Atomic Oxygen Absorption Research Articles

Detection of molecular oxygen using nanosecond-laser-induced plasma.

Molecular oxygen (O2) concentration is measured by employing nanosecond laser-induced plasmas (ns-LIP) over a broad temperature spectrum ranging from 300 K to 1000 K, in the presence of an additional oxygen-containing molecule, CO2. Typically, emission spectra emanating from ns-LIP are devoid of molecular information, as the ns-LIP causes the dissociation of molecular species within the plasma. However, atomic oxygen absorption lines that momentarily appear at 777 nm in the broadband emission from the early-stage plasma are determined to be highly sensitive to the O2 mole fraction but negligibly affected by the CO2 mole fraction. The atomic O absorbing the plasma emission originates from the O2 adjacent to the plasma: robust UV radiation from the early-stage plasma selectively dissociates adjacent O2, exhibiting a relatively low photodissociation threshold, thus generating the specific meta-stable oxygen capable of absorbing photons at 777 nm. A theoretical model is introduced, explicating the formation of the meta-stable O atom from adjacent O2. To sustain the UV radiation from the plasma under high-temperature and low-density ambient conditions, a preceding breakdown is triggered by a split laser pulse (532 nm). This breakdown acts as a precursor, seeding electrons to intensify the inverse-Bremsstrahlung photon absorption of the subsequent laser pulse (1064 nm). Techniques such as proper orthogonal decomposition (POD) and support vector regression (SVR) are employed to precisely evaluate the O2 mole fraction (<1% uncertainty), by analyzing the short-lived (<10 ns) O2-indicator depicted in the early-stage plasma.

Atomic Oxygen Absorption into Pt-Based Alloy Subsurfaces

Density functional theory is used to study atomic oxygen absorption into subsurfaces of various platinum-based alloys to investigate the effects of alloyed metals on the thermodynamics and kinetics of this process. The results show that alloying Pt with Ir and Rh increases the absorption energy barrier compared with pure Pt, making the O migration to the subsurface more difficult, and that the addition of Co and Ru to Pt can decrease the reverse energy barrier of absorption making O unstable in the subsurface. By comparison of the atomic oxygen absorption in Pt3X alloys with that in PtX alloys, it is found that both the nature of the alloyed metal species and the alloy composition have effects on the atomic oxygen absorption kinetics. Analyses of the atomic oxygen absorption into the subsurface of ternary alloys such as Pt2IrRu show that compared with pure platinum the presence of the two added metals can increase the barriers for surface diffusion and that for O absorption while simultaneously decreasing...

Chemical Environment Effects on the Atomic Oxygen Absorption into Pt(111) Subsurfaces

Density functional theory is used to study chemical environment effects such as surface coverage of oxygenated species and presence of adsorbed oxygen reduction intermediate OH and water on the atomic oxygen absorption process into Pt(111) subsurfaces. The results show that increasing the on-surface oxygen coverage can energetically and kinetically stabilize subsurface atomic oxygen present at 0.11 and 0.25 monolayer subsurface coverage. At constant subsurface coverage, the absorption energy barrier increases with increasing on-surface coverage. Adsorbed on-surface OH has similar effects on the atomic oxygen absorption process as those caused by on-surface adsorbed atomic oxygen. A monolayer of water over the on-surface oxygen does not significantly alter the thermodynamics and kinetics of the oxygen absorption process.

Computer-aided study of oxygen absorption by water clusters. IR spectra of heteroclusters

Spectral characteristics of ( H 2 O ) n , ( O 2 ) m ( H 2 O ) n , and ( O ) i ( H 2 O ) n cluster systems, where m ≤ 2, i ≤ 4, and 10 ≤ n ≤ 50 , are studied with the molecular dynamics method using a flexible molecule model. The IR absorption spectra are changed substantially as a result of O 2 molecule dissociation, and in the presence of atomic oxygen in the clusters, the spectra are characterized by a deep minimum at 520 cm -1 . The absorption of oxygen causes a marked reduction in reflection coefficient R of monochromatic IR radiation. The number of peaks in the R ( ω ) spectra decreases to two in the case of molecular oxygen absorption and is no larger than four in the case of atomic oxygen absorption. The absorption of atomic oxygen by the clusters is also accompanied by a significant increase in the dissipation of energy accumulated by the clusters. This effect weakens when molecular oxygen is absorbed. An increase in atomic oxygen concentration in the clusters renders their radia- tion harder.

Analysis of plume-buffer gas interaction through molecular and atomic oxygen absorption spectroscopy

We present results acquired by using in-situ diagnostics based on atomic and molecular oxygen absorption spectroscopy during laser ablation in the presence of an O2 environment. Our investigation provides detailed space- and time-resolved information on the relative density of atomic and molecular oxygen in the plume, and demonstrates a strong correlation between their behavior. The results shed light on the occurrence of reactive-collisional processes involving the ablated material and the environment, leading to O2 dissociation.

In situ diagnostics of pulsed laser ablation through atomic oxygen absorption spectroscopy

We present an in situ diagnostics for time- and space-resolved analysis of atomic oxygen during pulsed laser ablation in the presence of a molecular oxygen environment. Our diagnostics are based on transient atomic absorption spectroscopy and exploits diode laser as the probe source. The results, acquired during ablation of YBCO and NiTi targets, demonstrate the sensitivity of the technique in detecting the atomic oxygen produced through dissociation of O 2 environment gas, and show the formation of a relatively large density of atomic oxygen close to the plume range in the experimental conditions typical for deposition of superconductive thin films.

Studies of the reaction of atomic and molecular oxygen with niobium and niobium-(1 at.% zirconium)-(0.7 at.% carbon) (PWC-11) alloy at low pressures

The interaction of atomic and diatomic oxygen with niobium and niobium-(1 at.% zirconium)-(0.7 at.% carbon) alloy has been studied between 773 and 1373 K at an oxygen pressure in the range 9×10 −3–7×10 −2 Pa. At the initial stage of oxidation, when the dissolution of oxygen in niobium or alloy takes place, both the diatomic and atomic oxygen absorption probabilities are independent of the incident flux, apparently the rate of reaction is determined by the oxygen chemisorption on the metal surface. Atomic and molecular oxygen absorption probability at rather high temperatures are also almost independent of temperature, whereas at lower temperatures molecular oxygen absorption probability demonstrates a strong temperature dependence. Oversaturation of the metal surface with dissolved oxygen is observed if oxidation occurs in dissociated oxygen at a temperature below 973 K. At the oxide film growth stage, oxidation occurs according to a parabolic law, consequently the reaction rate is determined by diffusion through the oxide film. Nevertheless dissociation of oxygen increases the reaction rate.

Oxidation of vanadium in atomic and molecular oxygen at low pressures

The vanadium oxidation in atomic and molecular oxygen is investigated in the temperature range 873–1373 K at oxygen pressures of 9 × 10 −3−7 × 10 −2 Pa. At the initial stage of oxidation, when the dissolution of oxygen in vanadium takes place, both the diatomic and atomic oxygen absorption probabilities are independent on the incident flux. The absorption probability of atomic oxygen is not much higher than that of diatomic oxygen (approximately three fold). The rate of reaction at the oxygen dissolution stage is determined by the chemisorption of atomic or diatomic oxygen on the vanadium surface.

Emission line shapes produced by dissociative excitation of atmospheric gases

Special line shapes are derived fro the λ 1356 Å ( 5S 0- 3P ) transition of atomic oxygen from metastable ( 5S 0- 3P ) time-of-flight spectra produced by electron impact dissociative excitation of O 2, CO 2, CO, and NO, and they are compared with the broadened λ 1304 A resonance line shapes deduced by Poland and Lawrence (1973) from atomic oxygen absorption studies. The non-thermal line shapes for both airglow emission features are shown to have an effective width comparable to a 60,000 K thermal doppler line shape for an electron impact energy of 100eV. The variation of the effective line width with electron-impact energy from threshold to 300 eV is given. Since the effective line width of the resonance radiation produced by dissociative excitation is very large compared with the doppler absorption widths of the ambient O atoms at normal exospheric temperatures, the anomalously broadened resonance lines will propagate through a planetary atmosphere as though they were optically thin. Thus, electron-impact dissociation of CO and CO 2 will contribute to the observed optically thin component of the λ 1304 Å emission in the upper atmospheres of Venus and Mars. However, the process cannot account for more than 10% of the observed optically thin emission because of the small magnitude of the excitation cross-section and the comparatively high-energy threshold for the process. The possibility that the source of the kinetically energetic O( 3S ) atoms is the dissociative recombination of vibrationally excited CO 2 + ions is discussed.

Neutral atom bremsstrahlung

Predictions are given for the bremsstrahlung absorption cross section of atomic oxygen and atomic nitrogen. The electron-atom interaction potential energy is adjusted to give agreement with the photoabsorption measurements of the negative oxygen ion. The exchange force is treated in an approximate manner following a suggestion by Slater but adjusted to take account of the dependence on the configuration of the electron wave. The difference in the exchange force for s- and p-waves, as well as the difference between the triplet and quintet configurations in atomic nitrogen, must be preserved to obtain predictions for the bremsstrahlung which are in agreement with experiments. The atomic oxygen absorption cross section is about a factor 5 smaller than that of atomic nitrogen, in agreement with the measurements of Taylor. The Maxwell average atomic nitrogen bremsstrahlung absorption cross section is insensitive to temperature. The atomic nitrogen cross section deviates somewhat from the Kramers wavelengths dependence becoming relatively larger in the blue.