mid-IR Absorption Spectra Research Articles

Mid-IR absorption spectra of C1-C4 alkyl acetates at high temperatures

We present measurements of the temperature-dependent absorption cross-section of C1-C4 alkyl acetates (methyl acetate, ethyl acetate, n-propyl acetate, n‑butyl acetate) covering their strongest infrared absorption band near 1250 cm−1. The methodology employed here consists of a broadband rapid-tuning MIRcat-QT™ laser in conjunction with a shock tube. The spectral measurements were performed over the wavelength range of 7.52 – 8.62 μm (1160 – 1330 cm−1), temperatures of 580 – 980 K, and pressures near 1.3 bar. The reported IR spectra are the first experimental measurements of the high-temperature absorption spectra of these species, and the measured spectra showed strong temperature dependence. We provide herein absorption cross-section correlations for a wide range of spectra and a wide range of temperatures. Rapid measurements of alkyl acetate in transient environments may be performed in a fixed-wavelength mode by choosing a suitable wavelength. Based on our analysis, we propose a wavelength of 1221.27 cm−1 which exhibited minimal temperature and pressure dependence over the range of investigated conditions. We utilized this strategy for measuring methyl acetate concentration during its high-temperature pyrolysis.

Особенности инфракрасных спектров сыворотки крови больных множественной миеломой

Comparative analysis of infrared (IR) spectra of blood serum of healthy donors and patients with multiple myeloma (MM) was performed. MM is characterized by hyperproduction of the paraprotein, which manifests itself in a change in the spectral pattern of mid-IR absorption spectra. It has been shown that the most significant deviations in the spectra were observed for samples of MM near the Amide I and Amide II´ bands. As a result of a comparative analysis of the IR spectra of blood serum in the region of 1700-1350 cm-1, nine parameters were established, the average values of which in the samples obtained from patients with a secretory form of MM differ significantly from similar indicators for the serum of healthy donors.

High-temperature mid-IR absorption spectra and reaction kinetics of 1,3-dioxolane

Cyclic saturated ethers are proposed as alternative fuels for future sustainability. In particular, dioxolanes have been identified as promising biofuel candidates. However, pyrolysis and oxidation of dioxolanes are not well understood. In this work, we measured the temperature-dependent absorption cross-section of 1,3-dioxolane (13DO) in the mid-IR region over 8.4 – 10.5 μm (950 –1190 cm−1). We applied the spectroscopic knowledge to investigate the temperature and pressure dependence of the rate coefficients of the unimolecular decomposition of 13DO over the temperature range of 1000–1400 K and pressures near 0.7 and 2.4 bar. We employed a rapidly tuning MIRcat-QT™ laser in conjugation with a shock tube to carry out high-temperature spectroscopic and pyrolysis measurements. Measured IR spectra of 13DO exhibited a strong temperature dependence. For the kinetic study, we employed the vibrational feature of 13DO near 1120.5 cm−1 to monitor the decay of 13DO quantitatively. The measured rate coefficients did not show any discernible pressure dependence. This indicates that the rate coefficients of the unimolecular decomposition of 13DO are close to the high-pressure limit under the present experimental conditions. In addition, we rationalized the temperature and pressure dependence of the reaction by employing electronic structure/RRKM-ME calculations. Our theoretical model accurately captured the experimental trends of the rate coefficients of the unimolecular decomposition of 13DO.

Standoff Detection of Plastics

Rapid identification of different plastics for recycling is very important in overcoming the plastic waste challenge our society is facing today. An ideal plastic detector should be able to discern different plastics at the molecular level in a standoff fashion where the detector does not come in contact with the target plastic. We have demonstrated a standoff technique for the rapid identification of plastics based on their mid-IR absorption spectra. Since mid-IR region is free of overtones, this region is known as molecular finger print regime This technique is based on a variation of photoacoustic spectroscopy (PAS), where the light from a tunable infrared source, a quantum cascade laser (QCL), is scattered/reflected off the target plastic object. The returning scattered light is collected and made to create acoustic waves on a microfabricated cantilever sensor. Our experimental results show that the cantilever response, resonance frequency, amplitude, and bending, changes with infrared absorption characteristics of the target. A plot of cantilever response as a function of illuminating wavelength mimic the infrared absorption peaks of the plastics material producing a mechanical spectrum. The generated spectrum obtained for different plastics is then compared with that conventional spectrum for polymer identification.

Identification of Pink-Coloured CVD Synthetic Diamonds from Huzhou Sino-C Semiconductor Co. in China

In recent years, increasing numbers of pink-coloured CVD synthetic diamonds have appeared on the market. One of the major sources is Huzhou SinoC Semiconductor Science and Technology Co., Ltd., Zhejiang province of China. In this article, seven pink-coloured CVD-grown diamonds produced in the last two years by Huzhou have been investigated and identified, including their gemological and spectroscopic characteristics. In DiamondView, they fluoresced orange–red, with an obscure striated growth structure, which is common for CVD synthetics. The mid-IR absorption spectra of these samples showed some single nitrogen and hydrogen-related features (1130, 1344, 3123, 3323 cm−1), which indicated that the diamonds were type Ib and were CVD-grown diamonds. The H1a defect annealed out at approximately 1400 °C, whereas the 3107 cm−1 defect was produced by annealing above 1700 or 1800 °C. This implied that the samples had undergone two separate heat treatments: first, a high-temperature anneal (possibly an HPHT treatment to reduce any brown colour), which would have produced the 3107 cm−1 defects and a small number of A centres, followed by irradiation, followed by annealing above 800 °C to make the vacancies mobile. The UV–Vis–NIR absorption spectra showed distinct NV-related features (575 and 637 nm), the main reason for the pink colour. Photoluminescence spectra obtained at liquid nitrogen temperature recorded radiation-related emissions (388.9, 503.5 nm), a strong N-V centre, H3 and H2 defects, and many unassigned emissions. These pink CVD products can be separated from natural and treated pink-coloured diamonds by a combination of optical spectroscopic properties, such as fluorescence colour, and absorption features in the infrared and UV–Vis regions.

Improved white light emission in Dy3+ doped LiF–CaO–Bi2O3–B2O3 glasses

The effect of substituting LiF on physical, structural, thermal, optical and photoluminescence properties of Dy3+ doped calcium bismuth borate glasses is reported in the present work. These glasses have been synthesized in the novel compositional range xLiF–(30–x)CaO–20Bi2O3–50B2O3 + 1 mol% of Dy2O3 (x = 0, 2, 5, 7, 10 and 15 mol%, abbreviated as LFx) through convenient melt-quench route. Non-crystalline nature of each composition has been confirmed through X-ray diffraction. Fundamental vibrations of bismuth-borate groups are identified thorough mid-IR absorption spectra. Thermal properties reveal a non-linear trend in glass transition and crystallization temperatures. In order to evaluate optical band gap, analysis of fundamental absorption edge has been done by considering valid Mott's transitions. The compositional trends in optical band gap have supported thermal and infrared absorption results. Evaluation of photoluminescence emission spectra yielded different emission parameters viz. Y/B ratio, color coordinates (x, y) and CCT (correlated color temperature). It has been found that emission of all compositions lie within the white light region and the emission parameters for samples LF2, LF7 and LF10 lie very close to perfect white light (0.333, 0.333). Therefore, these glasses can play the role of useful materials for WLEDs.

FTIR measurements of mid-IR absorption spectra of gaseous fatty acid methyl esters at T=25–500 °C

Gas-phase mid-infrared (IR) absorption spectra (2500–3400cm−1) for eleven fatty acid methyl esters (FAMEs) have been quantitatively measured at temperatures between 25 and 500°C using an FTIR spectrometer with a resolution of 1cm−1. Using these spectra, the absorption cross section at 3.39μm, corresponding to the monochromatic output of a helium–neon laser, is reported for each of these fuels as a function of temperature. The data indicate that the 3.39μm cross section values of saturated FAMEs vary linearly with the logarithm of the number of CH bonds in the molecule.

High pressure structural and vibrational properties of the spin-gap system Cu2PO4(OH)

The structural and vibrational properties of the spin-gapped system Cu2PO4(OH) have been investigated at room temperature under high pressure up to ∼20 GPa by Raman scattering and synchrotron-based x-ray diffraction and infrared (IR) spectroscopic measurements. The orthorhombic phase (space group Pnnm, z = 4) remains stable up to at least 7 GPa where it undergoes a weakly first order structural transition (with negligible volume drop) to a monoclinic phase (space group P21/n, z = 4) with an abrupt monoclinic distortion. Refinement of atomic positions has been performed for the low pressure phase. The conspicuous changes in the vibrational spectra (Raman as well as far-IR) confirm this phase transition. At further higher pressures the monoclinic angle increases rapidly and the system transforms irreversibly into a disordered phase. Detailed vibrational analyses have been performed in the orthorhombic phase and pressure-induced structural evolution has been correlated with the vibrational modes corresponding to the Cu–O bonds. A strong negative pressure dependence of hydroxyl mode frequencies (as observed from the mid-IR absorption spectra) supports the pressure-induced structural disordering at higher pressures.

The modes of the one phonon infrared absorption spectra of nitrogen aggregate defects in diamond

The mid-IR absorption spectra of various nitrogen aggregate defects in diamond are calculated, starting from the vibrational density of states, and compared to the experimental spectrum of these defects. The single substitutional 1344 cm −1 peak is a local mode transforming as E, and does not shift with 15N isotopic substitution. The absorption spectra of the C and the A centres are the sum of a mode transforming as A 1 and E at a C 3v and D 3d symmetrical defect respectively. The absorption spectrum of the B defect is due to the interaction with modes transforming as T 2 at a T d defect. The maxima at 1095 cm −1 appearing in the absorption spectra of all types of nitrogen aggregates is completely determined by the total mass, the symmetry and the position of the various maxima in the vibrational density of states.

Temperature-dependent mid-IR absorption spectra of gaseous hydrocarbons

Quantitative mid-IR absorption spectra (2500–3400 cm −1) for 12 pure hydrocarbon compounds are measured at temperatures ranging from 25 to 500 °C using an FTIR spectrometer. The hydrocarbons studied are n-pentane, n-heptane, n-dodecane, 2,2,4-trimethyl-pentane ( iso-octane), 2-methyl-butane, 2-methyl-pentane, 2,4,4-trimethyl-1-pentene, 2-methyl-2-butene, propene, toluene, m-xylene, and ethylbenzene. Room-temperature measurements of neat hydrocarbon vapor were made with an instrument resolution of both 0.1 and 1 cm −1 (FWHM) to confirm that the high-resolution setting was required only to resolve the propene absorption spectrum while the spectra of the other hydrocarbons could be resolved with 1 cm −1 resolution. High-resolution (0.1 cm −1), room-temperature measurements of neat hydrocarbons were made at low pressure (∼1 Torr, 133 Pa) and compared to measurements of hydrocarbon/N 2 mixtures at atmospheric pressure to verify that no pressure broadening could be observed over this pressure range. The temperature was varied between 25 and 500 °C for atmospheric-pressure measurements of hydrocarbon/N 2 mixtures ( X hydrocarbon∼0.06–1.5%) and it was found that the absorption cross section shows simple temperature-dependent behavior for a fixed wavelength over this temperature range. Comparisons with previous FTIR data over a limited temperature range and with high-resolution laser absorption data over a wide temperature range show good agreement.

A mid infrared study of dynamic processes in iodine–pyridine charge transfer complexes

The mid IR absorption spectra of the iodine–pyridine charge-transfer complex diluted in an `inert' solvent have been measured as a function of the donor concentration in the ternary mixture. The enhanced internal modes of pyridine as well as the new vibrational modes of the complex were assigned on the basis of a recent ab-initio study. The results obtained confirm the observations and assignment reported in earlier literature measurement for the iodine–pyridine system very diluted in ternary mixture. The spectral characteristics (shifts, band centre frequencies and widths) of the profiles associated with the internal modes of the complex have been characterised using Lorentzian bandshape. The interpretation of the spectral changes upon the variation of the donor concentration in the mixture has been performed on the profiles associated with both the ν 1 and ν 3 internal modes ( A 1 symmetry) using a model of the dipolar interaction between the transition dipole moment of the internal mode with the dipoles of the surrounding solvent molecule. In this theoretical framework, the more relevant result concerns the mechanism governing the bandshapes. This is found to involve vibrational relaxation by pure dephasing, with an associated correlation time close to the rotational correlation time of the solvent molecules. These conclusions support fully the ones obtained from the study of the acceptor ( ν I–I) and intermolecular ( ν D–I) vibrations using far infrared spectroscopy that we have reported before. Finally, the merits and limits of the two approaches is critically assessed.