Journal of Quantitative Spectroscopy and Radiative Transfer

Published by Elsevier
Online ISSN: 0022-4073
Publications
Article
A calculation of the A2 sigma --> X2 pi (0, 0) band emission rate factors and line center absorption cross sections of OH applicable to its measurement using solar resonant fluorescence in the terrestrial atmosphere is presented in this paper. The most accurate available line parameters have been used. Special consideration has been given to the solar input flux because of its highly structured Fraunhofer spectrum. The calculation for the OH atmospheric emission rate factor in the solar resonant fluorescent case is described in detail with examples and intermediate results. Results of this calculation of OH emission rate factors for individual rotational lines are on average 30% lower than the values obtained in an earlier work.
 
Article
This note serves as an introduction to two papers by Klose et al. [Optical tomography using the time-independent equation of radiative transfer, Parts 1 (JQSRT 2002;72:691-713) and 2 (JQSRT 2002;72:715-732)] and provides a brief review of the latest developments in optical tomography of scattering tissue. We discuss advancements made in solving the forward model for light propagation based on the radiative transfer equation, in reconstructing scattering and absorption cross sections of tissue, and in molecular imaging of luminescent sources.
 
Article
The purpose of this study is to extend the capabilities of multispectral optical imaging techniques for morphological characterization of irregular particles, encountered in several applications. We have utilized the Gaussian random ellipsoid model to quantize the shape elongation and deviation in complex-shaped particles. Compared with the Gaussian random sphere model, it is more realistic and is applicable to wider range of irregular particles with minimum possible of free parameters. By processing the reduced light scattering spectra, the proposed inverse technique can simultaneously recover the size, volume fraction, elongation, and shape deformation of particles that are randomly oriented within a colloidal suspension. The discrete dipole approximation is employed in forward light scattering calculations and input synthetic data generation. To investigate the robustness of our algorithm in coping with real scenarios, we have added different levels of noise to the observed scattering spectra. The results demonstrate the potential of our technique to non-invasively recover the morphology parameters of irregular particles.
 
Conference Paper
Summary form only given. The manner in which L-K transitions reflect radiation impinging upon a plane layer of given thickness is investigated. It is assumed that the energy distribution of the incident photons is a Planck function. Fluorescence due to K-shell vacancies produced by photoionization is the only effect taken into consideration. Solving the transfer equation allows the reemitted flux and, consequently, the albedo of the layer to be calculated
 
Article
Absorption lineshapes of OH found in hot post-flame gases were measured using a rapid-tuning single-mode laser. Collisional linewidths due to broadening by H2O and CO2 were determined by fitting the observed lineshapes to standardized Voigt profiles. Lines corresponding to transitions with ground-state angular momentum quantum numbers (J″-values) ranging from 1.5 to 17.5 in the R1-branch of the A2Σ+ ← X2Π (0,0) band near 307 nm were probed. The temperature-dependence of collisional broadening was investigated over the range 1470–2370 K.
 
Article
Absorption spectra of nitric oxide in the γ(0,0) and γ(1,0) bands have been measured for hard temperature conditions up to in order to validate a model for the simulation of these two bands. The good agreement between experiments and calculations (relative errors of 2–5% for the γ(0,0) band and 10–15% for the γ(1,0) band) consolidates the two important assumptions concerning the intermediate Hund's case between (a) and (b) for the X2Π state of the γ(0,0) and γ(1,0) absorption bands and the use of collisional broadening parameters of γ(0,0) to simulate the γ(1,0) band. Using this simulation, a study of the Beer–Lambert law behavior at high temperature has been carried out. With the instrument resolution used for these experiments, it was shown that a correction of the Beer–Lambert law is necessary. To apply this technique for the measurements of NO concentrations inside the combustion chamber of an optical SI engine, a new formulation of the Beer–Lambert law has been introduced, since the modified form proposed in the literature is no longer applicable in the total column range of interest.
 
Article
The collision broadening cross sections of the OH (0, 0) (A → X) ultraviolet transition have been measured for 14 broadening gases at 293°K and for water vapor at 378°K. They were obtained by applying corrections for Doppler and instrumental broadening to direct width measurements of OH absorption lines in high resolution spectra. The OH was generated by flash photolysis of H2O2 or H2O in an excess of broadening gas. The assumption that the cross section is independent of the OH rotational quantum number J appears valid for all these gases except water, for which it was necessary to assume that the cross section is a decreasing function of J. The collision widths at 293°K and 580 torr range from a low of 0·04 cm-1 for helium to a high of 0·16 cm-1 for hydrogen. For water vapor at 378°K and 546 torr, the collision width varies from about 0·3 cm-1 for J = ; to about 0·06 cm-1 for J = 7;. The collision widths, when extrapolated to flame temperatures, appear to agree with earlier measurements as well as can be expected. The cross sections obtained are generally larger than those derived from transport property measurements, but all are within a factor of two of the latter values.
 
Article
Even for the well-studied and ubiquitous species, OH, the current state of theoretical development of broadening theory does not allow extrapolation from low-temperature laboratory measurements to the range of practical combustion devices. We performed a series of experiments at typical combustion conditions to determine the collision broadening of the P1(5) line of the (0,0) band of OH A2Σ+←X2Π transition by Ar in shock-heated H2–O2–Ar mixtures and by air in H2–air flames over a wide range of stoichiometry (φ=0.01–10.0), temperature (T=780–2440 K), and pressure (p=0.7–10.0 atm). The values of the collision width, ΔνC, were acquired by fitting Voigt profiles to the measured spectral line shapes in flames and to the peak absorption coefficients (kν0) in shock tube experiments. Collision broadening parameters (2γAr, 2γN2, and 2γH2O) were then calculated assuming the linear dependence of ΔνC with pressure—the 2γN2 and 2γH2O values were inferred from 2γAir and the equilibrium concentration of N2 and H2O of a given flame. The temperature dependences of 2γi in our temperature range are, respectively, 1.0, 0.75, and 0.87 for Ar, N2, and H2O. The collision broadening cross sections (σ) deduced from 2γi values are expressed with an assumed form, σi(T)=σi,0(T0/T)k, T0=1000 K: for Ar, σAr,0=63.3 (Å2), k=0.50; for N2, σN2,0=68.0 (Å2), k=0.25; for H2O, σH2O,0=188.8 (Å2), k=0.37.
 
Article
A review of the theory used by Davis et al. for determining the broadening of the NO γ(0,0) spectral lines by N2 has revealed several problems. This note discusses four significant errors and presents methods for their correction.
 
Article
Quantitative high-resolution spectroscopy was applied to the (0,0) and (1,0) U.V. absorption bands of OH and OD. Known concentrations of OH and OD were prepared in a high-temperature furnace containing a 2:1 mixture of water vapor and oxygen. Band oscillator strengths at 1425 K for the OH (0,0), OH(1,0), OD (0,0) and OD (1,0) bands were 9.6 × 10-4, 2.4 × 10-4, 9.5 × 10-4 and 2.6 × 10-4 with a statistical and systematic uncertainty of about 20 per cent. The use of the OH or OD rotational intensity distribution with vibration-rotation correction factors to determine gas temperature was verified. The collision width of OH or OD lines in the furnace at a total pressure of 580 torr is about 0.14 cm-1 at low J″ and appears to decrease at higher J″.
 
Article
Individual spectral line parameters including line positions, strengths, and intensities, have been generated for the A2∑-X2Π(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.
 
Article
We present a spectroscopic study of the water vapor continuum absorption in the far-IR region from 10 to 90 cm−1 (0.3–2.7 THz). The experimental technique combines a temperature-stabilized multipass absorption cell, a polarizing (Martin–Puplett) interferometric spectrometer, and a liquid-He-cooled bolometer detector. The contributions to the absorbance resulting from the structureless H2O–H2O and H2O–N2 continua have been measured in the temperature range from 293 to 333 K with spectral resolution of 0.04–0.12 cm−1. The resonant water vapor spectrum was modeled using the HITRAN04 database and a Van Vleck–Weisskopf lineshape function with a 100 cm−1 far-wing cut-off. Within experimental uncertainty, both the H2O–H2O and H2O–N2 continua demonstrate nearly quadratic dependencies of absorbance on frequency with, however, some deviation near the 2.5 THz window. The absorption coefficients of 3.83 and 0.185 (dB/km)/(kPa THz)2 were measured for self- and foreign-gas continuum, respectively. The corresponding temperature exponents were found to be 8.8 and 5.7. The theoretically predicted foreign continuum is presented and a reasonable agreement with experiment is obtained.
 
Article
Absolute intensities, self-broadening coefficients, and foreign-gas broadening by Ar and N2 were measured at temperatures of 197, 233 and 294 K for the 3001II←0000 band of CO2 at 6348 cm-1. Also, the intensity parameters and total band intensity were calculated. We obtained for the vibration-rotation interaction factor the value F(m) = 1 + (0.26 ± 0.06) × 10-2m + (0.92 ±0.32 × 10-4 m2; for the purely vibrational transition moment, we found |R00003001II|k{cy rillic}(0.4351 ± 0.0014)()10b3 debye; and, for the total band intensity at STP conditions, Sband(3001II←0000)STP = 1255 ± 9 cm-1 km-1 atm-1. Self-broadening coefficients at 197 and 294 K were also measured, as well as broadening by Ar and N2. Foreign-gas-broadening efficiencies (Ar and N2) were determined. Finally, a comparison is made with measurements by other authors and with theoretically calculated values.
 
Article
Measurements made at temperatures of 197, 233, and 294°K of the absolute intensities and self-broadening coefficients for the vibration-rotation lines of the 201III←000 band of the 12C16O2 molecule, are reported. From these measurements, values have been derived for the vibration-rotation interaction factor (FVR), the purely vibrational transition moment (|R(O)|), and the intensity (SBand). The results are: EVR(m) = 1+(2.2±0.7)×10−3m+(5.6±1.6)×10×5m2, |R(0)| = (2.064±0.017)×10−3 debye, SBand = 21,329±69 cm−1km−1atm−1STP. The results for the self-broadening coefficients are presented in the text.
 
Article
The NO2 absorption cross-section has been measured from 42 000 to 10 000 cm−1 (238–1000 nm) with a Fourier transform spectrometer (at the resolution of 2 cm−1, 0.01 nm at 240 nm to 0.2 nm at 1000 nm) and a 5 m temperature controlled multiple reflection cell. The uncertainty on the cross-section is estimated to be less than 3% below 40 000 cm−1 (λ > 250 nm) at 294 K, 3% below 30 000 cm−1 (λ > 333 nm) at 220 K, but reaches 10% for higher wavenumbers. Temperature and pressure effects have been observed. Comparison with data from the literature generally shows a good agreement for wavenumbers between 37 500 and 20 000 cm−1 (267–500 nm). Outside these limits, the difference can reach several percent.
 
Article
Using a complex version of Robert–Bonamy theory (CRBF), the role of the intermolecular potential in the pressure broadening of water perturbed by nitrogen and oxygen is studied. Investigation focuses on questions surrounding the convergence of calculated line widths, i.e., (i) why certain spectral lines are more sensitive than others to short-range interactions, and (ii) whether converged calculations containing short-range interactions represent an improvement over other treatments. Comparison with a large number of experimentally determined halfwidths and line shifts in the (301)←(000) and (221)←(000) bands is provided. It is found that the atom–atom component of the intermolecular potential plays an important role in determining the halfwidth and line shift. To obtain good agreement with measurement, the atom–atom potential needs to be expanded to at least eighth order for all water vapor transitions broadened by oxygen and many broadened by nitrogen.
 
Article
The energy rediated from an isothermal hydrogen plasma has been calculated considering both line and continuum emission processes. The principal line broadening mechanism for the plasma conditions considered herein was electrons interacting with the radiating system. Detailed line profiles were used for the lower members of the Lyman and Balmer series. The higher members were treated as having dispersion profiles. The continuum radiation was calculated using the well known expressions for the continuum absorption coefficients. Results were obtained for temperatures between 104 and 4 x 104°K, pressures between 10-1 and 101 atm, and plasma thicknesses between 10-1 and 101 cm.
 
Article
This review summarizes present knowledge of the atomic and molecular mechanisms that produce or remove rotationally, vibrationally, and electronically excited species in heated or excited gases. A logical classification scheme for these mechanisms is introduced, and the extent of present information on each class is indicated. The validity and utility of several general rules and regularities are also examined. An appendix includes a table of rate coefficients for vibrational and electronic excitation and deexcitation reactions, taken directly from or derived from data in the literature. This table provides comprehensive coverage of some classes of reactions and representative coverage of the others.
 
Article
An extensive tabulation of absorption coefficients of heated air including both molecular and atomic contributions has been carried out with the aid of several large digital computer programs. Tables are presented for temperatures between 1000 and 24 000°K and for eight densities between ten times normal atmospheric to 10-6 times normal. The photon energy range is 0·6–10·7 eV. Absorption coefficients have been averaged over an energy interval of 0·1 eV and are listed at each 0·1 eV step between the range limits.
 
Article
CO2 is the major constituent of the atmosphere of Venus. Absorption lines due to its 12C16O18O isotopologue have been observed for the first time in Venus spectra in the 2930–3015 cm−1 spectral region, where the HITRAN database does not contain any line from this isotopologue. The measurements were performed by the SOIR instrument, which is part of the SPICAV/SOIR instrument on board the Venus Express mission of ESA. SOIR measured the atmospheric transmission of the upper atmosphere of Venus (z>70 km) by performing a solar occultation experiment using the atmosphere as a gigantic absorption cell. The identification of this newly observed band was first made recently from Mars atmosphere observations by US colleagues. We have made independent theoretical calculations of the positions of the lines of this new 01111–00001 absorption band, which coincide perfectly with the positions of the observed lines. Assuming an oxygen isotopic ratio similar to the one measured previously in the lower atmosphere of Venus, the line strengths of each observed line are deduced and listed.
 
Article
Pressure-induced foreign-broadening lineshape parameters of the carbon dioxide rovibrational transitions belonging to the (30012)←(00001) overtone band near the 1.573 μm wavelength region are measured by using a tunable diode laser photoacoustic spectrometer. The spectroscopic analysis has concerned the first 11 lines of the R branch. For these lines, the air- and Ar-broadening coefficients are measured at room temperature (∼298 K). The measured broadening coefficients of all the transitions of 12C16O2 are compared with those given in the HITRAN04 database and former measurements with a different spectroscopic method. Agreements and discrepancies are underlined and briefly discussed. The recorded lineshapes are fitted with standard Voigt line profiles in order to determine the collisional broadening coefficient of carbon dioxide transitions.
 
Article
The study of the isotropiv Raman Q-branch of a hot band Π ← Π allows one to establish a direct connection between the vibration-rotation angular momentum coupling and the resulting spectra. Due to the l-doubling, the Q-branch is split into two subbranches characterized by either even or odd rotational quantum number j. The vibrational bending reduces the rotational transfer rates inside each of these subbranches by a factor of about two and induces an inter-subbranch coupling. The expected propensity rule towards conservation of the parity index for high rotational levels is well observed. Calculated spectra are in excellent agreement with CARS experiments for the v1 + v2 ← v2 band of CO2.
 
Article
Integrated intensities of acetylene bands at 3·04, 7·53 and 13·7 μm have been measured at 300°K using the Wilson-Wells-Penner-Weber technique and a spectral resolution of 0·6 cm−1. Our best estimates of the intensities are 294 ± 6 cm−2atm−1 for the 3·04 μ bands, 87 ± 2 cm−2atm−1forthe 7·53 μband and 729 ± 28 cm−2atm−1 for the 13·7 μ band at 300°K.
 
Article
The dependence of pressure broadening upon hyperfine component in the P(10) and P(70) lines of the (17,1) band of the I2 X1Σ(0g+)→B3Π(0u+) has been studied using laser saturation spectroscopy. By limiting absorption to the zero velocity group, Doppler broadening is removed, lineshapes with widths (FWHM) <9 MHz are detectable, and collision-induced broadening is measured at pressures of 0.2–1.2 Torr. The rates for broadening by argon are 8.3±0.3 and 10.7±0.4 MHz/Torr for the P(70) and P(10) lines, respectively. No significant variation in broadening rates is observed for the 15 hyperfine components of these even rotational lines. The effects of velocity cross-relaxation introduce a broad baseline into the spectra, which is strongly dependent on rotational state, pressure, and laser modulation frequency. The observed broadening rates correlate well with prior measurements and the polarizability of the collision partner.
 
Article
We have measured speeds of planar shocks in gold target foils impacted by ablatively driven gold flyer foils. The drive for the flyer foils was produced in a high-Z hohlraum by the Nova laser. Dynamic pressures inferred from the measurements were 0.75 ± 0.2 Gbar, higher than previous dynamic shocks produced in the laboratory. We suggest a technique which may allow the laboratory investigation of equations of state in the gigabar regime.
 
Article
It is well established that water plays a fundamental role in various atmospheric phenomena and that the accuracy of its collisional broadening parameters has a crucial influence on reduction of remote sensing data. Nevertheless, in this field the experimental data are still scarce and consequently the estimates reported in spectroscopic databases are not always reliable and/or accurate. In the view of filling this gap, the self-, N2- and O2-broadening parameters of the J=11,1←00,0 rotational transition of water (1.113 THz) have been determined at room temperature. The experimental investigation has also been supported by theoretical calculations.
 
Article
Tunable DFB InGaAsP diode lasers were utilized to determine water line strengths and self-broadening parameters of selected transitions between 7600 and 7640 cm−1 at temperatures up to 1100 K. The measured line strengths are compared with HITRAN96 and HITEMP96 databases. Measured line strengths for six lines or grouping of lines between 300 and 1100 K agree to within 20 to 40% with HITEMP96 databases. Self-broadening coefficients and their temperature dependence were measured on four lines and compared with theoretical predictions.
 
Article
Spectroscopic data are noticeably enriched in six spectral regions of the main isotopologue 12C2H2 of the acetylene molecule, namely, in the regions around 3, 2.2, 1.9, 1.7, 1.5, and 1.4 μm. Among these regions, only those at 3 and 1.5 μm were already presented partly in the databases. The results of line intensity measurements, performed for the first time in the 1.4 μm region, are given. Data available in the literature, or obtained in the present work, are compiled to set up line lists usable for applications in the quoted spectral regions. On the whole, 5748 new lines pertaining to 65 bands can be added to the databases.
 
Top panel: self-broadened width (FWHM) for the 51:4 cm −1 line of water vapor: 263 K (upper line, triangles), 300 K (diamonds) and 340 K (lower line, triangles). Bottom panel: lineshift for the same line: 263 K (triangles), 300 K (diamonds) and 340 K (rectangles). 
Collisional linewidths for water vapor lines at 300 K. Even initial states: experiment (open circles) and theory (solid triangles); odd initial states: experiment (open quadrates) and theory (solid diamonds). 
Water vapor linewidth (FWHM) at 200 Pa for the bands (cm −1 ) indicated in the plot. 
Article
The self-broadened linewidths of pure rotational lines of water vapor have been investigated in the temperature range 263– over a pressure range from 30– using an optically pumped THz photomixer spectrometer having a relative precision of . The lineshapes of several lines between 12 and were well fit by Lorentzian profiles over the spectral interval spanning ±5 FWHM. The Lorentzian FWHM linewidths varied between 6.6×10−6 and (0.67 and ) and were found to depend on the and Kc quantum numbers as well as temperature. The observed pressure-induced shifts, δν(P), ranged from 1.3×10−7– (0.013–. The measured linewidths also exhibited a (T0/T)n power law dependence on temperature. The best fit exponent n varied from 0.56 to 0.81, dependent on rotational line. A decrease in δν(T) with increasing temperature is also observed, varying between 2×10−8 and (2×10−3 and ) over the 300– temperature range.
 
Article
The self-broadening coefficients of acetylene at room temperature have been measured for 10 lines in the P branch of the bands of 12C2H2 and 13C12CH2 near 1.533 μm, using a high resolution tunable diode laser spectrometer developed for the Martian space mission PHOBOS-Grunt. The collisional widths are obtained by fitting each recorded line with the Voigt profile as well as the Rautian profile accounting for the collisional Dicke narrowing effect. The standard Voigt model provides slightly smaller broadening coefficients than the Rautian model. Our data are thoroughly compared to the main atmospheric molecule database HITRAN and previous values in various bands of acetylene. Moreover, it is worth noting that a large number of new transitions not listed in the latest HITRAN08 were measured and identified for the first time.
 
Article
This paper presents a study of absorption in N2-broadened P and R manifolds of the 2ν3 band of CH4 near 6000 cm−1 using high resolution laboratory and atmospheric spectra. This region is of prime importance for the retrieval of methane abundances in the Earth's atmosphere using ground-based or space-borne spectrometers. Recent laboratory investigations have been devoted to the methane spectroscopic parameters in this band, motivated by their previous poor knowledge and their increasing use by remote sensing experiments. In the absence of a better model, previous studies have used Voigt line shapes and thus purposely neglected line mixing (LM). In this paper, we first present direct comparisons between measured laboratory spectra and the results of a model which accounts for LM without adjusting any of the spectroscopic parameters. A good agreement is obtained and the results show that LM does have a significant influence on the shapes of P and R manifolds. Hence, most previously observed discrepancies were not due to improper broadening and shifting coefficients but to the neglect of this effect. This also confirms that widths and shifts derived in recent 2ν3 band studies neglecting LM are “effective” and lack physical meaning, as suggested in a previous work [17] (Frankenberg et al., 2008). In a second step, the conclusions from the laboratory data are tested using ground-based atmospheric solar absorption spectra. The fit residuals obtained confirm the quality of the proposed model and evidence the impact of line mixing on CH4 atmospheric spectra. The present results also confirm that laboratory and atmospheric spectra can alternatively be accurately modeled neglecting LM and using ad hoc broadening and shifting parameters. Conclusions of this exercise can be drawn from two perspectives. From the point of view of spectroscopy and understanding of processes, accurate line parameters will not be deduced from fits of laboratory measurements unless line-mixing effects are included in the spectral-shape model. In the meantime, and from the point of view of atmospheric retrievals, neglecting LM with suitable effective line parameters is convenient and accurate (within current retrieval uncertainties). Note that this is only true if this approach is not used for total pressures significantly above 1 atm (e.g. Jupiter).
 
Article
The important equilibrium emission processes in a hydrogen plasma have been investigated in the temperature range between 300°K and 10,000°K for pressures up to several hundred atmospheres. Representative emissivity calculations have been carried out for a transparent gas. For a nontransparent gas, the particular case of a total pressure of 100 atmos and a mean beam length of 30 cm has been considered.Important emissivity contributions are made by the pressure-induced fundamental vibration-rotation band and rotational lines of H2 at the lower temperatures, i.e., below approximately 4500°K. Above this temperature, the bound-free and free-free transitions of the H- ion and the continuum and line radiation of the H atom are the most important contributors to the emissivity. The following emission processes also have been investigated: the bound-free transitions of the H+2 ion, free-free transitions of colliding H atoms and H+ ions, electronic transitions of the H2 molecule, quadrupole vibration-rotation transitions of the H2 molecule, and vibration-rotation transitions of the HD molecule. In addition, the effects of the lowering of the ionization potentials by the fields of plasma ions and of the very broad wings of the Lyman α-line have been considered.
 
Article
We have computed the frequency-dependent absorption coefficient in the spectral range 6000–68,000 cm−1 of equilibrium mixtures of air and carbon for temperatures in the range 3000–10,000°K. These spectral absorption coefficients are used in the computation of a number of “opacity” coefficients over the spectral range considered. In the temperature range 3000–7500°K the main contribution to the absorption comes from molecular electronic transitions, and for equilibrium mixtures contining more than about 25 per cent by weight of carbon the Planck mean opacity is at least 1000 times that of air at the same temperature and density. The reason for this is that the molecules C2, CN,and C3, which are present in relatively large concentration, are much more efficient absorbers in the Planck mean sense than any of the air molecules. The computation takes into account 29 molecular band systems treated by the “Just-Overlapping-Rotational-Line Model” of Patch, Shackleford and Penner.The continuous absorption processes of photo-detachment from O− and C− and free-free absorption due to electrons in the fields of neutral and ionized species are also considered, and they become important at temperatures near 10,000°K. In a non-equilibrium situation in which the carbon is present as soot particles of radius 50–1000 Å, the Planck mean absorption coefficient at 3000–5000°K is another factor of 100 larger than for the case when the same amount of carbon exists as chemical compounds (C2, CN, C3) in the gas phase.
 
Article
The CH4 overtone bands from 4410 to 9990 Å, long known in the spectra of the major planets, were studied at room temperature with a long-path, high-pressure White cell. Band intensities and profiles were measured, and are more complete than other recent laboratory measurements of these bands. Vibrational assignments of these bands are suggested, which are compatible with the assignments of the overtone bands longward of 1μ; these assignments imply that all the bands studied are combinations increasingly dominated at shorter wavelengths by v1, the symmetric stretch fundamental. In this self-consistent analysis, the weak band at 6825 Å is assigned as 2v1+3v3, providing further laboratory evidence that it is probably not the 5v3 pure overtone that planetary astronomers had hoped it to be.
 
Article
The technique of nonlinear least squares spectral curve fitting has been used to derive the stratospheric vertical temperature profile from balloon-borne measurements of the 10.4 micron band of CO2. The spectral data were obtained at sunset with the approximately 0.02 per cm resolution University of Denver interferometer system from a float altitude of 33.5 km near Alamogordo, New Mexico, on 23 March 1981. The r.m.s. deviation between the retrieved temperature profile and correlative radiosonde measurements is 2.2 K.
 
Article
The collision-induced absorption (CIA) spectra of H2–H2 and H2–He are known to play an important role for modelling of low-metallicity cool and dense stellar atmospheres. In this paper we present collision-induced absorption spectra of H2–H2 complexes in the rototranslational (Δv=0), the fundamental (Δv=1), the first (Δv=2) and the second (Δv=3) overtone bands in the temperature range from 1000 to 7000 K, and in the frequency region from 0 to 20 000 cm−1. The translational spectral density functions are computed quantum mechanically, based on: (1) the newly developed ab initio collision-induced H2–H2 dipole functions of Zheng (Computational study of collision induced dipole moments and absorption spectra of H2–H2. Ph.D. thesis, Michigan Technological University, 1997), which account for the short-range H2–H2 intermolecular distances (as small as 2.5 a.u.) and for larger H2 internuclear distances (as large as 2.15 a.u.); (2) semiempirical isotropic H2–H2 potential (Ross et al, J Chem Phys 1983;79(3):1487) suitable for high temperatures. We include the collision-induced absorption coefficient of the vibrational transitions as v1,v2,v′1,v′2≤3 which we computed rigorously. We also give our estimate for the collision-induced absorption coefficients of single vibrational transitions such as in the first and second overtone bands. The dependence of CIA spectra on rotational states of H2 molecules is accounted for in our computations. We have previously (Borysow et al, Astronom Astrophys. 1997;324:185–95) studied the effect of CIA for stars of a wide range of fundamental stellar parameters (effective temperature, gravity, and chemical composition), and determined for which combinations of these parameters it is necessary to include CIA in the model and spectrum computation. These calculations showed that CIA from H2–H2 plays an important, and often even a dominating role for stellar atmospheres of a wide range of stars. The approximate character of the estimates of the H2–H2 absorption coefficient we used in our previous work combined with the large effect CIA had on the stellar atmospheres, were the main inspirations to initiate the more accurate computations of the absorption coefficient we present here. The absorption coefficient we compute in the present analysis is in qualitative agreement with our preliminary estimates (Borysow et al, Astronom Astrophys 1997;324:185–95), but in some spectral regions of high importance for the stellar structure, our computed absorption coefficient is up to a factor of 3 larger than our preliminary estimates. We therefore fully confirm our previous suspicion that H2–H2 CIA will have a pronounced effect on the atmosphere for a wide range of stars. In this paper we therefore quantify the effect the new data have on a typical cool dense stellar atmosphere, and compare our new results with our previous estimates.
 
Article
We present a high-temperature version, CDSD-1000, of the carbon dioxide spectroscopic databank. The databank contains the line parameters (positions, intensities, air- and self-broadened half-widths and coefficients of temperature dependence of air-broadened half-widths) of the four most abundant isotopic species of the carbon dioxide molecule. The reference temperature is and the intensity cutoff is . More than 3 million lines covering the 260–8310, 418–2454, 394–4662, and 429– spectral ranges for , , , and , respectively, are included in CDSD-1000. The databank has been generated within the framework of the method of effective operators and based on the global fittings of spectroscopic parameters (parameters of the effective Hamiltonians and effective dipole moment operators) to observed data collected from the literature. Line-by-line simulations of several low- and medium-resolution high-temperature (T=800–) spectra have been performed in order to validate the databank. Comparisons of CDSD-1000 with other high-temperature databanks HITEMP, HITELOR, and EM2C are also given. CDSD-1000 is able to reproduce observed spectra in a more satisfactory way than the high-resolution databank HITEMP for temperatures higher than . The databank is useful for studying high-temperature radiative properties of CO2. CDSD-1000 is freely accessible via the Internet.
 
Article
Absorption coefficients and cross-sections have been determined for the dissociation continuum 3Σ-u←3Σ-g for molecular oxygen as well as for some of the diffuse bands between 1100–1350Å. The regions of minimum absorption or oxygen “windows” for which k <1 cm-1 were remeasured. Both a discrete emission-type light source and a continuous source were used in this investigation. Repeated measurements in the region of continuous absorption (1380–1480 Å) show a k value of 402±20 cm-1 for the peak of the Schumann-Runge continuum.
 
Article
Molecular band models are used to derive absorption and pressure coefficients for the methane absorption spectrum from 4500 to 10500 Å at intervals of 10 Å. These coefficients provide a necessary basis for the interpretation of the large methane absorptions in the atmospheres of the major planets. Although only coefficients for the “random” or “Goody” band model are derived, the equivalence between these and the “regular” of “Elasser” coefficients is demonstrated. The effects of pressure on the absorption are surprisingly small, leading to large values of the pressure coefficient quite unlike any previous application of the band-model theory. They indicate a pseudo-continuum character of the methane spectrum throughout the visible and near infrared. A spectrum synthesis calculation using the derived coefficients shows the close fit to experimental data that can be realized.
 
Article
Photoabsorption and fluorescence cross sections of benzene, (o-, m-, p-) xylenes, naphthalene, 1-methylnaphthalene, and 2-ethylnaphthalene in the gas phase have been measured at 106–295 nm using synchrotron radiation as a light source. Fluorescences are observed from the photoexcitation of benzene and xylenes at 230–280 nm and from naphthalene and its derivatives at 190–295 nm. The absolute fluorescence cross section is determined by calibration with respect to the emission intensity of the NO(A-X) system, for which the fluorescence quantum yield is equal to 1. To cross-check the current calibration method, the quantum yield of the SO2(C̃-X̃) system at 220–230 nm was measured since it is about equal to 1. The current quantum-yield data are compared with previously published values measured by different methods.
 
Article
Measurements of the water absorption coefficient at 193 nm from 300 to 1073 K are reported. The measurements were made using broadband VUV radiation and a monochromator-based detection system. The water vapor was generated by a saturator and metered into a flowing, 99 cm absorption cell via a water vapor mass flow meter. The 193 nm absorption coefficient measurements are compared to room temperature and high temperature shock tube measurements with good agreement. The absorption can be parameterized by a nu3 vibrational mode reaction coordinate and the thermal population of the nu3 mode.
 
Article
The experimental status of Mössbauer linewidths are reviewed and reported for the three narrowest gamma resonances: 73Ge, 67Zn, and 181Ta. The crucial role played by the solid-state host in achieving narrow emission or absorption linewidths, as well as high recoil-free fraction are emphasized. Factors contributing to line-broadening in experiments with 181Ta and 67Zn gamma resonances are highlighted. Consequences of these observations on a choice of a suitable lasing medium for Mössbauer gamma-ray lasers is commented upon.
 
Article
We calculate the absorption efficiency of the composite grains, made up of host silicate spheroids and inclusions of ices/graphites/or voids, in the spectral region $7.0-14.0\mu$m The absorption efficiencies of the composite spheroidal grains for three axial ratios are computed using the discrete dipole approximation (DDA) as well as using the effective medium approximation & T-Matrix (EMT-Tmatrix) ap proach. We study the absorption as a function of the volume fraction of the inclusions and porosity. In particular, we study the variation in the $10.0\mu$m feature with the volume fraction of the inclusions and porosity. We then calculate the infrared fluxes for these composite grains and compare the model curves with the average observed IRAS-LRS curve, obtained for several circumstellar dust shells around stars. These results on the composite grains show that the wavelength of the peak absorption shifts and the width of the $10.0\mu$m feature varies with the variation in the volume fraction of the inclusions. The model curves for composite grains with axial ratios not very large (AR$\sim$1.3) and volume fractions of inclusions with f=0.20, and dust temperature of about 250-300$^{\circ}$K, fit the observed emission curves reasonably well.
 
Article
Absorption cross-sections, kv (cm-1 atm-1), have been measured in the 9.2 and 11.8 μm bands of CFC-11 (CCl3F) using a high-resolution Fourier transform spectrometer. Temperature and total (N2-broadening) pressure have been varied to obtain results at conditions representative of the atmosphere. The measured absolute intensities (in units of 10-17 cm · molecule-1) of the 9.2 and 11.8 μm bands are 2.591 ± 0.013 and 6.974 ± 0.038, respectively.
 
Article
Spectral absorption coefficients (or absorption cross-sections) kv (cm-1 atm-1) of CFC-11 and CFC-12 have been measured in the spectral region (8–12 μm) known as the atmospheric window. Data obtained with a grating spectrometer, which has wide spectral coverage and adequate spectral resolution (0.4 cm-1), are compared with the so-called NCAR cross-sections that have recently been introduced into the HITRAN Tape. We have also performed measurements, at various temperature-pressure combinations which are chosen to represent tangent heights (as in solar-occultation experiments) or layers in the atmosphere, of the kv of CFC-12 in the 921 and 923 cm-1Q-branches and at 924.1, 927.6, 931.6 935.0 and 1106 cm-1 with the Doppler-limited spectral resolution (∼10-4cm-1) of a tunable-diode laser spectrometer. The latter are especially well suited for atmospheric remote sensing, while the grating spectra are useful in global warming studies. The effects of temperature and pressure on the spectral absorption coefficients are discussed.
 
Article
Radiative forcing values have been calculated for 11 halogenated compounds which are in current use or which have been suggested as possible replacements for the chlorofluorocarbons. Absorption cross-sections measured over a range of atmospheric temperature and pressure conditions as part of a multi-laboratory programme have been used together with a narrow band radiative transfer model. We provide a “best estimate” radiative forcing taking into account the likely vertical profile of the gas in each case. The Global Warming Potential over a variety of time horizons has also been calculated where the lifetime is available. We present the first such information for 1,2-dichloroethane. For chloroform our radiative forcing is 5 times higher than the value used in previous assessments, possibly because these ignored the effect of absorption outside the 800–1200 cm−1 “window”. For several of the other compounds considered here, our forcing is between 10 and 30% lower than previous assessments. The perfluorocarbons have been found to have large global warming potentials, many times that of CFC-11, due to both strong absorption and long lifetimes. The importance of absorption features at wavenumbers below 800 cm−1 and the effect of temperature variations in absorption cross-section on the radiative forcing are also investigated.
 
Article
Employing the most recent laboratory absorption-coefficient data1 on the thermal infrared (i.r.) bands of CFC-11 (CFCl3) and CFC-12 (CF2Cl2), which were measured at several temperatures relevant to the troposphere and the stratosphere, the greenhouse effect produced by these two CFCs has been reexamined. The effect upon the atmospheric radiative fluxes due to the temperature dependence of the absorption coefficient, especially in the many hot bands present in this spectral region, has been studied. The validity of the often used optically-thin approximation has been scrutinized in view of the observed enhancement in the absorption by the CFCs at low temperatures. The influence of absorption by water vapor on the radiative transfer through columns of CFC-11 and CFC-12 has also been considered. It has been shown that, even though each of these individual refinements may modify the previously estimated effect due to the CFCs by a small amount only, the collective effect may be a non-negligible 35% change in the surface-troposphere heating for every ppbv of CFC-11 and CFC-12 each introduced into a model atmosphere.
 
Article
Shock-tube experiments to measure the gas phase FeO fundamental vibration-rotation radiative band intensity at 11.5 μ have been performed. In measurements behind incident shocks, equilibrium amounts of FeO formed quickly, and CO2 formation occured more quickly in the presence of Fe and FeO than can be understood on the basis of previous studies of CO + O2 induction times. Measurements with a calibrated optical system at 10.4–16.3 μ wavelength yielded an integrated band intensity for FeO of 450 ama−1 cm−2 ± 32% (2σ limits). A bound for the rate of the reaction Fe + O2→FeO + Ok ⩾ 5 x 10−12 cm3 molecule−1 sec−1 for T = 2400°K is given and a possible mechanism relating FeO to the rapid CO2 formation is discussed.
 
Article
The absorption spectrum of N2O, at room temperature, was recorded in the 5400–11 000 cm–1 region at resolutions ranging from 0.008 cm–1 near 5400 to 0.023 cm–1 near 11 000 cm–1 using a Bruker IFS120HR Fourier transform spectrometer. Sample pressure/absorption path length products ranging from 200 to 4700 mbar×m were used. More than 6000 absolute line intensities have been measured in 64 different bands of 14N216O. Using wavefunctions previously determined from a global fit of an effective Hamiltonian to more than 18 000 line positions [Tashkun SA, Perevalov VI, and Teffo JL, to be published], the experimental intensities measured in this work and by Toth [J Mol Spectrosc 1999;197:158–87] were fit using 62 parameters of a corresponding effective dipole moment, with residuals very close to the experimental uncertainty.
 
Article
The temperature dependence of the infrared absorption cross-sections of CFC-113 (1,1,2-trichlorotrifluoroethane) in a pure vapor phase has been recorded in the 600–1250 cm−1 spectral region using Fourier transform spectroscopy. Spectra at 0.05 cm−1 resolution have been used to derive the integrated band strengths of the five main absorption bands over a range of temperatures from 223 to 283 K. Our results show good agreement with previously published data. The new cross-sections will allow more accurate retrieval of atmospheric CFC-113 concentrations using infrared spectroscopic techniques.Research highlights►Mid-infrared absorption cross-sections of CFC-113 are recorded over a range of relevant atmospheric temperatures. ► Integrated band strengths are compared with values in literature. ►Temperature-induced band centroid shifts are evaluated. ► Conformational interconversions do not affect the spectrum shapes.
 
Top-cited authors
Robert Gamache
  • University of Massachusetts President's Office
Kelly V. Chance
  • Harvard University
Jonathan Tennyson
  • University College London
D. Jacquemart
  • Sorbonne Université
Valery Perevalov
  • V.E. Zuev Institute of Atmospheric Optics