Integrated Extinction Coefficient Research Articles

Impact and Suggestion of Column-to-Surface Vertical Correction Scheme on the Relationship between Satellite AOD and Ground-Level PM2.5 in China

As China is suffering from severe fine particle pollution from dense industrialization and urbanization, satellite-derived aerosol optical depth (AOD) has been widely used for estimating particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5). However, the correlation between satellite AOD and ground-level PM2.5 could be influenced by aerosol vertical distribution, as satellite AOD represents the entire column, rather than just ground-level concentration. Here, a new column-to-surface vertical correction scheme is proposed to improve separation of the near-surface and elevated aerosol layers, based on the ratio of the integrated extinction coefficient within 200–500 m above ground level (AGL), using the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP)) aerosol profile products. There are distinct differences in climate, meteorology, terrain, and aerosol transmission throughout China, so comparisons between vertical correction via CALIOP ratio and planetary boundary layer height (PBLH) were conducted in different regions from 2014 to 2015, combined with the original Pearson coefficient between satellite AOD and ground-level PM2.5 for reference. Furthermore, the best vertical correction scheme was suggested for different regions to achieve optimal correlation with PM2.5, based on the analysis and discussion of regional and seasonal characteristics of aerosol vertical distribution. According to our results and discussions, vertical correction via PBLH is recommended in northwestern China, where the PBLH varies dramatically, stretching or compressing the surface aerosol layer; vertical correction via the CALIOP ratio is recommended in northeastern China, southwestern China, Central China (excluding summer), North China Plain (excluding Beijing), and the spring in the southeast coast, areas that are susceptible to exogenous aerosols and exhibit the elevated aerosol layer; and original AOD without vertical correction is recommended in Beijing and the southeast coast (excluding spring), where the elevated aerosol layer rarely occurs and a large proportion of aerosol is aggregated in near-surface. Moreover, validation experiments in 2016 agreed well with our discussions and conclusions drawn from the experiments of the first two years. Furthermore, suggested vertical correction scheme was applied into linear mixed effect (LME) model, and high cross validation (CV) R2 (~85%) and relatively low root mean square errors (RMSE, ~20 μg/m3) were achieved, which demonstrated that the PM2.5 estimation agreed well with the measurements. When compared to the original situation, CV R2 values and RMSE after vertical correction both presented improvement to a certain extent, proving that the suggested vertical correction schemes could further improve the estimation accuracy of PM2.5 based on sophisticated model in China. Estimating PM2.5 with better accuracy could contribute to a more precise research of ecology and epidemiology, and provide a reliable reference for environmental policy making by governments.

A new method for measuring the solubility of slightly soluble substances in supercritical carbon dioxide

A self-consistent approach to the measurement of the solubility of biologically active compounds in supercritical (SC) media based on infrared spectroscopy is exemplified by paracetamol in supercritical CO2. According to this approach, the integral extinction coefficient for a chosen analytical spectral band is determined from additional spectroscopic measurement of the compound under study dissolved in an inert solvent at known concentrations in the considered range of the parameters of state (pressure and temperature, p and T). The values of solubility of the compound under study in the SC medium are calculated based on the above-obtained values of the extinction coefficient and the analytical values of the integral intensity of the chosen spectral band for saturated solutions in the p,T-range of interest. The method allows one to determine the solubility with a high accuracy even if the measured values are as low as 10–4–10–1 mol %.

A method based on iterative morphological filtering and multiple scattering for detecting layer boundaries and extinction coefficients with LIDAR

Layer boundaries detection with LIDAR is of great significance for the meteorological and environmental research. Apart from the background noise, multiple scattering can also seriously affect the detection results in LIDAR signal processing. To alleviate these issues, a novel approach was proposed based upon morphological filtering and multiple scattering correction with multiple iterations, which essentially acts as a weighted algorithm with multiple scattering factors in different filtering scales, and applies integral extinction coefficients as media to perform correction. Simulations on artificial signals and real LIDAR signals support this approach.

Comparing springtime ice-algal chlorophyll a and physical properties of multi-year and first-year sea ice from the Lincoln Sea.

With near-complete replacement of Arctic multi-year ice (MYI) by first-year ice (FYI) predicted to occur within this century, it remains uncertain how the loss of MYI will impact the abundance and distribution of sea ice associated algae. In this study we compare the chlorophyll a (chl a) concentrations and physical properties of MYI and FYI from the Lincoln Sea during 3 spring seasons (2010-2012). Cores were analysed for texture, salinity, and chl a. We identified annual growth layers for 7 of 11 MYI cores and found no significant differences in chl a concentration between the bottom first-year-ice portions of MYI, upper old-ice portions of MYI, and FYI cores. Overall, the maximum chl a concentrations were observed at the bottom of young FYI. However, there were no significant differences in chl a concentrations between MYI and FYI. This suggests little or no change in algal biomass with a shift from MYI to FYI and that the spatial extent and regional variability of refrozen leads and younger FYI will likely be key factors governing future changes in Arctic sea ice algal biomass. Bottom-integrated chl a concentrations showed negative logistic relationships with snow depth and bulk (snow plus ice) integrated extinction coefficients; indicating a strong influence of snow cover in controlling bottom ice algal biomass. The maximum bottom MYI chl a concentration was observed in a hummock, representing the thickest ice with lowest snow depth of this study. Hence, in this and other studies MYI chl a biomass may be under-estimated due to an under-representation of thick MYI (e.g., hummocks), which typically have a relatively thin snowpack allowing for increased light transmission. Therefore, we suggest the on-going loss of MYI in the Arctic Ocean may have a larger impact on ice–associated production than generally assumed.

Extinction Coefficients, Oscillator Strengths, and Radiative Lifetimes of CdSe, CdTe, and CdTe/CdSe Nanocrystals

In this paper we critically examine the literature and provide new data on fundamental optical properties of II–VI quantum dots (QDs). Specifically, we examine the integrated extinction coefficients and radiative lifetimes of different sizes of CdSe and CdTe QDs and different shell thicknesses in CdTe/CdSe core/shell QDs. We have synthesized particles having very high quantum yields and find that the measured radiative lifetimes are considerably longer and have a very different size dependence than what has been previously reported. In a simple two-level system the integrated extinction coefficients (or oscillator strengths) are related to the radiative lifetimes through the Einstein relations. The situation is more complicated in the case of II–VI QDs because of the thermal accessibility of dark states resulting from the valence band fine structure. There are significant but not equal populations in both bright and dark sublevels of the 1Se-1S3/2 exciton and in the dark 1Se-1P3/2 exciton. These Boltzmann populations depend on the QD size and shape. We find that in all three cases, quantitative or semiquantitative agreement between the measured radiative lifetimes and values calculated from the integrated extinction coefficients is obtained only if Boltzmann populations in all of the thermally accessible bright and dark states are considered. We also find that the shell thickness dependence of the radiative lifetimes of the CdTe/CdSe core/shell particles can be quantitatively understood in terms of overlap of calculated electron and hole wave functions. The results and analyses presented here clarify several discrepancies in the literature.

Integral Absorption Coefficients of C−H Stretching Bands in IR Spectra of Ethane Adsorbed by Cationic Forms of Y Zeolite

An attempt to measure absolute intensities of IR C-H stretching bands of ethane specifically adsorbed by Na+, Ca2+, or Mg2+ cations in Y zeolite was carried out via simultaneous transmission IR and volumetric measurements at very low pressures using self-supporting wafers. For wafers with a thickness of 7-9 mg/cm2 quantitative measurements of absorption coefficients of C-H stretching bands were possible. More pronounced shifts of C-H bands toward lower frequencies indicated that the perturbation of the corresponding bonds in ethane upon adsorption by the bivalent Ca2+ or Mg2+ ions was much stronger than by the monovalent Na+ ions. In addition, the integral extinction coefficient of the C-H stretching bands of ethane adsorbed by Na+ ions was only about 53% of that of gas-phase ethane. For adsorption on the bivalent Ca2+ or Mg2+ ions the coefficients exceeded those of the free ethane molecule, indicating strong polarization of the C-H bonds during the vibration. Bands representing the fully symmetric C-H stretching vibrations, which are IR inactive for free ethane, were perturbed most strongly upon adsorption. Their intensities reached up to 60% of the total intensity in the C-H stretching region. In contrast, the intensities of the other C-H bands were several times lower than for free ethane. These trends indicate anisotropy in the polarizability of the adsorbed molecules. In addition, the absorption coefficients indicate a weaker adsorption and polarization of ethane by Mg2+ than by Ca2+ ions in Y zeolite. Because of their smaller ionic radius, the Mg2+ cations are more strongly shielded by the surrounding oxygen atoms of the zeolite framework than the Ca2+ cations, and therefore, their polarizing ability is decreased.

Mutants of monomeric red fluorescent protein mRFP1 at residue 66: Structure modeling by molecular dynamics and search for correlations with spectral properties

To study the interrelation between the spectral and structural properties of fluorescent proteins, structures of mutants of monomeric red fluorescent protein mRFP1 with all possible point mutations of Glu66 (except replacement by Pro) were simulated by molecular dynamics. A global search for correlations between geometrical structure parameters and some spectral characteristics (absorption maximum wavelength, integral extinction coefficient at the absorption maximum, excitation maximum wavelength, emission maximum wavelength, and quantum yield) was performed for the chromophore and its 6 A environment in mRFP1, Q66A, Q66L, Q66S, Q66C, Q66H, and Q66N. The correlation coefficients (0.81-0.87) were maximal for torsion angles in phenolic and imidazolidine rings as well as for torsion angles in the regions of connection between these rings and chromophore attachment to beta-barrel. The data can be used to predict the spectral properties of fluorescent proteins based on their structures and to reveal promising positions for directed mutagenesis.

Extinction coefficients and critical solubilisation concentrations of photosystems I and II from Thermosynechococcus elongatus

The absorption properties of chlorophyll a (Chl a) in active core complexes of photosystems I (PSI) and II (PSII) isolated in high purity from the thermophilic cyanobacterium Thermosynechococcus elongatus were correlated with those of extracts in 80% acetone to determine effective extinction coefficients of protein-bound Chl a and molar extinction coefficients of core complexes and reaction centers (RC). These coefficients allow a quick determination of Chl a and protein concentrations from steady-state absorption spectra of intact samples without the need for pigment extraction and protein destruction. In the visible range, ε 680 p = 57 mM −1 cm −1 for trimeric PSI (PSIt) and ε 674 p = 70 mM −1 cm −1 for dimeric (PSIId) and monomeric (PSIIm) PSII (error ±6%; superscript “ p” refers to Chl a bound to intact protein, subscripts are the peak maxima in nm). The integral extinction coefficient ϕ p = 2.8 nm μM −1 cm −1 for the wavelength interval between 550 and 800 nm and the extinction coefficient ε B p = 14 mM −1 cm −1 for the smaller absorption maximum (B = 632 nm for PSI and 627 nm for PSII) were found to be essentially the same for both types of PS. The coefficients of PSIt are shown to remain unaltered when 65% (v/v) of the buffer is replaced with glycerol. Molar extinction coefficients of core complexes were determined using Chl a/RC ratios of 96±1 for PSI and 35±2 for PSII based on X-ray data. In addition, the critical solubilisation concentration of n-dodecyl-β- d-maltoside (βDM), necessary to keep the core complexes in solution, was determined by turbidimetric titrations. It was found that at least ∼500 βDM molecules per PSIt (∼2 βDM per Chl a) and 190 βDM molecules per PSIIm (∼5 βDM per Chl a, also for PSIId) in excess of the critical micelle concentration of 0.16 ± 0.03 mM are necessary for a complete solubilisation of the core complexes.

The crystal chemistry of birefringent natural uvarovites. Part III. Application of the superposition model of crystal fields with a characterization of synthetic cubic uvarovite

Synthetic, flux-grown uvarovite, Ca3Cr2 [SiO4]3, was investigated by optical methods, electron microprobe analysis, UV-VIS-IR microspectrometry, and luminescence spectroscopy. The crystal structure was refined using single-crystal X-ray CCD diffraction data. Synthetic uvarovite is optically isotropic and crystallizes in the “usual” cubic garnet space group Ia3¯d [a=11.9973 A, Z=8; 21524 reflections, R1=2.31% for 454 unique data and 18 variables; Cr–O=1.9942(6), Si–O=1.6447(6), Ca–Oa=2.3504(6), Ca–Ob= 2.4971(6) A]. The structure of Ca3Cr2[SiO4]3 complies with crystal-chemical expectations for ugrandite group garnets in general as well as with predictions drawn from “cubically averaged” data of non-cubic uvarovite–grossular solid solutions (Wildner and Andrut 2001). The electronic absorption spectra of Cr3+ in trigonally distorted octahedra of synthetic uvarovite were analyzed in terms of the superposition model (SM) of crystal fields. The resulting SM and interelectronic repulsion parameters are =9532 cm−1, =4650 cm−1, power law exponent t 4=6.7, Racah B35=703 cm−1 at 290 K (reference distance R 0=1.995 A; fixed power law exponent t 2=3 and spin-orbit parameter ζ=135 cm−1). The interelectronic repulsion parameters Racah B 55=714 cm−1 and C=3165 cm−1 were extracted from spin-forbidden transitions. This set of SM parameters was subsequently applied to previously well-characterized natural uvarovite–grossular solid solutions (Andrut and Wildner 2001a; Wildner and Andrut 2001) using their extrapolated Cr–O bond lengths to calculate the energies of the spin-allowed bands. These results are in very good agreement with the experimentally determined band positions and indicate the applicability of the superposition model to natural 3d N prevailing systems in geosciences. Single-crystal IR absorption spectra of synthetic uvarovite in the region of the OH-stretching vibration exhibit one isotropic absorption band at 3508 cm−1 at ambient conditions, which shifts to 3510 cm−1 at 77 K. This band is caused by structurally incorporated hydroxyl groups via the (O4H4)-hydrogarnet substitution. The water content, calculated using an integral extinction coefficient ɛ=60417 cm−2 l mol−1, is c H2O=33 ppm.

The crystal chemistry of birefringent natural uvarovites: Part I. Optical investigations and UV-VIS-IR absorption spectroscopy

Six garnet crystals with compositions close to the uvarovite-grossular binary from three different localities (Saranov, Veselovsk, and Saranka, Ural Mountains, Russia) were investigated by optical methods, electron microprobe analysis, and polarized UV-VIS-IR micro-spectroscopy. Under crossed polarizers the crystals display “strong” birefringence in the order of 0.006 and formation of domains, aligned parallel to the crystal faces of the form {110}. Referring to the cubic cell, Y is always parallel to a principal lattice direction, e.g., [010]cub, whereas X and Z are then parallel to [101]cub and [101]cub, respectively. The garnets are uvarovite-grossular solid solutions with 48 to 71 mol% uvarovite component and traces of Ti, Fe, Mn, and Mg, and exhibit no compositional zoning. Polarized single crystal infrared absorption spectra in the region of the OH stretching vibration display 14 discernible, partly superimposing, and strongly anisotropic absorption bands between 3470 and 3680 cm−1, which are caused by structurally incorporated hydroxyl groups. The polarization behavior observed for individual samples complies with orthorhombic, monoclinic, and triclinic crystal symmetry, respectively. The water content calculated using an integral extinction coefficient, e = 43800 L/cm2 ·mol, ranges from 0.07 to 0.34 wt%. Annealing experiments indicate that the incorporation of hydroxyl groups is not the primary cause for the anisotropic behavior. Instead, cation ordering on octahedral positions may play an important role. This assumption is substantiated by single crystal X-ray diffraction investigations reported in Part II of the present study (Wildner and Andrut 2001). Contrary to the IR spectroscopic data, single-crystal electronic absorption spectra show no significant polarization behavior in the UV-VIS-NIR spectral region. The observed absorption bands are caused by d - d transitions of Cr3+ cations in octahedral coordination. The linear extinction coefficients of the investigated uvarovites strongly indicate that the Cr3+ cations occupy centrosymmetric sites, regardless of the exact symmetry reduction from Ia 3 d .

Infrared Spectroscopic Characterization of the Alumina Surface: 1. Infrared Spectra of Cr(CO)6Adsorbed at Different Surface Sites on γ-Alumina

Infrared spectra of Cr(CO)6adsorbed at different surface centers on γ-alumina were investigated. The spectra of the probe complex revealed the existence of three types of strong Lewis centers and that of physisorbed Cr(CO)6. In the case of the physisorbed complexOhsymmetry was widely conserved, and addition to strong Lewis centers led to lowering of the symmetry. The assumption ofC4vsymmetry, caused by interaction of one CO group of the complex with a Lewis center, may explain the spectra. Approximate values for the integral extinction coefficients were determined.

The conjugation and effective charges of the atoms at the triple bond in germylacetylenes

The integrated extinction coefficients (A) of the C≡C stretching modes in the IR spectra of 12 germylacetylenes Me3GeC≡CR are determined by the resonance interactions of substituents with the triple bond. TheA1/2 values change linearly with change in the difference between the effective π-electron charges on the atoms at the triple bond and σ0R constants of organic substituents R. The average value of the σ0R constant of the Me3Ge substituent in the compounds studied is +0.06. The resonance acceptor effect of the Me3Ge substituent toward the triple bond (d,π-conjugation) is stronger than the donor effect (σ,π-conjugation).

Compositional dependence of the valency state of Cr ions in oxide glasses

Absorption spectra of Cr ions in multi-component oxide glasses melted in Ar were measured. The integrated extinction coefficient is used as a parameter to analyze the redox reaction of Cr 3+ and Cr 6+ in glass samples. The relative content of Cr 6+ increased and that of Cr 3+ decreased with increasing basicity in silicate and borate glasses; this result is consistent with previous studies. On the contrary, only Cr 3+ exist in phosphate glasses. Cr 4+ ions were found only in aluminate, gallate and alumino-silicate glasses with modifier contents ≥ 60 mol%. The relationship between point defects and Cr 4+ formation is examined on the basis of electron spin resonance measurements. We concluded that the superoxide ion radical (O 2 −) and the peroxy bonding (-O-O-) oxidize Cr 3+ to Cr 4+ in aluminate, gallate, and alumino-silicate glasses.

Intensity of bands of the C≡C stretching modes in the IR spectra and conjugation in silylacetylenes

A comparative study of the integrated extinction coefficients (A) of the C≡C stretching bands in the IR spectra of acetylene derivatives Me3SiC≡CR, HC≡CR, and Me3CC≡CR was carried out. The resonance interactions of substituents with a triple bond are the main cause of the changes in the values ofA. The total resonance effect of the Me3Si fragment involves both acceptor (d, π-conjugation) and donor (σ, π-conjugation) components; d, π-conjugation dominates in the silylacetylenes studied. TheσR0 resonance constant of the Me3Si substituent in compounds Me3SiC≡CR is 0.17±0.02.

Resolution of infrared profiles from variable temperature experiments on mixtures and conformers in rapid equilibrium by compensating for thermal and solvent effects

Abstract Curve resolution of infrared profiles from non-conformational mixtures and conformational equilibria is discussed. For successful resolution it is crucial that temperature and solvent induced variations observed as peak shifts and band broadening are accounted for. As changes in absorbance (in IR) or intensities (in Raman) with temperature may be different for different bands of the same conformer, the resolution must be performed on local parts of the spectra. An assumption about temperature independence of the integrated extinction coefficients in such a local region of the spectra must be made. The success of curve resolution by compensating for thermal effects is largely determined by the level of the experimental noise, the change in analyte concentrations with temperature and the thermal effects. Curve resolution of mixture spectra is illustrated using model spectra of toluene and cyclohexane and variable temperature spectra of chlorocyclohexane.

Near-infrared spectroscopic determination of water species in glasses of the system MAlSi 3O 8 (M = Li, Na, K) : an interlaboratory study

The near-infrared absorption bands at 5200 cm −1, assigned to molecular water, and at 4500 cm −1, assigned to hydroxyl groups bonded to network forming cations, were used to specify concentrations of water species in glasses of alkali feldspar composition MAlSi 3O 8 (M = Li, Na, K). To allow an accurate quantitative evaluation of the water species in hydrous glasses, we have determined the composition dependence of the density and the linear and integral extinction coefficients of the glasses. For each feldspar composition, 8–28 samples with various amounts of water have been synthesized. All samples were quenched isobarically to avoid desorption of water during cooling. Water contents of the glasses were analyzed by Karl-Fischer titration. Spectra of the same sample collected by four different FTIR micro spectrometers vary by up to 10% relative in peak intensities. The differences are attributed to the specific measurement conditions (e.g., magnification of the objectives, spectral ranges of the systems, characteristics of the detectors) applied in the laboratories. However, an unambiguous explanation of the differences is not possible due to the complexity of FTIR spectroscopy. In order to reduce the uncertainty in determination of water species and total water by FTIR spectroscopy a calibration of spectrometers against a reference system should be performed. For evaluation of linear and integral molar extinction coefficients we have chosen the FTIR spectrometer Bruker ® IFS88 of Hannover as the reference system. All spectroscopic data were recalculated on the basis of this spectrometer. For compositions of the system MAlSi 3O 8 the extinction coefficients are strongly dependent on the alkali cation and vary non-linearly along the binary joins of the system. The extinction coefficients of both the 4500- and the 5200-cm − 1 bands are significantly lower for a strong peralkaline glass than for glasses with feldspar compositions. This is attributed to strong H bonding of water species to adjacent non-bridging oxygens in the peralkaline glass. Probably, for the peralkaline composition only a part of the water species contribute to the NIR absorption bands. Variation of species concentration for glasses of the system MAlSi 3O 8 with same water content are attributed to differences in the fictive temperature of the glass which depends on cooling rate, water content and anhydrous composition of glass.

Infrared Spectroscopy and Temperature-Programmed Desorption Study of Adsorbed Thiophene on γ-Al2O3

The adsorption of thiophene (C4H4S) on γ-Al2O3 has been investigated in ultrahigh vacuum (UHV) using infrared (IR) spectroscopy and temperature-programmed desorption (TPD). Following thiophene adsorption onto γ-Al2O3 at 130 K, TPD reveals two peaks with maximum rates of desorption at 175 and ∼220 K. The former peak is assigned to desorption of multilayer thiophene while the latter peak is assigned to desorption of weakly chemisorbed thiophene from the alumina surface. IR spectroscopy of adsorbed thiophene at submonolayer coverages provides further evidence that thiophene interacts only weakly with the alumina support; no decomposition of the thiophene overlayer is observed upon heating to 600 K under UHV conditions or a partial pressure of thiophene of 3.0 Torr. Three kinds of adsorbed thiophene species exist on the alumina surface at saturation coverage: one in which thiophene interacts with hydroxyl groups, presumably via hydrogen bonding, a second in which thiophene is coordinated via its sulfur atom to coordinately unsaturated Al3+ sites on the surface, and a third species which is present only at high thiophene coverages. The heat of adsorption for thiophene on γ-Al2O3 has been determined under equilibrium conditions (PTh = 3.0 Torr) to be ΔHads = −28.9 kJ/mol. A direct correlation has been established between the IR and TPD data, permitting integrated extinction coefficients to be determined for adsorbed thiophene in both the monolayer and multilayer coverage regimes. Extinction coefficients in the two coverage regimes are markedly different, underscoring the need to use care when interpreting the IR spectral intensities for adsorbed species. While, as expected, this study has shown that thiophene adsorbs only weakly on γ-Al2O3, more importantly it has shown that the combined IR−TPD methods can be used to determine both the thiophene coverage and the mode of bonding with the surface.

Limitation in the application of pyridine for quantitative studies of brönsted acidity in relatively aluminous zeolites

The titration of Brönsted acid sites in H-Y ( Si Al = 2.7 ) and H-EMT ( Si Al = 4.0 ) with pyridine, monitored by Fourier transform infrared (FTIR) techniques has demonstrated that the amount of PyH + ions (the IR band at 1545 cm −1) formed at saturation is the same and does not depend on the Si Al ratio within the range considered, although the HF band (3650 cm −1) is fully perturbed in both cases. The integrated extinction coefficient, ε PyH + , has an effective value (1.1 cm μmol −1 at 150°C and 1.6 cm μmol −1 at 350°C) reflecting three processes simultaneously: (1) the interaction of HF hydroxyl groups with Py leading to PyH + ion formation; (2) the perturbation of HF hydroxyl groups by PyH + ions as OH··PyH +; (3) the perturbation of LF hydroxyl groups by Py resulting in hydrogen-bonded O··H··Py complexes. Py sorption cannot be used for quantification of Brönsted hydroxyls in faujasitic zeolites with Si Al < 4 since only a limited amount of PyH + ions per supercage can be generated.

The quantitative IR spectroscopic determination of structural OH groups in kyanites

Kyanites from different occurrences show in the near IR two relatively strong absorption bands at 3 380 and 3 270 cm−1 due to OH stretching frequencies. The integral molar extinction coefficient is 3201 · Mol−1 · cm−2. A quantitative IR spectroscopic microtechnique based on Beer's law allows to determine small amounts of structural OH groups in (100) cleavage plates of a few tenths mm in size proved to be free of inclusions and hydrous alteration products. There exists an obvious relation between the occurrence of the kyanites studied and their equivalent H2O+ content ranging from < 0.005 to 0.180 wt.%.

Infrared spectroscopic investigation of hydroxy-group siting in H faujasites

The total hydroxy-group and the separate high-frequency (h.f.) and low-frequency (l.f.) hydroxy-group concentrations in H faujasites, observed by i.r. spectroscopy and corroborated by other methods, show a dependence of the maximum occupation of h.f. OH groups on the Si/Al ratio of between 15 and 32 OH groups per unit cell for zeolites HY and HX, respectively. In the case of HX zeolites above 70% exchange, decomposition is unavoiable. As a result of band separation the separate amounts of seven kinds of h.f. OH subspecies have been obtained from measurements of their i.r. absorbance and the integrated extinction coefficients of the h.f. OH stretching band for HX and HY zeolites. These subgroups show the same i.r. sub-bands in both HX and HY zeolites, but of different intensities. This may be explained on the basis of different Si/Al ordering schemes by O1H groups bonded to silicon atoms, surrounded by 0–4 Al atoms, and bonded to Al atoms, which are influenced by electrostatic interactions with neighbouring aluminium atoms.