Normal vibrational modes in benzil crystals

A group-theoretical analysis of the vibrational spectrum of benzil crystals was carried out. The selection rules and normal coordinates were found. Raman scattering spectra of benzil single crystals were studied in polarized light within a broad temperature range from 100 K to the melting point (T _m=96°C). The experimental data were found to correlate with theory. The temperature dependences of the spectral-line half-widths were used to separate the observed vibrations into translational and librational modes, and the correspondence between the experimentally observed vibrations and their normal coordinates was established in some cases.     

Theory of multiphonon absorption in the wings of internal vibrational modes of impurities in ionic crystals

Green's function methods are applied to obtain the multiphonon absorption coefficient in crystals containing impurities with internal vibrational modes. The results imply that the shape of the wing absorption from such modes is determined by the host lattice density of states, but with a fall-off rate determined by the range of the lattice-impurity interaction potential.     

Influence of surface relaxation on the surface vibrational modes of some ionic crystals

In this paper we evaluate the effects of surface relaxation on the surface vibrational modes of the (001) surfaces of NaCl, NaI and MgO, using bulk shell models which have been modified to allow for distance dependence of the short-range interactions. It is found that these dynamical shell models do not lead to convergent results for the static surface relaxation. In spite of this inconsistency, it is found that surface relaxation gives rise to a new structure of relaxationinduced surface modes, which is common to the three crystals and independent of the details of the relaxation. By using assumed (convergent) relaxation configurations for the MgO (001) surface it is shown that relaxation can account for the high-frequency peak in the surface-excess density of vibrational states of MgO, as found in inelastic neutron scattering experiments on MgO microcrystals. In general, surface relaxation has a profound effect on surface vibrational phenomena, and better shell models will have to be developed to deal with the static and dynamical surface phenomena in a consistent fashion.     

Bi-induced vibrational modes in GaAsBi

We have studied GaAs_1−xBi_x (up to x3%) using Raman scattering with two different polarization configurations. Two Bi-induced phonon modes are observed at 186 cm⁻¹ and 214 cm⁻¹ with increasing Raman intensity as the Bi concentration increases. By comparing Raman selection rules for the observed Bi-induced phonon modes with those for the substitutional N vibrational mode (GaN mode) in GaAsN, the phonon mode at 214 cm⁻¹ is identified as originating from substitutional Bi at the As site in GaAsBi.     

Theory of optical generation of longitudinal phonon modes in ionic crystals

The optical generation of bulk phonon polaritons in ionic crystals is treated by the inclusion of the effects of spatial dispersion in classical dispersion theory. The theory is used to explain structural features of the resonance infra-red reflection spectrum of Cr₂O₃.     

Theory of cross phase modulation for the vibrational modes of trapped ions

We analyze nonlinear coupling between individual vibrational quanta for trapped ions. The nonlinear Coulomb interaction causes a Kerr-type Hamiltonian, for which we derive an analytical expression for the coupling constant χ. In contrast to a previously published formula [C.F. Roos, T. Monz, K. Kim, M. Riebe, H. Häffner, D.F.V. James, R. Blatt, Phys. Rev. A 77 (2008) 040302(R)], our result is in close agreement with experimental data.     

Lattice vibrational modes in potassium thiocyanate

Calculations on long-wavelength lattice vibrations have been made for cystallline KNCS within the framework of the rigid ion model. The short range force constants and effective charges of the ions have been determined from the observed frequencies. Unobserved frequencies are predicted, and normal coordinates have been obtained and schematized.     

Surface vibrational modes in disk-shaped resonators

The natural frequencies and distributions of displacement components for the surface vibrational modes in thin isotropic elastic disks are calculated. In particular, the research is focused on even solutions for low-lying resonant vibrations with large angular wave numbers. Several families of modes are found which are interpreted as modified surface modes of an infinitely long cylinder and Lamb modes of a plate. The results of calculation are compared with the results of the experimental measurements of vibrational modes generated by means of resonant excitation in duraluminum disk with radius of ≈90 mm and thickness of 16 mm in the frequency range of 130–200 kHz. An excellent agreement between the calculated and measured frequencies is found. Measurements of the structure of the resonant peaks show splitting of some modes. About a half of the measured modes has splitting Δ_fsplit/_fmode$\mathrm{\Delta }{f}_{\mathrm{split}}/f_{\mathrm{mode}}$ at the level of the order of 10⁻⁵. The Q-factors of all modes measured in vacuum lie in the interval (2…3) × 10⁵. This value is typical for duraluminum mechanical resonators in the ultrasonic frequency range.     

Low-frequency vibrational modes of glutamine

High-resolution terahertz absorption and Raman spectra of glutamine in the frequency region 0.2 THz-2.8 THz are obtained by using THz time domain spectroscopy and low-frequency Raman spectroscopy. Based on the experimental and the computational results, the vibration modes corresponding to the terahertz absorption and Raman scatting peaks are assigned and further verified by the theoretical calculations. Spectral investigation of the periodic structure of glutamine based on the sophisticated hybrid density functional B3LYP indicates that the vibrational modes come mainly from the inter-molecular hydrogen bond in this frequency region.     

Radiation-pressure-driven vibrational modes in ultrahigh-Q silica microspheres

Quantitative measurements of the vibrational eigenmodes in ultrahigh-Q silica microspheres are reported. The modes are excited via radiation-pressure-induced dynamical backaction of light confined in the optical whispering-gallery modes of the microspheres (i.e., via the parametric oscillation instability). Two families of modes are studied and their frequency dependence on sphere size investigated. The measured frequencies are in good agreement both with Lamb's theory and numerical finite-element simulation and are found to be proportional to the sphere's inverse diameter. In addition, the quality factors of the vibrational modes are studied.     

A first-principles study of vibrational modes in Cu2O and Ag2O crystals

A first-principles investigation of cuprite crystals (Cu₂O and Ag₂O) has been performed. For Cu₂O, the calculated frequencies at the Γ point of the Brillouin zone are in very good agreement with the experimental frequencies. For Ag₂O, the presence of E_u and F_2u vibrational modes with negative frequencies indicates a low temperature phase transition, in agreement with recent high resolution X-ray and neutron diffraction measurements. The energy scanning along these two modes shows a double-well potential, within which only the Ag atoms vibrate. As a result, the origin of the phase transition can be attributed to displacive disorder of the Ag atoms.     

Self-localized single-anharmonic vibrational modes in two-dimensional lattices

Many stationary forms of self-localized modes exist in a simple square and hexagonal lattice. They consist of a certain number of an elementary self-localized anharmonic mode (SLAM). This has several shapes depending on the uniform power of the nearest-neighbour interaction. By comparing SLAMs of the same vibrational frequency a binding energy can be derived for each stationary aggregated SLAM. Also infinite chains and whole lattices of elementary SLAMs are obtained. They have to be distinguished from standing waves of single-anharmonic phonons.     

Localized vibrational modes in optically bound structures

We show, through analytical theory and rigorous numerical calculations, that optical binding can organize a collection of particles into extended, periodic one-dimensional lattices. These lattices, as well as other optically bound structures, are shown to exhibit spatially localized vibrational eigenmodes. The origin of localization here is distinct from the usual mechanisms such as disorder, defect, or nonlinearity but is a consequence of the long-ranged nature of optical binding. For an array of particles trapped by an interference pattern, the stable configuration is often dictated by the external light source, but we observed that interparticle optical binding forces can have a profound influence on the dynamics.     

Long-lived amide I vibrational modes in myoglobin

Pump-probe experiments in the infrared measure vibrational relaxation rates. Myoglobin, which is almost entirely alpha helix in secondary structure, has an unusually long, nonexponential excited state relaxation generated by optically pumping at the blue side ( 5. 85 microm) of the amide I band. The amino acid alanine and the predominantly beta sheet protein photoactive yellow protein do not have such a long-lived state, suggesting that the alpha helix in proteins can support nonlinear states of 15 ps characteristic times.