Showing papers in "Journal of Quantitative Spectroscopy & Radiative Transfer in 1981"
TL;DR: In this article, energy levels and rotational constants for all carbon dioxide infrared absorption transitions of significance for terrestrial atmospheric transmission were calculated using new FTS measurements in the 4.3 μm region at elevated temperature and precise laser measurements around 10 μm, and high resolution grating spectrometer measurements of isotopically enriched samples.
Abstract: Energy levels and rotational constants are provided for all carbon dioxide infrared absorption transitions of significance for terrestrial atmospheric transmission. Constants have been recalculated using new FTS measurements in the 4.3 μm region at elevated temperature, new FTS measurements in the 15, 5, and 2 μm regions, precise laser measurements around 10 μm, and high resolution grating spectrometer measurements of isotopically enriched samples. Band centers, band strengths, and coriolis coupling constants are given for some 560 bands.
174 citations
TL;DR: In this paper, individual spectral line parameters including line positions, strengths, and intensities were generated for the A 2 ∑- X 2 Π(0,0) band of OH, applicable to atmospheric and high temperatures.
Abstract: Individual spectral line parameters including line positions, strengths, and intensities, have been generated for the A 2 ∑- X 2 Π(0,0) band of OH, applicable to atmospheric and high temperatures. Energy levels and transition frequencies are calculated by numerically diagonalizing the Hamiltonian. Line strengths are calculated using the dipole matrix and eigenvectors derived from energy matrix diagonalization. The line strengths are compared to those calculated from previously published algebraic line strength formulas. Tables of line parameters are presented for 240 and 4600°K.
134 citations
TL;DR: In this paper, the authors presented a simple analytical form, based on a set of parameters derived from distorted wave exchange cross-section calculations, for hydrogen, helium, and lithium-like ions.
Abstract: Electron impact ionization cross sections and rates for hydrogen-, helium- and lithium-like ions are presented in simple analytical form, based on a set of parameters derived from distorted wave exchange cross section calculations. Isoelectronic fits to the parameters used in the formulate allow rapid generation of cross sections and rates for any ion in these sequences with a minimum of computational effort. The use of accurate Bethe slopes in the cross section-fitting algorithm yields good accuracy both in the near threshold and high energy regions. The rate coefficient is given in the form of a correction to the commonly used Seaton formula and is thus readily adaptable to existing plasma modeling computer codes. Comparisons of the present results with other theoretical and experimental data are made.
127 citations
TL;DR: In this paper, the refractive indices of rare gases have been measured by Fabry-Perot interferometry down to 140 nm and a value of 0.268±0.008 was derived for the oscillator strength of the first resonance line at 146.9 nm.
Abstract: The refractive indices of rare gases have been measured by Fabry-Perot interferometry down to 140 nm. Dispersion relations of the Sellmeier form are given and the results are compared with data found in the literature. For xenon, a value of 0.268±0.008 is derived for the oscillator strength of the first resonance line at 146.9 nm.
122 citations
TL;DR: In this article, side-on observations of the visible spectrum emitted by a helium plasma generated in a wall-stabilized arc are reported, where electron densities range from 0.2 to 1.3 × 10 22 m -3 and electron temperatures vary from 10,000 to 20,000 K.
Abstract: Side-on observations of the visible spectrum emitted by a helium plasma generated in a wall-stabilized arc are reported. Electron densities range from 0.2 to 1.3 × 10 22 m -3 and electron temperatures vary from 10,000 to 20,000 K. Most of the seventeen measured lines are “isolated” at the conditions of the experiment. Here, “isolated” refers to quantum levels which are non-degenerate even in the presence of perturbing fields. Electron densities derived from the Stark-widths of the isolated lines agree to within 15% of the values determined from Hβ and from the quasi-degenerate He(I) lines at 4471 and 4921 A. Similar agreement is observed for the static-ion Stark broadening parameters. However, at the conditions of this experiment, the static-ion approximation is not valid near the center of some of the isolated lines. The observation of ion-dynamic effects in neutral isolated lines is reported here for the first time. In the isolated lines, the measured ion-dynamic effects are reasonably consistent with calculations based on an adiabatic “unified” theory for the ion perturbers. A simple parametric expression closely approximates the ion-dynamic contribution to the half-width of isolated lines. Hydrogenic (non-isolated) neutral helium lines exhibit a large discrepancy with theoretical profiles near the line center, where ion-dynamic effects are important.
100 citations
TL;DR: In this article, the transfer equation was generalized to encompass spherical and cylindrical geometries, as well as a Lorentz opacity profile, by using a reciprocity theorem relating the coupling constant from cell i to cell j to that from cell x to cell y.
Abstract: A previously developed technique for solving the transfer equation directly by using frequency-and angle-averaged escape probabilities in a planar, Doppler-broadened medium is generalized to encompass spherical and cylindrical geometries, as well as a Lorentz opacity profile. Two key elements permit this generalization to be made. The first is a reciprocity theorem relating the coupling constant from cell i to cell j to that from cell j to cell i. The second is the use of a universal but accurate mean angle of diffusivity.
60 citations
TL;DR: In this article, the spatial distribution of the atmospheric parameters measured with the differential absorption lidar technique is restored for pulsed emission only if the laser emission is monochromatic.
Abstract: The spatial distribution of the atmospheric parameters measured with the differential absorption lidar technique is restored for pulsed emission only if the laser emission is monochromatic. Due to the finite linewidth of the laser lines, a systematic error is introduced in the measurement of the local optical thickness, which is shown to depend on the propagation of the laser pulse along the line of sight and on the ratio γ L γ a of the laser linewidth to the absorption linewidth. Relative errors as large as 20% may be made under the usual experimental conditions for γ L γ a ≈ 1 . A 1% limit on this error is only obtained if γ L γ a ⪅0.3.
42 citations
TL;DR: In this article, exact integral equations are derived describing the source function and radiative flux in a two-dimensional, radially infinite cylindrical medium which scatters anisotropically.
Abstract: Exact integral equations are derived describing the source function and radiative flux in a two-dimensional, radially infinite cylindrical medium which scatters anisotropically. The problem is two-dimensional and cylindrical because of axisymmetric loading. Radially varying collimated radiation is incident normal to the upper surface while the lower boundary has no radiation incident upon it. The scattering phase function is represented by a spike in the forward direction plus a series of Legendre polynomials. The two-dimensional integral equations are reduced to a one-dimensional form by separating variables for the case when the radial variation of the incident radiation is a Bessel function. The one-dimensional form consists of a system of linear, singular Fredholm integral equations of second kind. Other more complex boundary conditions are shown to be solvable by a superposition of this basic Bessel function case. Diffusely incident radiation is also considered.
41 citations
TL;DR: In this article, a tunable diode laser was used to record fully resolved vibration-rotation absorption lines of CO in combustion products of an atmospheric pressure methane-air flame.
Abstract: A tunable diode laser was used to record fully resolved vibration-rotation absorption lines of CO in the combustion products of an atmospheric pressure methane-air flame. The measurements were made both at high temperature, in situ , and in gases cooled to room temperature. The in situ measurements were made on 26 lines in the 1 → 0, 2 → 1, and 3 → 2 vibrational bands of the CO fundamental. The room temperature measurements were performed on 19 lines in the 1 → 0 band. Results are presented for the dependence of the collision width, 2γ, on vibrational and rotational quantum numbers at 1850 and 300°K. The temperature exponent N , defined by the relation 2 γ 2 = 2 γ 1 ( T 2 / T 1 ) − N , was also determined and found to depend on rotational quantum number.
40 citations
Abstract: A completely quantum mechanical formalism has been developed to describe the high density plasma effects on fundamental atomic parameters. Both the bound and free electrons are treated by a method which in principle is similar to Hartree's self-consistent field method. The free plasma electrons' wavefunction is obtained from the Schroedinger equation with the effective potential representing the spherically averaged Coulomb interaction with bound and free electrons. Results are given for level shifts, coefficients of transition probabilities, and electron collision cross sections of Ne(9+) for temperatures of 200 and 500 eV for an electron density range of 1-6 x 10 to the 24th per cu cm.
37 citations
TL;DR: In this paper, the authors used laser absorption spectroscopy to measure relative concentration and translational temperature profiles of amidogen (NH 2 ) in premixed ammonia-oxygen flames operating at low pressure.
Abstract: Laser absorption spectroscopy has been used to measure relative concentration and translational temperature profiles of amidogen (NH 2 ) in premixed ammonia-oxygen flames operating at low pressure. The narrow-linewidth laser absorption technique used in the study is described, and the details of the spectroscopy of NH 2 necessary in the interpretation of the absorption spectra are discussed. Results are presented which illustrate the effects of mass flowrate and fuel equivalence ratio. The magnitude of the oscillator strength required to bring these measurements into agreement with flame calculations is of the same order of magnitude as previous estimates for oscillator strengths of other vibration-rotation lines in the same electronic band. Because of the high spectral resolution of the laser absorption technique, the previously unmeasured spin splitting of the doublet used in the analysis was obtained as a by-product of the research.
TL;DR: In this article, the line widths, pressure-induced shifts, and center frequency of the J = 1-0, K = 0 phosphine transition at 266.9 GHz have been determined.
Abstract: The line widths, pressure-induced shifts, and center frequency of the J = 1-0, K = 0 phosphine transition at 266.9 GHz have been determined. The widths and shifts are reported for collisions with phosphine, H2, and He.
TL;DR: The relationship between the maximum entropy Eddington factor and flux limited diffusion theory was established in this paper, where it was shown that a simple Pade approximant to the maximum-entropy angular distribution yields precisely the same angular distribution extant in a recently reported flux-limited diffusion theory.
Abstract: The relationship between the maximum entropy Eddington factor and flux limited diffusion theory is established. Although these two approaches to radiative transfer are philosophically very different (one treats an ensemble, while the other treats a specific system), the resulting variable Eddington factors are in semiquantitative agreement. It is shown that a simple Pade approximant to the maximum entropy angular distribution yields precisely the same angular distribution extant in a recently reported flux limited diffusion theory.
TL;DR: In this paper, the F N method is used to establish accurate numerical results for the albedo and the exit distribution of radiation relevant to an illuminated semi-infinite half space with an exponentially varying albedos for single scattering.
Abstract: The F N method is used to establish accurate numerical results for the albedo and the exit distribution of radiation relevant to an illuminated semi-infinite half space with an exponentially varying albedo for single scattering.
TL;DR: In this article, the authors derived a laboratory-frame redistribution function for the scattering of radiation in subordinate lines where both atomic levels are radiatively broadened, denoted as RV(x′, n′; x, n), which is the correct counterpart of Hummer's redistribution function RIV.
Abstract: Within the scope of the quantum-mechanical result of Omont, Smith and Cooper, we have derived a laboratory-frame redistribution function for the scattering of radiation in subordinate lines where both atomic levels are radiatively broadened. This new function, denoted as RV(x′, n′; x, n), is the correct counterpart of Hummer's redistribution function RIV. Moreover, it follows from the formalism developed here that RV contains all known redistributions Ri(i=I, II, III, IV) as special cases and we may therefore speak in some sense of a unified redistribution function. A simple method has been tested for the evaluation of RV and our numerical examinations of the properties of RV served, among others, as an independent verification of the results obtained by Reichel and Vardavas for RIII and RIV. Finally, it is shown in the conclusion to this paper that the function RV, discussed here, can be applied not only to the radiative redistribution, but also to a more general case of a collisional redistribution in subordinate lines.
TL;DR: In this paper, six algorithms and approximations for the calculation of Voigt profiles are compared for accuracy and time required for calculation, and for high-precision calculations, a GAUTSCHI program is recommended; for calculations with a few per cent of error, the Matvejev and the Kielkopf approximation is recommended.
Abstract: Six algorithms and approximations for the calculation of Voigt profiles are compared for accuracy and time required for calculation. For high-precision calculations, a GAUTSCHI program is recommended; for calculations with a few per cent of error, the Matvejev and the Kielkopf approximations are recommended.
TL;DR: In this article, a theory of microwave emission from an irregular layer of Rayleigh scatterers is developed by combining an existing matrix doubling method for volume scattering with the Kirchhoff method in surface scattering.
Abstract: A theory of microwave emission from an irregular layer of Rayleigh scatterers is developed by combining an existing matrix doubling method for volume scattering with the Kirchhoff method in surface scattering. Effects of the layer boundaries are illustrated by comparing layers with plane boundaries vs layers with rough top or bottom boundaries and irregular layers. It is found that the major effect of an irregular top layer boundary is to slow down the variation of the layer emission as a function of the nadir angle and the major effect of an irregular bottom boundary is to increase the level of the layer emission. Comparisons of the developed layer model with snow emission indicate the potential use of such models in data interpretation.
TL;DR: In this article, the authors measured the fluorescence-excitation profile of the red Na-D1 line wing from about 1 cm −1 to 1100 cm−1 and of the blue N-D2 line-wing from approximately 1 cm− 1 to 600 cm − 1 with respect to the corresponding line centre.
Abstract: In this paper, we report on measurements of the fluorescence-excitation profile of the red Na-D1 line wing from about 1 cm−1 to 1100 cm−1 and of the blue Na-D2 line-wing from about 1 cm−1 to 600 cm−1, with respect to the corresponding line centre. We have also measured the fluorescence-excitation profile of the red Na-D2 and blue Na-D1 inner (overlapping) line wings from 1 cm−1 with respect to the centre of each of the lines. All these wings were measured in several premixed, laminar, shielded H2O2Ar and H2O2N2 flames at 1 atm (1400 K ⪅ T ⪅ 2300 K). We also measured these wings in a vapor cell containing Ar or N2 perturbers (T ∼ 480 K, p ∼ 0.4 atm) in order to determine the influence of temperature on these wings. Using a tunable CW dye laser as excitation source, we determined the fluorescence-excitation profiles by measuring the total fluorescence intensity while tuning the laser wavelength. In order to specify the contributions that the different kinds of major flame perturbers (Ar, N2, H2O) make to the wings, we compared the wing profiles measured in various flames of different flame-gas compositions. In this comparison, the wing profiles were normalized with respect to the line-centre. We compared our measurements of far red Na-D1 and blue Na-D2 line-wings ( Δσ ⪆ 30 cm −1 ) specified to Ar perturbers (at T = 500 K and T = 2000 K) with the results derived from quasi-static theory using available interaction potential data. In the case of Ar perturbers at T = 500 K, we observed a satellite at about 8 cm−1 from the line-centre on the red Na-D1 wing: this satellite was absent at T = 2000 K. The position of this red satellite was explained with the help of a set of “modified” potentials, which were constructed for interpreting the collisional Na-D broadening- and shift-rates deduced from our line-core observations and which were reported in Part I of this paper.
TL;DR: In this paper, an analysis of Stark broadening problems based on Markovian model microfield statistics is presented, and the strengths and weaknesses of various models are discussed, emphasizing the kangaroo process of Brissaud and Frisch.
Abstract: Stark broadening theories which concentrate on the statistics of the plasma electric microfield rather than the dynamics of collisions have come to be known as Model Microfield Methods. In the present paper we present an analysis of Stark broadening problems based on Markovian model microfield statistics. Our derivation permits an easy comparison with traditional Stark broadening theories such as the impact and unified theories; this comparison is used to clarify the physical nature of the approximations employed by Markovian models. The strengths and weaknesses of various models are discussed, emphasizing the kangaroo process of Brissaud and Frisch, and methods are suggested for improving the current model microfield approach.
IBM1
TL;DR: In this paper, the authors compare three interpolation schemes: spherical harmonics, spline interpolation and Lagrange interpolation, and show that the most accurate way to interpolate the intensity curve is to use the integration of the source function method.
Abstract: The numerical methods used for solving the transfer equation for a planetary atmosphere often give the specific intensity at a predetermined set of zenith angles, often the Gauss quadrature points. Since these ordinates are not always the ones at which the intensities are needed, some form of interpolation is needed. First, we show that the intensities computed from the moments derived from the spherical harmonics method are identical to those computed from the discrete ordinates method at the Gauss quadrature points. After a discussion of the various contributions to the errors, we compare three interpolation schemes. By far the most accurate way to interpolate the intensity curve is to use the integration of the source function method. We show how this method can be used with a minimum of computational effort. Although less accurate, interpolations are much faster. Not surprisingly, we find that Lagrange interpolation can produce very inaccurate values of the intensities and should not be used. Spline interpolation, on the other hand, always produces reasonable intensities. The accuracy of the spline interpolation can be improved greatly by supplementing the intensities at the Gauss points with values computed by the integration of the source function method at a few key ordinates.
TL;DR: In this article, the arc emission method has been employed to measure transition probabilities for two hundred and seventy five lines of Cr(I) (of which thirty-five are blended) and for twenty-six lines of CR(II) lying between 422 and 484 nm.
Abstract: The arc emission method has been employed to measure transition probabilities for two hundred and seventy five lines of Cr(I) (of which thirty-five are blended) and for twenty-six lines of Cr(II) lying between 422 and 484 nm. The spectra were photographed by means of a large grating spectrograph. Plasma diagnostics were carefully performed to obtain accurate values of temperatures. The absolute scale was established for Cr(I) lines using precisely known Amn-values derived from life-time measurements for the resonance lines; for the Cr(II) lines, our absolute scale is based on accurate measurements for the line at 4242.56 A. The smallest and largest errors estimated for the Amn-values are ±10% and ±40%. There is generally good agreement with previous experimental data, although our values sometimes deviate by factor of 2–3 from the calculated estimates.
TL;DR: In this paper, the authors measured the absorption intesities for a number of rotation-vibration lines in the 4-0 through 7-0 overtone bands of HCl utilizing a Fourier transform spectrometer and a 409.6 m path length White cell.
Abstract: We have measured the absorption intesities for a number of rotation-vibration lines in the 4-0 through 7-0 overtone bands of HCl utilizing a Fourier transform spectrometer and a 409.6 m path length White cell. Individual line strengths, band strengths, dipole matrix elements, and Herman-Wallis factors are presented.
TL;DR: In this paper, the problem of radiative heat transfer in an absorbing, emitting, isotropically scattering two-layer slab with diffusely and specularly reflecting boundaries is solved by the FN method and results are presented for the transmissivity and reflectivity of the slab.
Abstract: The problem of radiative heat transfer in an absorbing, emitting, isotropically scattering two-layer slab with diffusely and specularly reflecting boundaries is solved by the FN method and results are presented for the transmissivity and reflectivity of the slab.
TL;DR: In this article, spectral line parameters for the X2II-X2II(1, 0) bands of OH and 35ClO and 37ClO for a temperature of 296 K were generated.
Abstract: Individual spectral line parameters, including line positions, energy levels, and intensities, have been generated for the X2II-X2II(1, 0) bands of OH and 35ClO and 37ClO for a temperature of 296 K. At this temperature the OH band intensity is 42.9 cm-1/atm-cm or 1.73 x 10-18 cm/molecule. For ClO, the band intensity for both isotopes in natural abundance is 11.8 cm-1/atm-cm or 4.76 x 10-19 cm/molecule. Tables of line parameters for both molecules are available from the authors.
TL;DR: In this paper, a rocket borne scanning 1 4m spectrometer was used to observe the night airglow between 1900 and 2300 A at a resolution of 15 A. An attitude control system oriented the payload horizontally near apogee (150 km) and pointed the field of view to the north and parallel with the terminator.
Abstract: A rocket borne scanning 1 4 -m spectrometer was used to observe the night airglow between 1900 and 2300 A at a resolution of 15 A. An attitude control system oriented the payload horizontally near apogee (150 km) and pointed the field of view to the north and parallel with the terminator. Progressions from the δ(0, v″) and γ(0, 0) band system of nitric oxide were observed. The observations of the δ-bands and γ-bands are consistent with the relative intensities produced in the preassociation of ground state atomic oxygen and nitrogen. An observation of the v′ = 0, e-band progression is suggested and is consistent with the presence of a resonance fluorescence contribution near apogee. The A2Σ+ (upper level of the γ-bands) can only be populated by cascade from the C2π state (upper level of the γ-bands) in the preassociation reaction. In the absence of quenching of the A2Σ+ state, the emission rate of the γ-bands can be used as a measure of the C−A transition and thus to deduce the branching ratio to the A2Σ+ state. This branching ratio is estimated to be 0.21±0.04.
TL;DR: In this paper, the Anderson-Tsao-Curnutte method was used to calculate the self-broadening coefficients of 16 doublet-lines, involving quasi-degenerate levels of the (000) and (010) vibrational states of water.
Abstract: From Fourier transform spectra (resolution ≈ 0.005 cm-1), the self-broadening coefficients of 16 doublet-lines, involving quasi-degenerate levels of the (000) and (010) vibrational states of water, have been measured using methods previously described. For doublet-lines, it is observed that self-broadening is about 40% smaller than for other lines. This effect is well reproduced by a calculation based on the Anderson-Tsao-Curnutte method, if one takes into account the four following intermolecular interactions: dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole. This improved calculation is also used to recalculate our set of 150 previously reported self-broadening coefficients: on the whole, the agreement between measured and calculated values is improved by about 18% as compared to the calculated values of Benedict and Kaplan instead of 14% for our previous calculations based only on the dipole-dipole intermolecular interaction. It is also demonstrated that the influence of the quadrupole moment is larger for doublet-lines than for other lines. Finally, the Anderson-Tsao-Curnutte method, taking into account the four intermolecular interactions mentioned above, leads to relative differences between observed and calculated values less than 20%, for 72% of the 166 measured lines.
TL;DR: In this article, the wide band-model parameters were determined and used to calculate total gas emissivities, which were found to be considerably different from previously published values, and good agreement was obtained between the present experimental and previous theoretical studies.
Abstract: The narrow band-model parameters S/d, γN/d and B have been obtained experimentally for the infrared bands of SO2. Good agreement was obtained between the present experimental and previous theoretical studies. The revised wide band-model parameters were determined and used to calculate total gas emissivities, which are found to be considerably different from previously published values.
TL;DR: In this paper, the errors caused by self-absorption in the wing-reversal method are obtained by using correction factors for temperature and potassium atom density in boundary layers, without numerical integration of the radiative transfer equation.
Abstract: The wing-reversal method is useful, with small influence by self-resonant absorption, for the measurement of MHD combustion-gas temperatures in the presence of cold boundary layers. We show how the errors caused by self-absorption in the wing-reversal method are obtained by using correction factors for temperature and potassium atom density in boundary layers, without numerical integration of the radiative transfer equation. The radiative transfer equation and the absorption coefficient of potassium may be simplified when the optical thickness is appreciably smaller than unity. We have used this method on MHD combustion gases. The measured main flow temperature agrees with the thermal equilibrium temperature within 1%, while the measured main flow potassium atom density is about 65% of the equilibrium density.
TL;DR: Several useful expressions for the population ratios of collisionally excited levels have been derived and different transitions of Tl and Ga atoms, seeded in a premixed atmospheric flame, have been excited in order to verify that the levels higher than the laser-excited level are populated approximately according to a Boltzmann equilibrium as mentioned in this paper.
Abstract: Several useful expressions for the population ratios of collisionally excited levels have been derived and different transitions of Tl and Ga atoms, seeded in a premixed atmospheric flame, have been excited in order to verify that the levels higher than the laser-excited level are populated approximately according to a Boltzmann equilibrium. This result confirms the possibility of using thermally assisted flourescence lines to measure local temperatures in flames. The Einstein spontaneous emission probability for the transition 6S1/2→4P3/2 at 2719.65A of Ga has also been calculated (A2719.65=0.41×108s-1) to fit the experimental point.
TL;DR: In this article, a water vapour continuum absorption in the 8 −13 μ region was investigated in the laboratory and under field conditions, and the results showed that the water vapor continuum absorption is stable in the field.
Abstract: A water vapour continuum absorption in the 8–13 μ region has been investigated in the laboratory and under field conditions.