Multiple Frustrated Total Internal Reflection Research Articles

Экспресс-анализ жидких смесей методом последовательного испарения компонентов на ИК-фурье-спектрометре ФТ-801 с приставкой МНПВО

Экспресс-анализ жидких смесей методом последовательного испарения компонентов на ИК-фурье-спектрометре ФТ-801 с приставкой МНПВО

H3O 2 - ions with a strong quasi-symmetrical H-bond and their hydration in aqueous solutions of NaOH and KOH

Ion-molecular interactions in aqueous solutions of NaOH (0–47.8%) and KOH (0–51.95%) are studied by multiple frustrated total internal reflection IR spectroscopy. Interpretation of the spectra and analysis of the spectral data are performed based on the results of DFT calculations (B3LYP/6-31++G(d, p)) of the characteristics of the free and double hydrated H3O2- ion. It is established that the changes in the IR spectra of NaOH and KOH aqueous solutions caused by increasing alkali concentration are due to the formation of H3O2- ions with a strong quasi-symmetrical hydrogen bond and their subsequent hydration by one or two water molecules. The influence of the cation nature on the degree of hydration of H3O2- ions is demonstrated. The equilibrium concentrations of monohydrate (H3O2- ∙ H2O) and dihydrate (H3O2- ∙ 2H2O) are calculated and their IR continuous absorption spectra are isolated.

Investigation of orientational order in a nematic liquid crystal with semiconductor CdSe/Zns QDs by IR spectroscopy

The dichroic ratio and orientational-order parameter of fundamental bands have been studied in the IR spectrum for a nematic liquid crystal based on alkylcyanobiphenyls and its suspensions with semiconductor CdSe/ZnS QDs with a core size of 5 nm. Analyses have been performed by the method of multiple frustrated total internal reflection. It is shown that an increase in the nanoparticle concentration from 0.5 to 1.3 wt % improves the orientation uniformity of the liquid crystal near the interface with the orienting surface. The orientational order parameter in a suspension with 1.3 wt % QDs has increased in comparison with the initial liquid crystal by more than 10% for the fundamental bands in alkylcyanobiphenyl molecules, the stretching vibrations of which correspond to the direction of their long axes.

Ions with strong symmetric H-bonds and their solvation in aqueous-ethanolic solutions of HCl

Ion-molecular interactions in the HCl-EtOH-H2O system are studied by means of multiple frustrated total internal reflection IR spectroscopy over a wide range of concentrations of the components. It is demonstrated that, in the investigated solutions, the acid is fully bound into ions and uncharged complexes formed by strong symmetric or quasi-symmetric H-bonds. There is a competition between H2O and EtOH molecules during the formation of the (H5C2(H)O…H…O(H)C2H5)+, (H2O…H…OH2)+, and (H2O…H…O(H)C2H5)+ proton disolvates. In dilute solutions of HCl in 2: 1 and 1: 1 EtOH-H2O mixtures, (H2O…H…OH2)+ proton dihydrates are mainly formed, whereas in concentrated HCl solutions, under conditions of a partial solvation of ions by solvent molecules, predominantly (H2O…H…O(H)C2H5)+ mixed proton disolvates arise. In concentrated solutions of HCl in EtOH with low water content, the acid is partially bound into (H5C2(H)O…H+…Cl−) uncharged complexes with the participation of the Cl− anion.

Surface modification of polypropylene materials by the cobalt complex of 5,10,15,20-tetrakis-(4-methylpyridyl)porphyrin tetratosylate

The process of immobilization of cobalt(II) 5,10,15,20-tetrakis(4-methylpyridyl)porphyrin tetratosylate on chemically activated surface of polypropylene materials was studied using infrared spectroscopy of multiple frustrated total internal reflection, electron spectroscopy, and atomic force microscopy. The modified materials were shown to have a sorption activity with respect to nitrogen bases, the structural analogs of blood toxines.

Infrared spectroscopy of bonded silicon wafers

Infrared spectra of multiple frustrated total internal reflection and transmission for silicon wafers obtained by direct bonding in a wide temperature range (200–1100°C) are studied. Properties of the silicon oxide layer buried at the interface are investigated in relation to the annealing temperature. It is shown that the thickness of the SiO2 layer increases from 4.5 to 6.0 nm as the annealing temperature is increased. An analysis of the optical-phonon frequencies showed that stresses in the SiO2 relax as the annealing temperature is increased. A variation in the character of chemical bonds at the interface between silicon wafers bonded at a relatively low temperature (20–400°C) is studied in relation to the chemical treatment of the wafers’ surface prior to bonding. Models of the process of low-temperature bonding after various treatments for chemical activation of the surface are suggested.

Features of the vibrational spectra of diamond-like and polymer-like a-C:H films

Comparative analysis of the IR spectra of multiple frustrated total internal reflection (MFTIR) in the range 4000–1000 cm−1 is performed for diamond-like and polymer-like a-C:H films with the refractive indices n ≥ 2.0 and n ≤ 1.7, respectively. The films are obtained by chemical-vapor deposition from octane, cyclohexane, toluene, and acetylene under various conditions using a dc glow discharge plasma. Characteristic features are found in the vibrational spectra of a-C:H films with different refractive indices. A peak at 1250 cm−1, which is independent of the initial hydrocarbon, is observed in the spectra of the diamond-like films. Additional peaks at 3400 and 1700 cm−1, due to O-H and C=H vibrations, are present in the spectra of the polymer-like films. It is shown that the integrated intensity of the band of CH vibrations peaked at ∼2900 cm−1 decreases exponentially by an order of magnitude with an increase in n from 1.55 to 2.4.

Combined element for multiple frustrated total internal reflection

Combined element for multiple frustrated total internal reflection

Kinetic study of the equilibrium in the methanesulfonic acid-water system

A kinetic study of the hydrolysis of ethyl isovalerate in the methanesulfonic acid-water system from pure water to 60.5% CH3SO3H at 25°C showed that the hydrolysis rate is directly proportional to the concentration of H5O2+ ions determined by IR spectroscopy. The hydrolysis mechanism is the same as in hydrochloric acid and sulfuric acid solutions. Evidence was found for correctness of the measurements of the equilibrium concentrations of molecules and ions in aqueous methanesulfonic acid solutions by multiple frustrated total internal reflection IR spectroscopy. The possibility was demonstrated for an independent measurement of the equilibrium concentrations of H5O2+ ions by a kinetic method in aqueous acid solutions.

Ir spectra of the simplest stable proton solvates in methanol and ethanol

The spectra of (MeOH)2H+ and (EtOH)2H+ proton disolvates formed by strong symmetrical hydrogen bonding were separated from the multiple frustrated total internal reflection (MFTIR) IR spectra of solutions of HCl in methanol and ethanol. These spectra show a large number of rather narrow bands, exceeding the number of bands in the spectra of the pure alcohols and are in accord with a model, in which the generation of continuous absorption in solutions of strong acids is a consequence of the interaction of vibrations for protons in a strong, symmetrical hydrogen bond with the vibrations of other groups of proton disolvates.

Investigation of acid-base interaction in H2SO4-diethyl ether system by means oe MFTIR infrared spectroscopy

1. By means of multiple-frustrated total internal reflection (MFTIR) infrared spectroscopy at 30°C, the equilibrium concentrations have been determined for the components forming the system H2SO4,-Et2O. The species existing in the system consist primarily of addition products with a 1∶1 composition, and also the complexes B·2H2SO4, and 2B·H2SO4. 2. In the region of concentrations close to 100% H2SO4, the complexes are completely dissociated into ions. Dilute solutions of H2SO4, in ether are made up of complexes of the molecular type and contact ion pairs. With an equimolar ratio of components, an equilibrium exists among the molecular complexes, contact ion pairs, and individual ions. 3. It is suggested that current transport in concentrated H2SO4 solutions is accomplished primarily by a hopping mechanism, owing to the presence of complexes B·2H2SO4 with a well-developed tructure of hydrogen bonds. 4. The optical density of continuous absorption has been measured at a frequency of 2000 cm−1, in relation to the composition of the H2SO4,-Et2O system, and molar extinction coefficients have been measured for dilute and concentration solutions of acid: 50 ± 10 and 120 ± 10 liters/mole · cm, respectively.

Influence of the surface layer on the optical strength of lithium niobate

The technique of multiple frustrated total internal reflection is applied to demonstrate the existence of a surface layer in lithium niobate. The thickness and absorption coefficient of this layer are determined. It is shown that when the surface of lithium niobate is irradiated at subthreshold energy densities, a cumulative effect of the action of the laser radiation is observed. The dependences of the surface damage threshold on the pulse duration and the focal spot diameter are determined. Results of an experiment to study the dependence of the optical strength on the pulse duration confirm that lithium niobate has an absorbing surface layer.