Journal of Quantitative Spectroscopy and Radiative Transfer

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.

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.

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.

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

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″.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.