Mid-infrared Reflectance Spectra Research Articles

Mid-IR spectral properties of different surfaces of silicate mixtures before and after excimer laser irradiation

The behaviour of the Christiansen feature (CF) and the Reststrahlen bands (RBs) in mid-infrared (IR) reflectance spectra on various silicate mixtures as pressed pellets and powders was investigated in high-vacuum. In addition, the influence of micrometeorite bombardment simulated with an excimer laser was studied. The mixtures cover a wide range of possible hermean surface compositions and include the minerals olivine, pyroxene (enstatite and diopside), and plagioclase.For the laser experiments, silicates were pressed into pellets and examined by reflectance infrared spectroscopy to identify changes caused by micrometeorite impacts as one tracer of space weathering on airless bodies such as Mercury. For comparison, measurements were also performed on loose powders with the same compositions under the same conditions. As a result, it can be shown that the RBs of olivine are rather affected by laser irradiation although SEM investigations show the destruction mainly of plagioclase, indicating that the RBs of plagioclase are masked by the “stronger” RBs of olivine and pyroxene. Furthermore, we found that the CF in mixtures with a plagioclase content of >50% does not shift significantly towards the CF of pyroxene or olivine. On the other hand, the CF of a mixture containing 50% olivine shifts significantly to shorter wavelengths when pyroxene or plagioclase are present in the mixture. Therefore, care is required when interpreting remote sensing data using the CF alone. We also found that the CF shifts to longer wavelengths in rough (regolithic) samples.Our work demonstrates large dependencies of the CF and the RBs positions on the composition of the silicates as well as on the nature of the surface, which is important for space missions, e.g., data acquired by the MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS) experiment onboard BepiColombo.

Visible to Mid‐Infrared Optical Constants of Orthopyroxenes

AbstractRadiative transfer models of remotely acquired infrared spectra result in quantitative identification of minerals on planetary surfaces. Optical constants, or the real (n) and imaginary (k) indices of refraction are necessary inputs in such models. Pyroxenes are ubiquitous on the surfaces of terrestrial bodies within our solar system and can be readily used as thermo‐barometers to interpret magmatic histories. However, optical constants for intermediate pyroxene compositions are undetermined. Here, we have determined the optical constants of two natural orthopyroxenes both in the visible/near‐infrared (VNIR) and mid‐infrared (MIR) regions. VNIR reflectance spectra were measured using powdered samples and modeled using a combination of Hapke theory and Kramers‐Kronig analysis. MIR reflectance spectra were measured on oriented single crystal samples with non‐normal incidence and modeled using Lorentz‐Lorenz dispersion theory. The optical constants derived here are available to the scientific community at https://doi.org/10.5281/zenodo.4758045 to be used in the interpretation of remote sensing data.

Mid-infrared spectroscopy of crystalline plagioclase feldspar samples with various Al,Si order and implications for remote sensing of Mercury and other terrestrial Solar System objects

We analyzed plagioclase feldspar samples that were well-characterized in terms of chemical composition as well as degree of Al,Si order in mid-infrared reflection spectra between 7 μm and 14 μm (1429 cm−1 and 714 cm−1). The chemical compositions were derived with an electron microprobe analyzer. To determine the degree of Al,Si order, powder X-ray diffraction methods were applied. For the interpretation of the infrared spectra, we used the wavelength of the Christiansen feature (CF) and the autocorrelation function for a specific wavelength region. The CF shifts from around 7.72 μm (1296 cm−1) in Na-richest samples to 8.10 μm (1234 cm−1) in the Ca-richest sample. Combining the CF position and the autocorrelation-derived value allowed to determine the degree of Al,Si order of the samples based on reflection spectra. The wavelength of the Transparency feature (TF) in the finest analyzed grain size fraction also depends on the chemical composition and the degree of Al,Si order. Our results are helpful for the interpretation of data returned by the MERTIS experiment onboard BepiColombo. The data help to distinguish between space weathering, shock effects, and ordering effects in plagioclase samples.

Quasiphonon polaritons

Mid-infrared reflection spectra of c- and m-plane bulk AlN show a reststrahlen band related to the formation of phonon polaritons. However, it is worth noting that there are additional hump- and spike-shaped peaks in the spectra, which cannot be explained by the phonon-polaritons model applicable to optically isotropic crystals. Here, considering the existence of quasiphonons in wurtzite crystals, we suppose that the extra peaks result from the generation of quasiphonon polaritons (QPPs) induced by the coupling between photon and quasi-transverse optical phonon. On the basis of this point, a QPPs model applicable to optically anisotropic wurtzite crystals is developed, which successfully explains the reststrahlen band of bulk AlN. Besides, on the ground of our model, a series of reststrahlen band of bulk AlN under various configurations is also predicted and presented.

Mid-infrared reflectance spectroscopy of carbonaceous chondrites and Calcium–Aluminum-rich inclusions

We obtained mid-infrared reflectance spectra of powdered size fractions (0–25 ​μm, 25–63 ​μm, 63–125 ​μm and 125–250 ​μm) of 5 carbonaceous chondrites HaH 280 (CK4), Allende (CV3), NWA 10574 (CM2) and Murchison (CM2), and C2 (ungrouped) Tagish Lake. In addition, in-situ micro-FTIR reflectance spectra of CAIs in Allende, Ornans and Vigarano have been made.These spectra are part of a database for the comparison with remote sensing data of asteroids and planetary bodies, but also for laboratory studies of meteorites.Carbonaceous chondrites HaH 280 (CK4), Allende (CV3) and NWA 10574 (CM2) show mid-IR spectra with Reststrahlen bands (RB) dominated by forsterite and pyroxene features. The transparency features (TF) are at 12.1 ​μm–12.9 ​μm and the Christiansen features (CF) at 8.5 ​μm–9.3 ​μm.Murchison (CM2) and ungrouped Tagish Lake (C2) show mainly phyllosilicate features in their spectra. The CF is between 8.6 ​μm and 9.0 ​μm.Micro-FTIR spectra of CAIs from Allende, Vigarano, and Ornans have spinel features between 14.1 ​μm and 14.3 ​μm. In addition, melilite was identified in the Vigarano and Ornans samples with characteristic features at 11.7 ​μm and 12.4 ​μm.Nepheline and sodalite features have been identified around 14 ​μm in the Allende CAI as alteration phases resulting from thermal metamorphism.A band shift in spinel with increasing Fe content from thermal metamorphism could be spectral indicator for parent body metamorphism.A comparison with other bulk samples from the same meteorites/type shows high similarity.Comparison of the finest size fractions modelled in emissivity with remote sensing data of asteroids shows some similarity between a linear mixture of Allende and Murchison and the spectra of asteroid 253 Mathilde. However, the main 10 ​μm plateau is clearly shifted by 0.5 ​μm between asteroid and meteorite spectra. Also, the general band shapes are different. Differences between asteroidal environment (e.g. fairy castle structure) and laboratory make direct comparisons difficult.

Linking mineralogy and spectroscopy of highly aqueously altered CM and CI carbonaceous chondrites in preparation for primitive asteroid sample return

AbstractThe highly hydrated, petrologic type 1 CM and CI carbonaceous chondrites likely derived from primitive, water‐rich asteroids, two of which are the targets for JAXA's Hayabusa2 and NASA's OSIRIS‐REx missions. We have collected visible and near‐infrared (VNIR) and mid infrared (MIR) reflectance spectra from well‐characterized CM1/2, CM1, and CI1 chondrites and identified trends related to their mineralogy and degree of secondary processing. The spectral slope between 0.65 and 1.05 μm decreases with increasing total phyllosilicate abundance and increasing magnetite abundance, both of which are associated with more extensive aqueous alteration. Furthermore, features at ~3 μm shift from centers near 2.80 μm in the intermediately altered CM1/2 chondrites to near 2.73 μm in the highly altered CM1 chondrites. The Christiansen features (CF) and the transparency features shift to shorter wavelengths as the phyllosilicate composition of the meteorites becomes more Mg‐rich, which occurs as aqueous alteration proceeds. Spectra also show a feature near 6 μm, which is related to the presence of phyllosilicates, but is not a reliable parameter for estimating the degree of aqueous alteration. The observed trends can be used to estimate the surface mineralogy and the degree of aqueous alteration in remote observations of asteroids. For example, (1) Ceres has a sharp feature near 2.72 μm, which is similar in both position and shape to the same feature in the spectra of the highly altered CM1 MIL 05137, suggesting abundant Mg‐rich phyllosilicates on the surface. Notably, both OSIRIS‐REx and Hayabusa2 have onboard instruments which cover the VNIR and MIR wavelength ranges, so the results presented here will help in corroborating initial results from Bennu and Ryugu.

Near‐ and mid‐infrared reflectance spectra of hydrated oxychlorine salts with implications for Mars

AbstractThe presence and distribution of oxychlorine salts (e.g., chlorates and perchlorates) on Mars have implications for the stability of water, most notably, that they lower the freezing temperature. To date, elemental chlorine has been measured by all lander missions, with the perchlorate ion identified at both the Phoenix and Curiosity landing sites, but detection by near‐infrared (NIR) and mid‐infrared (MIR) remote sensing has been limited to deposits of anhydrous chlorides. Given that oxychlorine salts can form numerous hydrated phases, we have measured their NIR and MIR reflectance spectra from 1 to 25 µm for comparison to data collected from orbiting spectrometers. Anhydrous oxychlorine salts show almost no features in the NIR, except for small bands of residual adsorbed water. However, hydrated oxychlorine salts show numerous features due to water in the NIR, specifically at ~1.4 and ~1.9 µm. Increasing the hydration state increases the depth and width of the water bands. All oxychlorine salts exhibit an additional feature at ~2.2 µm due to a Cl‐O combination or overtone feature, although it is less prominent in the hydrated perchlorate salts, likely overwhelmed by the ClO4‐H2O feature at 2.14 µm. All oxychlorine salts show features in the MIR due to the fundamental vibrations of Cl‐O longward of ~8 µm. The NIR spectral features of hydrated oxychlorine salts are similar to other hydrated salts, especially hydrated sulfates; thus, identification from orbit may be ambiguous. However by utilizing the NIR and MIR laboratory data presented here for comparison, oxychlorine salts may be detectable by orbiting spectrometers.

Serpentinization, iron oxidation, and aqueous conditions in an ophiolite: Implications for hydrogen production and habitability on Mars

Molecular hydrogen produced through iron oxidation during formation of serpentine and magnetite can sustain terrestrial subsurface ecosystems. The Fe3+ in serpentine partitions into octahedral and tetrahedral sites differently as serpentinization proceeds, and tetrahedral Fe3+ is present toward the end of serpentinization. We map Fe oxidation states in a serpentinite to determine the degree to which serpentinization progressed and where hydrogen production has been maximized to assess habitability at an abandoned chrysotile mine in Norbestos, Quebec, in association with the Canadian Space Agency's Mars Methane Analogue Mission. We also analyzed stable isotopes of carbon and oxygen in carbonates to constrain the conditions of water–rock interaction during serpentinization. Iron oxidation and coordination was determined through field imaging of rock walls with a visible hyperspectral imager (420–720 nm), and samples collected from imaged rocks and elsewhere in the mine were imaged in the laboratory (420–1100 nm). Sample chemistry, mineralogy, and oxidation state were determined with laboratory measurements of visible through mid-infrared reflectance spectra, major element chemistry, mineralogy, and Mössbauer spectroscopy. Mapping with hyperspectral imaging of outcrops and hand samples shows that tetrahedral Fe3+ is common in serpentinites at this site, and results are confirmed through other measurements. Major element chemistry and mineralogy are consistent with serpentine plus minor carbonate. Carbonate samples show an exceptional range in δ13C (−13.14 to +16.12‰ VPDB) and δ18O (−15.48 to −3.20‰ VPDB) that vary with location in the mine. Carbonates south of a shear zone (δ13C more positive) likely formed during periods of serpentinization in a carbon-limited reservoir closed to carbon addition but open to methane escape. Carbonates in a shear zone (δ13C more negative) probably formed later at low temperatures through CO2-metasomatism or atmospheric weathering, and isotopic trends are consistent with kinetic fractionation. The extensive presence of tetrahedral Fe3+ in serpentine shows the system liberally produced H2 while the isotope systematics have implications for preservation of indicators of the aqueous conditions that formed serpentinites on Mars and their habitability.

Experimental investigation of radiative thermal rectifier using vanadium dioxide

Vanadium dioxide (VO2) exhibits a phase-change behavior from the insulating state to the metallic state around 340 K. By using this effect, we experimentally demonstrate a radiative thermal rectifier in the far-field regime with a thin film VO2 deposited on the silicon wafer. A rectification contrast ratio as large as two is accurately obtained by utilizing a one-dimensional steady-state heat flux measurement system. We develop a theoretical model of the thermal rectifier with optical responses of the materials retrieved from the measured mid-infrared reflection spectra, which is cross-checked with experimentally measured heat flux. Furthermore, we tune the operating temperatures by doping the VO2 film with tungsten (W). These results open up prospects in the fields of thermal management and thermal information processing.

Measurement and modelling of the ingestion bioaccessibility of polyaromatic hydrocarbons in soils

Total and human ingestion bioaccessible polycyclic aromatic hydrocarbon fractions of individual polycyclic aromatic hydrocarbons were determined (representative of a combination of the saliva, gastric and upper intestine compartments) on 26 soil samples from 3 gasworks sites and from a domestic garden. A Random Forest model using the Infra-red spectra of the soils and the PAH properties successfully predicted the bioaccessibility of PAHs in the soils. The Near Infra-red and Mid Infra-red diffuse reflection spectra of the soils were subjected to a mixture resolution algorithm. Comparison with spectra of known minerals tentatively identified carbonate, silica, clay and iron oxide components in the Mid Infra-red spectra. Multiple linear regression analysis suggested that three Mid Infra-red components were associated with the organic carbon. Principal Component Analysis of polycyclic aromatic hydrocarbon properties identified three components associated with the hydrophobicity, the aliphatic nature and the vapour phase partition coefficient of the polycyclic aromatic hydrocarbons.

Aqueous alteration on asteroids: Linking the mineralogy and spectroscopy of CM and CI chondrites

CM/CI meteorites range in degree of aqueous alteration suggesting differences in initially accreted materials including water ice and possible spatial heterogeneities within their parent bodies. As alteration progresses, the total abundance and magnesium content of phyllosilicates increases. In this paper we present the results of a coordinated spectral–mineralogical study of a well-characterized suite of CM/CI meteorites that range from 60 to 90% alteration. By acquiring spectra the same meteorite powders as Howard et al. (Howard, K.T., Benedix, G.K., Bland, P.A., Cressey, G. [2009]. Geochim. Cosmochim. Acta 73, 4576–4589; Howard, K.T., Benedix, G.K., Bland, P.A., Cressey, G. [2011]. Geochim. Cosmochim. Acta 75, 2735–2751) and Bland et al. (Bland, P.A., Cressey, G., Menzies, O.N. [2004]. Meteorit. Planet. Sci. 39(1), 3–16), we are able for the first time to directly correlate mineralogy with features in reflectance spectra. At visible/near-infrared wavelength, the presence of a 0.7-μm charge transfer band is indicative of aqueous alteration. However, not all altered CM/CI meteorites exhibit this feature; thus the lack of a 0.7μm absorption band in asteroids does not necessarily signify a lack of aqueous alteration. Furthermore, the position and depth of 0.7-μm charge transfer band shows no correlation with the mineralogical changes associated with aqueous alteration. Similarly, the near-infrared slope, which is not directly related to the mineralogic progression associated with increasing alteration, is not unambiguously related to degree of alteration in the CM/CI meteorites studied. However, the mid-infrared reflectance spectra of CM/CI meteorites contain a broad absorption feature in the 10–13-μm region, which is a convolution of vibrational features due to Mg-rich phyllosilicates and unaltered olivine. The overall feature continuously changes with total phyllosilicate abundance from a shorter wavenumber/longer wavelength peak (815cm−1, 12.3-μm) for less altered meteorites to a longer wavenumber/shorter wavelength (875cm−1, 11.4-μm) peak in the highly altered meteorites, with roughly equal spectral contributions producing a doublet in intermediately altered meteorites, Using the results from the mid-infrared analyses of meteorite spectra, it is possible to estimate the degree of alteration on dark primitive asteroids. We find Asteroid (24) Themis to have a 1000–700cm−1 (10–13-μm) peak at longer wavelengths suggesting Themis has a complex surface mineralogy with approximately 70vol.% phyllosilicates and 25vol.% anhydrous silicates.

Retrieval of leaf water content spanning the visible to thermal infrared spectra

The objective of this study was to investigate the entire spectra (from visible to the thermal infrared; 0.390–14.0μm) to retrieve leaf water content in a consistent manner. Narrow-band spectral indices (calculated from all possible two band combinations) and a partial least square regression (PLSR) were used to assess the strength of each spectral region. The coefficient of determination (R2) and root mean square error (RMSE) were used to report the prediction accuracy of spectral indices and PLSR models. In the visible-near infrared and shortwave infrared (VNIR–SWIR), the most accurate spectral index yielded R2 of 0.89 and RMSE of 7.60%, whereas in the mid infrared (MIR) the highest R2 was 0.93 and RMSE of 5.97%. Leaf water content was poorly predicted using two-band indices developed from the thermal infrared (R2=0.33). The most accurate PLSR model resulted from MIR reflectance spectra (R2=0.96, RMSE=4.74% and RMSE cross validation RMSECV=6.17%) followed by VNIR–SWIR reflectance spectra (R2=0.91, RMSE=6.90% and RMSECV=7.32%). Using thermal infrared (TIR) spectra, the PLSR model yielded a moderate retrieval accuracy (R2=0.67, RMSE=13.27% and RMSECV=16.39%). This study demonstrated that the mid infrared (MIR) and shortwave infrared (SWIR) domains were the most sensitive spectral region for the retrieval of leaf water content.

The mineral chemistry, near-infrared, and mid-infrared reflectance spectroscopy of phengite from the Olympic Dam IOCG deposit, South Australia

Phengite is the main potassic dioctahedral mica identified at the Olympic Dam iron oxide–copper–gold (IOCG) deposit, South Australia, where its mineral chemistry is quite variable. These differences can be explained by contrasting degrees of hydrothermal alteration. In the heavily-sericitized, ore-bearing rocks, the phengites display a lower-Si content, a higher-Al content, and a lower Mg-number than the phengites from the weakly-sericitized alteration halo that surrounds the deposit. Variations are also observed in the near- and mid-infrared reflectance spectra collected from phengite-bearing rocks. In the near-infrared, high-Al phengite produces a spectral absorption feature at 2.206μm, and this feature is displaced to 2.213μm for low-Al phengite. In the mid-infrared, high-Al phengite produces a strong reflectance peak at 9.59μm, whereas this peak is observed at 9.57μm in the spectra from low-Al phengite. Additional peaks were also identified at 10.98, 12.22, and 13.33μm. These were most intense in the spectra from high-Al phengite. A drill core profile was produced using the results of the spectral analysis that shows the change in phengite mineral chemistry and phengite abundance as a function of depth. In general, near- and mid-infrared reflectance spectroscopy can be used to characterize the aluminum content of potassic dioctahedral micas like phengite, and this information can be used to infer the degree of sericitic alteration that has occurred as a result of hydrothermal fluid flow.

Prediction of the CEC to clay ratio using mid-infrared spectroscopy

The ratio of cation exchange capacity to clay (CCR) has been used as an index of clay mineralogy in subsoils low in organic matter in place of the standard X-ray diffraction measurement. Laboratory determination of this ratio is time-consuming and expensive and involves two analyses. In this paper, the CCR has been successfully predicted from mid-infrared diffuse reflectance spectra using partial least-squares regression (PLSR) with a square-root transformation of the CCR values (R2 = 0.860; root mean squared error of prediction = 0.089; relative per cent deviation = 2.660 for an independent validation set). The most important wavelengths used in the PLSR calibration were identified. The prediction of CCR using mid-infrared spectroscopy provides a cheaper and faster alternative to laboratory determination.

Ultra-broadband infrared pump-probe spectroscopy using synchrotron radiation and a tuneable pump

Synchrotron infrared sources have become popular mainly because of their excellent broadband brilliance, which enables spectroscopically resolved spatial-mapping of stationary objects at the diffraction limit. In this article we focus on an often-neglected further advantage of such sources - their unique time-structure - to bring such broadband spectroscopy to the time domain, for studying dynamic phenomenon down to the 100 ps limit. We describe the ultra-broadband (12.5 to 1.1 μm) Fourier transform pump-probe setup, for condensed matter transmission- and reflection-spectroscopy, installed at the X01DC infrared beam-line of the Swiss Light Source (SLS). The optical pump consists of a widely tuneable 100 ps 1 kHz laser system, covering 94% of the 16 to 1.1 μm range. A thorough description of the system is given, including (i) the vector-modulator providing purely electronic tuning of the pump-probe overlap up to 1 ms with sub-ps time resolution, (ii) the 500 MHz data acquisition system interfaced with the experimental physics and industrial control system (EPICS) based SLS control system for consecutive pulse sampling, and (iii) the step-scan time-slice Fourier transform scheme for simultaneous recording of the dual-channel pumped, un-pumped, and difference spectra. The typical signal/noise ratio of a single interferogram in a 100 ps time slice is 300 (measured during one single 140 s TopUp period). This signal/noise ratio is comparable to that of existing gated Globar pump-probe Fourier transform spectroscopy, but brings up to four orders of magnitude better time resolution. To showcase the utility of broadband pump-probe spectroscopy, we investigate a Ge-on-Si material system similar to that in which optically pumped direct-gap lasing was recently reported. We show that the mid-infrared reflection-spectra can be used to determine the optically injected carrier density, while the mid- and near-infrared transmission-spectra can be used to separate the strong pump-induced absorption and inversion processes present at the direct-gap energy.

Mid-infrared reflectance spectra and optical constants of six iron oxide/oxyhydroxide phases

We have determined the real and imaginary indices of refraction ( n and k) for six iron oxide/oxyhydroxide phases—magnetite, maghemite, goethite, lepidocrocite, akaganéite, and ferrihydrite. A single crystal of magnetite was used to derive bulk n and k values from 100–2000 cm −1 (5–100 μm). Synthetic nanocrystalline samples of maghemite, goethite, lepidocrocite, akaganéite, and ferrihydrite were pressed into compact pellets used to determine bulk n and k values from 100–1200 cm −1 (8.33–100 μm). All values of n and k (the optical constants) were determined from specular reflectance spectra acquired at 2 cm −1 spectral sampling using classical Lorentz–Lorenz dispersion theory. In this paper, we present the optical constants of all six minerals and the oscillator parameters with which they were modeled. Use of these optical constants could aid in radiative transfer models of terrestrial dust as well as Mars, the Moon, and airless bodies in the Solar System.

Regression rules as a tool for predicting soil properties from infrared reflectance spectroscopy

Pedometrics is the use of quantitative methods for the study of soil distribution and genesis and as a sustainable resource. A common research area in pedometrics and chemometrics is the calibration and prediction of soil properties from diffuse infrared reflectance spectra. The most common method is using partial least-squares regression (PLS). In this paper we present an alternative method in the form of regression rules. The regression-rules model consists of a set of rules, in which each rule is a linear model of the predictors. It is also analogous to piecewise linear functions. The accuracy is tested for prediction of soil properties from their mid-infrared (2500–25000 nm) diffuse reflectance spectra. In addition, we also tested it with the Chimiométrie 2006 challenge data which used the near-infrared spectra to predict soil properties. The results showed that, in comparison with PLS with spectra pretreatment and another data-mining technique, the regression-rules model provides greater accuracy, is simpler and more parsimonious, produces comprehensible equations, provides an optimal variable selection, and respects the upper and lower limits of the data.

ParLeS: Software for chemometric analysis of spectroscopic data

This paper describes the development and implementation of ParLeS, chemometrics software for multivariate modelling and prediction. ParLeS is shareware that was developed for teaching and research in chemometrics and spectroscopy; however, it may also be used with other types of multivariate data. ParLeS may be used to transform, preprocess and pretreat spectra using various algorithms; it may be used to implement principal components analysis (PCA); partial least squares regression (PLSR) with leave-n-out cross validation; and bootstrap aggregation-PLSR (bagging-PLSR). ParLeS facilitates the implementation of a large number of preprocessing techniques as well as bagging-PLSR, which can improve the robustness and accuracy of PLSR models. Other unique features of ParLeS include the provision of a number of assessment statistics and graphical output as well as a user-friendly interface and functionality. The implementation of ParLeS is demonstrated by modelling soil mid infrared (mid-IR) diffuse reflectance spectra for predictions of soil organic carbon.

Infrared reflectance of single-crystal jarandolite, CaB3O4(OH)3

AbstractPolarized far- and mid-infrared reflectance spectra were measured at room temperature for the new mineral species jarandolite, CaB3O4(OH)3, for the two principal directions. Thirty three vibration modes for and 32 for were observed and analysed numerically. Symmetry analysis predicts 41 and 40 vibration modes that include lattice and O–H modes. Mode assignment was made based on the structure of jarandolite. The values of the mode frequencies (ωTO), the damping factors (γ) and the oscillator strength (S) of each oscillator were obtained by fitting to a Lorentz model.

Multivariate regression models for the simultaneous quantitative analysis of calcium and magnesium carbonates and magnesium oxide through drifts data

In the present work multivariate regression models were developed for the quantitative analysis of ternary systems using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) to determine the concentration in weight of calcium carbonate, magnesium carbonate and magnesium oxide. Nineteen spectra of standard samples previously defined in ternary diagram by mixture design were prepared and mid-infrared diffuse reflectance spectra were recorded. The partial least squares (PLS) regression method was applied to the model. The spectra set was preprocessed by either mean-centered and variance-scaled (model 2) or mean-centered only (model 1). The results based on the prediction performance of the external validation set expressed by RMSEP (root mean square error of prediction) demonstrated that it is possible to develop good models to simultaneously determine calcium carbonate, magnesium carbonate and magnesium oxide content in powdered samples that can be used in the study of the thermal decomposition of dolomite rocks.