Frequency Shifts Of Modes Research Articles

Nonlinear Dispersion Relation of Geodesic Acoustic Modes

The energy input and frequency shift of geodesic acoustic modes (GAMs) due to turbulence in tokamak edge plasmas are investigated in numerical two-fluid turbulence studies. Surprisingly, the turbulent GAM dispersion relation is qualitatively equivalent to the linear GAM dispersion but can have drastically enhanced group velocities. In up-down asymmetric geometry the energy input due to turbulent transport may favor the excitation of GAMs with one particular sign of the radial phase velocity relative to the magnetic drifts and may lead to pulsed GAM activity.

High-pressure study of tetramethylsilane by Raman spectroscopy

High-pressure behavior of tetramethylsilane, one of the Group IVa hydrides, was investigated by Raman scattering measurements at pressures up to 142 GPa and room temperature. Our results revealed the phase transitions at 0.6, 9, and 16 GPa from both the mode frequency shifts with pressure and the changes of the full width half maxima of these modes. These transitions were suggested to result from the changes in the inter- and intra-molecular bonding of this material. We also observed two other possible phase transitions at 49-69 GPa and 96 GPa. No indication of metallization in tetramethylsilane was found with stepwise compression to 142 GPa.

Dynamic structures of aqueous oxalate and the effects of counterions seen by 2D IR

Two dimensional vibrational echo spectra of oxalate in the carboxylate asymmetric stretch region in D(2)O show two transitions having anomalously slow spectral diffusion and a third transition having relaxation properties typical of the free carboxylate ion. Quantitative analysis of the frequency shifts of the carboxylate asymmetric stretch modes caused by a singly charged cation in the oxalate hydration shell supports that ion pairs can be responsible for these new transitions. Experimental evidence and DFT calculations are consistent with oxalate forming a mixture of "side-on" and "end on" contact ion pairs wherein the carboxylate groups are protected from mobile heavy water molecules.

Measurement scheme for the Lamb shift in a superconducting circuit with broadband environment

Motivated by recent experiments on quantum mechanical charge pumping in a Cooper pair sluice, we present a measurement scheme for observing shifts of transition frequencies in two-level quantum systems induced by broadband environmental fluctuations. In contrast to quantum optical and related set-ups based on cavities, the impact of a thermal phase reservoir is considered. A thorough analysis of Lamb and Stark shifts within weak-coupling master equations is complemented by non-perturbative results for the model of an exactly solvable harmonic system. The experimental protocol to measure the Lamb shift in experimentally feasible superconducting circuits is analysed in detail and supported by numerical simulations.

Ultrafast Vibrational Frequency Shifts Induced by Electronic Excitations: Naphthols in Low Dielectric Media

We study the solvent-induced frequency shifts of the OH-stretching mode of 1-naphthol and 2-naphthol in nonpolar/weakly polar solvents, subject to electronic excitation, with ultrafast UV/mid-infrared pump-probe spectroscopy and theoretical modeling based on Pullin's perturbative treatment of vibrational solvatochromic effects. The model is parametrized at the density functional theory (DFT) level, including the B3LYP/TZVP and TD-B3LYP/TZVP descriptions, for the naphthol chromophores in the S(0)- and (1)L(b)-states and accounts for both the static and the optical dielectric response of the solvent on time scales comparable to that of the OH-stretching vibrational motions. The favorable comparison between experimental and theoretical values of the solvent-induced vibrational frequency shifts suggests that the ultrafast dielectric response of the solvent contributes predominantly to the solvatochromic shifts in solvents of moderate polarity where specific solute-solvent interactions are absent.

Raman scattering from TiNx (0.67 ≤ x ≤ 1.00) single crystals grown on MgO(001)

Epitaxial NaCl-structure δ-TiNx(001) layers, with x ranging across the single-phase compound field from 0.67 to 1.00, are grown on MgO(001) and analyzed by Raman spectroscopy. All samples, including stoichiometric TiN(001), exhibit first-order Raman peaks, which are forbidden by the Oh symmetry of NaCl-structure compounds. Thus, even stoichiometric TiN contains point defects, primarily N and Ti vacancies, consistent with previous electronic transport measurements. However, the presence of a well-resolved second-order longitudinal acoustic line at 615 cm–1 shows that the defect concentration is relatively low. The positions of the first-order acoustic lines are in good agreement with values obtained from calculated phonon density of states. As the N/Ti ratio x in TiNx and, hence, the number n of valence electrons per formula unit (n = 9 for stoichiometric TiN) decreases, the first-order acoustic lines shift to higher frequencies, due to the corresponding decrease in phonon anomalies associated with the acoustic branch. This is in agreement with the observed increase in the intensities of the first-order acoustic phonon peak with decreasing x, characteristic of a higher average N vacancy concentration adjacent to Ti atoms. However, the presence of antisite defects is also required to explain the frequency shift of the optical modes in under-stoichiometric TiNx.

Frequency shift of Raman modes due to an applied electric field and domain inversion in LiNbO3

We report changes in the frequency of Raman modes in lithium niobate that are observed under the application of external applied electric fields and after domain inversion. Inspection of the Raman peaks reveals that after domain inversion, the internal field of the crystal is reduced. A comparison of the respective frequency shifts for the different Raman modes indicates that this change in the local internal field is not limited to the ferroelectric axis, but the fields orthogonal to the ferroelectric axis also change. The Raman modes also reveal that the strength of the internal field is dependent on the concentration of intrinsic defects present in the crystal.

Collective mode frequency shifts in l-serine and a series of isotopologues in the terahertz regime

Terahertz (THz) time-domain spectroscopy was used to monitor collective mode shifts in l-serine, l-serine-2,3,3-d3, l-serine-d4, and l-serine-d7 at both room and liquid nitrogen (LN2) temperatures. Increasing the molecular mass by deuteration caused an expected absorbance red-shift; however, the magnitude of the displacement could not be predicted using normal mode analysis. Both modes at 67.8cm−1 and 91.4cm−1 demonstrated a greater peak shift upon deuterium substitution at non-hydrogen bonding sites than at sites that participated in hydrogen bonding. This is evident in the larger peak shifts observed in l-serine-d3 than in l-serine-d4, despite a smaller increase in mass. This leads to the conclusion that both peaks present in the room temperature spectra of l-serine likely arise primarily from other intermolecular interactions with <50% contribution from hydrogen bonding. This goes against the prediction that peaks in the THz spectra of amino acids are predominantly due to the hydrogen bonding network that makes up the crystal lattice.

Two Diode Lasers Simultaneously Optically Locked by Orthogonal Polarizations of a Monolithic Confocal Cavity

We demonstrate two self-injection locking extended cavity diode lasers (ECDLs) using resonant optical feedback independently from s- and p-polarizations of a monolithic folded Fabry—Perot confocal cavity (MFC). The relative frequency shift of adjacent axial modes of s resonance and p resonance of MFC is around 1.030 GHz. Beat note measurements between the two ECDLs are performed and present a relative linewidth of 4 kHz. With the help of a narrow-linewidth reference laser, the linewidth of s-component and p-component ECDLs are measured to be about 32 kHz and 40 kHz, respectively.

RAMAN AND OPTOELECTRONIC PROPERTIES OF Zn1-xMgxO THIN FILMS PREPARED BY RF MAGNETRON SPUTTERING

A series of Zn 1-x Mg x O (x = 0 ~ 0.16) films have been prepared on glass substrates by RF magnetron sputtering. The structure, surface morphology, composition, optical and electrical properties of the films were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, UV-Vis spectrophotometer and Hall measurement, respectively. It reveals that the obtained films are uniform hexagonal wurtzite polycrystalline with grain size about 100 nm.The optical transmittance are over 80% and the band gap (Eg) has linear relationship with Mg content: Eg = 1.67x + 3.274 (eV) (0 &lt; x &lt; 0.16). The resistivity of the films increases with the increase of Mg content. The Raman spectra of the films show that the position of E2 peaks (473 cm-1) has not changed, but the A1(LO) mode (577 cm-1) frequency shifts to lower wavenumbers with the increase of Mg content, indicating that Mg -doping does not cause intensive lattice deformation, but results in the decrease of the carrier concentration, which is corresponding to the degradation of the conductivity of ZnMgO films with the increase of Mg content.

High-Pressure Spectroscopic Study of Hydrous and Anhydrous Cs-Exchanged Natrolites

Structural phase transitions in hydrous Cs-exchanged natrolite (Cs-NAT-hyd) and anhydrous Cs-exchanged natrolite (Cs-NAT-anh) have been investigated as a function of pressure and temperature using micro-Raman scattering and synchrotron infrared (IR) spectroscopy with pure water as the penetrating pressure medium. The spectroscopic results indicate that Cs-NAT-hyd undergoes a reversible phase transition around 4.72 GPa accompanied by the discontinuous frequency shifts of the breathing vibrational modes of the four-ring and helical eight-ring units of the natrolite framework. On the other hand, we observe that Cs-NAT-anh becomes rehydrated at 0.76 GPa after heating to 100 °C and then transforms into two distinctive phases at 2.24 and 3.41 GPa after temperature treatments at 165 and 180 °C, respectively. Both of these high-pressure phases are characterized by the absence of the helical eight-ring breathing modes, which suggests the collapse of the natrolite channel and formation of dense high-pressure polymo...

Visualization of Dimensional Effects in Collective Excitations of Optically Trapped Quasi-Two-Dimensional Bose Gases

In quasi-two dimensions (quasi-2D), where excitations are frozen in one direction, the scattering amplitudes exhibit 2D features of the particle motion and a 3D to 2D dimensional crossover emerges in the behavior of scattering. We explore its physical consequences, capitalizing on a hidden connection between the Pitaevskii-Rosch dynamical symmetry and breathing modes. We find broken Pitaevskii-Rosch symmetry by arbitrarily small 2D effects, inducing a frequency shift in breathing modes. The predicted shift rises significantly from the order of 0.5% to more than 5% in transiting from the 3D-scattering to the 2D-scattering regime. Comparisons with other relevant effects suggest our results are observable within current experimental capabilities.

Structure–activity relationships of simple molecules adsorbed on CPO-27-Ni metal–organic framework: In situ experiments vs. theory

In this work we review experimental XRPD, EXAFS, Raman, IR, microcalorimetric data on the adsorption of H2O, NO, CO, CO2, N2, C2H4 and H2 molecules on CPO-27-Ni material, a metal–organic framework (MOF) showing a coordination vacancy at the Ni2+ site in its desolvated form. Literature data are complemented by few new experimental results. A systematic theoretical study performed at the B3LYP-D*/TZVP level of theory (using a periodic boundary conditions) allowed us to reach a complete understanding of the structural, vibrational and energetic features of the material in interaction with the different molecules obtained from the different experimental techniques. From both experimental and theoretical set of data, interesting trends have been obtained for the framework distances (Ni–O and Ni–Ni) and frequency shifts of the framework vibration modes as a function of the adsorption energy (enthalpy) of the different probe molecules. This multitechnical approach, already applied for UiO-66 MOF is of general validity and can be straightforwardly extended to all MOF materials.

Mass–stiffness change method for scaling of operational mode shapes

In Operational Modal Analysis (OMA) the structure is excited by unknown forces and only the response signals are measured. Therefore, the mode shapes cannot be scaled straightforward from the test. The mass change method is a well-known way to estimate the scaling factors of mode shapes by adding mass to the selected points of structure. In the mass change method, the scaling factors are estimated using the frequency shift due to the added masses to the structure. However, in the mass change method the frequency shifts for the first modes of structure are less than those of the higher modes based on the sensitivity analysis. In the conventional scaling methods, the mode shapes are required to change slightly by the mass change for all the modes under investigation. As a result, the first modes do not experience a significant frequency shift and they cannot be scaled precisely. In this paper a method is applied for scaling of the operational mode shapes on a basis of both mass and stiffness change of the test structure. It is shown that the advantage of the applied method is that the first modes of the structure are more affected by the stiffness changes and consequently the corresponding scaled mode shapes are more accurate. The numerical and experimental results show that the accuracy of the scaled mode shapes improves by using the proposed mass–stiffness change method.

Vibrational solvatochromism and electrochromism of infrared probe molecules containing C≡O, C≡N, C=O, or C−F vibrational chromophore

Solvatochromic vibrational frequency shifts of a few different infrared (IR) probe molecules have been studied by carrying out quantum chemistry calculations for a number of their water clusters. We are particularly focused on the vibrational solvatochromic and electrochromic effects on the CO, CN, and CF stretch modes in carbon monoxide, acetone, 4-cyanopyridine, p-tolunitrile, fluorobenzene, and 3-fluoropyridine. Using multiple interaction site antenna model, we show that their solvatochromic vibrational frequency shifts can be successfully described by considering spatially nonuniform electrostatic potential generated by the surrounding water molecules. It turns out that the CO and CF stretch mode frequencies are approximately proportional to the solvent electric field projected onto the bond axes, whereas the vibrational frequencies of the nitrile stretch mode in 4-cyanopyridine and p-tolunitrile are not. Consequently, it is confirmed that the vibrational Stark tuning rates of the CO and CF stretching modes can be directly used to describe their solvatochromic frequency shifts in condensed phases. However, the nitrile stretch mode frequency shift induced by solvent electrostatic potential appears to be more complicated than its electrochromic phenomenon. To examine the validity of the distributed interaction site model for solvatochromic frequency shifts of these vibrational chromophores, we thus calculated the vibrational Stark tuning rates of the CO, CN, and CF stretch modes and found that they are in good agreement with the experimental results found in literatures. This confirms that a collection of properly chosen distributed interaction sites can be an excellent electric antenna sensing local electrostatics that affects on vibrational frequencies of IR probe modes.

Effects of Size and Microstructures on Infrared Spectra of Pyrolusites

Nanofibrous pyrolusite (β-MnO2) was synthesized. The particle shape changes from nanofibers to nanoparticles after grinding, and the phase structure does not change. The local environment around the central manganese ion has a slight change in nanoparticles related to nanofibers. Fourier transform infrared (FTIR) spectra showed that A2u mode frequency shifts from 514 cm−1 to 574 cm−1 to 617 cm−1 gradually while the particle shape and size change from long nanofibers to short fibers and to nanoparticles. The extra vibrational band that is unpredicted by factor group analysis originates from the contribution of A2u mode of the particles with different sizes and shapes in the studied sample. On the basis of Rietveld refinement analysis of XRD profiles and the FTIR spectra, we think that two kinds of MnO6 octahedral geometries, i.e., 4 long+2 short and 4 short+2 long, could exist in pyrolusites synthesized by different route. The maximum vibrational frequency in the FTIR spectra of pyrolusites is sensitive to these micro-structures. Assignment of four vibrational bands in the middle and far infrared region has been made.

Force spectroscopy using bimodal frequency modulation atomic force microscopy

We propose a force-spectroscopy technique where a higher order mode of a cantilever is excited simultaneously with the first. Resonance tracking of both vibration modes through a frequency modulation scheme provides a way to extract topographical information and the gradient of the tip-sample interaction within a single surface scan. We provide an analytic treatment of the scheme, derive expressions relating frequency shifts of the higher mode and the tip-sample forces, and offer two methods of improving the accuracy of reconstruction of the force gradient. Finally, we confirm our predictions by numerical simulations.

Phonon anomalies and phonon-spin coupling in oriented PbFe0.5Nb0.5O3thin films

We present Raman data on both single-crystal and thin-film samples of the multiferroic PbFe${}_{0.5}$Nb${}_{0.5}$O${}_{3}$ (PFN). We show first that the number and selection rules of Raman lines are compatible with a face-centered-cubic $\mathit{Fm}$-3m structure, as is known in other $\mathit{AB}$O${}_{3}$ relaxors, such as PbSc${}_{1/2}$Ta${}_{1/2}$O${}_{3}$. We then compare Raman data with anomalies in magnetization and the dielectric constant near the magnetic-phase-transition temperature (${T}_{N}$), the diffuse ferroelectric-phase-transition temperature (${T}_{m}$), and the pseudostructural-phase transition temperature (Burns temperature \ensuremath{\sim}${T}_{B}$). The temperature evolution of the Raman spectra for the PFN film shows measurable changes in phonon positions, intensities, and full width at half maxima near 200, 410, and 650 K---temperatures that match well with experimentally observed ${T}_{N}$, ${T}_{m}$, and ${T}_{B}$, respectively. The increase in frequency with increasing temperature for the lowest-energy ${F}_{2g}$ phonon mode is particularly unexpected. These changes suggest the transition of the crystal structure from an ordered phase to a disordered phase near ${T}_{B}$. The Raman study revealed phonon anomalies in the vicinity of ${T}_{m}$ and ${T}_{N}$ that are attributed to the dynamical behavior of polar nanoregions and spin-phonon coupling owing to its relaxor and multiferroic nature, respectively, which is well supported by dielectric and magnetic properties of the PFN thin film. Softening of the Fe-O mode was observed near the ${T}_{N}$. We correlate the anomalous shift of the Fe-O mode frequency with the normalized square of the magnetization sublattice; agreement with the experimental results suggests strong spin-phonon coupling near ${T}_{N}$ owing to phonon modulation of the superexchange integral; however, the shifts in frequency with temperature are small (3 cm${}^{\ensuremath{-}1}$).

Variation of high-degree mode frequencies during the declining phase of solar cycle 23

We investigate the spatial and temporal variation of the high-degree mode frequencies during the declining phase of the solar cycle 23 and the extended minimum between the cycle 23 and 24. We find that the frequency shifts of high-degree modes obtained through the ring-diagram analysis in different phases of the solar cycle are not equally correlated with the local magnetic activity index.

The experimental visualisation of molecular structural changes during both photochemical and thermal reactions by real-time vibrational spectroscopy

Have you ever hoped to observe transition states? Chemists have long desired to monitor the deformation of molecular structures via transition states to understand the mechanisms of complicated reactions. Detailed knowledge of transition states helps find strategies to develop novel reaction schemes for introducing new functionalities to chemicals. Molecular structural changes via transition states can be observed by real-time vibrational spectroscopy using sub-5 fs laser pulses. In this paper, I report the direct observation of time-dependent frequency shifts of relevant molecular vibrational modes, which allowed for the clear visualization of ultrafast structural changes in molecules during bond breaking and bond reformation steps. Various mechanisms for photochemical reactions were clarified using sub-5 fs laser pulses. Moreover, a non-thermal vibrational excitation method for efficiently driving chemical reactions in the electronic ground state in solution with the use of broadband visible sub-5 fs laser pulses has been developed. The respective chemical reaction processes were directly observed, including transition states during not only "photochemical" but also "thermal" reactions. Time-resolved spectroscopy with a time resolution of a few femtoseconds enables observation of real-time vibrational amplitudes of complicated molecules and opens up new ways for clarifying reaction mechanisms and developing new chemical transformations.