A lattice dynamical investigation of the Raman and the infrared frequencies of the cubic Y2Ru2O7 pyrochlore

A short-range force constant model has been applied for the first time to investigate the Raman and the infrared frequencies in Y₂Ru₂O₇ pyrochlore in its cubic phase of space group Fd3m. The calculations of zone center phonons have been made with four stretching and three bending force constants. The calculated values of Raman and infrared frequencies are in good agreement with the observed ones.     

Phonons at the zone center for α-NaAlH4

A short-range force constant model has been applied for the first time to investigate the phonons in α-NaAlH₄ having body centered tetragonal Scheelite structure .The normal symmetry coordinates for the Scheelite structure were computed to investigate the phonons at the zone center. The phonons for α-NaAlH₄ have been calculated involving five stretching and two bending force constants .The calculated Raman frequencies exhibit good agreement with the available measured values. The infrared frequencies have been assigned proper modes for the first time.     

Lattice dynamical study of Sr2B′UO6 (B′=Ni, Co) double perovskites

A short range force constant model has been used within the normal coordinate analysis framework for the first time to investigate the lattice dynamics of Sr₂B′UO₆ (B′=Ni, Co) double perovskites having space group P2_1/n. The zone centre phonons have been calculated with ten stretching force constants and eight bending force constants in the nickel compound and ten stretching and nine bending force constants in cobalt compound. The theoretically obtained values of Raman and infrared wave numbers exhibit a satisfactory agreement with the experimental values. A complete assignment of these frequencies to specific modes has also been made.     

Zone center frequencies of the orthorhombic NdMnO3 perovskite

A short range force constant model has been applied for the first time to investigate the phonons in NdMnO₃ perovskite in the orthorhombic phase. The calculations with nine stretching and eight bending force constants provide good agreement for the observed Raman frequencies. The infrared frequencies have been assigned for the first time.     

Solvent and temperature dependence of the phosphorescence decay time of hexacyanochromate (III)

The temperature dependence of the ²E_g - ⁴A_2g phosphorescence of tetrabutylammonium hexacyanochromate (III) dissolved in various solvents has been measured within the liquid range of these solvents. In this limited temperature range, the reciprocal decay times obey Arrhenius relationship. From the absence of a solvent isotope effect, in ethanol and methanol and their monodeuterated analogues it is concluded that hydrogen bonds between the solvent and the complex ion do not provide promoting or accepting modes for the radiationless deactivation. The room temperature decay times have been found to correlate with the solvatochromic shift of the ⁴A_2g ? ⁴T_2g absorption bands and with Dimroth's E_T parameter. According to the selection rules for non-radiative decay a combination of CN stretching with either a Cr-C-N bending or a Cr-C stretching vibration is postulated as the promoting mode.     

Fano line shape and anti-crossing of Raman active E2g peaks in the charge density wave state of NbSe2

Low energy Raman scattering from the ab-plane of the 2H polytype single crystal NbSe₂ has been investigated in the normal (N), incommensurate charge density wave (ICDW) and superconducting (SC) phases. The temperature dependence of the polarization resolved Raman response has been obtained for the excitation wavelength of 647 nm and fitted to phenomenological models for the E_2g and A_1g symmetry channels. The A_1g response can be fitted by a simple damped oscillator peak superimposed on continuous background. The E_2g response displays an anti-resonance interference pattern between the inter-layer phonon and the CDW-induced mode such that a hybridized configuration (Fano line shape [1]) is required for modelling. The polarization specific peak maxima positions and line widths as a function of temperature, deduced in this manner, are presented. Partial suppression of the electronic continuum scattering in the Raman shift range up to 110 cm⁻¹ in the A_1g symmetry channel and beyond 300 cm⁻¹ in the E_2g symmetry channel is indicative of high energy electronic states far away from the Fermi surface participating in the ICDW formation.     

Lattice vibrations in the orthorhombic commensurate charge density wave phase of 2H-TaSe2

Lattice vibrations in 2H-TaSe₂ have been reinvestigated by Raman scattering in view of the recent orthorhombic structure of the commensurate charge density wave (CCDW) phase. The renormalization of six charge density waves on two layers gives four A_g modes and two B_1g modes in the orthorhombic CCDW phase, in place of two A_1g modes and two E_2g modes in the hexagonal CCDW phase which had been believed. The splitting of the E_2g modes to the A_g and B_1g modes in the orthorhombic symmetry depends on the interlayer interaction. The observed small splitting less than 3 cm^-1 shows the weak interlayer interaction. The energies of the four A_g modes and the two B_1g modes are presented as a function of temperature.     

A lattice dynamical investigation of Raman and infrared wavenumbers at the zone center of the orthorhombic NdNiO3 perovskite

A short-range force constant model has been applied for the first time to investigate the phonons in NdNiO₃ perovskite in the orthorhombic phase. The calculations with the ten stretching and ten bending force constants provide a good agreement for the observed Raman and infrared wavenumbers. The infrared wavenumbers have been calculated for the first time. All Raman and infrared wavenumbers are assigned to their specific mode of vibrations.     

BaVS3晶格动力学研究

采用基于密度泛函理论的平面波赝势方法,在局域密度近似下采用线性响应的密度泛函微扰理论研究了具有六角结构的BaVS₃化合物的晶格动力学性质,得到了整个声子谱.计算得到的Γ点拉曼频率和实验数据进行了比较,其中E²_2g模、A_1g模和实验测量值符合得比较好.对于E³_2g模,采用线性响应计算的结果与实验值差别较大.对该模应用冻结声子方法研究后认为差异主要是由于E³_2g模的较强的非谐性引起的.此外V原子在平面内的振动模E¹_2u出现了虚频.虚频的出现预示着六角相的BaVS₃结构的不稳定性,从而很好地解释了该材料由六角相到正交相的结构相变. 关键词： 晶格动力学 密度泛函 赝势方法 3')" href="#">BaVS₃     

The force field and rz structure of Ketene

Recently determined Coriolis coupling constants for H₂ and D₂ Ketene, centrifugal distortion constants for H₂, HD, and D₂ Ketene have enabled 16 of the 19 parameters in the general force field of Ketene to be determined with significance, the ambiguity between the choice of two sets of A₁ and B₁ species force constants being removed. The r₀ structure has been redetermined using the latest values of the rotational constants of H₂, HD, and D₂ Ketene and an r_z structure has been determined for the first time.     

A lattice dynamical investigation for the Raman and the infrared frequencies of Bi2W2O9

Studies on infrared and Raman-active phonons in the Aurivillius ferroelectric Bi₂W₂O₉ were performed theoretically. The Raman and infrared phonons were calculated by applying a short-range force constant model using normal coordinates having space group Pna2₁. Sixteen stretching, two repulsive and seventeen bending force constants were used for the calculations of the zone center phonons. The calculated Raman and infrared wavenumbers are in very good agreement with the experimental ones in the literature. Potential energy distribution for this compound has also been investigated for the contribution of each force constant towards the Raman and the infrared wavenumbers.     

Cartesian Dynamics of Simple Molecules. IX. Pyramidal Quadratomics (C3v Symmetry)

The vibrations of pyramidal AB₃ type molecules with C_3v symmetry are analyzed in terms of Cartesian co-ordinates, and analytical expressions for the four normal mode frequencies are derived as functions of two stretching and two bending force constants. Optimized values of these force constants are obtained for a number of tri-hydride and tri-halide molecules by substitution of available spectroscopic and geometric data. The physical validity of the model is confirmed by comparing the calculated and observed frequencies of several isotopic species.     

Features of the E 2 g phonon mode in MgB2

A model estimate of the energy eigenvalues of the E _2g phonon mode of the ion vibrations in the plane of boron atoms is obtained. It is shown that the anharmonic contribution to the energy of E _2g monotonously increases with the increase in z = A ₄/A ₂², where A ₄ is the fourth-order anharmonic coefficient and A ₂ is the harmonic constant. The results agree with the estimate in the Hartree-Fock approach. However, the discrepancy between these results and Raman spectroscopy data indicates the necessity to account for the influence of the electron-phonon interaction on the energy of E _2g in more detail. Original Russian Text ? V.V. Rzhevskii, 2009, published in Vestnik Moskovskogo Universiteta. Fizika, 2009, No. 1, pp. 93–94.     

Anomalous phonon intensities in the Raman spectrum of disordered CsMg1−xCoxCl3

The five Raman-active $\text{k}\text{= 0}$ phonons have been measured at low temperatures and for a range of x in the disordered lattice CsMg_1-xCo_xCl₃. While the E_2g^a, E_2g^b, E_2g^c and A_1g modes at 55.0, 132.0, 189.0 and 255.0 cm^?1 for x = 0 exhibit normal one-mode behaviour, the intensity of the E_1g phonon at 127.5 cm^?1 has a most unusual concentration dependence which requires a new theory.     

On the study of the vibrational energy levels of Arsine molecule

We compare two formalisms applied to the vibrational modes of the molecule of AsH₃ of C_3v molecular symmetry group. Indeed, the close stretching modes of this molecule may be considered as those of a three-dimensional oscillator whereas the bending modes may be considered either as a one-dimensional oscillator of symmetry A₁ and a two-dimensional oscillator of symmetry E or as an approximate three-dimensional oscillator. So, we have applied the U(p + 1) formalism to the both stretching and bending modes and introduced coupling terms acting on an appropriate coupled vibrational basis through a local mode formalism. We have then compared the result of our fitting with those obtained with the coupling of a local mode formalism adapted to the stretching vibrations with a normal mode formalism for the bending ones. Finally we compare our results with other methods recently proposed in the literature.     

Raman spectrum of metallic layered compound NbSe2

Raman spectrum of layer-type compound NbSe₂ has been obtained at liquid nitrogen temperature. The frequencies of the Raman active modes E²_2g, A_1g and E¹_2g are measured to be 29.6 cm^?1, 230.9 cm^?1 and 238.3 cm^?1 respectively. The observed second order Raman spectrum of NbSe₂ is very different from the corresponding spectrum of MoS₂. These results show that the force constants of NbSe₂ are less anisotropic than those of MoS₂.     

Raman scattering in FeF3

Peaks in the FeF₃ phonon Raman spectrum are assigned to the A_1g(312 cm^-1) and E_g(105, 187, 450 cm^-1) representations of the D⁶_3d group. Anomalous temperature dependence of the frequency, intensity and line width of the 187 cm^-1 line has been observed.     

The infrared spectrum of the ν1 and ν4 bands of 28SiH3D

The spectrum of the ν₁ and ν₄ SiH stretching bands of ²⁸SiH₃D have been recorded and analyzed. The degenerate stretching mode is at 2188.504 cm^?1, only 1.103 cm^?1 above the symmetric stretching mode. Several accidental and essential resonances affect these bands but all have been successfully analyzed by diagnolization of the secular determinant complete through the second order of the transformed Hamiltonian. One accidental resonance leads to a number of forbidden transitions through which a value of the rotational constant A₀ has been obtained.     

Phonon density of states of CdI2 deduced fro,the fine structure of the 3A2g → 1Eg electronic transition of CdI2:Ni2+

The absorption and MCD spectra of the ³A_2g → ¹E_g transition of CdI₂:Ni²⁺ at about 12,500 cm^?1 have been measured. The unusual vibronic fine structure is explained by the coupling of the phonons of the CdI₂ lattice to the electronic states of Ni²⁺. The dispersion curves for the acoustical and optical branches in the Brillouin Zone of CdI₂ are deduced.