Bands Of O2 Research Articles

Two-photon nitric oxide laser-induced fluorescence measurements in a diesel engine

A two-photon nitric oxide (NO) laser-induced fluorescence (LIF) technique was developed and applied to study in-cylinder diesel combustion. The technique prevents many problems associated with in-cylinder, single-photon NO planar-laser-induced fluorescence measurements, including fluorescence interference from the Schumann-Runge bands of hot O2, absorption of a UV excitation beam by in-cylinder gases, and difficulty in rejecting scattered laser light while simultaneously attempting to maximize fluorescence signal collection. Verification that the signal resulted from NO was provided by tuning of the laser to a vibrational off-resonance wavelength that showed near-zero signal levels, which resulted from either fluorescence or interference at in-cylinder pressures of as much as 20 bar. The two-photon NO LIF signal showed good qualitative agreement with NO exhaust-gas measurements obtained over a wide range of engine loads.

On the temperature dependence of the integrated intensity of the collision-induced fundamental band of O2–O2

The temperature dependence of the integrated intensity of the collision-induced fundamental band of O2–O2 pairs has been investigated. For T < 280 K, most of the intensity has been shown to arise through the long-range isotropic quadrupolar mechanism, which leads to a monotonic decrease with increasing T. Recent observations carried out at higher temperature show a small increase in the integrated intensity as T increases. Assuming that this increase in absorption is due to a short-range isotropic overlap dipole and fitting the theoretically calculated results to the experimental data, reasonable values are obtained for the magnitude and range of this dipole. The assumption is tested by calculating the corresponding spectral profiles, and it is found that these are in good agreement with the experimental measurements over the temperature range 190 K to 350 K.

Photoresponse of Zener tunneling junctions of Pb(Ti,Zr)O3/SrTiO3 at low temperature

Temperature (T) dependent current–voltage (IV) characteristics of epitaxial Pb(Ti,Zr)O3/SrTiO3 heterojunctions exhibiting the characteristics of Zener tunneling are measured in the dark and in the light. Ultraviolet light is found to induce a prominent photovoltaic effect at all T down to at least 50 K, while the open circuit voltage increases with decreasing T. In the dark the reverse bias current increases with decreasing T. In the light the reverse bias current at low T is a superposition of a photovoltaic current and a small component that is identical to the reverse bias current in the dark. These observations indicate that the anomalous T dependence of the reverse bias current in the dark is attributable to the tunneling from the Pb(Ti,Zr)O3 band to the SrTiO3 band. Additionally, short pulse voltages modulate the tunneling current, which is retained.

Experimental and theoretical study of distribution of O2 molecules over vibrational levels in O2(a 1Δg)–I mixture

The vibrationally excited oxygen in O2(a 1Δg)–I mixture was detected by emission spectroscopy. The analysis of a luminescence spectra of oxygen molecules on O2(b 1Σg+,v′)→O2(X 3Σg−,v″) transitions has shown that vibrationally excited O2(b 1Σg+) molecules up to v=5 are generated in the active medium of chemical oxygen–iodine laser (COIL). The highest values of relative O2(b 1Σg+,v=1) population of 22±2% and O2(b 1Σg+,v=2) of 10±3.5% are reached for I2 content in an oxygen flow ≈1%. It is shown theoretically that the relative populations of O2(X 3Σg−), O2(a 1Δg), and O2(b 1Σg+) molecules at the first and the second vibrational levels are approximately equal because of fast EE energy exchange between oxygen molecules. Up to 20% of oxygen molecules in COIL active medium are vibrationally excited. Comparison of intensities of O2(b 1Σg+,v′)→O2(X 3Σg−,v″) bands has demonstrated that a few percent of O2(b 1Σg+,v) molecules are vibrationally excited with v=3, 4, or 5. It is suggested that the following pooling reaction forms them: O2(a 1Δg,v=i)+I(2P1/2)→O2(b 1Σg+,v′=i+2)+I(2P3/2), where i=1, 2, or 3.

Quantitative spectrally resolved imaging through a spectrograph.

A grating spectrograph can be used for spectrally selective two-dimensional imaging if it is operated with a broad entrance slit. The resulting intensity distribution in its exit plane is a one-dimensional convolution of the spatial and spectral distributions of incident light. We present a dedicated deconvolution filter to reconstruct the spatial image from the spectrograph output. The algorithm is illustrated on Raman imaging of an underexpanded dry air jet. Recorded Raman images correspond to density maps convolved with the Raman spectrum of air; the latter essentially acts as a blurring function for the density map. The deconvolution filter combines the individual images recorded in the O2 and N2 Raman bands into a single image of relative air density.

Experimental verification of line- and band-shape asymmetry in the Schumann–Runge system of O2

High-resolution, laser-based photoabsorption cross-section measurements in the weakly absorbing windows between the (11,0) and (16,0) Schumann–Runge bands of O2 have been performed at liquid-nitrogen temperature and the results compared with corresponding coupled-channel Schrödinger-equation (CSE) and line-by-line model calculations. While the symmetric-line- shape-based line-by-line model cross sections differ significantly from experiment, the excellent agreement found between the CSE and experimental window cross sections serves to confirm clearly for the first time the CSE-model predictions of band shape asymmetry and quantum-mechanical interference effects, especially in the (11,0)–(14,0) band region.

Collisional relaxation of singlet O2 in neat gas investigated by laser-induced grating technique

Abstract Systematic experimental and theoretical studies of the feasibility to apply the diffraction at laser-induced gratings (LIGs) for getting information on parameters of collisional rotational, electronic and vibrational relaxation in molecular gases have been accomplished for the first time, using as an example the process of collisional relaxation of optically excited metastable O2 ( b 1 Σ + g ) molecules in neat gas. Temporal profiles of LIG signals have been recorded at densities 0.2–160 Amagat and room temperature within a broad range of time intervals (0.1–1000 μs) after ns-scale laser excitation at various rovibronic transitions of the b 1 Σ + g (v ′ =0)←X 3 Σ − g (v ′′ =0 ) band of O2. The experimental data have been analyzed within the framework of a model of a three-stage rotational (R–T), electronic (E–E,V,T + V–V and E–V,T + V–V) and vibrational (V–T) collisional relaxation. The results of the analysis are presented demonstrating temporal and amplitude variations of distinct contributions to the LIG signal within a large range of gas densities. These variations were described using a set of characteristic optical and relaxation parameters of O2. The parameters were derived from the experimental data and compared with the values known from the literature. Reasonable agreement was found between all the values provided by the LIG technique, and, in particular, the time constants of electronic and vibrational relaxation processes involved, and those previously obtained by other methods.

A new O2 band system: The c1∑u−−b1∑g+ transition in the terrestrial nightglow

A new O2 band system, the c1∑u−‐b1∑g+ transition, has been found in sky spectra of the terrestrial nightglow from the Keck telescopes. The spectral region is 380–550 nm, and emission occurs from highly vibrationally excited levels, exhibiting peak intensities at v = 9 and v = 10 of the c1∑u− state. The spectral lines are relatively sparse, and because of the nature of the transition, they extend to quite high rotational levels in a single Q branch. Population is observed from v = 4 to v = 11 of the c1∑u− state, and the estimated intensity of the entire system is 30 R. A comparison is made between the detectability of the new system and the c1∑u−‐X3∑g+ Herzberg II bands of O2, taking into consideration that the latter are the dominant visible emission in the nightglow of Venus, though only from v′ = 0.

Condensed O[TINF]2[/TINF] on Europa and Callisto

High signal-to-noise ratio spectra of Europa and Callisto's trailing side show a 0.3% deep 5771 A absorption band due to condensed O2 at the same wavelength as a stronger band previously identified on Ganymede. Excellent longitudinal coverage for Europa shows that unlike Ganymede, where the band is much stronger on the trailing side, Europa shows no significant longitudinal variation in the O2 band strength.

Global observations of the carbon budget, 2, CO2 column from differential absorption of reflected sunlight in the 1.61 μm band of CO2

This paper investigates the impact of uncertainty in atmospheric composition and state upon the feasibility of measuring the CO2 column from spectral analysis of sunlight reflected to space in the 1.61 μm absorption band of CO2. In principle, measurements of clear sky radiance at two frequencies, one where CO2 absorbs strongly and the other weakly, allow the difference between the optical thicknesses of the atmosphere at the two frequencies to be determined precisely. That difference, denoted by L, is a linear functional of the CO2 density profile, which depends strongly on the CO2 amount and only weakly upon its vertical distribution, thus suggesting that the CO2 column may be estimated from L. A simple model for the radiance reflected to space is used to estimate the magnitude of the error in the CO2 column inferred from L when the atmosphere contains thin cloud and aerosol. It emerges that measurements in two channels in the 1.61 μm CO2 absorption band are too sensitive to cloud and aerosol to allow the CO2 column to be inferred with precision better than a few percent in the presence of thin cloud and aerosol. However, simultaneous measurements of optical thickness in the nearby 1.27 μm absorption band of O2 are tightly correlated with those for CO2, even in the presence of aerosol and thin cirrus, and therefore may allow the CO2 column to be determined relative to the O2 column, provided that the latter is known independently from surface pressure. The correlation between O2 and CO2 optical thicknesses depends upon the mean scattering height, but this quantity may be estimated with sufficient accuracy from radiances measured in the O2 band. A prototype algorithm is developed to estimate the CO2 column from data in two CO2 channels and three O2 channels. The algorithm is used to estimate the probable bias and standard error of measurements of CO2 column from space under conditions where the optical thicknesses of aerosol and cirrus may be as large as 0.2 and 0.1, respectively, and where the temperature profile is known to within ±1 K. The simulations suggest that the error in the estimated CO2 column caused by these sources is approximately 0.5%. This conclusion is interpreted cautiously because the analysis assumes inter alia that the spectroscopic properties of both CO2 and O2 are known accurately, that the surface reflectance and the scattering properties of aerosol and cirrus vary predictably between 1.27 μm and 1.61 μm, and that difficult technical issues associated with high spectral resolution measurements can be resolved. Nevertheless, the importance of global measurements of CO2 is such that the method warrants further investigation.

Spaceborne measurements of atmospheric CO2 by high‐resolution NIR spectrometry of reflected sunlight: An introductory study

We introduce a strategy for measuring the column‐averaged CO2 dry air volume mixing ratio from space. It employs high resolution spectra of reflected sunlight taken simultaneously in near‐infrared (NIR) CO2 (1.58‐μm and 2.06‐μm) and O2 (0.76‐μm) bands. Simulation experiments, show that precisions of ∼0.3–2.5 ppmv for can be achieved from individual clear sky soundings for a range of atmospheric/surface conditions when the scattering optical depth τs is less than ∼0.3. When averaged over many clear sky soundings, random errors become negligible. This high precision facilitates the identification and correction of systematic errors, which are recognized as the most serious impediment for the satellite measurements. We briefly discuss potential sources of systematic errors, and show that some of them may result in geographically varying biases in the measured . This highlights the importance of careful calibration and validation measurements, designed to identify and eliminate sources of these biases. We conclude that the 3‐band, spectrometric approach using NIR reflected sunlight has the potential for highly accurate measurements.

Fast-J2: Accurate Simulation of Stratospheric Photolysis in Global Chemical Models

Modeling photochemistry in the stratosphere requires solution of the equationof radiative transfer over an extreme range of wavelengths and atmosphericconditions, from transmission through the Schumann–Runge bands ofO2 in the mesosphere, to multiple scattering from troposphericclouds and aerosols. The complexity and range of conditions makes photolysiscalculations in 3-D chemical transport models computationally expensive. Thisstudy pesents a fast and accurate numerical method, Fast-J2, for calculatingphotolysis rates (J-values) and the deposition of solar flux in stratosphere.Fast-J2 develops an optimized, super-wide 11-bin quadrature for wavelengthsfrom 177 to 291 nm that concatenates with the 7-bin quadrature (291–850nm) already developed for the troposphere as Fast-J. Below 291 nm the effectsof Rayleigh scattering are implemented as a pseudo-absorption, and above 291nm the full multiple-scattering code of Fast-J is used. Fast-J2 calculates themean ultraviolet-visible radiation field for these 18 wavelength binsthroughout the stratosphere, and thus new species and new cross sections canbe readily implemented. In comparison with a standard, high-resolution,multiple-scattering photolysis model, worst-case errors in Fast-J2 do notexceed 5% over a wide range of solar zenith angles, altitudes(0–60 km), latitudes, and seasons where the rates are important inphotochemistry.

The 1.27‐μm O2 continuum absorption in O2/CO2 mixtures

The collision‐induced, near‐infrared O2 continuum band overlapping the weak a1Δg−X3Σg−, v = 0−0, 1.27 μm discrete band of O2 has been investigated in O2/CO2 mixtures at room temperature (T = 296 K) for total densities from 1.8 to 9.3 times that of an ideal gas under standard conditions (T = 273.15 K and P = 101.325 kPa), i.e., from 1.8 to 9.3 amagats. Absorption spectra were recorded at 0.5 cm−1 resolution using a Fourier transform spectrometer and an 84‐m pathlength. A least squares analysis of the integrated band strength, Stotal = SO2ρO2 + SO2 − O2 ρO22 + SO2 − CO2ρO2ρCO2, as a function of the carbon dioxide density, ρCO2, and the oxygen density, ρ02, yields SO2‐Co2 = 2.953(32) × 10−43 cm−2 (molecule/cm3)−2 (i.e., 2.132(23) × 10−4 cm−2 amagat−2). The SO2‐CO2 coefficient is ∼3 times greater than the corresponding SO2‐N2 coefficient determined from studies of O2/N2 mixtures, illustrating the efficiency of large electric multipolar moments in inducing continuum absorption in the 1.27‐μm band of O2. The results support the calculations by Brown and Tipping [2000], which demonstrate the importance of water, with its large electric dipole moment, in enhancing the collision‐induced absorption bands of O2 and N2 in the atmosphere. We suggest that the apparent inability of radiative transfer models to accurately account for the increased atmospheric absorption present when water vapor levels increase may be due in part to the neglect of the intensity enhancement of a number of continuum bands and of the far wings of discrete bands by water molecule collisions.

Predicted predissociation linewidths in the Schumann–Runge bands of O2 compared with recent high resolution measurements

We derive and use new parameters to quantify the semiempirical expressions of Julienne and Krauss [J. Mol. Spectrosc. 56, 270 (1975)] for the Πu5, Σu+3, Πu3, and Πu1 potentials that predissociate the rovibrational levels of the B 3Σu− state of O2. Using the new parameters in the model of Julienne and Krauss we evaluate fine-structure predissociation linewidths for the Schumann–Runge bands that terminate on the v=13,14 rovibrational levels of the B 3Σu− state. We compare these linewidths and those calculated with several existing sets of parameters with the measurements of Dooley et al. [J. Chem. Phys. 109, 3856 (1998)]. We also show the deperturbing effect of the level shifts, calculated with the new parameters, on the energies of the rotationless v=0–17 vibrational levels of the B 3Σu− state.

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.

A new model for the Schumann-Runge bands of O2

A new quantum-mechanical model is presented of photoabsorption and photodissociation in the discrete and continuous Schumann-Runge regions of the molecular oxygen spectrum, based on the coupled-channel Schrödinger-equations method. The ability of the model to predict accurately temperature-dependent photoabsorption cross sections and photodissociation branching ratios is demonstrated, suggesting applications in the areas of atmospheric vacuum-ultraviolet opacity and photochemistry.

Temperature and Pressure Dependence of Line Widths and Integrated Absorption Intensities for the O2 aΔg − X3Σg- (0,0) Transition

The electric-dipole forbidden a1Δg − X3 (0,0) band of gas-phase O2 has been studied in absorption at wavelengths around 1.27 μm using Fourier transform spectroscopy and a long-path absorption cell. Experiments were conducted at temperatures of 294, 243, and 200 K and at pressures in the range 140−750 Torr. Both pure O2 and a mixture of 21% O2/79% N2 were studied, and line widths, integrated line intensities, and integrated absorption intensities (AIs) for the (0,0) vibrational band were measured. Integrated AIs were found to be independent of temperature, pressure, and gas composition, and the recommended value for the vibrational band from the current study is Sint = 3.210(15) × 10-24 cm molecule-1 (1σ error) for pure 16O2, corresponding to an Einstein A-coefficient of A = 2.256(10) × 10-4 s-1. The effect of including other oxygen isotopomers is to increase the integrated AI value for this origin band to Sint = 3.226(15) × 10-24 cm molecule-1. Widths of individual spectroscopic lines decrease with increasing molecular rotational quantum number. The temperature dependence of Lorentzian line width components, γT (fwhm), is well represented by the expression γT = γ294K(T/294 K)-0.85. The effects of pressure broadening of lines by N2 are indistinguishable from those for pure O2 at the same temperature and pressure.

Faint Emission Lines in the Blue and Red Spectral Regions of the Night Airglow11Lick Observatory Bulletin 1391. Based on observations obtained at the W. M. Keck Observatory, which is operated by the California Institute of Technology and the University of California.

ABSTRACTCo‐added night‐sky spectra, obtained as by‐products of exposures with the Keck I 10 m telescope on Mauna Kea and the HIRES high‐resolution echelle spectrograph over a period of approximately 4 years, all completely independent of similar data published earlier, are presented. The new data total over 150 hours exposure in one order (5505–5625 Å), more than 100 hours in 16 orders, and more than 50 hours in all orders in the spectral range 3923–7853 Å and include smaller numbers of hours over the entire range 3618–9023 Å. From these data, co‐added in the red region to the previously published data, two additional Meinel OH bands, 8–1 and 7–0, were found in emission in the spectrum of the night airglow, the presence of the 6–0 band was confirmed, and numerous lines of the 10–4 and 10–5 bands were detected. Three Hg i light‐pollution lines were detected as weakly present in the Mauna Kea night sky. Three other predicted Meinel bands are too faint and still were not detected with certainty. Similarly, neither OD nor the Rbi or Cs i resonance lines were seen. Upper limits were set on the latter, which are consistent with their abundance ratios to K and the observed strength of the K i resonance line λ7699, if the excitation mechanisms of all these three alkali atoms were equally effective. Brief references are given to other papers in press based on these new spectral data and to other work in progress on identifications of many additional O2 bands in the spectrum of the night airglow. A table summarizes all the identifications of all OH emission bands in the spectrum of the night airglow, in all spectral regions.

The application of a VUV-FT spectrometer and synchrotron radiation source to measurements of the NO and O2 bands at 295 K

Current research on the Earth's upper atmosphere requires molecular parameters of unprecedented detail and accuracy. 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 OZ in the UV to VUV region. To meet these requirements, we moved the VUV Fourier transform spectrometer at Imperial College, London to a synchrotron radiation facility (Photon Factory, KEK, Japan) and measured VUV photoabsorption cross sections of NO from 195 to 160 nm and OZ from 185 to 175 nm.

Absolute intensities for the O2 1.27 μm continuum absorption

Collision‐induced absorption coefficients for the 1.27 μm band of O2 have been measured at a resolution of 0.5 cm−1 and an optical path length of 84 m using a Fourier transform spectrometer. Spectra were recorded for sample densities ρ from 1 to 10 times that of an ideal gas under standard conditions (T = 273.15 K and P = 101.325 kPa) at temperatures of 253, 273, and 296 K for pure O2 and O2/N2 mixtures. After removing the contributions from the sharp lines of the υ = 0 ← 0 component of the O2 a1Δg ← X3∑g− band, which overlaps the continuum band, the integrated band strength per unit path length, S ≡ SO2−O2ρO22 + SO2−N2ρN2ρO2, has been determined for several values of the densities, ρO2 and ρN2, to give values for SO2−O2 and SO2−N2. At 296 K we find SO2−O2 = 4.847(22) × 10−43 cm−2 (molecule/cm3)−2 and SO2−N2 = 0.941(50) × 10−43 cm−2 (molecule/cm3)−2. Type A standard uncertainties are given, that is, ±1σ, from a least squares analysis of the integrated‐intensity‐versus‐density data. The SO2−O2 coefficient is in reasonable agreement with the previous measurements of Cho et al. [1963]; however, our value for SO2−N2is 2.6 times greater than their results. Our derived air coefficient SO2−air is 37% greater than the atmospheric value of Mlawer et al. [1998], after correcting their continuum value for an updated value for the absorption coefficients for the overlapping discrete structure of the O2a1Δg ← X3∑g− band.