OH Combination Bands Research Articles

Pyroxene and Hydroxyl Signatures in Vesta Newly Calibrated Data from Dawn Mission

Thanks to the VIR spectrometer onboard NASA’s Dawn spacecraft, which orbited Vesta in 2011–2012, thousands of hyperspectral images of its surface have been collected. The mission confirmed the HED (Howardite–Eucrite–Diogenite) meteorite composition of Vesta. Moreover, the VIR spectrometer detected the 2.8 µm absorption band, due to the presence of the OH molecule. In this work, we took advantage of the newly calibrated data of the VIR spectrometer by characterizing new spectral features thanks to the improved signal-to-noise (S/N) ratio for these spectra. The main goals of this work are as follows: (1) to characterize Vesta’s surface in the visible range and (2) to confirm, reinforce and characterize the OH distribution on Vesta by studying the 2.8 µm band and looking for OH combination bands around 2.2–2.4 µm. A possible relation between the 1.9 µm absorption band due to the presence of pyroxenes and the one at 0.5 µm was analyzed. Finally, the analysis of hydroxyl absorption bands evidenced an anti-correlation between the abundance of hydroxyl-bearing molecules and the surface reflectance. This confirms that the hydroxyl presence is linked to the dark units on Vesta.

Prediction of the extractives content of Eucalyptus globulus wood using NIR-based PLS-R models. Influence of spectral range and preprocessing on the percentage of outliers detected

Eucalyptus globulus is an important pulpwood source due to favorable wood characteristics, including low extractive content. However, there is significant tree-to-tree variation that can be exploited in breeding. This requires screening a large number of samples, which NIR and PLS-R make possible. Models are typically developed for a specific set of samples prepared in the same way. The question is: how well these models predict samples that are different from the ones used in the model. Models developed to determine the extractive content of Eucalyptus globulus wood from Australia were used to E. globulus wood from Argentina, which differed in age and sample preparation. The main difference between spectra of the two origins was in the OH combination band, despite the fact that samples were dried identically. Due to this difference, models that included the O-H band assigned above 73% of the spectra as outliers regardless of preprocessing, whereas models that did not include the O-H band assigned fewer spectra as outliers. The differences in the OH band were attributed primarily to differences in particle size and extractive content, rather than to differences in humidity content. However, all models predict similar results for all samples, including outliers.

Abundance and composition of kaolinite on Mars: Information from NIR spectra of rocks from acid-alteration environments, Riotinto, SE Spain

Investigation of Earth analogs and their environments is crucial for the full interpretation of geologic outcrops and processes on Mars. Phyllosilicates are important indicators of aqueous processes and their characterization is a significant piece of the geologic puzzle of Mars. They are chiefly investigated with Near-Infrared (NIR) spectroscopy from orbit. While these studies have revolutionized our understanding of aqueous processes on Mars, they are challenged by the chemical and structural complexity of phyllosilicates, non-linear response to mineral abundance, low penetration of infrared radiation in the target rocks, and spectral modifications caused by rock texture. Phyllosilicate-bearing samples from four locations in the Iberian Pyrite Belt (El Villar, Calañas, Quebrantahuesos, and Tharsis) were investigated using NIR, XRD and thermogravimetry in order to document the effects of acidic alteration under multiple environments and inform orbital detections on Mars. The samples are comprised of chlorite, illite, kaolinite, alunite, jarosite, goethite and interstratified chlorite-vermiculite and kaolinite-smectite. Kaolinite dominates the spectral signature relative to other phyllosilicates from abundances as low as 7 wt%. Only alunite and jarosite display spectral intensities similar to kaolinite. NIR spectra of bulk rock and <2 μm size fractions are very similar, indicating that spectra are dominated by the smaller particles. The octahedral Al-Fe-Mg composition of illite and kaolinite determine the positions of their OH combination band (~2.21 μm), commonly used for phyllosilicate characterization. The range of wavelength variation is narrower for kaolinite-dominated spectra, 2.205–2.216 μm, but wider than the spectral resolution of the orbital probe CRISM (~0.007 μm). Thus, in favorable conditions CRISM spectra can identify variations of kaolinite octahedral composition, a valuable tool to investigate kaolinite origin. A survey of kaolinite-bearing spectra from Mars (Leighton Crater, Mawrth Vallis and Nili Fossae regions) showed that most OH combination bands are within 2.205–2.212 μm. One spectrum displayed this band at 2.215–2.219 μm, and is a good candidate for kaolinite with significant Fe/Mg-substitution.

Optical phonons, OH vibrations, and structural modifications of phlogopite at high temperatures: An in-situ infrared spectroscopic study

The thermal behavior of optical phonons and OH vibrations of phlogopite (a trioctahedral mica) was examined at temperatures up to 1000 K using in situ infrared spectroscopy. The results showed that with increasing temperature, O–K bands in phlogopite exhibited a relatively strong variation in frequency in a manner similar to those in muscovite. The work revealed that different types of OH bands (fundamentals and combinations) have very different thermal behavior or temperature dependence, and their absorption coefficients are commonly not constant on heating. OH combination bands that are associated with summation processes of multi-phonon interactions commonly show a decrease in their intensities on heating, but in contrast combination bands due to difference processes generally exhibit an increase. This means that temperature dependencies of their absorption coefficients need to be considered when using the Beer-Lambert law to determine or estimate OH contents or hydrogen concentrations at high temperatures. The results showed a structural anomaly associated with a discontinuity in the temperature derivative of the wavenumber of Al–O and Si–O vibrations and O–H stretching near 600 K. However, framework-related phonon modes in the FIR and MIR regions do not suggest a break of the original monoclinic structural symmetry in the investigated temperature region. The complex changes are attributed to temperature-induced alteration of local configuration involving TO4 tetrahedra and a possible change of the orientation of OH dipoles, in addition to a previously reported distortion of MO6 octahedra. Increasing temperature to 1000 K also causes partial dehydroxylation, as evidenced by the disappearance of the OH band near 3623 cm−1 and the decrease in OH band height and area of other OH bands. The study did not record the formation of H2O inside phlogopite as a result of partial dehydroxylation. The work offers new data and findings that have important implications in understanding the complex structural modifications and the behavior of phonon modes and the thermal stability of hydroxyls on approaching the dehydroxylation, as well as the way hydrogen is released from micas at high temperatures. Our data also show that phologpite becomes less transparent with increasing temperature suggesting a change of radiative properties and ability to transmit heat, which could be of interest for modeling thermal-transmission in crustal rocks.

Synthesis of akaganeite in the presence of sulfate: Implications for akaganeite formation in Yellowknife Bay, Gale Crater, Mars

Akaganeite, a Cl-bearing Fe(III) (hydr)oxide, has been recently discovered in Yellowknife Bay in Gale crater on Mars by the Mars Science Laboratory (MSL) Curiosity Rover. Akaganeite was associated with sulfate and sulfide minerals at Yellowknife Bay indicating that sulfate ions could be present in solution during akaganeite formation. The mechanism and conditions of akaganeite formation in the Yellowknife Bay mudstone are unknown. We investigated formation of akaganeite through hydrolysis of ferric chloride solution in the presence of 0, 0.01, 0.05, 0.1 and 0.2M sulfate and at initial pH of 1.5, 2 and 4 at 90°C. Mineralogy of the precipitated Fe(III) phases was characterized by X-ray diffraction and infrared spectroscopy. The precipitates were also acid digested to determine total sulfate and chloride contents. Akaganeite and natrojarosite formed at initial solution pH of 1.5; akaganeite, goethite and natrojarosite precipitated in initial pH 2 solutions and goethite, hematite and 2-line ferrihydrite precipitated at initial solution pH of 4. Sulfate addition did not inhibit akaganeite formation. Increasing initial solution sulfate concentrations resulted in increasing sulfate to chloride ratio in the precipitated akaganeite. Infrared spectroscopy revealed akaganeite bands at ∼2μm (H2O combination band) and at ∼2.46μm (OH combination band). The H2O combination band position linearly correlated with total chloride content in akaganeite. Overall, laboratory studies demonstrated formation of akaganeite at initial sulfate concentration ⩽0.2M (sulfate to chloride molar ratio ⩽0.3) and pH⩽2, implying that those conditions might prevail (perhaps as micro-environments) during akaganeite formation in Yellowknife Bay mudstone. The occurrence of Fe(II) sulfides (pyrite and pyrrhotite) in Yellowknife Bay mudstone is a potential acidity source. Dissolution of sulfide minerals might occur under localized oxidizing water-limiting Cl-rich conditions creating favorable environments for akaganeite formation.

Akaganeite and schwertmannite: Spectral properties and geochemical implications of their possible presence on Mars

The ferric oxyhydroxide minerals akaganéite and schwertmannite are associated with acidic environments and iron alteration on Earth and may be present on Mars as well. These minerals have a tunnel structure and are crystallographically related. The extended visible region reflectance spectra of these minerals are characterized by a broad Fe 3+ electronic transition centered near 0.92 μm, a reflectance maximum near 0.73 μm, and a shoulder near 0.59 μm. The near-infrared (NIR) reflectance spectra of each of these minerals are dominated by broad overtones and combinations of the H 2 O vibration features. These occur near 1.44-1.48 and 1.98-2.07 μm (∼6750-6950 and 4830-5210 cm -1 ) in akaganéite spectra, while in schwertmannite spectra they occur at 1.44-1.48 and 1.95-2.00 μm (∼6750-6950 and 5005-5190 cm -1 ). Additional bands due to OH vibrational overtones are found near 1.42 μm (∼7040 cm -1 ) in akaganéite and schwertmannite spectra and due to OH combination bands in akaganéite spectra at 2.46 μm (4070 cm -1 ) with weaker components at 2.23-2.42 μm (4134-4492 cm -1 ). A strong and broad band is observed near 2.8-3.1 μm (∼3300-3600 cm -1 ) in reflectance and transmittance spectra of akaganéite and schwertmannite due to overlapping OH and H 2 O stretching vibrations. H 2 O bending vibrations occur near 1620 cm -1 (∼6.17 μm) in akaganéite spectra and near 1630 cm -1 (∼6.13 μm) in schwertmannite spectra with additional bands at lower frequencies due to constrained H 2 O molecules. OH bending vibrations occur near 650 and 850 cm -1 (∼15.4 and 11.8 μm) in akaganéite spectra and near 700 cm -1 (∼14.3 μm) in schwertmannite spectra. Sulfate vibrations are observed for schwertmannite as a ν 3 triplet at 1118, 1057, and 1038 cm -1 (∼8.9, 9.5, and 9.6 μm), ν 1 at 982 cm -1 (∼10.2 μm), ν 4 near 690 cm -1 (∼14.5 μm), and ν 2 at 608 cm -1 (∼16.5 μm). Fe-O bonds occur near 410-470 cm -1 (μm) for akaganéite and schwertmannite. Both minerals readily absorb H 2 O molecules from the environment and adsorb them onto the mineral surfaces and incorporate them into the tunnels. If akaganéite and schwertmannite were present on the surface of Mars they could enable transport of H 2 O from the near-surface to the atmosphere as the partial pressure of H 2 O varies diurnally.

Determination of Eucalyptus Globulus Wood Extractives Content by near Infrared-Based Partial Least Squares Regression Models: Comparison between Extraction Procedures

Wood extractives, the non-cell wall components that can be removed by solvents, can play an important role in the protection of the living tree as well as derived wood products. On the other hand they can be detrimental for pulp and paper, paint and varnish films and adhesives. The objective of this work was to develop near infrared-based partial least squares regression models for the prediction of wood extractives. The developed models are well suited for screening of the ethanol and total extractives content of Eucalyptus globulus wood. The models for the prediction of ethanol extractives with residual prediction deviations above 5 are also suited for quality control. It is shown that samples with high extractives content always have a more intense OH combination band than the samples with low extractives content and that near infrared can be used for a rough estimation of the relative performance of the reference methods.

Reflectance Spectroscopy of Beidellites and Their Importance for Mars

AbstractBeidellites may exist on Mars and represent intermediate alteration products; their presence would indicate different alteration environments than previously identified because montmorillonite is a low-grade alteration mineral whereas beidellite is a higher-temperature alteration mineral, and often represents a step toward illite formation. The reflectance spectra of beidellites are under study to support their orbital detection on Mars, where spectral signatures of other Al-rich phyllosilicates have been observed. Reflectance spectra of ten Al-rich smectites are presented here which include pure beidellites and Al smectites having compositions between those of beidellite and montmorillonite, and emphasis is placed here on the OH combination bands near 4545 cm−1 (2.2 μm) as these vibrational features are commonly used in the identification of phyllosilicates on Mars. Shifts were observed in the Al2OH band centers, which occur near 4590 cm−1 (2.18 μm) in reflectance spectra of beidellite and near 4525 cm−1 (2.21 μm) in reflectance spectra of montmorillonite. These are compared with the Al2OH bending vibrations observed near 941–948 cm−1 (10.5–10.6 μm) for beidellite and near 918–926 cm−1 (10.8–10.9 μm) for montmorillonite. Although the octahedral site cation composition provides the greatest influence on the vibrational energies of the M2OH groups, the tetrahedral site cation composition also influences these vibrations. Shifts were observed in the Si-O-Al bending vibrations from 552 and 480 cm−1 (18.1 and 20.8 μm) in beidellite spectra to 544 and 475 cm−1 (18.4 and 21.0 μm) in montmorillonite spectra. Gaussian modeling of the 4545 cm−1 (2.2 μm) bands led to the discrimination of four overlapping bands in each of the ten Al smectite spectra examined in this study. Shifts in the band center and area of the primary spectral band are coordinated with substitution of Al for Si in the tetrahedral sheet. This is consistent with beidellites having a greater tetrahedral layer charge than montmorillonites. The observed spectral differences were sufficiently large that these Al-rich smectites can be differentiated in orbital data of Mars. A pure beidellite-type spectrum is observed in an isolated Al phyllosilicate-bearing outcrop in Libya Montes, a region where Fe-rich smectite is common but Al-rich smectite is rare. Beidellite-type reflectance spectra were also observed in one area of the Nili Fossae region. In contrast, a variety of Al phyllosilicates were found in the ancient rocks at Mawrth Vallis, including some smaller clay-bearing regions exhibiting spectral signatures more consistent with beidellite-like than montmorillonite-like chemistry.

The study of different solid forms of Emodepside

Emodepside is an endoparasiticide used in veterinary drugs. It exists in four different crystal forms which were characterised using DSC, TGA, evolved gas analysis (using FT-IR spectroscopy), hot-stage microscopy, FT-Raman, FT-IR and FT-NIR spectroscopy and powder X-ray diffraction. Thermal analysis showed that the forms II–IV contain considerable amounts of water being easily lost upon heating. Hot-stage microscopy indicated that the crystal structures do not change upon the loss of water. To examine whether the forms II–IV are hydrates or modifications of Emodepside having water adsorbed to the crystal surface and/or absorbed into disordered defect regions, the behaviour of the forms at different relative humidities was analysed using FT-Raman and FT-NIR spectroscopy and vapour sorption analysis. Changes in the C O stretching region in the Raman spectra upon the removal of water revealed that all three forms represent non-stoichiometric hydrates forming isomorphic dehydrates. Sorption analysis indicated the presence of localised water molecules in the structure of form IV. Several OH combination bands of water were found in the NIR spectrum of each form indicating differently bound water molecules. Crystal structure analysis of form IV at ambient humidity revealed four well-defined water positions in the asymmetric unit.

Reflectance and emission spectroscopy study of four groups of phyllosilicates: smectites, kaolinite-serpentines, chlorites and micas

AbstractCoordinated visible/near-infrared reflectance/mid-infrared reflectance and emissivity spectra of four groups of phyllosilicates were undertaken to provide insights into the differences within and among groups of smectites, kaolinite-serpentines, chlorites and micas. Identification and characterization of phyllosilicates via remote sensing on Earth and Mars can be achieved using the OH combination bands in the 2.2–2.5 μm region and the tetrahedral SiO4 vibrations from ~8.8–12 μm (~1140–830 cm–1) and ~20–25 μm (500–400 cm–1). The sharp and well resolved OH combination bands in the 2.2–2.5 μm region provide unique fingerprints for specific minerals. Al-rich phyllosilicates exhibit OH combination bands near 2.2 μm, while these bands are observed near 2.29–2.31, 2.33–2.34 μm and near 2.35–2.37 μm for Fe3+-rich, Mg-rich and Fe2+-rich phyllosilicates, respectively. When a tetrahedral substitution of Al or Fe3+ for Si occurs, the position of the Si(Al,Fe)O4 stretching mode absorption shifts. Depending on the size of the cation, the Si(Al,Fe)O4 bending mode near 500 cm–1 is split into multiple bands that may be distinguished via hyperspectral remote sensing techniques. The tetrahedral SiO4 vibrations are also influenced by the octahedral cations, such that Al-rich, Fe-rich and Mg-rich phyllosilicates can be discriminated in reflectance and emissivity spectra based on diagnostic positions of the stretching and bending bands. Differences among formation conditions for these four groups of phyllosilicates are also discussed. Hyperspectral remote sensing can be used to identify specific phyllosilicates using electronic and vibrational features and thus provide constraints on the chemistry and formation conditions of soils.

Detection of Tenderness, Post-Rigor Age and Water Status Changes in Sheep Meat Using near Infrared Spectroscopy

The tenderness (objective measure is shear force) of sheep meat ( longissimus thoracis et lumborum) during post-rigor ageing at 15°C can be predicted using near infrared (NIR) analysis ( r2 = 0.85). Measurements ( n = 260 from 65 lambs) were made at 0, 8, 24 and 72 h post-rigor using an interactance system operating over the spectral range from 400–1700 nm. There was no predictive power in the NIR models to segregate tenderness measurements made at any one particular post-rigor time. NIR measurements could segregate the post-rigor ages with good accuracy ( r2 = 0.91). The OH combination band at 840 nm is the dominant feature of the predictive models and suggests that the underlying chemistry is related to the post-rigor changes in the water status of the meat. Observations on another similar data set ( n = 48 from 12 lambs), involving NIR and water content measurements, confirmed there are significant water changes in meat during aging. We speculate that the NIR models may be sensitive to the accumulation of free water arising from the degradation of cytoskeletal proteins during ageing, releasing the water normally tightly bound up in the tertiary protein structures.

Physical properties of selected illites, beidellites and mixed-layer illite–beidellites from southwestern Idaho, and their infrared spectra

The silver–gold ore deposits of the De Lamar mine, the mines in Florida Mountain and the mines in War Eagle Mountain occur in conjunction with large seams of clay minerals, which consist mainly of mixed-layer illite–beidellite. When saturated with groundwater, these clay seams have caused slope failures during mining and processing of ore. The illite–beidellite clays have effective internal friction values, Ø e, as low as 4° and cementation C values of about 1.0 kg f/cm 2. The Fe-beidellite used for the clay core of the mill pond dam has an average Ø e value of 8.3° and C value of 0.79 kg f/cm 2, with an average permeability ( K-value) of 5.6×10 −7 cm/s. The fundamental OH spectra of beidellite, illite and muscovite are similar with beidellite having bands near 3635, 3654 and 3653 cm −1. Montmorillonite has one Al–OH libration band near 915 cm −1, whereas beidellite has a second band near 942 cm −1. In like manner, illites and muscovites have bands from 928 to 933 cm −1, as well as the Al–OH libration bands from 912 to 917 cm −1. The OH libration bands vary both in position and intensity with particle orientation and heating. Combination bands for Fe-bearing muscovite show moderate bands at 4451 cm −1 for ferrous muscovite and at 4471 cm −1 for ferric muscovite. These bands also are present for illites. The dominant Al–OH combination band wave numbers of muscovites form a linear relationship with the Al 2O 3 muscovite contents, but not so precisely for illites. Chemical analysis of illites indicates that the compositions are a continuum into muscovites. Illites from the Miller–Walters mine contain a rather large amount of certain trace elements, whereas the adjacent beidellites do not.

Field reflectance spectrometry for detection of swelling clays at construction sites

AbstractWe have developed techniques to map the distribution and composition of clay‐rich soils with portable field spectrometers on the ground. Spectral reflectance measurements in the 1800–2400‐nm region with 10‐nm resolution can distinguish smectites, which cause swelling, from illites and kaolinite that do not swell significantly. Illites and smectites are often mixed in the soil and result in varying swell potential. Standard engineering soil tests are too time consuming and costly to be used in areas where there is highly varying swell potential. Therefore, in many instances in regions of steeply dipping sedimentary layers, beds of swelling clay go undetected. We show that it is possible to determine smectite content with a standard cross‐validation error of 10% based on partial least‐squares analysis of second‐derivative reflectance spectra. Loadings show that the 1800–2000‐ and 2150–2250‐nm regions contain the most relevant information for the detection and quantification of smectite content and these correspond to the bound water in the clay lattice interlayer and the Al–OH combination band, respectively. Correlations as high as 87% were obtained with the Seed swell‐potential index. The correlations are higher when the samples were dried rather than measured in their moist condition shortly after collection in the field, as in an earlier study. Correlation with other swell indices shows that reflectance spectroscopy would be a reliable indicator that could divide samples into low, medium, and high swell potential. The effect of sample moisture was studied and the results show that the surface of the field samples must first be dried before measurement, in order to obtain a reliable swell potential value from the model. © 2001 John Wiley &amp; Sons, Inc., Field Analyt Chem Technol 5: 143–155, 2001

Effects of chemical composition and temperature of heating on the infrared spectra of Li-saturated dioctahedral smectites. (II) Near-infrared region

AbstractDiffuse reflectance spectra in the near-infrared region are presented for Li-saturated smectites heated up to 200°C. The smectites included three montmorillonites, an Fe-beidellite and a ferruginous smectite. Unheated samples showed a complex band near 7060 cm-1 assigned to the first overtone of the OH-stretching mode of structural hydroxyl groups and bound H2O. The OH combination bands appeared in the 4600-4300 cm-1 region. Spectra of heated montmorillonites showed an upward shift and splitting of the OH-overtone band into two components near 7170 and 7110 cm-1. The presence of a band near 7170 cm-1, assigned to the overtone of the AlMgLiOH-stretching vibration, implied that local trioctahedral domains were created upon Li(I) fixation in the previously vacant octahedral positions of montmorillonites. The OH combination bands were shifted to higher frequencies and a new band appeared near 4472 cm-1 in the spectra of montmorillonites heated to temperatures in excess of 130°C. No features indicating Li(I) in the structure of Fe-beidellite or ferruginous smectite were observed in the NIR spectra.

Effect of pressure on OH and OD impurities in

The fundamental vibrational transition frequencies of OH and OD defects, as well as the first OH overtone and the vibrational-librational OH-combination band, are investigated in under pressure using the diamond-anvil technique. The absorption bands shift to lower wavenumbers and become considerably broader at higher pressures. The experimental results are alternatively discussed within a single oscillator model and a recently developed model for hydrogen bonds in solids.

NHN] + and [OHO] − hydrogen bridges in the 1:1 adduct of 1,8-bis(dimethylamino)naphthalene with 3,4-furandicarboxylic acid

1,8-Bis(dimethylamino)naphthalene (DMAN) hydrogen 3,4-furandicarboxylate monohydrate crystallizes in the space group P2 1/ c, Z = 4, a = 11.328(3), b = 10.341(3), c = 19.915(5) Å, β = 122.68(5)°. The NHN + hydrogen bond in protonated DMAN is relatively long ( R Nţdot;N = 2.621(3) Å), bent ( ∢NHN = 55(2)°) and asymmetric ( r NH = 1.06(2) Å). In deprotonated 3,4-furandicarboxylic acid (FDCA), the OHO −1 hydrogen bridge is also asymmetric R Oţdot;O = 2.468(3) Å, ∢ OHO = 167(3)°, r OH = 1.04(3) Å). These features are reflected in the infrared spectrum. Thus, the v NH absorption band which is usually located at about 500 cm −1 is shifted markedly towards higher frequencies with the appearance of a broad band at about 2000 cm −1. The v OH combination band at about 1000 cm −1 for the OHO − bridge is analogous to that determined for potassium hydrogen 3,4-furandicarboxylate by S. Jaulmes, Acta Crystallogr., Sect B, 34 (1978) 116.

Measurement of the Near-Infrared Spectra of H2O-SiOH-Bearing Siliceous Materials at High Pressures

Techniques for measuring OH-combination bands of water and other OH-group bearing solid or liquid materials in the near-infrared (6000 to 4000 cm−1) at high pressures by means of a modified diamond anvil cell, adapted to a single beam micro-spectrometer, have been developed and applied to opals, i.e., minerals in the system SiO2-H2O containing relatively high amounts of water and SiOH. Liquid embedding, using the gasket technique and poly-fluoro-carbon oils as embedding liquids, which provide a hydrostatic pressure environment at least up to 50 kbar, is applied for solid materials. The high pressure near-infrared spectra of gel-like, spherulitic opal-AG show a strong relative decrease of the high energy components of the complex (v1 + v2)H2O-band system at around 5200 cm−1 in favor of the low energy components of this band system. This is tentatively interpreted as due to an increase of fully hydrogen bonded water at the expense of water in which only one OH-group is H-bonded. The corresponding effect in opal-AN with a glass-like continuous SiO4/2-tetrahedral network is much smaller.

Association and the assignment of the OH overtones in hydrogen bonded alcohols

The long-standing problem of the assignment of the first overtone of the OH stretching vibration of hydrogen bonded alcohols is examined for the cases of methanol, ethanol, and tertiary butanol. The spectra of the related deuterated alcohols were measured and isotopic isolation experiments were carried out at temperatures ranging from 25° to − 190°C. Dilute solutions were studied as well as the pure liquids. For the latter the second overtones were also measured. The first OH overtones, although overlapped by CH + OH combination bands were definitely identified and the anharmonicity constants were determined. They show a moderate but appreciable increase with respect to free OH stretching vibrations. Bands due to simultaneous excitation or coupling of two contiguous OH groups bound together by hydrogen bonds are also present.