IR spectra of hydrated CaSO4 in the mid-infrared range

Background and Objectives: This work is devoted to the study of the influence of moisture of alabaster (building plaster) samples on the profiles of their IR spectra in the wave number range of 500–4000 cm−1. Materials and Methods: IR spectra of distilled water and alabaster samples with the moisture of 0, 26, 106, 132, 159, 185 and 212% at 23°C were investigated by experimental methods of disturbed total internal reflection. Wave numbers and intensities of components of IR spectra of CaSO4(H2O)n clusters for 0<n<16 were calculated by the methods based on density functional theory with exchange-correlation potential XLYP. Using Gaussian curves with the widths estimated from experiment, the profiles of water valence oscillation bands were determined. When calculating the structure of CaSO4(H2O)n, the positions of atoms in various structural modifications of clusters were optimized. The minimum total energy served as a criterion for choosing the optimal cluster structure, and for the clusters with a large number of atoms, this criterion was applied to an initially selected isomer. Conclusion: On the basis of the calculation results the transformations of the measured spectra (changes of wave numbers and intensities) with changes in the moisture content of the samples have been explained. Comparison of experimental and theoretical spectra in the 3500–3900 cm−1 range allowed to attribute the investigated alabaster powder to a combination of clusters of different sizes:2(CaSO4(H2O)0.5), 2(CaSO4(H2O)0.5 + 0.5H), 4(CaSO4(H2O)0.5), including a cluster of crystalline gypsum: 2(CaSO4(H2O)2). The achieved agreement in the the positions and profiles of the experimental and theoretical water bands in the spectra of samples of different moisture justifies the adequacy of the theoretical description of hydration of CaSO4. &nbsp

MULTIPARTICLE EFFECTS IN FIELD OF IONIZATION ENERGIES OF ATOMS AND SIMPLE MOLECULES

The aim of the work is to investigate the symptoms of electron correlations and oscillations of the nuclei in the near-threshold absorption spectrum region. The new one-centre method for calculation of the one-electron wave functions permitted to investigate firstly the influence of electron correlations in the original and finite transition states on the absolute photoabsorption sections in the ionization threshold region have been calculated. The processes of single and multiple ionization excitation have been taken into consideration. Application field: absorption spectra, electron spectraAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

Iteration Scheme for Solving the System of Coupled Integro-Differential Equations for Excited and Ionized States of Molecular Systems

Investigation of the interaction of electromagnetic radiation with molecular systems provides most of the information on their structure and properties. Interpretation of experimental data is directly determined by the knowledge of the structure of energy levels and its change in the transition of these systems to an excited state. A key task of the methods for calculating the molecular orbitals of excited states is to accurately describe the emerging vacancies of the molecular core, leading to radial relaxation of the electron density. We propose an iterative scheme for solving a system of coupled integro-differential equations for obtaining molecular orbitals of electron configurations with excited/ionized deep and subvalent shells in a single-center representation. The numerical procedure of the iterative scheme is reduced to solving a boundary value problem based on a combination of the three-point difference scheme of Numerov and Thomas algorithm. To increase the rate of convergence of the computational procedure, an accurate account is taken of the behavior of the electron density near the nuclei of the molecular system. The realization of the algorithm of the computational scheme is considered on the example of a diatomic hydrogen fluoride molecule. The energy characteristics of the ground and ionized states of the molecule are estimated, and also the spatial distribution of the electron density is presented for the example of the σ-symmetry shell

Scattering of Photons by Many-Electron Systems

This book deals with quantum physical calculations of anomalous scattering of photons by bound electrons. The main attention is paid to studies of the process of photon scattering in the energy range of deep levels of such many-electron systems as atoms, atomic ions and simple molecules. The book is written for scientists and graduate students, working in the field of atomic and molecular spectroscopy, physics of plasmas, lasers, solid state, ionizing radiation and astrophysics. It can also be used as additional textbook for a special topic of quantum mechanics

Comparative Study of the Hydrophobicity of Organo-Montmorillonite Modified with Cationic, Amphoteric and Nonionic Surfactants

In this work, a series of comparative studies for the effect of the nine commercially available cationic, amphoteric and nonionic surfactants on the structure and wettability of the montmorillonite based organoclays were performed. The pristine and modified clays were characterized by X-ray diffraction (XRD), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and water contact angle (CA) measurements. It has been observed that the maximum basal spacing and the hydrophobicity of the organoclays increased with the alkyl chain length and chain number of the surfactant. It was found out that this effect is most pronounced when using cationic surfactants. The maximum value of contact angle corresponded to the organoclay obtained using di(hydrogenated tallow) ammonium chloride (DDA). The outcomes of this study are important and relevant to the preparation of effective organoclays for geotechnical, petroleum and polymer nanocomposite applications

Effect of Sodium Chloride on the Profiles of the IR Spectrum Bands of Kaolinite at Moistures under Plastic Limit

This study presents data on the IR spectra of kaolinite at a moisture of 26% and after drying. The preparation of moistened samples was made with distilled water, and the solutions of NaCl with limiting and 50% of limiting concentrations at a temperature of 21 °C. To experimentally evaluate the effect of the interaction between liquid water and sorbing basal surfaces of kaolinite on the profile of the IR spectrum bands, the spectra of distilled water and NaCl solutions were additionally studied. Comparison of the band profiles in the wavenumber range of 2750–4000 cm−1 for kaolinite samples allows the conclusion that, when going from distilled water to the most saline water, the adsorption effect is inferior to the effect of solvation, and it decreases with increasing salinity. During drying of the samples, an increase in the peak intensities of the bands in the wavenumber range of 3550–3750 cm−1 is observed. Observed spectral variations are qualitatively interpreted by the results of calculations performed by the DFT method with the XLYP exchange–correlation potential. The presented data can be used to test theoretical approximations and computer models for calculating the structure and properties of moist minerals and salt adsorption mechanisms

Mid-Infrared Spectroscopic Assessment of Plasticity Characteristics of Clay Soils

This work presents a method to determine the plasticity of clay soils using Fourier transform mid-infrared (FT-MIR) spectroscopy. Samples of mono- and polymineral soils of varying water contents are studied. The FT-MIR results are compared with the results obtained from standard Russian and international methods for the plasticity range. The correlation between the consistency of clay soils, when displaying their plastic properties, and the position of the Si–O stretching band in the FT-MIR spectra is established. The possibility of, and interest in, determining the plasticity characteristics of clay soils using mid-infrared spectroscopy is demonstrated: it yields effectively higher precision results compared to standard test methods. It is shown that the method of IR spectroscopy allows the fixing of the start and the completion of the series of “phase transitions” of the soil in the plastic and liquid state. The significant effect of the concentration of non-clay minerals on the Si–O ν line is that a moisture content curve is noticed, which may help to predict the clay content of the soil without undertaking XRD analysis

Ab Initio Simulation of the IR Spectrum of Hydrated Kaolinite

The hydration of the basal surfaces of kaolinite is studied by theoretical methods. The cluster method was used to simulate the positions of atoms. The positions of the atoms of the basal surfaces of dry and hydrated minerals are optimized by minimizing the total energy in the Hartree–Fock approximation. The adsorption energies of water molecules were calculated taking into account the fourth-order correlation corrections of Møller–Plesset perturbation theory. The formation of the IR spectrum of kaolinite in the range of wave numbers 2500–4500 cm−1 is studied. The experimentally observed effect of the change in relative intensity and position of the band with a change in the moisture content of the sample is interpreted

Monte-Carlo study of the effect of small admixture of iron atoms on the energy absorbed by solid disordered neon irradiated by near-Fe1s-threshold photons

Energy absorption processes in iron-doped solid disordered neon under photon irradiation are studied by Monte Carlo simulation with accurate accounting for the processes of the cascade decay of vacancies in the electron shells of ionized atoms. Cascade decay processes of ionized atoms in matter under ionizing radiation are demonstrated to be a crucial factor in the mechanisms of energy absorption in irradiated samples. Small (0.25–4%) admixtures of iron atoms to solid neon samples lead to noticeable enhancement of energy absorption in a sample (1.2–2.7 times) at incident photon energies exceeding Fe1s ionization threshold. Since the neon atom is isoelectronic with H2O, this effect may well be expected in tissues of organisms under ionizing radiation

Energy sharing between final-state electrons upon electron impact ionization of second-row atoms

Cross sections of 1s-, 2s- and 2p-ionization by electron impact and energy distributions for the knocked-off electrons are calculated in first Born approximation with Pauli-Fock wave functions for the second-row atoms from Li to Ne. Analytical formulas approximating knocked-off electron energy distributions for wide intervals of incident electron energies are suggested