Lattice-vibrational symmetry of ZnP2 and ZnAs2 in the monoclinic system

The vibrational representation is decomposed into irreducible representations in the symmetry points of the Brillouin zone. The selection rules are found for a one-phonon IR absorption and Raman scattering of light. In the IR absorption, 17 frequencies are active with polarization along the second-order axis and 16 frequencies are active with a perpendicular polarization. There are 36 frequencies active in the Raman scattering. The basis vectors of the normal vibrations are found for symmetry points of the Brillouin zone and the nature of the long-wave vibrations is investigated. The decomposition of the direct product of irreducible representations is found (selection rules).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 75–78, May, 1976.The authors thank G. F. Karavaev and N. V. Kudryavtsev for consultations.     

Review on the symmetry-related properties of carbon nanotubes

In this work we review the basic properties of carbon nanotubes from the standpoint of group theory. The zone folding scheme is reviewed in the light of the helical symmetry of the nanotube. The group theory for chiral and achiral nanotubes is reviewed, and the representations of the factor group of the wavevector k are obtained. The similarities and differences between the formalism of the group of the wavevector and that of line groups are addressed with respect to the irreducible representations and quantum numbers associated with linear and angular momenta. Finally, we extend the results of group theory to illuminate the electronic and vibrational properties of carbon nanotubes. Selection rules for the optical absorption and double resonance Raman scattering are discussed for the case where the electron–electron interaction is negligible (metallic nanotubes) and for the case where exciton binding energies are strong and cannot be neglected.     

Theory of Raman scattering in Europium-chalcogenides

The intensity of the spin assisted Raman scattering in the Eu-chalcogenides is calculated using the excited states which were used in the analysis of the optical absorption. Various mechanisms are examined for the Raman scattering. In these mechanisms, the cross effect of the 4f spin-orbit interaction and the exciton-phonon interaction is found to be the most important for the scattering intensity. The characteristics of the Raman scattering from this mechanism are as follows: When the frequency of the incident light is in the tail region of the absorption peak, the polarization of the scattered light is perpendicular to that of the incident light; when the light in the middle region of the absorption peak is applied, the polarization of the incident light is depolarized in the scattered light; the scattering intensity decreases when the spin fluctuation is suppressed by an application of magnetic field or by lowering temperature through the Curie temperature. These characteristics in the Raman scattering have been observed in the experiments.     

Single crystal polarized Raman spectra of the solid electrolyte Cu2HgI4; attempt frequencies for ion motion in Ag2HgI4

The polarized Raman scattering from small single crystals of Cu₂HgI₄ provided assignments for the more prominent Raman features to specific irreducible representations. The E symmetry assignment, mass dependence, and pressure dependence of the 36 cm^?1 band in Cu₂HgI₄ and 24 cm^?1 band in Ag₂HgI₄ indicate that these features approximate the attempt frequency for ion hopping. The unusually high pre-exponential factor in the Arrhenius expression for ion hopping is discussed in light of the observed attempt frequency; we conclude that despite the high activation energy the conduction mechanism is similar to other heavy-metal solid electrolytes.     

1,4-萘醌的太赫兹,远红外及低频拉曼光谱研究

本文对1,4-萘醌进行了太赫兹时域光谱,远红外吸收光谱及低频拉曼散射谱的测试研究。1,4-萘醌的太赫兹吸收光谱与远红外谱仪测得的光谱取得了在1.75 THz(58.3 cm-1)/1.63 THz(54.3 cm-1)等处吸收峰位基本相同、两者相互佐证和补充的结果。将太赫兹和远红外吸收谱与低频拉曼散射谱进行比较,表明两种选择机制不同的光谱在1.04,1.72和4.59 THz等处的峰位基本重合,结合群论的不可约表示理论分析,表明该样品在低频波段具有拉曼活性和红外活性的振动属性(A1、B1或B2)。采用Gaussi-an03软件的密度泛函理论B3LYP函数和6-311基组模拟单分子红外与拉曼光谱,结合实验分析,对部分分子基团或原子振转模式给与了指认。     

Symmetry properties of the lattice vibrations of cadmium diarsenide crystals

The symmetry of the normal vibrations of crystals with the CdAs₂ lattice is established. Selection rules are derived for the infrared absorption and Raman scattering of light; also derived are the selection rules for the inelastic scattering of slow neutrons.     

The superposition of one- and two-phonon absorption and radiation in TeO2 crystal

Raman scattering and IR reflectivity for actual configuration have been investigated. The contours of reflectivity spectra rave been calculated. Phonon parameters have been determined. The temperature dependence of Raman scatterung and IR reflectivity indicated absence of soft modes in optical oscillations. Two-phonon processes of light absorption and radiation have been investigated. In the one-phonon mode frequency range, a two-phonon radiation which is completely absorbed by the crystal itself has been observed.     

Coherent anti-Stokes Raman spectroscopy (CARS)

By putting the non-linear susceptibility tensors in irreducible spherical form it is found that orientation averaging, selection rules, and the angular dependence of intensity on field polarizations all follow in a straightforward way. These spherical tensor techniques are used to treat coherent anti-Stokes Raman scattering (CARS) in detail and a comparison is made with conventional Raman scattering. The selection rules for both processes are shown to be the same. The paper concludes with a brief discussion of the rotational structure in CARS.     

类胡萝卜素的分子光谱研究

类胡萝卜素是含有9个CC共轭双键的短链多烯类生物分子. 特殊的分子结构, 使其不仅在光采集, 光防护, 防癌, 抗癌等生物学领域有重要应用, 而且在分子导线, 光开关, 滤光器等光电器件研制中也有重要的非生物学应用. 本文对它的分子光谱进行研究和总结, 结果表明, 类胡萝卜素具有宽带荧光, 将其用于荧光增强受激拉曼散射可以获得宽带受激拉曼散射; 电子能隙随温度降低而收缩, 电子吸收光谱红移, 这特性使它能研制优质半导体元件; 极大的拉曼活性和三阶非线性系数, CC键基频拉曼散射截面可以比普通分子大10个数量级, 和频、倍频拉曼散射强度也很高, 低温下与基频强度比可达0.5. 类胡萝卜素分子的这些光谱特性对多烯类分子结构、性能研究及其在非生物学中的应用有重要参数价值.     

Der Resonanz-Raman-Effekt bei Erregung im Absorptionskontinuum

When the frequency used for excitation of Raman spectra of gases is high enough to reach the region of continuous absorption typical resonance Raman spectra may be observed. It is shown theoretically that the scattering formula for this case leads to selection rules at variance with the normal Raman effect, allowing an enhanced appearance of overtones. Also this resonance Raman effect has to be understood as a single quantum process.     

Unification of 3-3-1 models

A 3-3-1 model is constructed for three families that can be embedded into a single SU(8) unified model. Assuming appropriate branching rules and symmetry-breaking pattern, a complete fermion content is found within irreducible representations of SU(8), where light Standard Model fermions, heavy 3-3-1 fermions and superheavy fermions may be distinguished.     

Surface-Enhanced Hyper-Raman Spectroscopy

Abstract

Hyper-Raman scattering (HRS), first theoretically predicted by Decius and Rauch in 1959 [l] and experimentally demonstrated by Terhune et al. in 1965 [2], is a nonlinear optical process involving two incident photons (ω₀) and one emitted photon (ω). The emitted hyper- Raman photon frequencies are Raman-shifted relative to the second harmonic frequency (2ω₀) of the incident laser radiation [3–6]. The energy difference (2ω₀ – w) corresponds to one of the characteristicvibrational frequencies of the scattering medium or molecule. In Fig. 1 is given a schematic illustration of resonant and nonresonant HRS. The primary advantage of this nonlinear optical technique lies in its more relaxed selection rules compared with IR and Raman [7,8]. AlllR-active vibrational modes are hyper-Raman allowed, and those modes inactive in both IR and Raman (i.e., the “silent” modes) may be active in hyper-Raman scattering.     

Brillouin scattering studies of rare gas solids

Abstract

The scattering of light by elementar excitations in the matter is results in two phenomena, discriminated by the zero wavevector frequency of the excitation: if this frequency is zero, one deals with Brillouin scattering, and with Raman scattering in the other case. Brillouin scattering results from the interaction of light with thermal excitations (acoustic phonons in a crystal) of a material, or, from a classical point of view, with density waves. Contrary to Raman scattering, the selection rules allow always the observation of at least one mode. It is a powerful technic in the study of rare gases under pressure: at ambient temperature, rare gases crystallize in the face centered cubic structure (except helium which structure was recently found to be hexagonal) and are therefore Raman and infrared inactive.

Experimental results will be reviewed on rare gases and rare gas mixtures in the fluid phase, like He-Ne and He-H₂. These results will be discussed in relation with recent measurements of the frequency of global oscillations of Jupiter.     

Raman scattering using vortex light

We re-examine the theory of Raman scattering in cubic crystals. The unconventional vector potential of vortex light leads to new selection rules. We show that in this novel optical process, (a) silent phonon modes become active and (b) scattering tensors change for ordinary Raman active phonon modes. Calculation based on a simplified model shows that the vortex Raman scattering intensity can be comparable with that of ordinary Raman process.     

Angular dependence of Raman scattering selection rules for long-wavelength optical phonons in short-period GaAs/AlAs superlattices

The angular dependence of Raman scattering selection rules for optical phonons in short-period (001) GaAs/AlAs superlattices is calculated and experimentally studied. Experiments are performed using a micro-Raman setup, in the scattering geometry with the wavevectors of the incident and scattered light lying in the plane of superlattices (so-called in-plane geometry). Phonon frequencies are calculated using the Born model taking the Coulomb interaction into account in the rigid-ion approximation. Raman scattering spectra are calculated in the framework of the deformation potential and electro-optical mechanisms. Calculations show an angular dependence of the selection rules for optical phonons with different directions of the wavevectors. Drastic differences in the selection rules are found for experimental and calculated spectra. Presumably, these differences are due to the Fröhlich mechanism in Raman scattering for short-period superlattices.     

Infrared and Raman spectroscopies of InP/II–VI core-shell nanoparticles

We use infrared (IR) and Raman spectroscopies to investigate the optically active phonon modes in InP nanoparticles and InP/II–VI core-shell nanoparticles fabricated by similar colloidal chemistry methods. The IR transmission spectra of several InP nanoparticle samples exhibit a common absorption feature, which we assign to the Fröhlich mode. The Raman results for the same samples show transverse and longitudinal optical phonon peaks, and scattering strength in between due to surface optical (SO) modes. Infrared spectra of the InP/ZnSe core-shell nanoparticles () exhibit three absorption features, one due to the InP core, and the others associated with the ZnSe shell layer. Raman measurements (12–292 K) also show three phonon-related peaks, whose intensities vary sharply with temperature. The frequencies of the IR and Raman lines are in approximate accord with dielectric continuum theory.     

Point Source of Nonstationary Polarized Radiation in a Homogeneous Fluctuating Medium

Based on the method of irreducible representations of the rotation group, we obtain an analytical expression for the source function of the radiative transport equation with allowance for polarization of light. The scattering indicatrix is assumed Rayleigh. It is shown that not all polarization characteristics of light in a fluctuating medium are lost in time. Some of them always carry information about the emitter and the scattering medium.     

Three phonon processes in GaN

In the harmonic approximation the Hamiltonian of the vibrational states gives the picture of non-interacting phonons in a crystal. At finite temperatures all crystals contain anharmonic lattice forces. The effect of anharmonicity introduces the interactions of independent phonons in crystals. The number of independent vibrational modes originating from the high symmetry points and lines in the Brillouin zone is determined by lattice mode representation (LMR). The three phonon processes such as overtones and combinations are subjected to group theoretical selection rules. The overtones result from the Symmetrized Cubes of active species (irreducible representations (irrps)) and combinations from the complete reduction of the triple Kronecker product of different irrps according to which the vibrational states of crystals are classified. We have determined the symmetry allowed overtones, simple and general combinations of three phonon processes in GaN. The back-scattering Raman spectroscopy from GaN in the region 900–2200 cm⁻¹ yields several optically active transitions; these are analyzed in terms of the derived three phonon Raman selection rules.     

C60-聚甲基丙烯酸甲脂复合膜的结构、光学和电荷转移特性

描述了通过溶胶-凝胶法制备的C₆₀-PMMA复合膜的结构、紫外-可见吸收特性、R aman 散射特性和红外吸收特性.通过对C₆₀紫外-可见吸收光谱，Raman散射谱和红外 吸收谱的实验和理论分析，研究了C₆₀与PMMA之间的电荷转移. 关键词： 溶胶-凝胶法 60-PMMA复合膜')" href="#">C₆₀-PMMA复合膜 电荷转移     

Pressure and temperature dependence of Raman scattering and optical absorption in crystalline S4N4

Raman scattering and optical absorption in crystalline S₄N₄ have been measured both as a function of pressure at 295 K and low temperatures. Polarized single crystal Raman data were also obtained as an aid in the assignment of the Raman active phonons. The pressure coefficients of the Raman active external and S-S stretching modes show a discontinuity near 7 kbar indicative of a second order phase change. The optical absorption edge at about 2.5 eV of a sublimed film of S₄N₄ shows red shifts of 1.3 × 10^?5 eV bar^?1 and 6.3 × 10^?4 eV K^?1 with pressure and temperature respectively. In the light of these results, the electronic, vibrational and structural properties of the crystal are discussed.