Quantitative Infrared Spectroscopy Research Articles

Improving the performance of artificial neural networks trained on synthetic data in gas spectroscopy – a study on two sensing approaches

Abstract Artificial neural networks (ANNs) are used in quantitative infrared gas spectroscopy to predict concentrations on multi-component absorption spectra. Training of ANNs requires vast amounts of labelled training data which may be elaborate and time consuming to obtain. Additional data can be gained by the utilization of synthetically generated spectra, but at the cost of systematic deviations to measured data. Here, we present two approaches to train ANNs with a combination of comparatively small, measured data sets and synthetically generated data. For the first approach a neural network is trained hybridly with synthetically generated infrared absorption spectra of mixtures of N2O and CO and measured zero-gas spectra, taken with a mid-infrared dual comb spectrometer. This improves the mean absolute error (MAE) of the network predictions from 0.46 to 0.01 ppmV and 0.24 to 0.01 ppmV for the concentration predictions of N2O and CO respectively for zero-gas measurements which was previously observed for training with purely synthetic data. At the same time a similar performance on spectra from gas mixtures of 0–100 ppmV N2O and 0 to 60 ppmV CO was achieved. For the second approach an ANN pre-trained on synthetic infrared spectra of mixtures of acetone and ethanol is retrained on a small dataset consisting of 26 spectra taken with a mid-infrared photoacoustic spectrometer. In this case the MAE for the concentration predictions of ethanol and acetone are improved by 45 % and 20 % in comparison to purely synthetic training. This shows the capability of using synthetically generated data to train ANNs in combination with small amounts of measured data to further improve neural networks for gas sensing and the transferability between different sensing approaches.

Multicomponent Alkane IR Measurement System Based on Dynamic Adaptive Moving Window PLS

Infrared (IR) spectroscopy for multicomponent alkane measurement has shown excellent potentials in unconventional oil and gas exploration. However, the cross-sensitivity of alkane IR absorption and the complexity of unconventional oil and gas components place extreme demands on quantitative IR spectroscopy models. To cope with these problems, an adaptive moving partial least square (AMW-PLS) modeling method for the quantitative analysis of IR spectra is proposed in this paper. Based on the designed moving control function and dual endpoint independent moving strategy, AMW-PLS can quickly determine the optimal local modeling interval location and width by tracking the accuracy of the calibration model dynamically. By transposing the proposed AMW-PLS into the designed infrared gas logging system in this paper, 88 samples of 2 different mixture types were tested and compared with the other three typical analytical methods. The experimental results show that AMW-PLS can dynamically track the IR characteristic shifts caused by the changes in the gas mixture component complexity and concentration distribution, and thus achieves the best performance. The instrument achieved an average relative error of 3.3651% for five alkane substances in three standard industrial gas mixtures under strong interference, which provides new technical support for early discovery of oil and gas reservoirs.

Research on quantitative analysis method of PLS hydrocarbon gas infrared spectroscopy based on net signal analysis and density peak clustering

As an important part of integrated logging, gas logging can directly measure the content and composition of hydrocarbon gas in the formation, and plays an irreplaceable role in the discovery and evaluation of oil and gas while drilling and real-time drilling parameter monitoring. Traditional gas logging uses chromatographs to analyze downhole gas. However, due to its long measurement period, many additional instruments, long lines, strict environmental requirements, complex operations, and easy distortion, it has been difficult to meet the requirements of current exploration work in complex oil and gas reservoirs. With the advantages of fast analysis speed, rich detection parameters, short delay time, good stability, and strong anti-pollution ability, the quantitative infrared spectroscopy technique can replace chromatography for hydrocarbon gas measurement. However, when it is used for the quantitative analysis of downhole hydrocarbon gases, a large span of absorption spectra and overlapping characteristic peaks can occur due to the complexity of gas components, making quantitative identification more difficult. To address the above problems, this paper proposes a method of net signal analysis (NAS) combined with density peak clustering (DPCA) for local PLS modeling. The method first obtains the net signals of the unknown and correction samples by the net signal analysis and then clusters the net signals by DPCA to select the corresponding local correction for PLS modeling prediction. The experimental results show that the NAS-DPCA-PLS method proposed in this paper is significantly better than the traditional method in the quantitative analysis of hydrocarbon mixed gas components, and the average accuracy of mixed component prediction reaches more than 98%, which effectively improves the detection accuracy of quantitative analysis of mixed component infrared spectroscopy and provides important theoretical support for the use of infrared spectroscopy in gas logging.

Understanding the Stability and Recrystallization Behavior of Amorphous Zinc Phosphate

Zinc phosphate, an important pigment in phosphate conversion coatings, forms protective films on rubbing surfaces. We have simulated the underlying reactions under shear by ball-milling zinc phosphate and monitored the reaction of hopeite (Zn3(PO4)2·4H2O) and the retarded recrystallization of the amorphous reaction product by powder X-ray diffraction (PXRD) and quantitative infrared (IR) spectroscopy. Abrasion of stainless steel was simulated by addition of pure 57Fe. The results provide insight into the chemistry of phosphate conversion coatings or during battery cycling of metal phosphates and give theoretical guidance for the preparation of amorphous phosphates. Thermal analysis revealed that the release of structural water is a key step during the reaction of hopeite under shear to ball-milled amorphous zinc phosphate. The back-reaction and associated recrystallization kinetics of amorphous zinc phosphate show a classical Langmuir behavior. Fe impurities inhibit the recrystallization of ball-milled amorphous zinc phosphate strongly. 57Fe Mössbauer spectroscopy and PXRD revealed that Fe is oxidized to Fe2+ and Fe3+ during ball-milling and incorporated locally at the tetrahedral and octahedral sites of the structure. Ball-milled amorphous zinc phosphate is metastable as γ-Zn3–xFex(PO4)2. EPR studies showed the incorporation of Fe3+ to be coupled with the formation of Zn2+ vacancies. The Fe3+ defect sites bind water because of their higher Pearson hardness (compared to Fe2+ and Zn2+), thereby reducing water mobility and inhibiting further reactions like the recrystallization to hopeite. Our findings reveal the amorphization mechanism of Zn3(PO4)2·4H2O in stainless steel ball mills at the atomic scale and highlight how the reactivity of amorphous products is affected by impurities associated with the processing method.

Quantitative infrared spectroscopy of environmentally sensitive and rough materials.

Fourier transform infrared (FTIR) spectroscopy is a widely used characterization technique for studying chemical compositions and light-matter interactions in the infrared range. However, it remains challenging to use conventional FTIR equipment to characterize materials that are environmentally sensitive and/or have rough surfaces due to their dynamic response to external stimuli (e.g., humidity) and light scattering from the sample surface. Here, we describe an approach enabling quantitative infrared spectroscopy measurements of these challenging samples, including transmittance, reflectance, and emissivity. We designed and 3D-printed a miniaturized environmental chamber that can be directly inserted into the sample holder of a conventional integrating sphere to perform total transmission and reflection measurements in controlled environments. Moreover, a calibration method was developed to exclude light scattering from rough surfaces of the sample and the distortion created by infrared windows. To illustrate the potential application of this method, we have performed quantitative infrared measurements, both specular and diffusive, on a sapphire standard reference with a specular surface, as well as a textile sample that has a rough surface and is dynamically responsive to changes in humidity. The calibrated results measured with the equipped chamber match those measured without the IR windows, demonstrating the viability of our environmental chamber and the proposed calibration method. This quantitative infrared spectroscopy measurement technique may help advance fields such as metasurfaces and adaptive textiles, where samples are often rough, dynamically responsive, and/or environmentally sensitive.

Comparative analysis of the mineralogical composition of the natural chalk deposits of Ukraine

Using the methods of quantitative infrared spectroscopy and the X-ray phase analysis it is analyzed sedimentary chalk of five different domestic deposits compared to chemically precipitated and import calcite. Presence of calcite, dolomitic, aragonite in their composition is fixed. It is given a quantification of the content (for half-width within the 562-1047 cm -1 for imported calcite, 440-703 cm -1 for the national sedimentary chalk and 530 cm -1 for the chemically-deposited chalk, and the ratio of the intensities of characteristic absorption bands of carbonate anion respectively 10,38-45,33; 26,80-47,33 and 35,15) of the main structure minerals of these kinds of carbonates. It is received the data confirmation of IR spectroscopy by X-ray phase analysis of the main types of natural chalk and it is obtained quantitative structure of main content (calcite, dolomite) and extrinsic (quartz, kaolinite, iron hydroxide) minerals. According to the parameters of characteristic absorption bands in the range of 712-876 and 2512-2522 cm -1 modification of calcium carbonate - calcite – it is conducted differentiation of quantitative indicators, depending on the origin of the material. It is noted greater uniformity of mineralogical composition of import carbonates. These data allow formulate reasonable frameworks of use of domestic sedimentary chalk and assess its competitiveness compared with chemically-deposited chalk and Turkish calcite.

(Invited) Organization in Molecular Layers Covalently Attached to Oxide-Free Silicon Surfaces

The grafting of molecular layers on oxide-free silicon surfaces is an approach widely used for preventing surface oxidation and/or for the construction of functional surfaces with specific properties. In particular, this strategy is often used for the passivation/functionalization of porous silicon. If the large specific surface area makes porous silicon especially interesting for applications, the porous structure makes delicate and sometimes difficult the use of surface techniques for the characterization of surface properties. The molecular organization within the layer on the pore’s wall remains an open issue despite the fact that this aspect is of prime importance for the final properties of the system. In the present work, we have investigated the properties of organic monolayers grafted onto model Si(111) surfaces in order to gain generic knowledge on the molecular physico-chemical processes governing the molecular organization, which should also apply to more complex, real systems such as porous silicon. The model system consisting of mixed alkyl/carboxy-alkyl layers grafted on atomically flat Si(111) surfaces has been carefully studied using Atomic Force Microscopy (AFM) in dynamic mode, and quantitative Fourier-Transform InfraRed (FTIR) spectroscopy. The mixed layers were produced by direct, UV-activated reaction of decene/undecylenic acid mixtures on hydrogenated silicon surfaces. Different concentrations of undecylenic acid in decene (from 0.01 to 100% by vol) have been investigated in order to change the composition of the grafted layer. The composition of the mixed layers has been determined by quantitative infrared spectroscopy. For concentrated (above 20%) acid solutions, the fraction of acid molecules in the grafted layer is found to be larger than in solution, in agreement with previous reports [1]. Surprisingly, this trend is much amplified at lower acid concentration, with an acid content of ~30% weakly dependent on the grafting solution composition for acid contents in the range 0.1% to 10%. The surfaces were characterized by AFM imaging in non-contact mode. When the acid fraction in the monolayer exceeds ~40%, phase images, which are sensitive to tip-surface interactions, are featureless, suggesting a uniform spreading of acid chains. A phase separation is found at large scale (a few µm-size domains) on molecular layers obtained from grafting solutions with an acid content varying from 0.1% to 10%. This chemical contrast is consistent with acid-rich domains. However, the domain coverage turns out to be much too low in order to account for the total acid content of the molecular layer, as stated by FTIR analysis. For molecular layers obtained from grafting solutions with a very low acid content (0.01%), nanometric (typical size below 10 nm) domains are also revealed. In this case, the acid amount derived from the domain coverage is in agreement with the acid content of the layer determined by FTIR spectroscopy. All these observations reveal that the mixed alkyl/carboxy-alkyl layers formed on Si(111) surfaces exhibit a multi-scale inhomogeneous structure, characterized by a phase separation down to the nanometer scale. This picture can be made slightly more precise by complementary spectroscopic investigations. All the observations can be rationalized by the formation of supramolecular assemblies in the grafting solution and their transfer to the surface during the grafting process. A consistent picture will be presented and the applicability of the results to real systems like porous silicon will be discussed. [1] A. Faucheux et al., Langmuir 22 (2006) 153.

Speciation of adsorbates on surface of solids by infrared spectroscopy and chemometrics

Speciation, i.e. identification and quantification, of surface species on heterogeneous surfaces by infrared spectroscopy is important in many fields but remains a challenging task when facing strongly overlapped spectra of multiple adspecies. Here, we propose a new methodology, combining state of the art instrumental developments for quantitative infrared spectroscopy of adspecies and chemometrics tools, mainly a novel data processing algorithm, called SORB-MCR (SOft modeling by Recursive Based-Multivariate Curve Resolution) and multivariate calibration. After formal transposition of the general linear mixture model to adsorption spectral data, the main issues, i.e. validity of Beer–Lambert law and rank deficiency problems, are theoretically discussed. Then, the methodology is exposed through application to two case studies, each of them characterized by a specific type of rank deficiency: (i) speciation of physisorbed water species over a hydrated silica surface, and (ii) speciation (chemisorption and physisorption) of a silane probe molecule over a dehydrated silica surface. In both cases, we demonstrate the relevance of this approach which leads to a thorough surface speciation based on comprehensive and fully interpretable multivariate quantitative models. Limitations and drawbacks of the methodology are also underlined.

Automated Quantification of Tumor Viability in a Rabbit Liver Tumor Model after Chemoembolization Using Infrared Imaging

The rabbit VX2 tumor is a fast-growing carcinoma model commonly used to study new therapeutic devices, such as catheter-based therapies for patients with inoperable hepatocellular carcinoma. The evaluation of tumor viability after such locoregional therapies is essential to directing hepatocellular carcinoma management. We used infrared microspectroscopy for the automatic characterization and quantification of the VX2 liver tumor viability after drug-eluting beads transarterial chemoembolization (DEB-TACE). The protocol consisted of K-means clustering followed by principal component analysis (PCA) and linear discriminant analysis (LDA). The K-means clustering was used to classify the spectra from the infrared images of control or treated tumors and to build a database of many tissue spectra. On the basis of this reference library, the PCA-LDA analysis was used to build a predictive model to identify and quantify automatically tumor viability on unknown tissue sections. For the DEB group, the LDA model determined that the surface of tumor necrosis represented 91.6% ± 8.9% (control group: 33.1% ± 19.6%; Mann-Whitney P = 0.0004) and the viable tumor 2.6% ± 4% (control group: 62.2% ± 15.2%; Mann-Whitney P = 0.0004). Tissue quantification measurements correlated well with tumor necrosis (r = 0.827, P < 0.0001) and viable tumor (r = 0.840, P < 0.0001). Infrared imaging and PCA-LDA analysis could be helpful for easily assessing tumor viability.

Quantitative assessment of the multivalent protein-carbohydrate interactions on silicon.

A key challenge in the development of glycan arrays is that the sensing interface be fabricated reliably so as to ensure the sensitive and accurate analysis of the protein-carbohydrate interaction of interest, reproducibly. These goals are complicated in the case of glycan arrays as surface sugar density can influence dramatically the strength and mode of interaction of the sugar ligand at any interface with lectin partners. In this Article, we describe the preparation of carboxydecyl-terminated crystalline silicon (111) surfaces onto which are grafted either mannosyl moieties or a mixture of mannose and spacer alcohol molecules to provide "diluted" surfaces. The fabrication of the silicon surfaces was achieved efficiently through a strategy implicating a "click" coupling step. The interactions of these newly fabricated glycan interfaces with the lectin, Lens culinaris, have been characterized using quantitative infrared (IR) spectroscopy in the attenuated total geometry (ATR). The density of mannose probes and lectin targets was precisely determined for the first time by the aid of special IR calibration experiments, thus allowing for the interpretation of the distribution of mannose and its multivalent binding with lectins. These experimental findings were accounted for by numerical simulations of lectin adsorption.

PRELIMINARY DATA ON BRAZILIAN MONOFLORAL HONEY FROM THE NORTHEAST REGION USING FT-IR ATR SPECTROSCOPIC, PALYNOLOGICAL, AND COLOR ANALYSIS

Fourier transform infrared attenuated total reflectance (FT-IR ATR) spectroscopy was used to determine 14 different measurands in northeast Brazilian honey samples. Nine different honey samples (six monofloral and three polyfloral) from 2009 obtained from the company CEARAPI underwent FT-IR ATR, palynological, color, and sensorial analysis to obtain preliminary results for these types of honey. The results showed that there are five monofloral, three bifloral, and one extrafloral honey, and also that mid-infrared spectrometry can be used as a screening method for the routine analysis of Brazilian honey, with the advantages of being rapid, nondestructive, and accurate. Infrared (IR) Spectroscopy deals with the infrared part of the electromagnetic spectrum. It measures the absorption of different IR frequencies by a sample positioned in the path of an IR beam. Currently, infrared spectroscopy is one of the most common spec- troscopic techniques used in the food industry. With the rapid de- velopment of infrared spectroscopic instrumentation software and hardware, the application of this technique has expanded into many areas of food research. It has become a powerful, fast, and nondes- tructive tool for food quality analysis and control. Fourier Transform (FT) Spectroscopy is an instrumental technique in which spectra are acquired based on measurements of electromagnetic radiation using time domain or space domain and a mathematical method (F T) is applied to convert the raw data to frequency domain. The main application of FT Spectroscopy is the acquisition of absorption spectra.1 IR is based on the absorption of electromagnetic radiation at wavelengths in the range between 800 and 2500 nm. This technique has many advantages such as being rapid and nondestructive, and allows the determination of multiple measurands in a single step.2 Quantitative Infrared Spectroscopy is generally based on calibra- tions by partial least squares (PLS) regression between the spectra and the results obtained by physicochemical reference methods. Building the statistical model is relatively time consuming, and is only profitable if a large number of samples can be analyzed. 2 In this study, a previously published calibration was used,3 which had been successfully used for predicting the physicochemical parameters in the quality control of stingless bee Brazilian honey.4 Infrared Spectroscopy of different monofloral honey samples and subsequent statistical analysis using principal component analysis (PCA) and linear discriminant analysis (LDA) showed that successful classification of the botanical origin of honey is possible. MIR (mid - -infrared) spectroscopy has been successfully used for classification of monofloral European honey. 2,5,6

Electrical and electrochemical properties of polystyrene/polyaniline core–shell materials prepared with the use of a reactive surfactant as the polyaniline shell precursor

Series of polystyrene/polyaniline core–shell composites were synthesized by adding reactive surfactant anilinium dodecylsulfate (DS-AN) as the monomer of polyaniline. DS-AN conversion to polyaniline was calculated by quantitative infrared spectroscopy and thermogravimetric analysis, showing both methods small differences. Composites particle size distribution showed no clear evidence of increment in the overall composite particle diameter as function of polyaniline content; however, electron microscopy (HR mode) showed that the conductive polymer was deposited over the polystyrene cores in the form of thin coatings. Composites electrical conductivity, determined by the 4-probe technique, was in the range 10−6 to 10−2Scm−1. The percolation–tunneling mechanism, according to the curve of conductivity (Scm−1) versus polyaniline (wt%), was the electron transfer mechanism. Finally, all the composites were electroactive, as shown by cyclic voltammetry.

Application of Raman spectroscopy to quantify trace water concentrations in glasses and garnets

We present a new technique for the quantification of water in glasses down to the parts per million level, using confocal microRaman spectroscopy with the recently developed “Comparator Technique.” To test this method, we used a suite of glasses and gemstone-quality garnets with varying chemical compositions. Water contents were independently determined with proton-proton (pp) scattering and infrared (IR) spectroscopy. Moreover, water concentrations obtained for the garnets were compared to data from a study by Maldener et al. (2003) using nuclear reaction analysis (NRA). For each sample, we recorded Raman spectra in the frequency range from 3100 to 3750 cm -1 and standardized them using an independently well-characterized glass. In this paper, we demonstrate the usefulness of this technique for quantifying water concentrations in natural and synthetic glass samples and garnets, and verify its adaptability for concentrations from 40 wt ppm up to 40 wt% H 2 O. However, in the case of absorbing material (e.g., Fe-bearing samples), the suggested method needs to be modified to overcome problems due to heating and melting of those phases. Furthermore, we propose an integrated molar absorption coefficient for water in quartz glass, ε itot = 72 000 ± 12 000 Lmol -1 H₂O cm -2 , for quantitative IR spectroscopy that is higher than a previously reported value of Paterson (1982) or that predicted by the general calibration trend determined by Libowitzky and Rossman (1997).

New pitches with very significant maturation degree obtained by supercritical extraction of Moroccan oil shales

In the present work, new pitches were obtained by supercritical extraction of Moroccan oil shales with water–shale oil as solvent. The aim of the research was to obtain pitches with very significant maturation degree of the organic matter. The evolution of the pitch structure was studied through indexes calculated from quantitative infrared spectroscopy. The classification of the pitches enabled us to assess their degree of maturation. This allowed us to establish the water–shale oil mixture composition likely to give the best maturation of the oil shale′s organic matter.

Physical and Electronic Structure Effects of Embedded Dipoles in Self-Assembled Monolayers: Characterization of Mid-Chain Ester Functionalized Alkanethiols on Au{111}

Self-assembled monolayers (SAMs) on Au{111} prepared from the midchain ester functionalized thiols, HS(CH2)mCO2(CH2)n-1CH3 with m,n = 10,5; 10,10; 15,5; and 5,10, along with deuterated analogs, were characterized by wetting, ellipsometry, near edge X-ray absorption fine structure spectroscopy, quantitative infrared spectroscopy, high resolution X-ray photoelectron spectroscopy (HRXPS), and density functional theory calculations. The SAMs can be viewed as layered structures in which the bottom −(CH2)− alkyl segment (between the ester group and the substrate) exhibits typical conformational ordering and orientation analogous to long chain alkanethiolate SAMs, while the upper segment (ambient side) is significantly more conformationally disordered. The presence of the ester moiety leads to the formation of a strong electric dipole layer with a component of 1.05(±0.09) Debye normal to the surface. This dipole layer exhibits a strong electrostatic effect on the XPS spectra in which the C 1s photoelectron kinetic energies are consistently shifted by 0.85(±0.03) eV between the top and bottom −(CH2)− alkyl segments, regardless of relative lengths. This shift correlates, within error, with the value of 0.81(±0.06) eV predicted via classical electrostatics due to the presence of the ester dipole layer. Overall, these data show that SAMs assembled from molecules with appropriately selected internal groups can be used to prepare internally layered structures with highly controlled electrical characteristics and further demonstrate that simple XPS shifts in core level energies can be used to derive accurate molecular dipole values in structured thin films.

Kinetics of the Formation of Poly(Methyldecylsiloxane) by Hydrosilylation of Poly(Methylhydrosiloxane) and 1-Decene

Poly(methylhydrosiloxane) [PMHS], prepared by siloxane equilibration reaction, was used for the hydrosilylation with 1-decene to obtain poly(methyldecylsiloxane) [PMDS]. Pt(0)-1,3- divinyltetramethyldisiloxane complex was used as a catalyst for hydrosilylation reaction. In order to investigate the kinetics of the formation of PMDS, a series of experiments was performed at different reaction temperatures (from 48 to 64 °C) with catalyst concentrations of 7.0 · 10-7 mol of Pt per mol of CH=CH2. All reactions were carried out in bulk, with equimolar amounts of the reacting Si-H and CH=CH2 groups. The course of the reactions was monitored by following the disappearance of the Si-H bands by quantitative infrared spectroscopy. The obtained results show that an induction period occurs at lower reaction temperatures and that the rate of Si-H conversion follows the first-order kinetics.

Quantitative Infrared Investigation of the Acido-Basic Equilibrium at a Carboxy-Terminated Silicon Surface

Silicon surfaces grafted with mixed alkyl/carboxylic acid monolayers have been investigated by in-situ quantitative infrared spectroscopy at the contact with electrolytes of various pH. Ionization of the carboxy groups is found to start around pH 6 and to extend over a wide pH range. Ionization is not complete even at pH 11. These observations point to the importance of the interactions between surface charges. This effect may be accounted for by a simple model taking into account the change in the Helmholtz potential associated with the surface charge. However, the agreement is only qualitative, which indicates that the surface charge is screened more efficiently than expected, possibly due to ion penetration between the carboxy groups.

Charge states and quantitative infrared spectroscopy of electrically active oxygen centers in gallium arsenide

Oxygen-doped gallium arsenide crystals have been investigated by Fourier transform infrared spectroscopy. Samples with the Fermi level at about 0.4eV below the conduction band exhibit under thermal equilibrium conditions both stable states of electrically active oxygen Ooc, identified optically by the associated local vibrational modes at 730 and 715cm−1. Based on the analysis of compensating centers in the material and comparative Hall measurements, the charge states +1 and −1, respectively, are assigned to these bands. This result favors the (AsGa)2–OAs (two arsenic antisites and one off-center substitutional oxygen atom) microscopic model for the Ooc defect, presented recently, and is in disagreement with the earlier isolated OAs models. Systematic investigations related to the quantitative optical spectroscopy of this center using optically induced conversion experiments confirm that the absorption strengths of the two bands differ by 15%. A calibration factor of 3.6×1016cm−1 is suggested for the band at 730cm−1, derived indirectly from the variation of the +1 and −1 charge states with the carbon acceptor concentration.

Spectral resolution of fluxional organometallics. The observation and FTIR characterization of all-terminal [Rh4(CO)12

In situ FTIR spectroscopy at 1 cm(-1) resolution was conducted on n-hexane solutions of the bridged [Rh4(CO)9(mu-CO)3] in the interval T= 268-288 K and P(T)= 0.1-7.0 MPa using either helium or carbon monoxide as dissolved gas. Analysis of the spectral data sets was conducted using band-target entropy minimization (BTEM), in order to recover the pure component spectra. A new spectral pattern was recovered with terminal vibrations at 2075, 2069.8, 2044.6 and 2042 cm(-1). The new spectrum is consistent with an all-terminal [Rh4(CO)12] species with a C(3v) anticubeoctahedron structure where 2 different [Rh(CO)3] moieties exist, although the presence of some Td structure can not be entirely excluded. The equilibrium between all-terminal [Rh4(CO)12] and the bridged [Rh(4)(CO)9(mu-CO)3] was determined in the presence of both helium and CO. The equilibrium constant K(eq)=[Rh4(CO)12]/[Rh4(CO)9(mu-CO)3] at 275 K was ca. 0.011 and the determined equilibrium parameters were Delta(r)G= 12.63 +/- 4.8 kJ mol(-1), Delta(r)H=-21.45 +/- 2.3 kJ mol(-1) and Delta(r)S=-114.3 +/- 8.35 J mol(-1) K(-1). The free energy indicates a very small difference between the bridged and terminal geometry, and the lower entropy is consistent with a higher symmetry. This finding helps to address a long-standing issue concerning the existence of various [M4(CO)12] symmetries. In a more general context, the present study illustrates the considerable utility of quantitative infrared spectroscopy (occurring on a fast vibrational timescale) combined with sophisticated deconvolution techniques in order to resolve systems which have been demonstrated to be fluxional on the NMR timescale.

Characterization of insoluble organic matter of the Lokpanta oil shales Anambra Basin, by quantitative infrared spectroscopy

Conventional infrared (IR) spectroscopy was used to get quantitative information on the structure of the isolated kerogen of the Lokpanta oil shales in the Anambra basin. The kerogen was extracted from six shale samples collected from different geographical locations in the basin. Only about 1 to 14% of the kerogen present in the fine – grained sedimentary rock extract was recovered from the sedimentary organic residue. Quantitative IR spectroscopy indicates that the kerogen structure consists of about 19% of aliphatic groups ( bands around 2920- 2900, 1450- 1420 cm-1) ; 53% of C=C, C= O, COO- groups (bands around 1610 –1600cm-1) and 28% of aromatic groups (bands around 900 –560 cm-1). These percentages indicate that these kerogens are relatively richer in oxygen bearing functional groups than aliphatic and aromatic groups. This suggest not only that the kerogens are of intermediate maturity but also that they likely correspond to type 11 series, are marine – derived, anoxic, capable of generating oil and gas and originated from the same parent materials. Variation in the intensity of IR bands shows that kerogens from Lokpanta –Lekwesi area are more mature relative to those from Ndeaboh – Awgu. KEY WORDS: Infrared spectroscopy, kerogen, characterization, oil- shales, source –rock, insoluble organic matter, correlation, Lokpanta, Anambra basin. Global Jnl of Pure and Applied Sciences Vol.10(4) 2004: 585-593