Temperature investigations of Raman spectra of stoichiometric and congruent lithium niobate crystals

In the temperature range 100–450 K, we have investigated Raman spectra of congruent and stoichiometric LiNbO₃ crystals. We have found that, in this temperature range, frequencies and widths of all the spectral lines depend linearly on temperature. However, the width of the line that corresponds to vibrations of the A₁(TO) symmetry of Li⁺ ions depends on temperature much more weakly than the width of the line that corresponds to vibrations of the A₁(TO) symmetry of Nb⁵⁺ ions. This fact indicates that the anharmonicity of vibrations of Nb⁵⁺ ions along the polar axis is much stronger compared to vibrations of Li⁺ ions. It is likely that this anharmonicity is noticeably contributed by O^2? ions, which are characterized by an anharmonic potential, vibrations of which, according to calculations from first principles, are mixed with vibrations of Nb⁵⁺ ions. The anharmonicity of vibrations of O^2? ions is evidenced by a strong temperature dependence of the width of the line that corresponds to vibrations of the A₁(TO) symmetry of O^2? ions perpendicularly to the polar axis. We have found that the temperature dependence of the intensity of lines that correspond to fundamental vibrations is nonmonotonic. At the same time, the temperature dependence of the intensity of “superfluous lines” is strictly linear. It is likely that this behavior of the intensities of lines of fundamental vibrations is related to the occurrence of clusters and microstructures in the crystal structure.     

Collective excitations and a backbending phenomenon in <Superscript>156</Superscript>Dy

We propose a self-consistent practical method to study collective excitations in rotating nuclei within the cranking + random phase approximation approach. It consists in solving the cranking Hartree-Bogolyubov equations for the modified Nilsson potential + monopole pairing forces. Further, the mean field results are used to construct collective vibrations treated in the random phase approximation (RPA). Special attention is paid to fulfill all conservation laws in the RPA to separate spurious and physical solutions. We demonstrate that the backbending in ¹⁵⁶Dy can be explained as a result of the disappearance of collective γ vibrations of the positive signature in the rotating frame.     

Role of nuclear surface vibrations in low energy heavy ion collisions

Nuclear surface vibrations cause dissipation as well as fluctuations of the relative motion between heavy ions. Viewing these as transport phenomena, we derive explicit formulae for the induced force and the correlation functions in terms of the spectrum of the nuclear vibrations and the coupling form factor. We provide a general proof that the path integral approach and the density operator formalism lead to equivalent transport coefficients as long as the influence functional takes a standard form. As an illustration, we then analyze⁸⁴Sr+²⁰⁸Pb scattering. We discuss the properties of the potential renormalization, and explain the mechanism of the high lying vibrations becoming dominant in dissipation with increasing bombarding energy by examining the properties of the retarded friction function.     

Relativistic mean-field description of collective motion in nuclei: the pion field

The influence of the pion field on isovector dipole and spin-dipole collective oscillations is investigated in a time-dependent model based on relativistic mean field theory. We find that the inclusion of the long range pion-nucleon interaction provides an additional strong damping mechanism for the isovector dipole vibrations. The inclusion of the pion field has also a strong effect on the dynamics of spin-dipole vibrations, and in particular on the splitting of excitation energies of theJ ^π (0^?,1^?,2^?) components of the isovector spin-dipole resonance.     

Collective bands in doubly even Sn nuclei

Starting from a simplified picture treating proton two-particle two-hole excitations coupled with spherical quadrupole vibrations, in interaction with the low-lying quadrupole vibrational states in the doubly even Sn nuclei, we are able to account for a regular ΔJ = 2 band structure on top of excited J^π = 0⁺ states. We compare in some detail results for ¹¹⁶Sn concering energy spectra and E2 transition rates.     

Raman spectroscopy of the nickel silicate mineral pecoraite—an analogue of chrysotile (asbestos)

The molecular structure of the mineral pecoraite, the nickel analogue of chrysotile of formula Ni₃Si₂O₅(OH)₄, was analysed by a combination of Raman and infrared spectroscopies. A comparison is made with the spectra of the minerals nepouite and chrysotile and a synthetic pecoraite. Pecoraite is characterised by OH stretching vibrations at 3645 and 3683 cm⁻¹ attributed to the inner and inner surface hydroxyl stretching vibrations. Intense infrared bands at around 3288 and 3425 cm⁻¹ are assigned to the stretching vibrations of water strongly hydrogen‐bonded to the surface of the pecoraite. The asbestos‐like mineral is characterised by SiO stretching vibrations at 979, 1075, 1128 and 1384 cm⁻¹, OSiO chain vibrations at 616 and 761 cm⁻¹ and Ni O(H) vibrations at 397 and 451 cm⁻¹. Copyright © 2008 John Wiley & Sons, Ltd.     

Full-Optical Two-Channel Adaptive System for Detecting Microcantilever Vibrations

We demonstrate a full-optical two-channel system for measuring mechanical vibrations of microoscillators, which is based on adaptive holographic interferometer using multiwave mixing in a photorefractive crystal. The orthogonal geometry of dynamic hologram recording makes possible independent operation of the measurement channels. The absolute detection limit of the system to cantilever vibrations in a channel amounted to 2.6·10 ^?6 nm·W^1/2 ·Hz ^?1/2. We tested the system in simultaneous detection of vibrations of two cantilevers with dimensions 215×40×15 μm.     

Nature of some features in Raman spectra of hydroxyapatite‐containing materials

A very broad vibrational band ranging from 1000 up to 4000 cm⁻¹ and two relatively sharp bands at 5000 and 5027 cm⁻¹ are found in the Raman scattering spectrum of hydroxyapatite‐containing films obtained by gas detonation spray method. We developed a theoretical model that interprets the broad band as a result of strong interaction between the high‐frequency hydrogen bond vibrations and lattice phonons. Both sharp bands around 5000 cm⁻¹ are assigned to the overtones of v‐OH vibrations. Copyright © 2016 John Wiley & Sons, Ltd.     

Intermediate coupling model description of55Fe and57Fe

The properties of the negative parity states of⁵⁵Fe and⁵⁷Fe are investigated in the framework of the intermediate coupling model. In the model, a neutron or a quasineutron is coupled to anharmonic vibrations of the core. Anharmonicities of the vibrations are estimated through the observed properties of the core. Energy levels, spectroscopic factors and electromagnetic properties have been calculated. The results of the present calculations are also compared with available experimental results and other theoretical results. The model reasonably accounts for many of the properties of the low-lying states.     

Intensities of DNA ion-phosphate modes in the low-frequency Raman spectra

The Raman intensities of counterion vibrations with respect to the phosphate groups of the double-helix backbone (ion-phosphate modes) in the low-frequency spectra (< 200 cm^-1) of B -DNA with different alkali metal counterions have been calculated using the model for DNA conformational vibrations and the valence-optic approach. The results have showed that the spectra of DNA with heavy counterions ( Rb⁺ and Cs⁺ differ from the spectra of DNA with light counterions ( Na⁺ and K⁺ . The calculated spectra of DNA with heavy counterions are characterized by intensive modes of ion-phosphate vibrations that form one united band near 115cm^-1. Ion-phosphate modes in the spectra of DNA with light counterions are characterized by higher frequencies (near 180cm^-1) and much lower intensity. Our calculations explain why the modes of ion-phosphate vibrations are observed in Cs-DNA spectra rather than in Na-DNA. The determined sensitivity of the intensities of DNA low-frequency spectra to the counterion type proves the existence of the ion-phosphate modes.     

Temperature dependent isomer shift in Sn119 — Pseudopotential approach

The theory formulated by Inglesfield based on the pseudopotential method was modified by the thermal lattice vibrations to interpret the explicit temperature dependence of the isomer shift in Sn¹¹⁹. A temperature dependent conduction electron charge density at the nucleus was derived by this method and the change of the isomer shift ib Sn¹¹⁹ with temperature was calculated. We found that the results of Sn¹¹⁹ in SnMg₂ and SnTe were in good agreement with the experimental results of Lin and Rothberg.     

Field emission of electrons from a single carbon fiber with a nanostructured emitting surface

The field emission of electrons from a single fine carbon fiber with a nanostructured emitting surface is studied experimentally. It is found that the fiber can serve as an effective field emitter of electrons at voltages of ∼10²–10³ under the conditions of technical vacuum and the emission current density may reach ∼10² A/cm². At a certain threshold voltage, the fiber starts executing flexural mechanical vibrations. The onset of mechanical vibrations is accompanied by a change in the field emission conditions. Namely, in the absence of vibrations, the mode of steady current extraction is observed. When mechanical vibrations set in, the field emission switches to the mode of current periodic oscillations with a constant component.     

Collisional damping of giant monopole and quadrupole resonances

Collisional damping widths of giant monopole and quadrupole excitations for ¹²⁰Sn and ²⁰⁸Pb at zero and finite temperatures are calculated within Thomas-Fermi approximation by employing the microscopic in-medium cross-sections of Li and Machleidt and the phenomenological Skyrme and Gogny forces, and are compared with each other. The results for the collisional widths of giant monopole and quadrupole vibrations at zero temperature as a function of the mass number show that the collisional damping of giant monopole vibrations accounts for about 30 - 40% of the observed widths at zero temperature, while for giant quadrupole vibrations it accounts for only 20 - 30% of the observed widths at zero temperature. Received: 9 January 2001 / Accepted: 29 March 2001     

Investigation of the phonon broadening of core levels in NaCl

We have investigated the temperature dependence of the Na⁺-2p-photoemission linewidth from thin films of NaCl. We found a large contribution to the linewidth due to coupling to lattice vibrations. Widths of the Na⁺-2s, Cl^?-3s, Cl^?-2p lines are given at T=300K.     

Study of the ion mobility in a Li0.03Na0.97Ta0.4Nb0.6O3 solid solution by raman spectra

We have studied ion mobility in a Li_0.03Na_0.97Ta_0.4Nb_0.6O₃ solid solution by its Raman spectra. It has been revealed that, as the temperature of the solution is increased to approach the point of the phase transition to a state with a high conductivity with respect to lithium, the lines with frequencies at 77, 118, and 142 cm^?1, which refer, respectively, to librations of oxygen octahedra Nb(Ta)O6 as a whole and vibrations of Li and Na ions in octahedra, considerably broaden, decrease in intensity, and smear into the wing of the Rayleigh line. Remaining lines are preserved in the spectrum. We have observed that the width of the line with a frequency of 118 cm^?1 depends exponentially on temperature, while the width of the line with a frequency of 142 cm^?1 changes linearly with it, which makes it possible to attribute to the line with the frequency of 118 cm^?1 to vibrations of Li⁺ cations, whereas the line with the frequency of 142 cm^?1 should be attributed to vibrations of Na⁺ cations in AO₁₂ cuboctahedra. The average lifetime of Li⁺ ions in equilibrium positions and the jump barrier have been estimated to be ～8 × 10^?12 s and ～20 kJ/mol, respectively. This agrees well with the data in the literature on measurements of electric conductivity.     

Dynamics of photoprocesses induced by femtosecond infrared radiation in free molecules and clusters of iron pentacarbonyl

The dynamics of photoprocesses induced by femtosecond infrared radiation in free Fe(CO)₅ molecules and their clusters owing to the resonant excitation of vibrations of CO bonds in the 5-μm range has been studied. The technique of infrared excitation and photoionization probing (λ = 400 nm) by femtosecond pulses has been used in combination with time-of-flight mass spectrometry. It has been found that an infrared pulse selectively excites vibrations of CO bonds in free molecules, which results in a decrease in the yield of the Fe(CO)₅⁺ molecular ion. Subsequent relaxation processes have been analyzed and the results have been interpreted. The time of the energy transfer from excited vibrations to other vibrations of the molecule owing to intramolecular relaxation has been measured. The dynamics of dissociation of [Fe(CO)₅]_n clusters irradiated by femtosecond infrared radiation has been studied. The time dependence of the yield of free molecules has been measured under different infrared laser excitation conditions. We have proposed a model that well describes the results of the experiment and makes it possible, in particular, to calculate the profile of variation of the temperature of clusters within the “evaporation ensemble” concept. The intramolecular and intracluster vibrational relaxation rates in [Fe(CO)₅]_n clusters have been estimated.     

Optical properties of BiTeI semiconductor with a strong Rashba spin-orbit interaction

We have modeled the 4f ¹-5d ¹ absorption spectrum of a LiYF₄:Ce³⁺ crystal at zero temperature using a microscopic model of the electron-phonon interaction and the real spectrum of LiYF₄ lattice vibrations. Effects caused by mixing of the wave functions of different states of the 5d ¹ excited configuration of the Ce³⁺ ion, which is induced by the electron-phonon interaction, are considered based on the calculations of the second-, third-, and fourth-order exact moments of curvature of the spectrum envelope. We have shown that the large value of the splitting between the maxima of the bands in the absorption spectrum that correspond to transitions to the third and fourth 5d ¹ levels is a result of the nonadiabatic interaction of 5d electrons with lattice vibrations.     

Counterion vibrations in the DNA low-frequency spectra

The vibrations of univalent metal cations with respect to phosphate groups of the DNA backbone are described using the four-mass model approach (S.N. Volkov, S.N. Kosevich, J. Biomol. Struct. Dyn. 8, 1069 (1991)) extended in this paper. The force constant of the counterion-phosphate interaction is determined by considering the DNA with counterions as a lattice of ion crystal. For such ion-phosphate lattice the Madelung constant and the dielectric constant are estimated. The obtained value of the Madelung constant is lower than for the NaCl crystal, and its value is about 1.3. The dielectric constant is within 2.3-2.7 depending on the counterion type and form of the double helix. The calculations of the low-frequency spectra show that for the DNA with metal cations Na⁺ , K⁺ , Rb⁺ and Cs⁺ the frequency of ion-phosphate vibrations decreases from 174 to 96cm^-1 as the counterion mass increases. The obtained frequencies agree well with the vibrational spectra of polynucleotides in a dry state which prove our suggestion about the existence of the ion-phosphate lattice around the DNA double helix. The amplitudes of conformational vibrations for DNA in B -form are calculated as well. The results demonstrate that light counterions ( Na⁺ do not disturb the internal dynamics of the DNA. However, heavy counterions ( Cs⁺ have effect on the internal vibrations of the DNA structural elements.     

First principles study of structural, electronic and vibrational properties of heavily boron-doped diamond

The structural, electronic and vibrational properties of a series of heavily B-doped diamond models have been investigated using the density functional theory within a local density approximation. The doped models C_64 − nB_n (n=1-3) were constructed using supercell techniques. The structural and electronic calculations confirmed that the B dimers are always energetically stable and electrical inactive. The superconducting transition temperature TC is not only decided by the B concentration, but also by the lattice configurations of boron atoms. The vibrational frequencies and eigenmodes were determined using the linear response approach, while Raman intensities were obtained by the second response method. The Raman analysis in terms of atomic vibrations found that the “500 cm⁻¹” and “1230 cm⁻¹” bands are both superposed bands including not only C vibrations but also B-B vibrations and B-C vibrations, respectively. The calculated Raman spectra with isotopic substitutions are in excellent agreement with corresponding experimental results. The reasonable explanation was provided for no obvious Raman shift of main bands from ¹⁰B¹²C to ¹¹B¹²C model.     

Temperature dependence of recoilless fraction in tungsten

The Mössbauer recoilless fractions of¹⁸²W,¹⁸³W,¹⁸⁴W, and¹⁸⁶W have been calculated by using Born-von Karman model of lattice vibrations. There is a good agreement between the experimental and calculated results.