Determining Eigenfrequencies and Homogeneous Widths of Lines of Intermolecular Vibrations in Water and in Aqueous Solutions of Hydrogen Peroxide Using Raman Spectroscopy

We have examined low-frequency Raman spectra of intermolecular vibrations of weak aqueous solutions of hydrogen peroxide and water. The differences between the observed Raman frequencies and the data from the literature on the IR-absorption frequencies of the same vibrations, as well as the interrelations between the frequencies and the widths of Lorentzian contours that approximate the vibrational spectra of the dynamic susceptibility, have been discussed. Based on a model of free damped vibrations of a classical oscillator with an inhomogeneous broadening, we have explained these effects for the first time. The homogeneous line widths and the damping times of the observed intermolecular vibrations have been determined. The eigenfrequencies of these vibrations have been calculated, and they have been shown to agree well with the data from the literature on the frequencies of IR absorption of water. We have shown that these parameters of intermolecular vibrations for water and for aqueous solutions of hydrogen peroxide differ from each other.     

Davydov splitting and rigid-layer modes in InS crystal

Polarized infrared reflection spectra of InS layer crystal have been measured. Both components of the Davydov doublets caused by the splitting of intralayer vibrations due to the interlayer interactions are active in i.r. spectra. Doublet frequencies have been used to calculate the rigid-layer mode frequencies which are correlated with the experimental ones. It has been established that in InS crystal the frequencies of rigid-layer modes are much higher than those of ordinary layer crystals. Atomic displacements have been found at i.r.-active normal modes.     

Vibrational Spectra of a Linear Alternating L,D Hexapeptide with a Type II β-Turn Structure

Raman and infrared spectra of Boc-(D-aIle-L-Ile)₃-OMe (ILEU-6) and its N-deuterated derivative have been measured. Conformationally sensitive amide vibrations have been identified and compared with the observed and calculated frequencies of Pro-Leu-Gly-NH₂ which has a type II β-turn structure. The observed frequencies of ILEU-6 have also been compared with the normal mode calculations of a standard model type II β-turn structure and a good agreement has been found in these comparisons. The additional frequencies observed for this particular structure are assigned to the residues that are not involved in the β-turn.     

Dimensional resonances of elastic and magnetoelastic vibrations in two layered structure

Peculiarities of dimensional resonances of elastic and magnetoelastic waves in bi-layered insulator structure: ferromagnetic film–non-magnetic elastic substrate have been investigated. Dependences of resonant frequencies of vibration modes upon thicknesses of magnetic and non-magnetic layers, elastic and magnetoelastic parameters, applied magnetic field have been calculated. The presence of peculiarities of resonant frequencies harmonics behavior with change of magnetic layer thickness have been shown.     

Vibrational Spectroscopic Analysis of L,D-Dipeptides

Raman and infrared spectra of Boc-D-Leu-L-Leu-OMe, Boc-L-Ile-D-aIle-OMe and its N-deuterated derivative have been obtained. Normal mode frequencies on the models of these dipeptides have been calculated and the conformationally sensitive amide I, II, III and V modes are compared with the experimentally observed frequencies. The calculated frequencies are in good agreement with the observed frequencies. It is observed that the amide frequencies in these dipeptides are not very sensitive to their backbone conformation. This is in contrast to the well established conformational dependence of the amide modes in peptides, polypeptides and proteins. The normal mode calculations on these peptides also show absence of mixing in amide I and II modes, and hence lack of appreciable splitting in these modes due to transition dipole coupling.

     

Density Functional Theory Calculations of Normal Modes and Infrared Intensities for Tetraazaporphin

By the DFT/B3LYP method with a 6-31G(d) basis set, the structure, normal vibration frequencies, and band intensities in the IR spectra of porphin, tetraazaporphin (TAP), and three of its isotopomers have been calculated. Scaling of the force constants for porphin vibrations in nonredundant natural coordinates has been performed. The obtained scaling factors are used to predict the force field and normal modes of TAP and three of its isotopomers. To carry out a reliable assignment of the TAP frequencies, two alternative methods have been used: a wavenumber-linear scaling method and the frequency-shift method. There is good agreement between the frequencies predicted by the three methods used. The IR absorption spectrum of TAP has been simulated. Assignments of the observed experimental frequencies of TAP of odd symmetry types are suggested.     

Plasmon oscillations in ellipsoid nanoparticles: Beyond dipole approximation

The plasmon oscillations of a metallic triaxial ellipsoid nanoparticle have been studied within the framework of the quasistatic approximation. A general method has been proposed for finding the analytical expressions describing the potential and frequencies of the plasmon oscillations of an arbitrary multipolarity order. The analytical expressions have been derived for an electric potential and plasmon oscillation frequencies of the first 24 modes. Other higher orders plasmon modes are investigated numerically.     

Radiometric Measurements of Rain Attenuation at 22.2 and 31.4 GHz Over Calcutta

Measurements of rain attenuation over Calcutta have been made using radiometers operating at frequencies of 22.235 and 31.4 GHz. The results have been correlated with observations of rainfall rates made with a fast-response rain gauge. The distributions of peak rain rates over Calcutta for two different years and the cumulative occurrences of rainfall rates and attenuations at the two frequencies are presented.     

Vibrational spectra and elastic piezoelectric and polarization properties of the α-SrB4O7 crystal

The crystal lattice vibrational frequencies in the center of the Brillouin zone have been determined with the Raman spectroscopy method. The lattice vibrational frequencies, the phonon density of states, elastic and piezoelectric moduli, Born dynamic charges, and high-frequency dielectric constant have been calculated using the density functional method. All calculated quantities have been compared to the experimental data. A model of a nonpolar paraelectric phase for this compound, as well as a mechanism of the formation of domain in it, has been proposed. The polarization in the experimentally observed polar phase has been calculated.     

Vibronic Structures of the Ground and Excited Singlet Electronic States of Dimethylnaphthalenes Cooled in a Supersonic Jet

Abstract

Fluorescence excitation and dispersed fluorescence spectra of jet-cooled naphthalene and 2,6-, 2,7-dimethylnaphthalenes have been measured. The frequencies of optical active vibrations in the ground and first excited singlet states have been determined. The new technique for calculation of planar vibration frequencies of polycyclic benzenoid hydrocarbons in the excited electronic states has been developed. The vibration frequencies in the ground and first excited singlet states of these molecules were calculated using the developed technique and the Ohno's model. The interpretation of vibronic spectral lines based on the comparison of the calculated and experimental data was made. The calculation rms errors for the vibration frequencies in the ground electronic states of the investigated molecules do not exceed 20 cm^?1 and are approximately 1.5 times higher for excited states without additional adjustment of parameters for individual molecules.     

Normal modes and quality factors of shielded composite dielectric spherical resonators

Electromagnetic field analysis of shielded composite dielectric spherical resonator in which the dielectric sphere is composed of two concentric spheres with different dielectric materials has been made. Characteristic equations for the TE_nmℓ and TM_nmℓ modes have been derived. From these characteristic equations, the resonant frequencies and quality factors have been calculated using numerical method. Computations of the resonant frequencies and quality factors have been made for resonators with parameters suitable for the optical and microware regions. In this paper we have presented the analysis and the results obtained from the numerical computations for shielded composite dielectric spherical resonator in which the dielectric sphere is composed of two concentric spheres with different dielectric materials. Starting from the Maxwell’s equations for such a resonators have been derived and resonant frequencies and quality factor’s have been calculated for the TE_nmℓ and TM_nmℓ modes using numerical method.     

Free vibration analysis of stiffened plates using finite difference method

Free vibration characteristics of rectangular stiffened plates having a single stiffener have been examined by using the finite difference method. A variational technique has been used to minimize the total energy of the stiffened plate and the derivatives appearing in the energy functional are replaced by finite difference equations. The energy functional is minimized with respect to discretized displacement components and natural frequencies and mode shapes of the stiffened plate have been determined as the solutions of a linear algebraic eigenvalue problem. The analysis takes into consideration inplane deformation of the plate and the stiffener and the effect of inplane inertia on the natural frequencies and mode shapes. The effect of the ratio of stiffener depth to plate thickness on the natural frequencies of the stiffened plate has also been examined.     

Free vibration of thin circular rings on periodic radial supports

Natural frequencies and normal modes are obtained for in-plane, inextensional vibrations of a thin circular ring with equi-spaced, identical radial supports. A wave approach is used. Natural frequencies are determined from the propagation constants of the ring by considering it as an endless periodic structure. Normal modes are obtained by superposition of a pair of opposite-going free wave groups. Numerical results have been presented for both rigid and circumferentially guided supports. It has been shown that at certain frequencies two different natural modes can exist. This has been verified experimentally.     

Absolute frequency measurements of the 2-0 band of CO at 2.3 μm; Calibration standard frequencies from high resolution color center laser spectroscopy

The absolute frequencies of 20 lines of the 2-0 band of CO near 4260 cm^?1 have been measured by heterodyne frequency measurement techniques. Eleven of the lines were measured by saturated absorption techniques which produced linewidths of about 3 MHz. New rovibrational constants have been fitted to these measurements. A table of calculated transition frequencies is given with estimated absolute uncertainties as small as 0.0000023 cm^?1 (70 kHz) near the band center. The pressure shifts of three lines have been measured and fall in the range from ?0.9 to ?3 kHz/Pa (?122 to ?400 kHz/Torr). It is suggested that the generally accepted frequencies of the 1-0 band of CO should be lowered by 7 MHz.     

Vibration of a parallelogram membrane

The approximate natural frequencies of oblique membranes have been determined for arbitrary skew angles and side ratios. The response of such a membrane to a forcing function is then obtained in a similar fashion. The lower natural frequencies have been presented for various side ratios of the membrane as a function of the skew angle and vice versa. With increasing skew angle they increase rapidly. For large skew angles the lower natural frequencies are mainly made up by those of the index n = 1. This is especially valid for membranes of large side ratio.     

Frequencies of two running circular electromagnetic waves in a rotating frame of reference

The frequencies of two running electromagnetic waves interacting with a system of identical two-level atoms in a rotating frame of reference have been calculated with the help of quantum electrodynamics and the covariant formalism.The existence of two states of the perturbed electromagnetic field with degenerate and nondegenerate frequencies has been shown.     

Observation of the modulation instability and spin wave solitons in ferromagnetic films under the conditions of coexistence of four-wave and three-wave parametric processes

Nonlinear phenomena that arise during the propagation of spin waves in thin ferromagnetic films under conditions of the simultaneous existence of three-wave and four-wave parametric processes have been investigated. Investigations have been performed for single-frequency and double-frequency regimes of excitation of intense spin waves. The spontaneous modulation instability of the monochromatic running spin wave has been revealed for the first time at frequencies at which three-wave decay processes are allowed. The pronounced generation of a periodic sequence of bright spin wave solitons has been observed under excitation of two monochromatic spin waves at the same frequencies.     

Vibration of ZnO nanotubes: a molecular mechanics approach

We investigate the vibrational properties of two kinds of single-wall ZnO nanotubes. The simulations are carried out for three types of zigzag nanotubes (5,0), (8,0), (10,0) and armchair nanotubes (3,3), (4,4), (6,6). The natural frequencies are determined by means of the molecular mechanics approach with the universal force field potential. The first four natural frequencies are obtained for length/diameter ratio of about 5–20. The vibration modes associated with these frequencies have been computed. Closed-form analytical expressions have been derived using the continuum shell theory for the physical explanations of the simulations results. We observe that the natural frequencies decrease as the aspect ratios increase. The results follow similar trends with results of previous studies for carbon nanotubes (CNT). However, the magnitudes of the frequencies are lower from the corresponding CNT counterparts, indicating that ZnO nanotubes are comparatively less stiff.     

Further Theoretical Investigations for Laser Relative Intensity Noise with Fiber Nonlinearities and Higher Order Dispersion

In this article, we theoretically investigate relative intensity noise (RIN) in optical communication systems with fiber nonlinearities due to optical Kerr effects and higher order dispersion. The impact of modulation frequencies, launch power, and laser bias current on RIN has been illustrated. We show that RIN increases with modulating frequencies up to the resonance frequency and launch power, and decreases in the laser bias current. We also show that higher order dispersion terms have no impact on the RIN, but with first order dispersion compensation the higher order dispersion terms have significant impact at high modulating frequencies. The RIN with and without fiber nonlinearities is further investigated. It has been shown that the RIN with fiber nonlinearity is more than the RIN without nonlinearity and the effect of nonlinearity appears at higher modulation frequencies only.