygen at pressure from 1 to 45 N/sq m between 1050 and 1250 K was investigated. In these ranges, the oxidation was found to follow the parobolic rate law, viz., K sub p = 0.0000114 exp(-13410/T) g squared/cm4/sec for films of greater than 1 micron thickness and was pressure independent. The activation enthalpy for the oxidation reaction was 112 + or - 11 kj/mole (27 + or - 3 kcal/mole). Of a number of possible mechanisms and defect structures considered, it was shown that the most likely was a saturated surface defect model for atomic oxidation, based on reaction activation enthalpies, impurity effects, pressure independence, and magnitudes of rates. A model judged somewhat less likely was one having doubly ionized cationic defects rate controlling in both atomic and molecular oxygen. From comparisons of the appropriate processes, the following enthalpy values were derived: enthalpy of activation (Ni diffusion in Ni0) = 110 + or - 30 kj/mole and standard enthalpy change for reaction formation (doubly ionized cation vacancies in Ni0 from atomic oxygen)= -9 + or - 25 kj/mole.
Polymer materials samples mounted on a passive carrier tray were flown aboard the STS-46 Atlantis shuttle as complement to the EOIM-3 (Evaluation of Oxygen Interaction with Materials) experiment to evaluate the effects of atomic oxygen on the materials and to measure the gaseous shuttle bay environment. The morphological changes of the samples produced by the atomic oxygen fluence of 2.07 x 10(exp 20) atoms/cm(exp 2) are being reported. The changes have been verified using Electron Spectroscopy for Chemical Analysis (ESCA), gravimetric measurement, microscopic observations and thermo-optical measurements. The samples, including Kapton, Delrin, epoxies, Beta Cloth, Chemglaze Z306, silver Teflon, silicone coatings, 3M tape and Uralane and Ultem, PEEK, Victrex (PES), Polyethersulfone and Polymethylpentene thermoplastic, have been characterized by their oxygen reaction efficiency on the basis of their erosion losses and the oxygen fluence. Those efficiencies have been compared to results from other experiments, when available. The efficiencies of the samples are all in the range of E-24 g/atom. The results indicate that the reaction efficiencies of the reported materials can be grouped in about three ranges of values. The least affected materials which have efficiencies varying from 1 to 10(exp 25) g/atom, include silicones, epoxies, Uralane and Teflon. A second group with efficiency from 10 to 45(exp 25) g/atom includes additional silicone coatings, the Chemglaze Z306 paint and Kapton. The third range from 50 to 75(exp 25) includes organic compound such as Pentene, Peek, Ultem, Sulfone and a 3M tape. A Delrin sample had the highest reaction efficiency of 179(exp 25) g/atom. Two samples, the aluminum Beta cloth X389-7 and the epoxy fiberglass G-11 nonflame retardant, showed a slight mass increase.