二维凝聚体系中单轴取向分子的偏振Raman散射强度

分析了薄膜体系几种常用测量坐标下的偏振Raman散射强度表达式,发现当测量坐标与膜坐标重叠对,各种偏振Raman散射强度只需用膜坐标中的Raman散射活性来表达。如果这两个坐标不重叠,需进一步求出膜坐标中Raman张量元二次交叉项的平均值。本文给出了单轴唯一角取向模型下这些二次交叉项的平均值表达式及取向分布模型下膜坐标中所有Raman张量元二次项平均值。     

Effect of the components of the raman scattering tensor on band intensities

The Raman scattering (RS) tensor as a function of excitation radiation frequency is studied taking into account, the vibration quantum. It is shown that the corresponding asymmetric components of the tensor are described by fast converging series. Expressions are obtained for the antisymmetric and symmetric components of the RS tensor. A convenient formula is proposed for the calculation of the RS tensor and its components, where the tensor is represented as a sum of the derivative of static polarizability and the terms containing fast converging series. The formula makes it possible to avoid infinite summation. Computer experiments simulating the dependence of the intensity of RS bands and their components on the excitation frequency are carried out. Moscow State University of Building Engineering. V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 6, pp. 1006–1015, November–December, 1996. Translated by I. Izvekova     

A raman scattering study of the lattice vibrations in disordered α-(CH3)3NHCl and α-CH3NH3Cl

The polarized low-frequency (0–250 cm^?1) Raman spectra of single crystals of the title compounds, in their high temperature orientationally disordered phases are investigated. The lattice vibrations exhibit well-defined polarization selections, which in general can be accounted for by the K = 0 selection rules derived from the time-averaged structure of the crystal. The most striking feature due to disorder appears as a broad diffuse scattering centered at zero frequency and corresponding to specific. Raman tensor elements. This phenomenon is tentatively interpreted in terms of dynamical correlations associated with the reorientational mechanism.     

Raman Scattering Activities for Uniaxially Oriented Molecules

Raman scattering activities were derived for uniaxially oriented molecules. The unique axis of the molecules is assumed to rotate around one of the axes of space-fixed coordinate in a fixed orientation angle with respect to the axis, while the other two principal axes of the molecules are randomly oriented. Expressions for Raman scattering activities in terms of the elements of derived polarizability tensor are given as the function of orientation angle and are tabulated for various symmetries of point groups.     

Polarization selectivity of third-order and fifth-order Raman spectroscopies in liquids and solids

Polarization selectivity of third-order and fifth-order Raman spectroscopies is examined for both isotropic liquids and periodic lattices. Our approach directly applies the symmetry property of the probed system to decompose the polarization tensor elements into independent components. The polarization selectivity predicted by symmetry analysis is rigorous and applicable to higher-order Raman spectroscopy. The different polarization selectivities of isotropic systems and periodic lattices can be used as a signature of the liquid-solid phase transition.     

Dependence of the Daman intensities of combinations and overtones on the frequency of incident light

is shown that the combined method for calculating the Raman tensor elements suggested earlier [1, 2] may be extended to calculations of the intensities of second-order Raman bands (overtones and combinations). The behavior of the intensities of the first- and second-order Raman bands is studied in a wide range of frequencies of incident light, including the resonance region. The resulting equations for the Raman scattering tensor elements are convenient from computational viewpoint; this is especially important for the intermediate frequencies, which are most difficult for calculations. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 3, pp. 465–469, May–June, 1997.     

States of molecular assembly and physical properties of crystalline long-chain compounds studied by vibrational spectroscopy

Various types of molecular assembly of long-chain compounds in solid states were investigated by means of infrared absorption, Raman and Brillouin spectroscopic methods. As for the polymorphism in even-numbered n-fatty acids, three monoclinic modifications, B, C, and E, all consisting of the orthorhombic polyethylene sublattice, give rise to their characteristic infrared and Raman spectra. A dynamical equilibrium between cis and trans conformations of the hydrogen-bonded carboxyl groups in modification C, which is related to the high-temperature stable character of this phase, is reflected to a dramatic change with temperature in the low-frequency Raman spectra. A new type of reversible solid state phase transition was found between two A-type (triclinic) modifications of myristic, palmitic, and stearic acids. The γ→α phase transition of oleic acid was found to be caused by a conformational disordering of polymethylene chains at the lamellar interfacial region. Two basic polytype structures, Mon and Orth II, of stearic acid B were investigated, and it was found that the low-frequency phonon frequencies (below 50 cm⁻¹) were strongly influenced by the polytype structure. Based on the spectroscopic considerations, Orth II was predicted as the thermodynamically stable phase around room temperature compared with Mon, and the stability is responsible for the vibrational free energy term. Some experimental findings which support this prediction were obtained. The values of the stiffness tensor elements of Mon and Orth II, measured by Brillouin scattering, indicate that the mechanical behavior of bulk crystals is very dependent on the polytype structure. The relationship between the mobility of chain molecules and the width of the spectral bands was investigated in a quantitative manner for the case of n-alkane molecules entrapped in the urea inclusion adducts. The changes in the half-width for the polarization components of various Raman bands on the transition from the orthorhombic to the hexagonal phase are interpreted in terms of the correlation functions of the Raman tensor related to the rotational motion of the alkane molecules around the chain axes.     

Temperature study of a glycine radical in the solid state adopting a DFT periodic approach: vibrational analysis and comparison with EPR experiments

The major radiation-induced radical in crystalline glycine is examined using DFT calculations, in which both molecular environment and temperature are accounted for. This is achieved by molecular dynamics simulations of the radical embedded in a supercell under periodic boundary conditions. At 100 and 300 K, a vibrational analysis is performed based on Fourier transformation of the atomic velocity autocorrelation functions. By the use of a novel band-pass filtering approach, several vibrational modes are identified and associated with experimental infrared and Raman assignments. Decomposition of the calculated spectra in terms of radical motion reveals that several vibrational modes are unique to the radical, the most prominent one at 702 cm(-1) corresponding to out-of-plane motion of the paramagnetic center, inversely coupled with similar motion of the carboxyl carbon. A hybrid periodic/cluster scheme is used to evaluate the EPR properties of the glycine radical along the MD trajectories resulting in temperature dependent magnetic properties. These are compared with available experimental data conducted at 77 K and room temperature. Ground state or low temperature calculations yield very good agreement with 77 K experimental EPR properties. From the 300 K simulations, an important improvement is achieved on the isotropic hyperfine coupling of the (13)C tensor, which becomes closer to the value measured at room temperature. It is established that this is the result of a nonlinear relation between the planarity of the radical center and the isotropic couplings of the nuclei bound to it. Finally, a critical reevaluation of the experimental (14)N hyperfine tensor data strongly suggests that an erroneous tensor was reported in literature. It is convincingly shown that from the same experimental data set a different tensor can be derived, which is in substantially better agreement with all calculations.     

Polarization-dependent effects in surface-enhanced Raman scattering (SERS)

A few key examples of polarization effects in surface-enhanced Raman scattering (SERS) are highlighted and discussed. It is argued that the polarization of the local field, which is felt by an analyte molecule in a location of high electromagnetic field enhancement (hot-spot), can be very different from that of the incident exciting beam. The polarization dependence of the SERS signal is, therefore, mostly dictated by the coupling of the laser to the plasmons rather than by the symmetry of the Raman tensor of the analyte. This sets serious restrictions for the interpretation of both single-molecule SERS polarization studies and for the use of circularly polarized light in techniques like surface-enhanced Raman optical activity.     

Resonant Raman spectra of diindenoperylene thin films

Resonant and preresonant Raman spectra obtained on diindenoperylene (DIP) thin films are interpreted with calculations of the deformation of a relaxed excited molecule with density functional theory (DFT). The comparison of excited state geometries based on time-dependent DFT or on a constrained DFT scheme with observed absorption spectra of dissolved DIP reveals that the deformation pattern deduced from constrained DFT is more reliable. Most observed Raman peaks can be assigned to calculated A(g)-symmetric breathing modes of DIP or their combinations. As the position of one of the laser lines used falls into a highly structured absorption band, we have carefully analyzed the Raman excitation profile arising from the frequency dependence of the dielectric tensor. This procedure gives Raman cross sections in good agreement with the observed relative intensities, both in the fully resonant and in the preresonant case.     

Theory of raman scattering from molecules. Summation over vibrational states

Upper and lower bounds of the vibrational sums involved in the polanzability tensor are derived. The lower bound leads to a simplified formula applicable to resonance Raman scattering in both weak and strong coupling cases. A new expansion of the vibrational sum is introduced and useful expressions for excitation profiles are obtained.     

Convergence of vibrational angular momentum terms within the Watson Hamiltonian

Vibrational angular momentum terms within the Watson Hamiltonian are often considered negligible or are approximated by the zeroth order term of an expansion of the inverse of the effective moment of inertia tensor. A multimode expansion of this tensor up to second order has been used to study the impact of first and second order terms on the vibrational transitions of N(2)H(2) and HBeH(2)BeH. Comparison with experimental data is provided. The expansion of the tensor can be exploited to introduce efficient prescreening techniques.     

Combined method for calculating raman band intensities with consideration for the dependence of the raman tensor on the frequency of exciting radiation

It is shown that at certain assumptions the tensor of Raman bands can be represented as a sum of the Placzek term and the fast convergent series that contains information on the sensitivity of the tensor elements to the frequency of exciting radiation. The convergences of the corresponding series and the frequency dependences of the Raman band intensities for particular molecules are studied by computer experiments. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Moscow State Civil-Engineering University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 241–249, March–April, 1996. Translated by I. Izvekova     

Analogy between real irreducible tensor operator and molecular two-particle operator

. Molecular matrix elements of a physical operator are expanded in terms of polycentric matrix elements in the atomic basis by multiplying each by a geometrical factor. The number of terms in the expansion can be minimized by using molecular symmetry. We have shown that irreducible tensor operators can be used to imitate the actual physical operators. The matrix elements of irreducible tensor operators are easily computed by choosing rational irreducible tensor operators and irreducible bases. A set of geometrical factors generated from the expansion of the matrix elements of irreducible tensor operator can be transferred to the expansion of the matrix elements of the physical operator to compute the molecular matrix elements of the physical operator. Two scalar product operators are employed to simulate molecular two-particle operators. Thus two equivalent approaches to generating the geometrical factors are provided, where real irreducible tensor sets with real bases are used. Received: 3 September 1996 / Accepted: 19 December 1996     

Theoretical study of sum-frequency vibrational spectroscopy off electronic resonance on limonene chiral liquids

The sum-frequency vibrational spectroscopy (SFVS) off electronic resonance on chiral liquids is analyzed using the approach of antisymmetric nonresonant vibrational Raman scattering tensor calculation, which is based on the direct Taylor expansion of electronic transition moments in vibrational normal coordinates. A single-excitation configuration interaction treatment is applied to compute the SFVS off electronic resonance for (R)-limonene molecules, and the model spectra compare favorably with experimental data. This direct evaluation approach may provide a method of computing antisymmetric nonresonant vibrational Raman polarizabilities and predicting and assigning the SFVS off electronic resonance on chiral liquids.     

Polarized vibrational,electron absorption and luminescence spectra of Nd(NO3)3(DMSO)4 single crystal

Infrared and Raman spectra of polycrystalline and single crystal Nd(NO₃)₃(DMSO)₄ have been measured. The molecular and crystal structure is analysed in terms of a monoclinic unit cell of C2/c symmetry. A comparison of i.r. spectra measured parallel and perpendicular to the b axis of the unit cell as well as Raman spectra for several tensor elements was used to describe the internal and external optical modes. The optical absorption and luminescence spectra of neodymium nitrate tetra dimethyl sulphoxide single crystal were recorded at 77 and 300 K between 4000–30 000 cm⁻¹. The electronic transitions were assigned to the crystal field splitting manifolds. The band intensity measurements performed for | and ⊥ b polarizations are related to Judd—Ofeld parameters and the anisotropy of these values is discussed.     

Excitation profiles in resonance Raman scattering: Comparison between the displaced oscillator model and the reflection approximation

We study the resonance Raman scattering tensor with a model based on a displaced harmonic oscillator. It is shown that when the lines of the absorption spectrum are broadened, the Raman excitation profiles are determined by the formulas of the reflection approximation.     

FT-IR and FT-RAMAN investigations of nicotinaldehyde

The Fourier transform Raman and infrared spectra of nicotinaldehyde were recorded and the observed frequencies were assigned to various modes of vibration in terms of fundamentals by assuming Cs point group symmetry. A normal coordinate analysis was also carried out using a simple valence force field. A complete vibrational analysis is presented here for this molecule and the results are briefly discussed.