Detection Of Atomic Oxygen Research Articles

Direct detection of atomic oxygen on the dayside and nightside of Venus

Atomic oxygen is a key species in the mesosphere and thermosphere of Venus. It peaks in the transition region between the two dominant atmospheric circulation patterns, the retrograde super-rotating zonal flow below 70 km and the subsolar to antisolar flow above 120 km altitude. However, past and current detection methods are indirect and based on measurements of other molecules in combination with photochemical models. Here, we show direct detection of atomic oxygen on the dayside as well as on the nightside of Venus by measuring its ground-state transition at 4.74 THz (63.2 µm). The atomic oxygen is concentrated at altitudes around 100 km with a maximum column density on the dayside where it is generated by photolysis of carbon dioxide and carbon monoxide. This method enables detailed investigations of the Venusian atmosphere in the region between the two atmospheric circulation patterns in support of future space missions to Venus.

Detection of atomic oxygen in a plasma-assisted flame via a backward lasing technique.

In this Letter, we have investigated 845nm lasing generation in atomic oxygen, present in a lean methane-air flame, using two-photon pumping with femtosecond 226nm laser pulses, particularly focusing on the impact of nanosecond repetitively pulsed glow discharges forcing on the backward lasing signal. Characterizations of the backward lasing pulse, in terms of its spectrum, beam profile, pump pulse energy dependence, and divergence, were conducted to establish the presence of lasing. With plasma forcing of the flame, the backward lasing signal was observed to be enhanced significantly, ∼50%. The vertical concentration profile of atomic oxygen was revealed by measuring the backward lasing signal strength as a function of height in the flame. The results are qualitatively consistent with results obtained with two-dimensional femtosecond two-photon-absorption laser-induced fluorescence, suggesting that the backward lasing technique can be a useful tool for studies of plasma-assisted combustion processes, particularly in geometries requiring single-ended standoff detection.

Radar resonance-enhanced multiphoton ionization for measurement of atomic oxygen in non-equilibrium pulsed plasmas

In this work, coherent microwave Rayleigh scattering for the detection of resonance-enhanced multiphoton ionization (Radar REMPI) was used for the measurement of atomic oxygen in a nonequilibrium pulsed plasma discharge. Specifically, the detection of atomic oxygen is demonstrated in a pulsed discharge at 100 Torr in a molecular oxygen and helium gas mixture. REMPI was conducted using Nd:YAG pumped dye radiation at 618.9 nm mixed with the Nd:YAG 355 nm radiation, generating 225.6 nm laser light, of which two photons match the energy of the 2P33p(3P) electronically excited intermediate state of atomic oxygen. A third photon from the laser source then readily ionizes the atom in the 2 + 1 photon REMPI scheme. The Radar REMPI results are compared to two-photon absorption laser-induced fluorescence measurements from the literature, which shows reasonable agreement.

Detection of atomic oxygen O(3PJ) with vacuum ultraviolet emission subsequent to two-photon absorption

Observation of infrared emission following two-photon absorption has been widely employed to detect atomic oxygen O(3PJ) so far. In the present study, a method of detecting O(3PJ) with vacuum ultraviolet (VUV) instead of infrared emission has been developed. The scheme of detection is (i) 2p33p3PJ ←← 2p43PJ (UV two-photon absorption); (ii) 2p33p3PJ → 2p33s3S (transfer to the 3S state); and (iii) 2p33s3S → 2p43PJ (VUV emission). The present method is favorable under the conditions at high ambient pressures because the effect of undesirable collisional quenching is smaller than that on the detection of infrared. An application to the kinetic measurement relevant to O(3PJ) also has been demonstrated.

Use of solid N2 surfaces in metastable particle detection.

A novel detector is described in which solid nitrogen at 17 K is used as the most significant element. Metastable particles impinge on this element and immediately transfer their internal energy to the solid nitrogen producing photons, via excimer formation or otherwise, whose wavelength depends on the metastable being detected and the energy transfer process. The performance of the instrument for the detection of atomic oxygen and molecular nitrogen metastables is discussed.

Detection of atomic oxygen and nitrogen created in a radio-frequency-driven micro-scale atmospheric pressure plasma jet using mass spectrometry

In this paper we show mass spectrometry results for a radio-frequency-driven micro-atmospheric pressure plasma jet (μ-APPJ) discharge obtained using a mass analyzer with triple differential pumping allowing us to sample directly in ambient atmospheric pressure environment (Hiden HPR-60). The flow of the buffer gas (mixture of helium and 1% oxygen) was 2 slm and 3 slm and the excitation frequency was 13.56 MHz. We monitored production of atomic oxygen and nitrogen in the plasma for different flows and powers given by the RF power supply. These measurements were made for energies of electrons emitted from the ionization filament below the threshold for dissociation of O2 and N2. In addition to oxygen and nitrogen atoms, yields for O2, N2, NO and O3 are recorded for different powers and gas flows. It is shown that the μ-APPJ is symmetrical and operates in α-mode. The power transmitted to the discharge was below 5 W in all measurements.

Sensitivity enhancement of laser absorption spectroscopy for atomic oxygen measurement in microwave air plasma

A high sensitive laser absorption spectroscopy system has been developed for the detection of atomic oxygen in a microwave plasma. Firstly, the sensitivity of this system was evaluated by ring-down time measurement. The effective absorbing pass length was extended up to 640 times as long as that of the conventional laser absorption spectroscopy. Then, the system was applied to the air plasma diagnostics. As a result, the absorption signal from the meta-stable atomic oxygen at 777.19 nm could be observed at the input enthalpy range from 0.93 MJ/kg to 467 MJ/kg. The detected minimum number density was 1.6 × 10 11 m −3 with temperature of 388 K, which correspond to the center fractional absorption of 1.4 × 10 −2% in the LAS.

Nitric Oxide Production from Surface Recombination of Oxygen and Nitrogen Atoms

ठExperimental results are presented that support the surface-catalyzed production of nitric oxide from the recombination of oxygen and nitrogen atoms on quartz. The experiments employ two-photon laser induced fluorescence detection of atomic oxygen and atomic nitrogen to characterize changes in gas-phase atom concentrations as the ratio of O to N atoms is varied at the opening of a diffusion-tube side-arm reactor. The measurements verify a correlation between decreased O-atom loss and enhanced N-atom loss in N2/N/O mixtures. Computational simulations of the side-arm reactor with a multi-species reaction-diffusion model strengthen the case for NO surface formation, reproducing observed changes in O- and N-atom concentration profiles with varying O/N ratios at the side-arm entrance when surface-catalyzed NO production is included in the boundary conditions.

A kinetic study of the reaction of atomic oxygen with SO 2

The effective second-order rate constant for O + SO 2 (+Ar) → SO 3 (+Ar) has been measured by pulsed laser-photolysis with resonance fluorescence detection of atomic oxygen under pseudo-first-order conditions. The pressure dependence was determined at five temperatures in the range 290–840 K. The results obtained at pressures up to 880 mbar reveal fall-off behavior. With an estimated broadening parameter F c , Troe fits to the measurements yield the low-pressure limit k 0 = 9.5 × 10 −23 T −3 exp (−2400/ T) cm 6 molecule −2 s −1 and the high-pressure limit k ∞ = 6.1 × 10 −13 exp (−850/ T) cm 3 molecule −1 s −1. An RRKM extrapolation of the present k 0 values yields k 0 = 6.7 × 10 −21 T −3.6 exp (−2610/ T) cm 6 molecule −2 s −1, which is in good accord with several literature values over 220–2500 K. At low temperatures, k 0 shows a positive activation energy rationalized in terms of a barrier of 15.9 kJ mol −1, and k 0 reaches a maximum at around 750 K. Our expression for k ∞ is in order-of-magnitude accord with values used to model a flow reactor and indicates a small pre-exponential factor. This may reflect the probability of triplet–singlet transitions in the spin-forbidden addition reaction and/or a tight transition state.

Photolytic interference affecting two-photon laser-induced fluorescence detection of atomic oxygen in hydrocarbon flames

This study reports on photochemical interferences affecting atomic oxygen detection using two-photon laser-induced fluorescence at 226 nm. In contrast to previous studies in which molecular oxygen was proven to be the relevant photochemical precursor molecule in a hydrogen-fueled flame, the present investigations were carried out in a laminar diffusion flame of methane and air. The most significant interferences were found at the fuel side of the flame in the absence of molecular oxygen, and vibrationally excited carbon dioxide was identified as the most probable precursor molecule for the photochemical production of oxygen atoms.

Detection of atomic oxygen: Improvement of actinometry and comparison with laser spectroscopy

The density of atomic oxygen in an oxygen rf discharge in the Gaseous Electronics Conference reference cell is determined from the intensity ratios of the argon λ=750 nm line (2p1–1s2) and the atomic oxygen lines λ=777 nm (5P–5S) and λ=844 nm (3P–3S). Laser induced fluorescence spectroscopy with two-photon excitation is applied to the oxygen plasma, and the results of both methods are compared. The improved actinometry is based on the calculation of electronic collisional excitation of the upper levels of these transitions. The required information on the electron energy distribution function is obtained from a model calculation of the discharge. Good agreement of the results are obtained, if excitations via dissociative channels and also quenching rates are accounted for.

Atomic oxygen detection in flames using two-photondegenerate four-wave mixing

We report a theoretical and experimental investigation of atomicoxygen detection in an atmospheric-pressure flame by two-photondegenerate four-wave mixing (TPDFWM). We present analyticalexpressions for the TPDFWM signal that are based on the diagrammaticperturbation theory. The description of several polarizationarrangements is given and used in our experiments. Theimportance of the polarization scheme is emphasized and the mostefficient scheme is found by investigating signal and noisecontributions. In this case, thermal grating contributions aregreatly reduced and this allows quantitative concentrationmeasurements in flame to be performed using TPDFWM.

The generation and detection of high flux atomic oxygen for physical vapor deposition thin film growth

The growth of many epitaxial thin-film oxides is significantly enhanced with the use of an oxidizing agent such as atomic oxygen, ozone, or NO2. We developed a flow-through microwave plasma source to generate large atomic oxygen fluxes while maintaining vacuum pressures of less that 1×10−4 Torr. Continuous and real-time detection of the atomic oxygen was achieved by atomic absorption of the 130 nm atomic oxygen lines. Atomic oxygen fluxes of at least 1.4×1018 atoms/cm2 s and dissociation efficiencies of around 100% were obtained.

Diamond-sensing microdevices for environmental control and analytical applications

Abstract For the fabrication of microdevices with line widths approching 1 μm, a patterning methodology has been developed by the modification of an existing plasma etching process, which is suitable for any form and type of diamond. These microdevices have been tested as active sensing elements for both environmental control and metrological applications: voltammetric detection of chlorine, detection of atomic oxygen for space and terrestrial applications, the measurement of ultraviolet (UV) light, and finally, conductive atomic force microscopy (AFM), which is successfully performed today with microfabricated diamond tips.

Atomic oxygen detection using two-photon degenerate four wave mixing

We report a new application of Forward Degenerate Four Wave Mixing to the two-photon transition 2p → 3p of atomic oxygen. This spectroscopy has been used to detect oxygen atoms produced in a microwave discharge. The possibility to determine number densities over a range of microwave plasma parameters is investigated. In contrast to conventional linear techniques, quantitative data are relatively easy to obtain even for environments with high background luminosity, limited optical access and inhomogeneous quenching.

Detection of atomic oxygen in flames by absorption spectroscopy

The absolute concentration of atomic oxygen in an atmospheric pressure hydrogen/air flame has been measured using Intracavity Laser Spectroscopy (ICLS) based on a dye laser pumped by an argon-ion laser. Absorptions at the highly forbidden transitions at 630.030 nm and 636.380 nm were observed at an equivalent optical length of up to 10 km. The relatively low intensity of the dye laser avoids photochemical interferences that are inherent to some other methods for detecting atomic oxygen. The detection sensitivity is about 6 × 1014 atom/cm3 and can be improved with better flame and laser stabilization.

Detection of atomic oxygen and hydrogen in the vacuum UV using a frequency-doubled, Raman-shifted dye laser

Tunable radiation between 130.6 and 121.5 nm has been generated with a frequency-doubled dye laser, the wavelength of which has been shifted by stimulated Raman scattering in molecular hydrogen. With the eighth and ninth anti-Stokes Raman lines (energies > 0.1 μJ, pulse length < 2 ns), the densities of atomic oxygen and hydrogen, produced by dissociation of O2 or H2 on a hot tungsten wire or in sputtering devices, have been measured by resonance fluorescence at λ = 130.2 nm and at λ = 121.5 nm, respectively. The detection limit in our experimental setup has been estimated near 107/cm3. The corresponding spectral profiles have been determined with a resolution of at best 0.1 cm−1. With a Raman cell cooled in liquid nitrogen, the shift and broadening of the 8th anti-Stokes line have been measured as a function of the hydrogen pressure between 300 and 1000 mbars, through the apparent profile of the O i line.

Photodissociation processes in carbon monoxide at 193 nm

The photodissociation of carbon monoxide at 193 nm has been investigated using resonance enhanced multiphoton ionization detection of atomic oxygen and carbon fragments. The results of these experiments indicate a quadratic photodissociation process in CO at 12.8 eV. In addition, the nascent fine structure branching ratios of atomic oxygen 2p4 (3P2,1,0) produced in the 193 nm photodissociation of CO are reported using both multiphoton laser induced fluorescence and ionization detection. Analysis of the experimental data and computer generated simulations indicate that the distributions are not statistical.

Atomic oxygen detection by a silver-coated quartz deposition monitor

A method for measuring the flux of atomic oxygen utilizing a silver film on a quartz-crystal deposition rate monitor is described. Measuring the initial oxidation rate of the silver, which is proportional to the atomic oxygen flux, determines a lower limit on the atomic oxygen flux. This method is more direct than measuring the conductance of the silver film, has an intrinsic flux detection range of 1013–1017 atoms/cm2 s, and is reversible by exposing the sensor to an atomic hydrogen flux.

Photochemical effects in two-photon-excited fluorescence detection of atomic oxygen in flames

This paper describes photochemical effects observed using 226-nm two-photon-excited fluorescence detection to measure the atomic oxygen concentration in hydrogen-oxygen flames. In a study of a lean atmospheric-pressure flame, we observed artificially high atomic-oxygen concentration levels in the postflame gases using all but the most gentle excitation conditions (intensities greater than ~0.1 GW/cm(2)). A similar study of a lean low-pressure (72-Torr) flame showed little evidence of photochemical production of atomic oxygen. Using a second laser system in a pump-probe configuration, with the probe laser monitoring the atomic oxygen concentration in a very lean flame while the pump laser was scanned across molecular-oxygen Schumann-Runge bands at 221 nm, we demonstrated that excess atomic oxygen concentrations can be produced by single-photon excitation of these bands in vibrationally excited oxygen molecules present in the flame. This production mechanism explains at least part of the artificially high concentration levels observed in the atmospheric-pressure flame.