Integrated Absorption Coefficient Research Articles

Inversionless radiation amplification by ions having certain velocities in a magnetic field

It is shown that the imposition of external magnetic field on a gas of ionised particles may give rise to inversionless radiation amplification by the ions having certain velocities, which is due to their Larmor rotation. In this case, the majority of ions may reside in the ground state. The integrated absorption coefficient remains positive due to an increase in the radiation absorption by the other half of ions.

Isotope effects in the vibrational spectrum of the SF6 molecule

The IR absorption spectra of solutions of SF6 in liquid argon are studied at a temperature of 93 K in the concentration interval 10−5–10−7 mole fractions. A sample with a natural abundance of isotopes and a monoisotope 34SF6 sample are studied. The frequencies, half-widths, and relative intensities of bands in the vibrational spectrum of all isotopomers of the molecule are determined. For the 34SF6 molecule, the ratio of integral absorption coefficients of fundamental bands A(ν4)/A(ν3)=0.07(6) is larger than 32SF6:A(ν4)/A(ν3)=0.66(4) for the 32SF6 molecule, which corresponds to the same signs of P′3 and P′4. The change in the intensity of the ν2+ν6 and ν5+ν6 bands upon isotopic substitution is explained by the change in the resonance contributions of due to the isotope shift of the ν3 band.

Noninversive partial velocity amplification of radiation by ions due to their rotation in a magnetic field

It is shown that upon the application of an external magnetic field, a gas of ionized particles may experience noninversive partial velocity amplification of radiation by ions due to their Larmor rotation. In this case, virtually all ions may be in the ground state. It may happen that approximately half the number of ions in the medium amplify the incident radiation. The integrated absorption coefficient remains positive due to the enhancement of absorption of radiation by the other half of ions. Noninversive amplification of radiation takes place when the condition ωc≳Γ2/kv T is satisfied ωwc is the cyclotron frequency of ions in the magnetic field; Γ is the homogeneous half-width of the absorption line for ions, and kv T is the Doppler width). In the case of interaction of atomic ions with radiation in the optical range, this corresponds to magnetic fields B≳600 G (for the ion mass M∼10 amu). Noninversive partial velocity amplification of radiation is a “latent” effect in the sense that it disappears upon averaging over all velocity directions of ions. This effect is associated with the emergence of phase incursion of the induced dipole moment oscillations for ions moving in circular cyclotron orbits, which depends on the ion velocity.

On the critical use of molar absorption coefficients for adsorbed species: the methanol/silica system

The ambient temperature adsorption of methanol vapour on two preparations of non-porous silica (Aerosil 50 and Aerosil 300) activated at two different temperatures (∼300 and 1073 K) has been studied by gas-volumetric and in situ transmission FTIR spectroscopic methods, in order to check the validity of equations of the Beer–Lambert type in the case of heterogeneous systems. The results indicate that, for both physically adsorbed and chemisorbed methanol, the calculated integral molar absorption coefficients are of the right order of magnitude (as compared with those typical of methanol in homogeneous phase), but the actual values vary much from one sample to another, depending on several factors. Among the factors, very important turn out to be: the specific surface area of the adsorbent, the sample thickness, the surface dehydration level of the adsorbing system and, most probably, the scattering properties of the adsorbent. In particular, the first two factors of variability imply that, when dealing with the spectral response of adsorbed species, an adequate normalization of the observed band intensities against sample surface area as well as against sample weight is difficult to achieve. The conclusion is that: (i) in the case of either physically adsorbed or chemisorbed species, the concept of molar absorption coefficient is virtually impossible to apply in general terms; (ii) the values calculated as “apparent” absorption coefficients cannot be transferred from one system to another, even if the ε figures calculated for adsorbed species do fall in the range of ε values determined for homogeneous systems.

The crystal chemistry of birefringent natural uvarovites: Part II. Single-crystal X-ray structures

The crystal structures of six birefringent uvarovite-grossular garnets from three localities (Saranov, Veselovsk, and Saranka, Ural Mountains, Russia) were investigated using single-crystal X-ray CCD diffraction data. The intensity and lattice parameter data attest to the violation of the cubic garnet space group Ia 3 d and the symmetry reduction to subgroups with triclinic ( I 1), monoclinic ( I 2/ a ), or at most orthorhombic symmetry ( Fddd ). Careful structure refinements starting in space group I 1 reveal that partial long-range Cr 3+ /Al ordering on the octahedral sites is the most prominent non-cubic feature. For each crystal, a nearly perfect linear correlation of the individual octahedral size with its Cr occupancy is observed. Considering the dependence on the bulk Cr mole fraction, the individual octahedral size in non-cubic uvarovite-grossular solid solutions is represented by (A) = 1.9247 + 0.0147 X Cr(bulk) + 0.0534 X Cr(individual) . These uvarovites also structurally incorporate traces of hydrous component ( 2 O) as O 4 H 4 “hydrogarnet” substitution in a non-cubic way, thus leading to further subtle deviations from cubic symmetry. Within the range of these low water contents, the refined Si-O bond length, averaged over crystallographically different tetrahedra, correlates with the total integral OH absorption coefficient α i through the equation > (A) = 1.6455 + 1.0074·10 −7 α i (cm −2 ). Although the Si and Ca atoms occupy general positions in I 1, they deviate little from their respective special positions in Ia 3 d . Consistent with the respective angular lattice distortions, the refined Cr 3+ /Al site distribution pattern is definitely triclinic in the Saranka sample, somewhat less pronounced triclinic (pseudomonoclinic) in the Veselovsk sample, and distinctively pseudoorthorhombic or orthorhombic in all four samples from the Saranov locality. Considering crystal chemical evidence, three of the pseudoorthorhombic Saranov samples with elevated water content appear to have triclinic symmetry as well, while one low-water uvarovite is classified as orthorhombic. These results are in good agreement with those of optical and UV-VIS-IR spectroscopic investigations reported in Part I of the present study (Andrut and Wildner 2001). Previous structure data for birefringent garnets reported in the literature as non-cubic are compared and discussed. Special emphasis is also drawn to structural and crystal chemical details exhibiting a non-ideal mixing behavior along the uvarovite-grossular join. Evidence for and against the cation ordering models postulated in the literature are discussed.

Oxide Layer Formed on the Surface of Ozone-Treated InP

Oxides are formed on InP substrates under UV/ozone illumination. The thickness of the formed oxides increases as the exposure time to the UV source increases, and tends to saturate after three hours of exposure. The optical transmission and X-ray diffraction measurements predict the formation of the oxide layer. X-ray diffraction shows that the oxide film is a mixture of In2O3 and InPO4 and seems to be In2O3-rich. The integrated absorption coefficient of the formed oxide layer does not depend on the wavelengths in the range of 800–1400 nm, and is found to be in the order of 107 cm-1. The reflections from the sample surface after UV/ozone oxidation at different exposure times are also measured.

Compositional dependence of molar absorptivities of near-infrared OH- and H 2O bands in rhyolitic to basaltic glasses

Molar absorption coefficients (molar absorptivities) of the near infrared combination bands at 4500 and 5200 cm −1 assigned to OH groups and H 2O molecules, respectively, were determined for glasses of dacitic, andesitic and basaltic compositions. Total water contents (range 1.5–6.3 wt.%) of the samples used in the calibration were determined by pyrolysis and subsequent Karl–Fischer Titration. Different combinations of baseline types and intensity measure (peak height/area) were applied to investigate the effect of evaluation procedure on infrared spectroscopic determination of apparent species concentrations and total water. The best reproducibility of total water was obtained by modeling the baseline of the combination bands by two gaussians at ∼5700 and ∼4000 cm −1 (GG type baseline) and evaluating peak heights (maximum deviation of ±0.17 wt.% water). Plots of normalized absorbances are consistent with identical ratios of the absorption coefficients, ε H 2O / ε OH, for dacitic, andesitic and basaltic compositions as well as for a rhyolitic composition (data from Withers and Behrens [Withers, A.C., Behrens, H., 1999. Temperature induced changes in the NIR spectra of hydrous albitic and rhyolitic glasses between 300 and 100 K. Phys. Chem. Minerals, 27, 119–132]). A parabolic equation is proposed to predict the molar linear and integrated absorption coefficients as a function of the SiO 2 content of the glass within the range of water contents used in the calibration. For example, using the GG type baseline and evaluating peak heights, we obtained ε H 2O / ε OH=1.13 and ε H 2O [in l mol −1 cm −1]=2.290×10 −4×(wt.% SiO 2) 2. At a given water content and quench rate, OH concentrations are higher in andesitic than in dacitic glasses which is consistent with higher fictive temperatures of hydrous andesitic glasses containing more than 1.5 wt.% water.

Quantitative determination of water speciation in aluminosilicate glasses: a comparative NMR and IR spectroscopic study

Water speciation in hydrous aluminosilicate glasses (with NaAlSi 3O 8, KAlSi 3O 8, LiAlSi 3O 8 and LiAlSi 4O 10 compositions) was studied with infrared (IR) and static 1H nuclear magnetic resonance (NMR) spectroscopy. Using IR spectroscopy, the water speciation was determined from the peak intensities (linear absorbance as well as integrated intensity) of the near-infrared (NIR) absorption bands at 4500 and 5200 cm −1 assigned to structurally bonded hydroxyl groups and molecular H 2O, respectively. For LiAlSi 4O 10 glasses, a new calibration of the linear and integral molar absorption coefficients of the IR absorption bands at 4500 and 5200 cm −1 is presented. Using NMR spectroscopy, the water speciation was determined from the static 1H NMR spectra acquired at temperatures between 170 and 130 K, where the 1H NMR signal consists of a well-defined Pake doublet due to rigid water molecules and an overlapping, but narrower, central peak due to structurally bonded OH groups. The distinct nature of these two signals (doublet and Gaussian) enables a reliable deconvolution of the 1H NMR spectra and quantitative determination of water speciation in the glasses. For a series of hydrous NaAlSi 3O 8 glasses containing 1.5–10 wt.% water, we found a very good agreement of water speciation determined by NMR and IR spectroscopy (about 4% standard deviation in OH concentration), demonstrating the reliability of both methods. Total water contents determined with 1H NMR spectroscopy are in excellent agreement with results from Karl–Fischer titration (KFT, <2% standard deviation). Depending on whether peak heights or peak areas are used for the evaluation of NIR spectra, relatively large deviations in water speciation (12–24% in OH content) are observed for KAlSi 3O 8, LiAlSi 3O 8 and LiAlSi 4O 10 glasses. Static 1H NMR spectroscopy on KAlSi 3O 8 and LiAlSi 4O 10 glasses containing 2.80–4.25 wt.% water tends to support the use of peak areas instead of peak heights for calculation of water speciation from NIR spectra. However, in the case of the LiAlSi 3O 8 glass (4.04 wt.% water), no clear conclusion can be drawn from the NMR data and other effects such as the choice of the baseline for the NIR peaks or water-dependent molar absorption coefficients may have to be taken into account. In order to resolve these questions, more systematic NMR and IR spectroscopic studies on glass series covering a large range of water concentrations are required.

OXIDE LAYER FORMED ON THE SURFACE OF OZONE-TREATED InP

Oxides are formed on InP substrates under UV/ozone illumination. The thickness of the formed oxides increases as the exposure time to the UV source increases, and tends to saturate after three hours of exposure. The optical transmission and X-ray diffraction measurements predict the formation of the oxide layer. X-ray diffraction shows that the oxide film is a mixture of In 2 O 3 and InPO 4 and seems to be In 2 O 3-rich. The integrated absorption coefficient of the formed oxide layer does not depend on the wavelengths in the range of 800–1400 nm, and is found to be in the order of 107 cm-1. The reflections from the sample surface after UV/ozone oxidation at different exposure times are also measured.

High-Temperature Integral Absorption in Glasses

The information published in various sources concerning IR absorption of certain glasses is summarized. The results are supplemented by the data of research carried out by the authors. It is proposed to use the integral absorption coefficient calculated for the considered glass compositions in solving the problems of radiation-conductive heat exchange. The resulting data bank will make it possible to predict the integral absorption of glasses containing certain transition elements, primarily, iron.

Absorption coefficient spectra of μc-Si in the low-energy region 0.4–1.2 eV

Optical absorption spectra in the low-energy region 0.4–1.2 eV is reported for μc-Si:H using a photothermal deflection spectroscopy technique. Absorption coefficient spectra in the low-energy region contain important information related to defects and hydrogen. It is demonstrated that there is a good correlation between electron spin densities and integrated absorption coefficient spectra from 0.7 to 1.2 eV. The amount of the hydrogen molecules in microvoids is much larger in μc-Si:H than that in a-Si:H. Light illumination effects in PDS spectra has also been studied from a view point of photo degradation of the μc-Si:H.

Thermochemical purification of sulfur from hydrocarbons

The behavior of carboniferous impurities during thermochemical purification of sulfur was studied. The integral absorption coefficient for the IR absorption band at 2920 cm-1, related to aliphatic hydrocarbons, was determined. The detection limit for aliphatic hydrocarbons in sulfur was evaluated to be 2 x 10-5 wt % (3σ criterion).

Experimental equipment for studies of interaction of IR-radiation with liquid hydrides of groups IV–VI elements

The complex of special experimental apparatus for studies of interaction between IR-radiation and the thermally-stable volatile inorganic hydrides of groups IV–VI elements of the 2nd, 3rd and 4th periods in the liquid state and in the liquefied gas solutions is described. The main methods of solute concentration and integral absorption coefficients measurement are considered. The results of studies of IR-radiation absorption by volatile inorganic hydrides such as SiH 4, NH 3, PH 3, AsH 3, H 2S, and H 2Se in the liquid state and in the cryogenic solutions are presented. Using intensity, frequency and IR-absorption band contour data, the main mechanisms of intermolecular interactions in these liquids are discussed.

Temperature- and pressure-dependent absorption coefficients for CO 2 and O 2 at 193 nm

Absorption of laser radiation at 193 nm by CO2 and O2 was studied at a series of different temperatures up to 1273 K and pressures up to 1 bar. The spectrum for CO2 was found to be broadband, so that absorption could be fitted to a Beer–Lambert law. On the other hand, the corresponding O2 spectrum is strongly structured and parameterisation requires a more complex relation, depending on both temperature and the product (pressure × absorption path length). In this context, the influence of spectral structure on the resulting spectrally integrated absorption coefficients is discussed. Using the fitting parameters obtained, effective transmissions at 193 nm can be calculated for a wide range of experimental conditions. As an illustration of the practical application of these data, the calculation of effective transmission for a typical industrial flue gas is described.

Temperature-induced changes in the NIR spectra of hydrous albitic and rhyolitic glasses between 300 and 100 K

Near-infrared (NIR) absorption bands related to total water (4000 and 7050 cm−1), OH groups (4500 cm−1) and molecular H2O (5200 cm−1) were studied in two polymerised glasses, a synthetic albitic composition and a natural obsidian. The water contents of the glasses were determined using Karl Fischer titration. Molar absorption coefficients were calculated for each of the bands using albitic glasses containing between 0.54 and 9.16 wt.% H2O and rhyolitic glasses containing between 0.97 and 9.20 wt.% H2O. Different combinations of baseline type and intensity measure (peak height/area) for the combination bands at 4500 and 5200 cm−1 were used to investigate the effect of evaluation procedure on calculated hydrous species concentrations. Total water contents calculated using each of the baseline/molar absorption coefficient combinations agree to within 5.8% relative for rhyolitic and 6.5% relative for albitic glasses (maximum absolute differences of 0.08 and 0.15 wt.% H2O, respectively). In glasses with water contents >1 wt.%, calculated hydrous species concentrations vary by up to 17% relative for OH and 11% relative for H2O (maximum absolute differences of 0.33 and 0.43 wt.% H2O, respectively). This variation in calculated species concentrations is typically greater in rhyolitic glasses than albitic. In situ, micro-FTIR analysis at 300 and 100 K was used to investigate the effect of varying temperature on the NIR spectra of the glasses. The linear and integral molar absorption coefficients for each of the bands were recalculated from the 100 K spectra, and were found to vary systematically from the 300 K values. Linear molar absorption coefficients for the 4000 and 7050 cm−1 bands decrease by 16–20% and integral molar absorption coefficients by up to 30%. Depending on glass composition and baseline type, the integral molar absorption coefficients for the absorption bands related to OH groups and molecular H2O change by up to −5.8 and +7.4%, respectively, while linear molar absorption coefficients show less variation, with a maximum change of ∼4%. Using the new molar absorption coefficients for the combination bands to calculate species concentrations at 100 K, the maximum change in species concentration is 0.08 wt.% H2O, compared with 0.39 wt.% which would be calculated if constant values were assumed for the combination band molar absorption coefficients. Almost all the changes in the spectra can therefore be interpreted in terms of changing molar absorption coefficient, rather than interconversion between hydrous species.

Investigation of the Light Absorption Mechanisms near Exciton Resonance in Layered Crystals

Low temperature exciton absorption spectra of InSe crystals have been studied. A simple analytical dependence has been established when the integral absorption coefficient Kexc of the n = 1 exciton band is a function of its half-width. Such light absorption mechanisms as polariton mechanism, indirect phototransitions, “resonant exciton” and exciton states degenerated with 2D conduction electrons distributed in quantum wells have been considered. It has been shown that the phenomena connected with the spatial dispersion of light make the main contribution to Kexc growth for InSe crystals in the vicinity of the exciton resonance at low temperatures. A comparison of the Pekar and Davydov models with the experiment permitted establishing the field of application for each of them. The oscillator strength of the exciton and band-to-band optical transitions fexc = fcv = 0.11, plasma frequency ωp = 2.05 × 1014 s—1 and value of longitudal–transversal splitting ΔL-T = 0.57 cm—1 of polariton branches have been found for InSe crystals.

Rovibrational intensities in the ν4 band of ammonia

Absolute line intensities of sixteen rovibrational transitions in the ν4 band of 14NH3 were measured around 1800cm−1 using a tunable diode laser spectrometer with a sweep modulation of the laser frequency. Individual laser scans over the line region were recorded to disk storage separately and the spectrum accumulation was performed off-line using a computer to reduce a significant line broadening because of a lower accuracy of the hardware on-line accumulation.From integrated absorption coefficients obtained by the numerical analysis of the measured line profile, the effective transition moments of individual rovibrational lines were derived. Using the second order perturbation theory of the transition moment of rovibrational transitions of the symmetric top molecules, the effective vibrational transition moments for the ν4 fundamental band of 14NH3 were estimated.

Absorption intensities of zero-phonon double transitions involvingpara−H2–ortho−H2pairs in solid hydrogen

The infrared spectrum of solid ${\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{a}\ensuremath{-}\mathrm{H}}_{2}$ containing ${\mathrm{o}\mathrm{r}\mathrm{t}\mathrm{h}\mathrm{o}\ensuremath{-}\mathrm{H}}_{2}$ at trace level shows relatively weak features due to zero-phonon double transitions involving ${\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{a}\ensuremath{-}\mathrm{H}}_{2}{--\mathrm{o}\mathrm{r}\mathrm{t}\mathrm{h}\mathrm{o}\ensuremath{-}\mathrm{H}}_{2}$ pairs. Formulas are developed for the intensities of such double transitions and the theoretical results compared with experimental findings.

Integrated infrared absorption coefficients of several partially fluorinated ether compounds: CF 3OCF 2H, CF 2HOCF 2H, CH 3OCF 2CF 2H, CH 3OCF 2CFClH, CH 3CH 2OCF 2CF 2H, CF 3CH 2OCF 2CF 2H and CH 2CHCH 2OCF 2CF 2H

The integrated absorption coefficients of CF 3OCF 2H, CF 2HOCF 2H, CH 3OCF 2CF 2H, CH 3OCF 2CFClH, CH 3CH 2OCF 2CF 2H, CF 3CH 2OCF 2CF 2H and CH 2CHCH 2OCF 2CF 2H have been measured at 298 K for use in calculations of their global warming potentials. The results for the ethers were compared to the integrated absorption coefficients of a standard compound, CCl 3F. To assess the potential impact of the ethers on terrestrial infrared radiation, the absorption coefficients were both weighted by the Plank function and also used in the simple method of estimating the instantaneous radiative forcing given in Pinnock et al. (1995, Journal of Geophysical Research 100 (011), 23,227–23,238).

Electric multipolar induction in the far-infrared spectra of CO in liquid Ar: Translational/rotational contributions and static cancellation effects

We have analyzed by means of molecular dynamics simulations the temperature and density dependence of the different pure induced components of the far-infrared integrated absorption coefficient of CO in liquid Ar (an interesting example for which experimental far-infrared spectra show the existence of high order electric multipolar induction). The main contribution to these components (for all the thermodynamic conditions we elected) comes from the rotation of the diatomic except for dipole induced-dipole absorption, where quantitatively rotation and translation are similar. By studying static cancellation effects separately in rotation and translation, we can assert an interesting result: All those contributions to the integrated absorption coefficient with radial decay equal or faster than the first repulsive decay of the solute–solvent interaction present enhancement effects and all those decaying slower present cancellation effects.