16O Cross Section Research Articles

High‐temperature, high‐resolution photoabsorption cross sections of O2 in the 108.5‐nm region

The high‐resolution absorption cross‐section measurements of O2 in the 108.0‐ to 108.7‐nm spectral region have been carried out with a resolution of 0.0008 nm and at temperatures of 295 and 535 K. The absorption features in this spectral region exhibit primarily a blue‐shaded broad band with a band head peaked at 108.52 nm. The center of gravity of the diffuse band is located at 108.452 nm. The present room temperature cross‐section data of the NII 108.5‐nm sextuplets agree well with the unpublished data of J.A.R. Samson (private communication, 1990). As the temperature increases from 295 to 535 K, we observe a decrease in cross‐section values by as much as 30% over the contour of the diffuse band. Similarly, the cross‐section values of the sharp features decrease as temperature increases. The NII 108.5‐nm multiplets are one of the prominent emissions in the Earth's airglow. The EUV‐UV day glow limb scans of the thermosphere and ionosphere have currently been gathered by satellite, e.g., ARGOS, at a tangent ray height of 200 km, above where the ambient absorption due to O2 and N2 is expected. The present temperature‐dependent cross sections of O2 provide the important database required for modeling the dayglow observations.

Photodissociation of nitric oxide in the middle and upper atmosphere

Absorption of solar radiation of wavelengths between 175 to 205 nm plays a fundamental role in the photochemistry of the middle atmosphere. Nitric oxide photodissociates in the δ(0-0) and δ(1-0) bands near 191 and 183 nm, respectively, initiating the primary mechanisms for NOx removal in the middle atmosphere. The spectrally rich Schumann-Runge (S-R) bands of O2 are the main source of atmospheric opacity at these wavelengths. A re-evaluation of O2 absorption has been made based on recent advances in understanding of S-R line shapes, leading to differences with conventional approaches assuming Voigt line profiles in line-by-line calculations of the O2 cross section. The new results are used to examine the impact of O2 transmission on the photodissociation of NO in the δ(0,0) and δ(1,0) bands.

16O(n,p)16N Reaction Cross Sections around 14 MeV

The (n,p) reaction cross sections of 16O in the neutron energy range from 13.6 to 14.9 MeV were measured by the activation method. The gamma-ray counting technique was applied, and the cross sections were determined relative to the 27Al(n,p)27Mg reaction cross sections. The neutrons were produced via the 3H(d,n)4He reaction on a SAMES T-400 neutron generator, and the induced gamma activities were measured by a high-purity germanium (HPGe) detector. The efficiency calibration of the HPGe detector for gamma-ray energies above 6 MeV was determined by means of gamma rays emitted from the decay of 11Be. An automated fast sample transport system was combined with the neutron generator in order to carry out the measurements in cyclic mode. The experimental method is described and the sources of systematic errors are discussed. The results obtained are compared with the experimental data in the available literature and recent evaluations.

Loss of electrons by fast H− ions in gases

The characteristic angles and cross sections for a \((\mathop 1\limits^ - 0) + (\mathop 1\limits^ - 1)\) reaction in which H− atoms with an energy of 0.1–10 000 MeV lose electrons when scattered on C, N, or O atoms were calculated for the relativistic case of the Bethe scattering theory. The cross sections for N2, O2, and CO2 molecular targets were obtained using the additivity rule. The results presented are compared with known experimental and theoretical data.

Electron-impact excitation/emission and photoabsorption cross sections important in the terrestrial airglow and auroral analysis of rocket and satellite observations

The UV line intensities appearing in the spectra of terrestrial auroral and airglow observational data by rockets and high altitude satellites contain important diagnostic information on energy input taking place into the thermosphere. The intensities of the observed emissions are dependent on the atomic and molecular cross sections for both electrons and photons. UV extinction weakens the emission intensity along the line-of-sight to the spacecraft and is determined by the absorption cross sections of the principal constituents: O2, N2□ and O. An accurate knowledge of both excitation (emission) and photoabsorption cross sections of the dominant atmospheric molecular gases (O2 and N2) is needed for the analysis and interpretation of rocket and satellite observations of airglow and auroral emissions. The absorption cross sections of O2 and N2 are difficult to measure since they are highly structured in the UV from predissociation of Rydberg and valence states.The aim of this article is to focus upon certain outstanding issues concerning the available experimental excitation (emission) and photoabsorption cross section data primarily in the far UV (FUV) spectral region. These cross sections are important to terrestrial airglow and auroral observations of N2 and O UV emission fluorescence and to critically review the available data.

A Unified Description of Elastic, High Energy Electron – Molecule Scattering

We present a unified description of elastic, high energy electron – molecule scattering in terms of a scaled differential cross section regarded as a universal function of a scaled momentum transfer. The predictions of the function are in agreement with the experimental cross sections for CH4, C2H4, C2H6, CO, N2, O2, H2O and CO2.

New electron energy transfer and cooling rates by excitation of O2

Abstract. In this work I present the results of a study of the electron cooling rate, the production rates of vibrationally excited O2, and the production frequency of the O2 vibrational quanta arising from the collisions of electrons with O2 molecules as functions of the electron temperature. The electron energy transfer and cooling rates by vibrational excitation of O2 have been calculated and fitted to analytical expressions by use of the revised vibrationally excited O2 cross sections. These new analytical expressions are available to the researcher for quick reference and accurate computer modeling with a minimum of calculations. It is also shown that the currently accepted rate of electron energy loss associated with rotational transitions in O2 must be decreased by a factor of 13.

Experimental Determination of SO2, C2H2, and O2 UV Absorption Cross Sections at Elevated Temperatures and Pressures

A heated and pressurized quartz cell with 150.5-mm pathlength was used to experimentally determine UV absorption spectra and further absorption cross sections of SO2, C2H2, and O2 in the wavelength range between 200 and 400 nm. Spectra were recorded at room temperature, and at 600 and 800 °C and at absolute pressures between 1 and 6 bar. A 30-W deuterium lamp was used as a light source, and the light was detected with a photomultiplier tube through a 0.4-m Czerny–Turner monochromator. Slit widths of the monochromator were adjusted to achieve a 5 Å measurement bandwidth, and the scan through the wavelength range was made in 5 Å steps. For each individual temperature and pressure level, a reference spectrum was first recorded with the cell filled with nitrogen. After this, the cell was filled with the selected species mixed with nitrogen, and the absorption spectra were recorded in similar conditions. The studied gas mixtures were calibrated to 3% accuracy.

Measurement of elastic recoil cross sections of light nuclei by 35Cl using inverse scattering

The elastic recoil cross sections of 6Li, 12C, 16O and 19F by 35Cl below the incident energy of 10 MeV have been measured by the inverse scattering method. About 10 17 Cl/cm 2 BaCl 2 vacuum-deposited on 1 μm DLC (Diamond Like Carbon) was used as a target. During the irradiation the target showed good stability. The Cl isotope effect has an influence on the recoil cross section of less than 0.5%. In the useful energy region for quantitative analysis by elastic recoil detection, the measured recoil cross sections agree with the Rutherford's values within a few percent.

Removal rates for the collisional quenching of various vibronic levels of ground state NCO by simple molecules (N2, O2, NO, CO2, N2O, and SO2)

The collisional behavior of NCO[X̃(0,n,0)] in specific vibronic states in the gas phase has been investigated in the time-domain by laser-induced fluorescence (LIF) on transitions within the system NCO(Ã 2Σ+–X̃ 2Π). The NCO radical was generated by the infrared multiphoton dissociation (IRMPD) of phenyl isocyanate (PhNCO) by means of a TEA-CO2 laser operating on the 9R24 line at λ=9.25 μm with subsequent monitoring of the vibronic levels of the X̃ state, characterized by Renner–Teller coupling, in the presence of N2, O2, NO, CO2, N2O, SO2, and PhNCO itself. The states probed were as follows: (0010)2Π3/2, (0010)2Π1/2, (0100)μ2Σ+, (0120)2Δ5/2, (0120)2Δ3/2, (0210)μ2Π3/2,1/2, (0230)2Φ7/2, and (0230)2Φ5/2. Various pairs of spin–orbit states were found to be tightly coupled kinetically. Thus, the time-evolution of the pairs of vibronic states (0010)2Π3/2 and (0010)2Π1/2; (0120)2Δ5/2 and (0120)2Δ3/2; (0230)2Φ7/2 and (0230)2Φ5/2 were found to be equal, yielding an effective local equilibrium within these spin–orbit components within experimental error. Further, states such as NCO(0100) and NCO(0120) were characterized by relatively long decay profiles in the presence of molecules such as CO2 and O2 where the contribution of rotational quenching to the overall decay process could be neglected. By contrast, NCO(0210) and NCO(0230) were removed on significantly faster time scales on collision with SO2. In the absence of extensive information required for solving the large set of coupled differential kinetic equations, albeit reduced in number of those states strongly coupled kinetically, such as a detailed knowledge of the nascent state distributions in NCO following IRMPD, not necessarily Boltzmann in character, the vibronic states were taken to behave independently as the most practical approach to this study. Absolute second-order rate data for the collisional quenching of NCO in the vibronic states (0010), (0100), (0120), (0210), and (0230) by the above molecular species are reported. No clear selection rules are apparent except for the low propensity rule ΔK=2 within the same vibronic state, i.e., μ 2Σ+(0100)–2Δ5/2(0120) and Π43/2,1/2(0210)–2Φ7/2(0230). This is presumed to reflect the role in the collisional interaction of the oscillating dipole in the vibronic state, facilitating ΔK=1, whereas ΔK=2 would involve the quadrupole which is smaller. It is found that the data for (V–V) and (V–T) energy transfer correlate best with the attractive part of the potential curves between the collision partners using the established Parmenter–Seaver plots, yielding well depths [(εMM/kB)1/2] for the vibronic states NCO[μ 2Σ+(0100), ∂25/2(0120), (0210), and Φ47/2(0230)], significantly larger than those of the closed shell collision partners and equal within experimental error. The data are also considered in terms of a multipolar attractive force model involving a collision complex where a sensible correlation is found between the computed and observed collision cross sections for O2, N2, CO2, N2O, and SO2 assuming no change in the multipoles with vibrational state.

Quenching of fluorescence from Na(3 2 P ) and K(4 2 P ) atoms following photodissociation of NaCl and KCl at 193 nm

Quenching of fluorescence from Na(32P) and K(42P) atoms by various collision partners was studied at 973 and 1273K. Excited alkali atoms were produced photolytically by excimer laser light at 193nm. For each collision pair, the appropriate relative velocity was computed and used to evaluate the quenching cross-section from the measured rate constants. Cross sections for CO2, O2 and N2 are large (10–60A2) while for Ar, the values are <1 A2. The results are compared with those of previous investigations as a function of relative velocity. Finally, implications for combustion diagnostics are briefly discussed.

Analysis of the total 12C( alpha, gamma )16O cross section based on available angular distributions and other primary data.

Because a knowledge of the 12C/16O ratio is crucial to the understanding of the later evolution of massive stars, new R- and K-matrix fits have been completed using the available angular distribution data from radiative α capture and elastic α scattering on 12C. Estimates of the total 12C(α,γ)16O rate at stellar energies are reported. In contrast with previous work, the analyses generally involve R- and K-matrix fits directly to the primary data, i.e., the energy- and angle-dependent differential yields, with all relevant partial waves fitted simultaneously (referred to here as surface fits). It is shown that, while the E1 part of the reaction is well constrained by a recent experiment on the β-delayed α-particle decay of 16N, only upper limits can be placed on the E2 ground state cross section factor which we take conservatively as SE2(300)<140 keV b. Simulations were then carried out to explore what kind of new data could lead to better restrictions on SE2(300). We find that improved elastic scattering data may be the best short-term candidate for such restrictions while significantly improving S(300) with new radiative capture data may require a longer-term effort. Theoretical models and estimates from α-transfer reactions for the E2 part of 12C(α,γ)16O are then discussed for comparison with the R- and K-matrix fits of the present work.

A comparison of K- and R-matrix parameterizations of s-wave 16O+p elastic scattering

Abstract Values for the reduced proton width of the 1 2 + bound state of 17F are extracted using K- and R-matrix fits to s-wave 16O+p phase shifts. The reduced proton width is also calculated using a potential model which reproduces the elastic scattering data and also the 16O(p, γ) cross section into the 1 2 + state. The fitted K-matrix reduced proton width is inconsistent with the R-matrix value and also the potential model calculation. Investigations using the potential model reveal that the likely cause of the discrepancy is the complicated nature of the K-matrix background. We find that the background cannot be adequately represented by the sum of real-energy pole and a constant.

Cross sections for 16O(He,He)16O resonant elastic scattering and application to elemental analysis of YBa2Cu4O8 and Nd1+xBa2−xCu3O7−δ films grown on SrTiO3

The differential cross sections for 16O(He,He)16O resonant elastic scattering at 3.034 and 3.078 MeV have been measured using stoichiometric thin (100 Å) and thick (6000 Å) SiO2 layers formed on Si(100) wafers by thermal oxidation at 900 °C under H2 and O2 flows. We have determined the resonance widths (Γ) and interaction radii (a), which are the parameters defining the cross sections in the partial wave analysis, by best fitting the angular and energy dependent scattering yields from oxygen. A computer simulation program for Rutherford backscattering including the 16O(He,He)16O resonant scattering has been synthesized and applied to the elemental analysis of thin YBa2Cu4O8 and Nd1+xBa2−xCu3O7−δ films grown on SrTiO3 substrates. The present elemental analysis is compared with the transition temperatures of superconductivity (Tc) in the context of the oxygen deficiency. The accuracy of oxygen content is estimated to be better than 0.1 (a few %). How to improve the accuracies of the elemental analysis, in particular the oxygen content, is discussed in detail.

The combination of a VUV Fourier-transform spectrometer and synchrotron radiation

Current research on the Earth’s upper atmosphere requires molecular parameters of unprecedented detail and accuracy. For example, state-of-the-art models of the vacuum-ultraviolet (VUV) absorbing properties of the atmosphere call for absorption cross sections with details on the scale of the Doppler linewidths. As a consequence, spectroscopic data at resolving powers of the order of 106 are needed. Current particular needs are for ultra-high-resolution absorption cross-section data for some bands of NO and O2 in the 170–185 nm spectral region. To meet these requirements, an existing, portable, VUV Fourier-transform (FT) spectrometer will be moved to a synchrotron-radiation facility (Photon Factory, KEK, Japan) and VUV photoabsorption cross sections of NO and O2 will be measured. It has been demonstrated so far with emission line sources that the FT spectrometer will perform to ≤139 nm. Extension of work on absorption measurements to shorter wavelengths and with ultrahigh resolution requires an improved light source. Synchrotron radiation from a storage ring facility is the best alternative.

Coupled-channels analyses of scattering and fusion cross sections of 16O+152,154Sm, 186W systems at sub- and near-Coulomb barrier energies.

Coupled-channels calculations are performed to predict fusion, elastic scattering, and inelastic scattering cross sections for the $^{16}\mathrm{O}$${+}^{152,154}$Sm and $^{16}\mathrm{O}$${+}^{186}$W systems at sub- and near-Coulomb barrier energies, taking into account the lowest rotational states of the target up to ${\mathit{I}}^{\mathrm{\ensuremath{\pi}}}$=${8}^{+}$ explicitly. It is shown that experimental data of fusion cross sections taken recently with high precision, partial fusion cross sections, and also average spin values of compound nuclei formed after fusion are well reproduced by the calculations using optical potential parameters that can reproduce elastic and inelastic scattering data. The fusion-barrier distribution, defined as the second derivative of the fusion cross section ${\mathit{d}}^{2}$(E\ensuremath{\sigma})/${\mathit{dE}}^{2}$, is also calculated and compared with experimental data. Particular attention is focused on effects of the ${\mathit{Y}}_{4}$ deformation of the target on various physical quantities.

Photodissociation of O2 and H2O in the middle atmosphere: Comparison of numerical methods and impact on model O3 and OH

We have compared three photochemical diurnal models of O3 and OH in the upper stratosphere and mesosphere which use different techniques for calculating the absorption of solar ultraviolet radiation by the O2 Schumann‐Runge bands. One model uses a detailed line‐by‐line representation of the O2 cross section from 1750–2050 Å, while the two others use lower resolution, parameterized cross sections. Using the parameterized cross sections, the calculated O3 profiles for both day and night agree with those obtained from the line‐by‐line model to within 6%. This appears to eliminate inaccuracies in the parameterized O2 cross section as a major cause of previously reported model O3 deficits. A portion of the residual differences from the line‐by‐line model are attributed to inaccuracies in the calculated H2O photolysis rate. A parameterized H2O cross section is offered which improves the accuracy of this calculation.

The fusion of 16O with an aligned 165Ho target

Coupled channels calculations of the fusion cross sections for 16O with an aligned 165Ho target are presented. Predictions are made for the orientation dependence that would be observed in an experiment and these are compared with previous predictions. We predict that in an experiment aligning the target will change an unpolarized cross section of order 10 mb by between 40% and 175%, depending on the experimental conditions. The coupled channels results are compared with the results of eigenchannel and semiclassical methods 165Ho(16O,X).

A Study of 16O+12C Elastic Scattering at E/A = 10 MeV in the α-Particle Model11The project supported in part by National Natural Science Foundation of China and by the Grant LWT2-1298 of the Chinese Academy of Sciences.

Using a folding model based on the α-particle model, the differential cross sections for 16O+12C elastic scattering at 168 MeV have been calculated. This folding model, having no need of the renormalization, provides a good description of the experimental data.

High temperature quenching cross sections for nitric oxide laser-induced fluorescence measurements

Collisional quenching cross sections for laser-induced fluorescence from NO A(v′=0) are measured for H2O, CO2, O2, NO, N2, H2, Ar, C2H6, and CO as a function of temperature from 300 to 1750 K. Room temperature cross sections vary widely (≤0.03 Å2 for N2, H2, C2H6, and Ar to ≥100 Å2 for H2O). As temperature increases, cross sections for H2O and CO2 decrease, cross sections for O2 and NO remain constant, and cross sections for N2, H2, CO, and C2H6 increase. These data provide quantitative quenching corrections for laser-induced fluorescence measurements of NO concentrations in nonreacting and reacting flows. Physical quenching models (based upon NO–Q and NO+–Q− collision complexes) are reviewed and used for experimental data correlation and extrapolation. A new quenching mechanism is proposed for weak quenchers.