Mid-infrared Absorption Spectra Research Articles

Infrared reflection spectra of forsterite crystal

Polarized infrared reflectance of large single crystals of forsterite was measured for each crystal axis at frequencies between 5000 cm-1 and 100 cm-1 with a resolution of 1 cm-1. The reflectance spectra were analyzed based on classical dispersion theory. A set of oscillator parameters for crystalline axes of forsterite was obtained. Those parameters are used to derive optical constants of forsterite, which are important for analyses of observed spectra of astronomical objects and laboratory spectra of particle samples. Calculations of absorption for small particles using the bulk optical constants are compared with mid-infrared and far-infrared absorption spectra measured in the laboratory.

Mid-infrared absorption spectroscopy of methane using a broadband femtosecond optical parametric oscillator based on aperiodically poled lithium niobate

We describe the implementation of optical absorption spectroscopy in which aT i:sapphire pumped femtosecond optical parametric oscillator based on aperiodically poled lithium niobate was used as a broadband source to directly acquire a mid-infrared absorption spectrum of methane gas. Fourier transform spectroscopy was performed using the idler output from the optical parametric oscillator to directly acquire spectra spanning over 600 nm (14.4 THz or 480 cm −1 )w ith around 2.2 nm (55 GHz or 1. 9c m −1 ) resolution. Data are presented of absorption measurements in methane at pressures of 2 bar, 250 mbar and 25 mbar. This approach combines the advantages of spectroscopy using a broadband thermal source with the high power and excellent beam quality of a modelocked laser source.

Mid-Infrared Fiber-Optic Attenuated Total Reflection Spectroscopy of the Solid—Liquid Phase Transition of Water

Measurements of mid-infrared (MIR) absorption spectra of water and heavy water were carried out by fiber-optic evanescent wave spectroscopy, using silver halide (AgClBr) infrared fibers. Such measurements were performed for the first time on one sample, during the solid-liquid phase transition. From the variation of the spectra with temperature we found a new isosbestic point (at 3280 cm(-1) for H(2)O or at 2475 cm(-1) for D(2)O) and we identified five components of the O-H (O-D) stretch band. These phenomena have provided new information about the molecular structure of water.

Infrared spectroscopic taxonomy for carbonaceous chondrites from speciation of hydrous components

Abstract— Mid‐infrared absorption spectra for all types of carbonaceous chondrites were obtained in this study to establish a versatile method for spectroscopic classification of carbonaceous chondrites. Infrared spectra were measured using a conventional KBr pellet method and diamond press method. Spectra of hydrous carbonaceous chondrites exhibit intense O‐H stretching vibrations. CI chondrites are identifiable by a characteristic sharp absorption band appearing at 3685 cm−1, which is mainly attributable to serpentine. X‐ray diffraction analysis showed the presence of serpentine. However, Yamato (Y‐) 82162 (C1) does not have the band at 3685 cm−1 because of its thermal metamorphism. CM and CR chondrites have an intense absorption band at approximately 3600 cm−1. This absorption tends to appear in CM chondrites more strongly than CR chondrites because the intensity ratios of an OH stretching mode at 3520 cm−1 compared to 3400 cm−1 for CM chondrites are in the range of 0.95–1.04, which is systematically higher than those of CR chondrites (0.86–0.88). Therefore, the two types of chondrites are distinguishable by their respective infrared spectra. The spectrum feature of the Tagish Lake meteorite is attributable to neither CI nor CM chondrites. CO chondrites are characterized by weak and broad absorption at 3400 cm−1. CV chondrites have weak or negligible absorption of water. CK chondrites also have no water‐induced absorption. CH and CB chondrites have a sharp absorption at 3692 cm−1 indicating the presence of chrysotile, which is also supported by observations of X‐ray diffraction and TEM. The combination of spectroscopic classification and the diamond press method allows classification of carbonaceous chondrites of very valuable samples with small quantities. As one example, carbonaceous chondrite clasts in brecciated meteorites were classified using our technique. Infrared spectra for a fragment of carbonaceous clasts (<1 μg) separated from Willard (b) and Tsukuba were measured. The 3685 cm−1 band found in CI chondrites was clearly detected in the clasts, indicating that they are CI‐like clasts.

Determining the Conformer Populations of (R)-(+)-3-Methylcyclopentanone Using Vibrational Absorption, Vibrational Circular Dichroism, and Specific Rotation

Experimental mid-infrared absorption and vibrational circular dichroism (VCD) spectra of (R)-(+)-3-methylcyclopentanone were measured in CCl4 solution. Theoretical absorption and VCD spectra were obtained with B3LYP functional and large basis sets, namely aug-cc-pVDZ, 6-311++G(2d,2p), and aug-cc-pVTZ. From the temperature dependent absorption spectra, ΔH° for equatorial ↔ axial equilibrium was determined to be 4.84 kJ/mol, and the ratio of percent populations of equatorial-methyl:axial-methyl conformers, to be 87:13. The populations of equatorial-methyl and axial-methyl conformers were also determined using the experimental and predicted vibrational intensities. However, the errors associated with the populations determined from infrared absorption and VCD band intensities are fairly large. Optical rotation of (+)-3-methylcyclopentanone at 589 nm was measured as a function of concentration in CCl4, CH3OH, and CH3CN solvents, and intrinsic rotation was extracted therefrom. Theoretical specific rotations were predicted using the B3LYP functional and the same basis sets as those used for infrared absorption and VCD. The populations determined from predicted specific rotations and experimental intrinsic rotation are within the error ranges of those determined from infrared absorption and VCD intensities. Using the populations determined from temperature dependent absorption spectra, the predicted population weighted specific rotation for an isolated molecule is found to be larger than the observed intrinsic rotation. The incorporation of solvent influence in specific rotation calculation increased the deviation of predicted value from experimental value, indicating the need for improved models for solvent influence.

Moissanite (SiC) as windows and anvils for high-pressure infrared spectroscopy

The optical properties of the moissanite (single-crystal 6H-SiC) and its performance as anvil material for high-pressure infrared spectroscopic measurements have been examined. Tests were carried out to 53 GPa using moissanite anvil cells combined with synchrotron radiation and globar as infrared sources. In the region of characteristic phonon absorption of diamond (1900–2300 cm−1), the transmitted signal measured through 4 mm of moissanite single crystals is 5–10 times higher than that obtained with type-II diamond anvils. No significant change of the transmission spectra through the moissanite anvils was observed over the pressure range studied; however, we also present mid infrared absorption spectra of powdered SiC to 43 GPa.

Mid-infrared absorption spectroscopy across a 14.4THz spectral range using a broadband femtosecond optical parametric oscillator

We describe the implementation of optical absorption spectroscopy in which a Ti:sapphire pumped femtosecond optical parametric oscillator based on periodically poled lithium niobate was used as a broadband source to directly acquire a midinfrared absorption spectrum of methane gas. Fourier-transform spectroscopy was performed using the idler output from the optical parametric oscillator to directly acquire spectra spanning over 600nm (14.4THz or 480cm−1) with around 3nm (78GHz or 2.6cm−1) resolution. This approach combines the advantages of spectroscopy using broadband thermal sources with the high power and excellent beam quality of a mode-locked laser source.

Wavelength and Average Power Density Dependency of the Surface Modification of Root Dentin Using an MIR-FEL

Surface modification of root dentin by mid-infrared (MIR) pulsed-laser irradiation is one of the candidates for a novel, non-invasive treatment to prevent root surface caries. To modify root dentin effectively and non-invasively it is essential to estimate quantitatively and qualitatively the laser parameters, such as the wavelength and the power density, required for surface modification. The key aspect is to bring about effective surface modification of root dentin while minimizing the unwanted removal of the underlying dentin. Using a tunable, MIR Free Electron Laser (FEL) in the wavelength region of 8.8-10.6 μm, we have investigated macroscopically the extent of surface modification (morphological and chemical changes) of root dentin. We have obtained experimental results related to the ablation depth, the MIR absorption spectrum, and the elemental chemical composition of the irradiated dentin. The observations showed that the surface modification of root dentin was inclined toward well-recrystallized, HAp-like material, leading to an increase in the acid resistance and dentinal tubule sealing. The laser parameters, at which efficient surface modification without enhanced ablation occurred, were estimated to be at λ= - 9.0 μm or - 9.7 μm and in the average power density region of - 10-20 W/cm2 (resulting in energy density per macropulse and peak power density regions of - 1-2 J/cm2 and - 66.7-133.3 kW/cm2). Thus, it was found that the surface modification of root dentin strongly depends on the laser conditions applied. We conclude that the optimum laser wavelengths for (1) root surface caries treatment without restorative procedure and (2) hard tissue ablation without water irrigation are around (1) λ= 9.0 μm or 9.7 μm and (2)λ= 9.0 μm in the absorption bands due to P-O stretching, respectively.

The mid-IR absorption spectrum of gas-phase clusters of the nucleobases guanine and cytosine

The mid-infrared (IR) absorption spectrum of jet-cooled clusters of the nucleobases guanine and cytosine has been recorded in the 500–1800 cm−1 range by ion-dip spectroscopy. Some 30 clearly separated and sharp resonances are observed. The combination of the experimental data with new high-level ab initio calculations is consistent with a previous structural assignment and a tentative assignment is made to the K7-1E structure of guanine–cytosine. These data can serve as a test of the method in the mid-IR regime.

Thermal behavior of dental enamel and geologic apatite: An infrared spectroscopic study

Teeth and bones consist of an apatite-type structure and such biogenic apatites usually occur in nano-crystalline form. Because of the small particle size in biological tissues, local structural details of biogenic apatite have still not been resolved in detail. Comparison of the phonon spectra of enamel apatite with those of inorganically formed apatite was carried out to improve our understanding of the vibrational behavior of biogenic apatite. In situ mid-infrared absorption spectra of dental enamel and geologic fluorapatite were recorded from 300 K to ca. 750 K. Lattice vibration modes were studied at low temperature in the infrared region of 150 to 650 cm-1. The IR excitations indicate that geologic apatite undergoes heavier thermal changes than enamel apatite at temperatures between 60 K and 300 K. In situ high-temperature IR spectra confirm the different thermal evolution of dental enamel and geologic fluorapatite. The P-O overtones or combinational vibrations and hydrous species of enamel apatite show two different thermal regions below and above 600 K. The thermal behavior in the region below 600 K corresponds to the loss of adsorbed and part of the lattice water, combined with an increase of structural OH groups. In the second thermal region (above 600 K), the similarity of thermal response of dental enamel to that of the geologic apatite from 300 K suggests the existence of a highly ordered system. This result may be explained by the dehydration and atomic rearrangements in the channels of enamel apatite structure below 600 K.

Infrared microscopy of epithelial cancer cells in whole tissues and in tissue culture, using synchrotron radiation.

Oral epithelial tumour tissue, and cultured cervical epithelial carcinoma cells have been studied using synchrotron infrared microspectroscopy. Mid infrared absorption spectra collected at cellular spatial resolution from within oral tumours were found to be sufficiently distinct, when analysed by principal component analysis, to distinguish between three different cell types within the tumour. The resulting data were sufficiently robust to allow correct classification of spectra from cells within subsequent tissue samples. These results go some way to demonstrate the potential of infrared spectroscopy as a tool in the post-operative screening of oral cancer patients by the examination of exfoliated epithelial cells. To gain a better understanding of the inherent variability in the infrared spectra of such epithelial cells, we have studied A431 carcinoma cells under the stimulus of the growth-stimulating hormone EGF. We have detected key changes in the infrared spectrum that relate to the activation of the growth factor signalling mechanism.

Wavelength and average power density dependency of the surface modification of root dentin using an MIR-FEL.

Surface modification of root dentin by mid-infrared (MIR) pulsed-laser irradiation is one of the candidates for a novel, non-invasive treatment to prevent root surface caries. To modify root dentin effectively and non-invasively it is essential to estimate quantitatively and qualitatively the laser parameters, such as the wavelength and power density, required for surface modification. The key aspect is to bring about effective surface modification of the root dentin while minimizing the unwanted removal of the underlying dentin. Using a tunable, MIR Free Electron Laser with lambda = 8.8-10.6 microm, we have investigated macroscopically the extent of the surface modification (morphological and chemical changes) of root dentin. We have obtained experimental results related to the ablation depth, the MIR absorption spectrum, and the elemental chemical composition. The observations showed that the surface modification of root dentin was inclined toward well-recrystallized HAp-like material, leading to an increase in the acid resistance and dentinal tubule sealing. The laser parameters, at which efficient surface modification without enhanced ablation occurred, were estimated to be approximately in the wavelength region around lambda = approximately 9.0 or approximately 9.7 microm and in the average power density region of approximately 10-20 W/cm2 (resulting in total energy density and peak power density regions of approximately 1-2 kJ/cm2 and approximately 0.67-1.2 kW/cm2). The surface modification of root dentin strongly depends on the laser parameters applied. We conclude that the optimum wavelengths for laser treatment of root surface caries are lambda = approximately 9.0 or approximately 9.7 microm, corresponding to the absorption peak due to P-O stretching.

Resonant photoionization absorption spectra of spherical quantum dots

We study theoretically the mid-infrared photon absorption spectra dueto bound–free transitions of electrons in individual spherical quantumdots. It is established that change of the dot size in one or two atomiclayers or/and number of electrons by one or two can change the peakvalue of the absorption spectra in orders of magnitude and energy ofabsorbed photons by tens of millielectronvolts. The reason for this is theformation of specific free states, called resonance states. Numerical calculationsare performed for quantum dots (QDs) with radius varying up to 200Å, and one to eight electrons occupying the two lowest bound states. Itis supposed that realistic QD systems with resonance states would beof much advantage to design novel infrared QD photo-detectors.

Identification of Overlapped Near-Infrared Bands of Glucose Anomers Using Two-Dimensional Near-Infrared and Middle-Infrared Correlation Spectroscopy

Near-infrared (NIR) spectroscopy is a useful tool in determining glucose in biological matrices. Because α-anomers and β-anomers of glucose are in equilibrium in the solution, the observed NIR bands may come from the overlapping of vibrational modes of the anomers. We have conducted NIR and mid-infrared (MIR) absorption spectra measurements to determine the nature of the observed NIR features by using two-dimensional (2D) NIR and MIR correlation spectroscopy. The 2D NIR correlation spectra and 2D synchronous NIR and MIR correlation heterospectra are constructed based on the spectral changes of individual anomers upon mutarotation. We have identified a new NIR feature at 4350 cm−1 for the α-anomers and two new NIR features at 4200 and 4250 for the β-anomers. The 4350-cm−1 band of the α-anomers could be assigned to the combination band of C–H stretch at 2945 cm−1 and a mixed mode of C–H bending and O–H bending at 1415 cm−1. The 4200/4250-cm−1 bands of the β-anomers might be tentatively assigned to the combination band of C–H stretching at 2870 cm−1 and a mixed mode of C–H bending and O–H bending at 1315/1370 cm−1. This finding provides the spectral information needed for implementation of a highly selective coherent two-dimensional vibrational spectroscopic method, the DOVE-Raman four wave mixing for selective identification of glucose anomers from aqueous solutions.

Density functional theory characterization of the structure and gas-phase, mid-infrared absorption spectrum of 2-azido- N, N-dimethylethanamine (DMAZ)

Non-local density functional theory utilizing the B3LYP exchange-correlation functionals with a 6-311++G(d,p) basis set was employed to characterize the geometric parameters and normal modes of 12 equilibrium conformations of 2-azido- N, N-dimethylethanamine. Also known as DMAZ, an experimentally acquired, mid-infrared absorption spectrum of this fuel's vapor is analyzed based on the computational results. The analysis indicates that the relative populations of DMAZ conformers in a room temperature sample do not deviate significantly from expectations based on a Boltzmann distribution calculated from their theoretically determined zero-point corrected energies. The most abundant conformer is found to have the central nitrogen atom of the azido group aligned over the amine lone pair electrons. Since this configuration is likely to inhibit proton transfer to the amine site, it may play an influential role in DMAZ's performance as a hypergol.

Classification of maize contaminated withFusarium Graminearum Using Mid-infrared Spectroscopy and Chemometrics

Advances in the development of a novel method for the detection ofFusarium graminearum employing mid-infrared spectroscopy are described. The dried and ground sample was sieved and the fraction with particle sizes between 250 and 100 μm was used for spectroscopy. The sample was pressed against a diamond ATR-crystal, mounted in the sample chamber of an FT-IR spectrometer and the mid-infrared absorption spectrum was recorded. The most prominent features in the spectrum were identified as protein, lipid and carbohydrate bands, which are changed by fungal infection. Multivariate data analysis was employed to detect the spectral changes: Principal component analysis (PCA) of mean centred data proved to be the most efficient method for the separation of contaminated maize from uninfected samples using the first two principal components. Ergosterol and the toxin deoxynivalenol (DON) served as reference parameters and were obtained from each sample using conventional analytical techniques. Samples with a toxin content of as low as 309 μg/kg could be separated from blank samples, which is well in the range of natural contamination. Investigated concentration ranges were 0.73-4.5 mg/kg for ergosterol and 0-2.6 mg/kg for DON. The percentage of correctly classified samples was between 75 and 100%.

IR-spectroscopic studies of Zymomonas mobilis and levan precipitate

The mid-infrared (mid-IR) absorption spectra of Zymomonas mobilis 113 “S” bacterial biomass grown in sucrose or glucose medium, and levan precipitate in the fingerprint region were studied. IR-qualitative and quantitative analyses were carried out. The principal component concentration changes in Z. mobilis biomass at different growth phases showed that protein concentration was higher in case of glucose-based medium, but the total carbohydrate concentration was higher if grown in sucrose-based medium. Low concentration of intracellular carbohydrates was a characteristic parameter of levan-producing Z. mobilis cells. It was shown that during 2-month storage of Z. mobilis inoculum in sucrose medium at 4 °C the content of nucleic acids decreased, but other cell macromolecular component content did not change significantly. The levan precipitate IR-spectra in the 800–3400 cm −1 region indicated fructans as the main component, with negligible amounts of other carbohydrates. Qualitative analysis of IR-absorption spectra showed the presence of some amino acids in the precipitate. Thereby, the mid-IR-spectra proved the extent of purity of the obtained preparation.

Fourier transform mid-infrared spectroscopy with attenuated total reflection (FT-IR/ATR) as a tool for the detection of Fusarium fungi on maize

The application of Fourier transform mid-infrared spectroscopy with attenuated total reflection (ATR) for the detection of Fusarium graminearum as an indicator for the presence of the mycotoxin deoxynivalenol (DON) is described. This rapid screening method for the determination of Fusarium fungi, which produces DON as its main metabolite, could speed up analysis time, resulting in a higher sample throughput, as conventional determination is a time-consuming and tedious task. In this study the fungus itself was determined on maize by pressing the ground sample against a diamond ATR-crystal with 3 internal reflections and recording the mid-infrared absorption spectrum. Reference measurements were performed by determining ergosterol with HPLC-DAD. Obtained concentrations of ergosterol served as a parameter for the total fungal biomass contained in the sample. DON was determined with GC-ECD after extraction with acetonitrile and clean-up with Mycosep™ columns. Principal component analysis (PCA) was used to separate contaminated maize from blank samples using the first derivative of spectra. Results showed that, for concentrations greater than 8.23 mg/kg ergosterol and 0.13 mg/kg DON at least 75% of samples were correctly classified. Exceptions are due to inhomogeneities in the sample, which will be dealt with in future studies. The PCA score plots for the first two principal components illustrate the feasibility of this approach as a separation between the two sample sets can be clearly seen. Concentrations of ergosterol and DON in tested samples ranged from 0.79–947 mg/kg (ergosterol) and from 0.13–2.59 mg/kg (DON). For PCA these samples were always compared with a blank.

Using mid-infrared Fourier-Transform-Spectroscopy with attenuated total reflection (FT-IR/ATR) as a tool for the determination ofFusarium graminearum on maize

A novel method for the detection ofFusarium graminearum employing mid-infrared spectroscopy is described. In this study the fungus itself was determined on maize by pressing the ground sample against a diamond ATR-crystal, mounted horizontally in the sample chamber of an FT-IR spectrometer and recording the mid-infrared absorption spectrum. Multivariate data analysis was employed for the interpretation of spectra: Principal component analysis (PCA) was used to separate contaminated maize from uninfected samples. For concentrations higher than 8.23 mg/kg >80% of the samples were correctly classified with PCA. Spectra were correlated with HPLC results from reference measurements for ergosterol using principal component regression (PCR). A correlation coefficient of 0.9786 with an F-statistic of 107 was calculated (concentration range: 0.79-947 mg/kg ergosterol).

Vibrational circular dichroism and absolute configuration of chiral sulfoxides: tert-butyl methyl sulfoxide.

Mid-infrared vibrational unpolarised absorption and vibrational circular dichroism (VCD) spectra of CCl4 solutions of tert-butyl methyl sulfoxide (1) are reported. The spectra are compared to ab initio density functional theory (DFT) calculations carried out using two functionals, B3PW91 and B3LYP, and two basis sets, 6-31G* and TZ2P. The VCD spectra are calculated using Gauge-invariant atomic orbitals (GIAOs). The analysis of the VCD spectrum confirms the R(-)/S(+) absolute configuration of 1. The advantages and disadvantages of VCD spectroscopy in determining the absolute configurations of chiral sulfoxides are discussed.