Absorption Cross Sections Of Oxygen Research Articles

Influence of photoionization rates on positive streamer branching in atmospheric air

Streamer is a strong ionizing region which advances very quickly in gases, liquids and solids. Streamer is a low-temperature plasma, which produces a variety of chemically reactive substances efficiently. So, streamer discharge has been widely adopted in industry. Furthermore, streamer is the initial stage of electric breakdown in long air gap. Studying the streamer discharge characteristics and its mechanism is the basis of external insulation in power transmission systems.Streamer branching is a significant characteristic during its development. Lichtenberg figure is the first clear recording of the filamentary structure of streamers. One of acceptable explanations is that the random fluctuations of the electron density ahead of streamer trigger branching. Furthermore, photoionization provides the necessary free electrons for the development of positive streamers. The experimental results show that the branching characteristics are closely related to the photoionization rate in streamer head. The streamer shows higher possibility of branching if the photoionization rate decreases. Since previous experiment is indirect evidence of this deduction, we turn to numerical models to study the influence of photoionization rates on positive streamer branching in atmospheric air. A three-dimensional particle-in-cell model with Monte Carlo collision (PIC-MCC) scheme called Pamdi3D (Teunissen J, Ebert U 2016 <i>Plasma Sources Sci. Technol.</i> <b>25</b> 044005) is employed in this paper. The development and branching of positive streamersin a millimeter-scale needle-plane gap are simulated at atmospheric pressure. Different streamer branching behaviors are investigated by artificially changing the nitrogen-oxygen ratio, the absorption cross section of oxygen, and the photoionization efficiency coefficient.The effects of different photoionization parameters are systematically studied. When the nitrogen-oxygen ratio, photon absorption cross section or photoionization efficiency coefficient are reduced, the streamer branching occurs earlier in three cases after reducing the photoionization rate. These results imply that the streamer shows higher possibility of branching if the photoionization rate decreases. When the streamer propagates in a non-uniform electric field region and the photoionization rate decreases to a certain value, it is believed that the seed electron distribution is more susceptible to random fluctuations. It will lead to instability in the space charge layer of streamer, thus causing the streamer to branch. Hence it is proposed that streamer branch will be triggered more easily if the photoionization rate in the streamer head decreases, in the case without considering other seed electron sources.

Sensitive dual sensing system for oxygen and pressure based on deep ultraviolet absorption spectroscopy

In this study, a highly sensitive monitoring system for dual sensing of oxygen and pressure has been developed. The absorption of oxygen in the wavelength range of 186–196 nm was observed and the corresponding absorption cross-section of oxygen in this band was achieved. An approach based on differential optical absorption spectroscopy was used to describe the concentration of oxygen. The detection limit of oxygen was determined to be 150 ppm per meter. No relation between pressure and oxygen absorption line shape in the related wavelength band was confirmed. Based on the absorption of oxygen, pressure detection was realized and a detection limit of 180 Pa was obtained. A dual sensing system for oxygen and pressure was constructed.

Water Aerosol Formation upon Irradiation of Air Using KrF Laser at 248 nm

Abstract We report water aerosol formation upon irradiation of wet air with a KrF laser at 248 nm. It occurred at temperatures ranging from 0 to 50 °C and at relative humidity values from ca. 10% to 100%. Aerosols were detected either by light scattering or by differential mobility analyses, and particle growth from 10 nm to sub-micrometers was observed. Photodissociation of oxygen was proposed as the initial step of the reactions leading to formation of the final stable molecule of hydrogen peroxide as a nucleus with a low vapor pressure. Simulations of the chemical kinetics by considering wet air revealed that the amount of the final product could be controlled by laser operational conditions such as laser repetition rates and pulse energies. KrF laser light can reach a few kilometers in the atmosphere owing to a small absorption cross section of oxygen and yet can produce water aerosol.

Absorption cross section of molecular oxygen in the transition E3Σu-v= 0 – X3Σg-v= 0 at 38 K

Aims. This investigation was undertaken to determine the absorption cross sections of oxygen in the VUV region at temperatures <50 K. Methods. The absorption spectra of gaseous samples cooled with a slit jet and near 300 K were measured with the same absorption system coupled to the VUV beam line of a synchrotron. Results. The maximum absorption cross section for the transition from X 3 Σ − v = 0 to state E 3 Σ − v = 0f or 16 O2 at 38 K was determined to be 98.7 Mb (or 9.87 × 10 −18 cm 2 ). The value of this maximum absorption cross section at 38 K is 1.7 times the value at 303.7 K.

Absorption cross‐section measurements of water vapour and oxygen at 185 nm. Implications for the calibration of field instruments to measure OH, HO2 and RO2 radicals

Absorption cross sections for oxygen and water vapour were measured using a low‐pressure mercury lamp optically filtered to isolate the emission close to 184.9 nm. The cross‐sections were determined for conditions typically used in the calibration of OH, HO2 and RO2 field instruments that employ photolysis of water vapour as a radical source, and O2 absorption as the actinometer for lamp flux. For water vapour, an absorption cross‐section of 7.22 (± 0.22) × 10−20 cm² molecule−1 was determined at 25°C, in excellent agreement with recent studies, but ∼30% higher than the recommended value. The absorption cross‐section for O2 was found to vary with the O2 column and the choice and operating current of the lamp, reinforcing the requirement that practitioners of OH, HO2 and RO2 field measurements who calibrate by this method should measure effective O2 cross‐sections at frequent intervals under their particular field conditions.

The sensitivity of stratospheric photodissociation rates to the solar spectral resolution in the Schumann-Runge bands

Several molecules important in the chemistry of the stratosphere, including N 2O, H 2O, HNO 3, and several chlorofluorocarbons photodissociate in the wavelength interval 1750–2050 Å. The transmission of solar radiation in this spectral region is largely controlled by the Schumann-Runge (S-R) bands of molecular oxygen. The absorption cross sections of oxygen in this region vary by several orders of magnitude as a function of wavelength, resulting in large variations in the magnitude of solar radiation penetrating into the middle atmosphere. It is thus of interest to examine the potential effects that a knowledge of the fine structure of the solar spectrum would have on the accurate calculation of stratospheric photodissociation rates. A U.S. Naval Research Laboratory solar spectrum with a resolution of 0.07 Å has been used to compute high resolution photodissociation rates for several molecular species. Computations have also been performed in which this solar spectrum has been degraded by roughly a factor of 100. These calculations show that knowledge of the fine structure in the S-R region of the solar spectrum produces only a marginal (1–2%) improvement in the computation of the photodissociation rates. This results from the fact that the photodissociation rate is a spectrally integrated quantity, and that there is, on average over the S-R bands, no correlation between the solar spectrum and the oxygen absorption cross sections. This very small improvement should be compared with the much larger uncertainties in important chemical reaction rates, absorption cross sections, and quantum yields, which are often 50–100%.

Effect of nitrogen on oxygen photolysis at 214 nm

The effect of nitrogen, 0-1,200 Torr, on ozone formation in the 214-nm photolysis of oxygen, 125-300 Torr, was investigated. Addition of nitrogen was found to enhance the rate of ozone generation. This observation can be rationalized in terms of the effect of nitrogen on oxygen absorbance in the Herzberg continuum. This result is utilized for the estimation of the combined pressure effect of nitrogen and oxygen pressure on the stratospheric absorption cross sections of oxygen.

The role of oxygen dimer in oxygen photolysis in the Herzberg continuum: a temperature dependence study

The effect of temperature on ozone formation in the 214-nm photolysis of oxygen was investigated as a means of assessing the role of oxygen dimer in the photodissociation of oxygen excited in the Herzberg continuum. Throughout the entire temperature range of 297-387 K, evidence was found for the importance of (O{sub 2}){sub 2} in oxygen photolysis. For the reaction 2O{sub 2}{leftrightarrow} (O{sub 2}){sub 2} a {Delta}H value of -0.2 {plus minus} 0.5 kcal mol{sup {minus}1} is estimated. This result indicates that (O{sub 2}){sub 2} is a very weakly bound metastable dimer, the formation of which nevertheless has a pronounced effect on oxygen absorption cross sections in the Herzberg continuum.

Measurements of N2O photolysis coefficients in the stratosphere: Comparison with model calculations

A balloon-borne continuous actinometer has been developed which measures stratospheric N2O photolysis coefficients, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOAamaaBa% aaleaacaGGobWaaSbaaWqaaiaaikdaaeqaaSGaci4taiabg2da9iab% gkHiTiGacsgaciGGSbGaaiOBaiaacIcaciGGobWaaSbaaWqaaiaaik% daaeqaaSGaci4taiGacMcacaGGVaGaciizaiaadshaaeqaaaaa!44F2!\[j_{N_2 \operatorname{O} = - \operatorname{d} \ln (\operatorname{N} _2 \operatorname{O} )/\operatorname{d} t} \], with a time resolution of approximately 100 s, and a lower detection limit approaching 10-10 s-1. The instrument performed successfully, or was at least partially successful, on five stratospheric balloon flights between October 1982 and September 1986. The experimental profiles are compared with model calculations of % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOAamaaBa% aaleaacaGGobWaaSbaaWqaaiaaikdaaeqaaSGaci4taaqabaaaaa!39A3!\[j_{N_2 \operatorname{O} } \]. The model takes full account of the sphericity of the atmosphere and of the specific flight conditions, but neglects scattering, which should have a negligible effect on % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOAamaaBa% aaleaacaGGobWaaSbaaWqaaiaaikdaaeqaaSGaci4taaqabaaaaa!39A3!\[j_{N_2 \operatorname{O} } \]. The quantitative results, particularly the altitude and solar zenith angle dependences under extreme conditions, support the low absorption cross-sections of oxygen in the Herzberg continuum as recommended by WMO in 1986 and are inconsistent with Ackerman's tabulations of 1971. It is shown that the altitude dependence of Brewer and Wilson's historical irradiance measurements in the stratospheric window region is well reproduced by our model, but should be multiplied by a factor of 1.75.

Ozone generation in the 214-nm photolysis of oxygen at 25.degree.C

Ozone formation in the 214-nm photolysis of oxygen at pressures ranging from 380 to 1300 Torr was investigated. The rates of ozone formation increase with the square of oxygen pressure mirroring the pressure dependence of the absorption cross sections of oxygen. This observation demonstrates the importance of the collision-induced changes in oxygen absorbance and points to a need to examine the role of oxygen dimer (O/sub 2/) in reactions initiated by its photodissociation. Because of the high dilution of ozone, its formation was found to be linear with time even though, on the average, its rate of photolysis exceeded the rate of its generation from oxygen. The quantum yield of ozone formation was 1.86 /plus minus/ 0.17 independent of O/sub 2/ pressure. From this result the quantum yield of the primary process O/sub 2/ + hv (214 nm) ..-->.. 2O(/sup 3/P) is estimated as being equal to 0.93 /plus minus/ 0.08 (2sigma). Based on the observed linear buildup of ozone and on model calculations, an upper limit of about 0.03 is estimated for O/sub 3/ photolysis via a channel which leads to O(/sup 3/P) and an excited O/sub 2/ species that can regenerate ozone in its reaction with oxygen.

Long pathlength measurements of oxygen absorption cross sections in the wavelength region 205–240 nm

New measurements of molecular oxygen photoabsorption cross sections and pressure coefficients have been made at room temperature in the wavelength region 205–240 nm of the Herzberg continuum. The experimental conditions [ p(O 2) < 100 Torr, pathlenths up to 1400 m] ensure accurate extrapolation to zero pressure of the pressure -dependent continuum cross sections. The results are in good agreement with recent laboratory data and are consistent with most of the stratospheric measurements. The O 2 cross sections are found to be lower than values previously used in many photochemical stratospheric modelling calculations.

Oxygen absorption cross sections in the herzberg continuum and between 206 and 327 K

The ultraviolet absorption cross sections for molecular oxygen have been determined for wavelengths between 205 and 225 nm, for temperatures between 206 and 327 K, and at a pressure from 100 to 750 torr. No temperature effect on the O2 cross sections was observed in the Herzberg continuum. It was necessary to separate the extremely weak O2 absorption from the stronger collision‐induced absorption. These experimental data and similar data by others were interpreted in terms of a theoretical expression for the shape of the Herzberg continuum absorption spectrum. The O2 absorption cross sections are in good agreement with the values measured in the stratosphere by Herman and Mentall (1982).

Herzberg continuum cross section of oxygen in the wavelength region 193.5‐204.0 nm: New laboratory measurements and stratospheric implications

The absorption cross section of oxygen at 300 K and at pressures in the range 50‐760 torr has been measured throughout the wavelength region 193.5‐204.0 nm with a 6.65 m scanning spectrometer having an instrumental full width at half maximum of 0.0013 nm. The absorption features in this region are the discrete lines of some Schumann‐Runge bands and two underlying dissociation continua, viz., the weak Herzberg continuum of oxygen and a pressure dependent continuum involving two molecules of oxygen. The instrumental width is small enough to permit measurement of the total continuum cross section, as a function of pressure, at a number of wavelengths at which interference from the discrete lines is negligible. Analysis of the pressure dependence of the total continuum cross section yields the Herzberg continuum cross section, which decreases monotonically from 14 barn at 193.58 nm to 5.5 barn at 204.06 nm. At all wavelengths in this region, our values of the Herzberg continuum cross section are smaller than previous laboratory values, much smaller than values used in many photochemical models, and consistent with recent in situ stratospheric values. The acceptance of reduced Herzberg continuum cross sections implies significant changes in photochemical modelling predictions of the stratospheric concentrations and altitude profiles of ozone, chlorofluorocarbons and nitrous oxide.

Radiation and chemistry in the stratosphere: Sensitivity to O2 absorption cross sections in the Herzberg continuum

We propose that a significant overestimate of the molecular oxygen absorption cross sections in the important spectral window from 200‐220 nm is in large part responsible for the discrepancy between observed and modeled vertical profiles of some halocarbons (CFCl3 in particular), as well as for the long‐standing problem of simultaneously fitting N2O, CH4, CF2Cl2 and CFCl3 profiles with a single eddy diffusion model. Recent measurements of the direct solar flux in the stratosphere by J.R. Herman and co‐workers seem to support this idea. Replacing our current O2 cross sections in the 200‐220 nm range by values in better agreement with the results of the above group leads to a reduction in N2O, CF2Cl2 and CFCl3 concentrations (by factors of 0.70, 0.62 and 0.19, respectively, at 30 km), while CH4, H2 and CO profiles are essentially unchanged. Moreover, the predicted concentration of HNO3 above 30 km is reduced by ∼50%, yielding better agreement with observations. The reduction in O2 cross sections produces a 10‐20% decrease in ozone above about 35 km, but a fairly large increase (∼30%) near the peak around 20‐25 km. The changes in other stratospheric species are also briefly discussed.

Atmospheric pressure, density and scale height calculated from H Lyman-α absorption allowing for the variation in cross-section with wavelength

Observations of the extinction in the Earth's upper atmosphere of hydrogen Lyman-α radiation from the Sun has been used to calculate atmospheric pressure, density and scale height. The importance of allowing, in these calculations, for the variation in the absorption cross-section of oxygen across the width of the Lyman-α line profile is discussed. In addition, allowance has been made for the absorption produced by other atmospheric constituents. Atmospheric parameters are presented for the height range 67–95 km determined from Lyman-α observations made aboard a rocket launched from South Uist, Scotland, on 19 June 1969.

Nitrogen and oxygen absorption cross-sections in the vacuum ultra-violet

The first page of this article is displayed as the abstract.

The absorption of molecular oxygen between 1850 and 2500 Å

Absorption cross-sections for oxygen in the region 1850–2500 Å have been measured. There is a variation with pressure (probably due to the formation of O 4). The values obtained by extrapolation to zero pressure vary from 15 × 10 −24 cm 2 at 1900 Å to 3 × 10 −24 cm 2 at 2300 Å. The absorption, which is about one million times weaker than that of the Schumann-Runge (S-R) system is the Herzberg continuum corresponding to the forbidden transition 3Σ g − → 3Σ u + . The absorption cross-sections for this continuum have been calculated for different values of the internuclear distance r e ; those for r e = 1.50 Å agree best with the experimental results. The calculation indicates that the maximum value of the absorption is 15 × 10 −24 cm 2 at 1870 Å, but this could not be checked experimentally because of the overlying S-R absorption. The dissociation of oxygen in the upper part of the earth's atmosphere, above 80 km, is predominantly due to absorption in the S-R continuum (1850–1350 Å). The present measurements indicate that (as has previously been suggested) absorption in the Herzberg continuum is the principal source of oxygen atoms at levels below 80 km. Thus, this continuum is important in relation to the formation of the ozone layer. At wavelengths near 2100 Å the Herzberg continuum absorbs more of the sun's radiation than does the ozone continuum. Most of this absorption takes place below 25 km. The ƒ- value of the Herzberg continuum is 3.5 × 10 −5.

Absorption cross-sections in the vacuum ultra-violet - II. The Schumann-Runge bands of oxygen (2000 to 1750Å)

Absorption cross-sections for oxygen in the region 2000 to 1750 Å, corresponding to the process O 2 X 3 Σ - g + hv → O 2 B 3 Σ - u have been measured. The oscillator strengths for the vibrational transitions have been calculated from these results. The total oscillator strength (including the continuum) is found to be 0·259. The cross-sections for intermolecular collisions causing deactivation of the upper state are found and analyzed. The (0-19) and (0-20) members of the system are observed, and the dissociation limit found to be 57140 ± 20 K .

Absorption cross-sections in the vacuum ultra-violet. - I. Continuous absorption of oxygen (1800 to 1300 Å)

Absorption cross-sections for oxygen in the region 1670 to 1360 Å, corresponding to the process O 2 3 Ʃ g - + hv → O( 3 P ) + O( 1 D ), have been measured. The cross-section has a maximum value of 1⋅81 x 10 -17 cm 2 at 1450 Å and falls to half-value at 1567 and 1370 Å. The paper includes an account of technical methods of quantitative absorption spectrophotometry in this part of the vacuum ultra- violet.