Vibrational Interaction Research Articles

Quantum-chemical calculation of two-dimensional infrared spectra using localized-mode VSCF/VCI.

Computational protocols for the simulation of two-dimensional infrared (2D IR) spectroscopy usually rely on vibrational exciton models which require an empirical parameterization. Here, we present an efficient quantum-chemical protocol for predicting static 2D IR spectra that does not require any empirical parameters. For the calculation of anharmonic vibrational energy levels and transition dipole moments, we employ the localized-mode vibrational self-consistent field (L-VSCF)/vibrational configuration interaction (L-VCI) approach previously established for (linear) anharmonic theoretical vibrational spectroscopy [P. T. Panek and C. R. Jacob, ChemPhysChem 15, 3365-3377 (2014)]. We demonstrate that with an efficient expansion of the potential energy surface using anharmonic one-mode potentials and harmonic two-mode potentials, 2D IR spectra of metal carbonyl complexes and dipeptides can be predicted reliably. We further show how the close connection between L-VCI and vibrational exciton models can be exploited to extract the parameters of such models from those calculations. This provides a novel route to the fully quantum-chemical parameterization of vibrational exciton models for predicting 2D IR spectra.

Rapid vibrational relaxation dynamics and strong Solute-Solvent interactions of the nitrite anion

In this work, we have used steady-state and ultrafast vibrational spectroscopy to measure the absorption band centers and widths, as well as vibrational energy relaxation (VER) lifetimes for the antisymmetric ν3 stretching band of the nitrite (NO2–) anion in H2O, D2O, and DMSO. The nitrite IR absorption bands are very broad and the excited state has an extremely short VER lifetime in all three solvents, suggesting that NO2– interacts quite strongly with all of them. We also measured and analyzed reflection spectra for NaNO2 pressed pellets and determined that the damping is fast in the reststrahlen band.

Theoretical investigation of turn off–on mechanism of a new fluorescence probe L

In this paper, themechanism of probe L and derivative L-HK inthe detection ofCys was researched. The infrared vibration spectrum, geometric parameters and interaction region indicator (IRI) isosurface prove that the hydrogen bond enhancement in the excited state is beneficial to excited state intramolecular proton transfer (ESIPT). The potential energy curve (PEC) shows L-HK has an ultra-fast ESIPT process, so it emits single fluorescence. In addition, the intramolecular charge transfer (ICT) process was verified by the frontier molecular orbitals (FMOs). Throughcalculating the reorganizationenergy, the quenching mechanism of probe L was explored.

Minimal model of excited-state symmetry breaking in symmetric dimers and covalently linked dyads.

A model of symmetry breaking (SB) charge separation in symmetric excited dyads and dimers is presented. The minimal model should include at least four basis electronic states due to a small energy gap between the locally excited and charge separated (zwitterionic) states of the chromophores. There are electronic couplings between all these states. The model includes the following interactions: (i) the Coulomb interaction between charges on the chromophores of the dyad, (ii) the interaction of the dipole moment of the asymmetric dyad with the solvent polarization, and (iii) the electronic-vibrational interaction. SB becomes possible only if the intensity of these interactions exceeds a threshold value. The threshold vanishes if there is a degeneration of the levels. Unusual resonant dependencies of the dissymmetry degree on the model parameters are revealed. Resonances arise due to the degeneration of energy levels. The ranges of the parameters in which energy level crossings occur are established. The oddity lies in the dependence of the resonance shape on the parameters of the model. A variation in the electronic couplings and the energy gap between the locally excited and ionic states, which leads to a broadening of the resonance, simultaneously leads to an increase in the resonant height. This opens up wide possibilities for controlling the charge separation degree. The predictions of the theory agree with the available experimental data. The charge separation SB is predicted to accompany by SB in the excitation distribution on the branches of dyads.

Use of probabilistic fastener velcro as a friction-induced vibration damping treatment

Probabilistic fasteners are biologically inspired clamping devices that are interlocked by stems on each surface. Due to dynamic characteristics of fastening mechanism, friction inevitably occurs between stems in a vibrating environment. The use of the probabilistic fastener as a vibration reduction component were investigated with advantages from friction-induced damping in this study. The dynamic stiffness and loss factor of the probabilistic fastener were derived from the vibration interaction with a mechanical structure. This allowed determination of energy dissipation due to the friction in hook and loop from the wave propagation analysis. As the vibration amplitude increased, the loss factor of the fastener gradually increased because the friction between multiple stems increased. With the probabilistic fastener application, the vibration generation and transmission were reduced compared to the bolted joint due to the inherent frictional contacts. With this unique advantage, the probabilistic fastener has potential applications when large damping is required with additional benefit on the reduced weight.

Nonlinear interaction of parametric excitation and self-excited vibration in a 4 DoF discontinuous system

Interaction between parametric excitation and self-excited vibration has been subjected to numerous investigations in continuous systems. The ability of parametric excitation to quench self-excited vibrations in such systems has also been well documented. But such effects in discontinuous systems do not seem to have received comparable attention. In this article, we investigate the interaction between parametric excitation and self-excited vibration in a four degree of freedom discontinuous mechanical system. Unlike majority of studies in which oscillatory nature of stiffness accounts for parametric excitation, we consider a much more practical case in which parametric excitation is provided by a massless rotor of rectangular cross section with a cylinder-like mass concentrated at the center. The rotor arrangement is placed on a friction-induced self-excited support in the form of a frame placed on a belt moving with constant velocity. This frame is connected to a supplementary mass. A Stribeck friction model is considered for the mass in contact with the belt. The frictional force between the mass and the belt is oscillatory in nature because of the variation of normal force due to parametric excitation from the rotor. Our investigations reveal mutual synchronization of parametric excitation and self-excited vibration in the system for specific parameter values. The existence of a stable limit cycle with constant synchronized fundamental frequency, for a range of parametric excitation frequencies, is established numerically. Investigation based on frequency spectra and Lissajous curves reveals complex synchronization patterns owing to the presence of higher harmonics. The system is also shown to exhibit Neimark–Sacker bifurcations under the variation of belt velocity. Furthermore, variation in belt velocity and coupling stiffness is seen to cause a breakup of quasi-periodic torus with small-amplitude oscillations to form large amplitude chaotic orbits. This points toward the possibility of vibration suppression in the system by tuning the parameters for stabilizing the small-amplitude quasi-periodic response. An example of co-existence of different attractors in the system is also presented.

Determination of spectroscopic constants from rovibrational configuration interaction calculations

Rotational constants and centrifugal distortion constants of a molecule are the essence of its rotational or rovibrational spectrum (e.g., from microwave, millimeter wave, and infrared experiments). These parameters condense the spectroscopic characteristics of a molecule and, thus, are a valuable resource in terms of presenting and communicating spectroscopic observations. While spectroscopic parameters are obtained from experimental spectra by fitting an effective rovibrational Hamiltonian to transition frequencies, the ab initio calculation of these parameters is usually done within vibrational perturbation theory. In the present work, we investigate an approach related to the experimental fitting procedure, but relying solely on ab initio data obtained from variational calculations, i.e., we perform a nonlinear least squares fit of Watson's A- and S-reduced rotation-vibration Hamiltonian to rovibrational state energies (resp. transition frequencies) from rotational-vibrational configuration interaction calculations. We include up to sextic centrifugal distortion constants. By relying on an educated guess of spectroscopic parameters from vibrational configuration interaction and vibrational perturbation theory, the fitting procedure is very efficient. We observe excellent agreement with experimentally derived parameters.

Direct Probing of Vibrational Interactions in UiO-66 Polycrystalline Membranes with Femtosecond Two-Dimensional Infrared Spectroscopy

UiO-66 is a benchmark metal-organic framework that holds great promise for the design of new functional materials. In this work, we perform two-dimensional infrared measurements on polycrystalline membranes of UiO-66 grown on c-sapphire substrates. We study the symmetric and antisymmetric stretch vibrations of the carboxylate groups of the terephthalate linker ions and find that these vibrations show a rapid energy exchange and a collective vibrational relaxation with a time constant of 1.3 ps. We also find that the symmetric vibration of the carboxylate group is strongly coupled to a vibration of the aromatic ring of the terephthalate ion. We observe that the antisymmetric carboxylate vibrations of different terephthalate linkers show rapid resonant (Förster) energy transfer with a time constant of ∼1 ps.

Підхід до аналізу поздовжньої стійкості рідинної ракети-носія пакетної схеми компонування

The “core and strap-on boosters” layout of launch vehicle (LV) stages is quite common in heavy LV development. However, POGO oscillations in liquid-propellant LVs with this stage layout have some features. It is shown that the structure of LVs of this type as a dynamic object has a dense spectrum of natural frequencies and complex spatial mode shapes. The longitudinal oscillations of the identical elements of the LV side strap-on boosters may be in phase or in antiphase, while the longitudinal mode shapes of the LV central core and strap-on boosters may differ both in phase and in amplitude. In flight, the thrust of the engines of the side strap-on boosters may also oscillate in phase or in antiphase, as a result of which the interaction of the LV structure with the sustainer propulsion systems of the side strap-on boosters may have both a stabilizing and a destabilizing effect on the POGO stability of a liquid-propellant LV. This paper presents a mathematical model of the “liquid-propellant propulsion systems – LV structure” dynamic system. The model describes the interaction of the longitudinal vibrations of the structure of a two-stage “core and strap-on boosters” LV with the core and strap-on booster propulsion systems. The free longitudinal vibrations of the structure of a ‘core and strap-on boosters’ LV were simulated using computer-aided finite element design tools (CAE systems). The simulation was the first to account for the dissipation of the liquid propellant and LV structure oscillation energy. The paper suggests an approach to analyzing the POGO stability of liquid-propellant “core and strap-on boosters” LVs with the use of the Nyquist criterion generalized to the case of multidimensional dynamic systems. The approach is based on opening the thrust feedback loops of the “liquid-propellant propulsion systems – structure” closed-loop dynamic system and studying the stability of the one-channel systems obtained in this way. Based on the proposed approach, the interaction between the longitudinal vibrations of the “core and strap-on boosters” LV structure and low-frequency processes in the liquid-propellant sustainer propulsion systems of the LV first stage was studied numerically.

A downwind-vibrating piezoelectric energy harvester under the disturbance of a downstream baffle

Wind energy harvesting using piezoelectric transduction is becoming a promising alternative for battery-free wireless electronics. To offer a promising solution for low structure reliability of Piezoelectric Wind-induced Vibration Energy Harvesters (PWVEHs) under fairly high wind speed, a Downwind-Vibrating Piezoelectric Energy Harvester under the disturbance of a downstream baffle (DVPEH) is proposed in this paper. Unlike the most existing PWVEHs of which the bluff body swung against the wind, the structure reliability of energy harvester was improved with the downstream structure of the DVPEH. A downstream baffle was introduced to adjust the working characteristics of DVPEH to avoid the disadvantage of small amplitude of downwind structure. Meanwhile, the dynamic and electrical characteristics of the DVPEH under the disturbance of a downstream baffle was explored to enhance the power generation capacity. To prove the structural feasibility and ascertain the influence of the downstream baffle, theoretical investigation, simulation, fabrication and experimental testing were conducted. The results showed that the interaction of vortex-induced vibration and galloping was induced by the downstream baffle to accelerate the oscillation of the bluff body. Besides, the distance-diameter ratio, width-diameter ratio and length ratio brought significant effects on the performance in terms of electric output and cut-in wind speed. A maximum power of 0.42 mW was achieved at the optimal load resistance of 100 kΩ with the wind speed of 16 m/s and 20 blue LEDs in series was successfully driven by the DVPEH. It was expected that this study could provide a reference for improving the structure reliability and electric output of traditional PWVEHs.

On the method and results of calculation of vibrational tetrahedral sub-level energies and resonance interactions in vibrational spectra of high symmetry molecules: CH[formula omitted] and GeH[formula omitted] as an application of the XY[formula omitted] (T[formula omitted]) molecule

We report here the analytical description of one of the important problems in the study of XY4 (Td) molecules, namely, description of vibrational tetrahedral sub-level structures and resonance interactions caused by the high symmetry of a molecule. The results obtained are applied to description of the vibrational energy spectrum of the CH4 and GeH4 molecules.

Computational examination on monomeric, dimeric, trimeric structural and vibrational interactions, AIM, Hirshfeld, IGM and oxygenated solvent effect on optical properties for pyridine N-oxide

This work reports DFT (Density functional theory) and topological examination by means of AIM (Atom in molecule) theory, Laplacian electron density (ED), Electron –Localization function (ELF) and Hirshfeld surface were executed monomer, dimer and trimer structure of PNO molecule. These structures were optimized and Structural parameters like bond – length and Angles are compared by using B3LYP/6-311G++(d,p) basis set. Computed vibrational – frequencies and corresponding PED (Potential energy – Distribution) were also compared. Polarizability, Dipole moment and the electronic properties were calculated for all three cases of PNO molecule. Hirshfeld surface investigation has been executed to achieve the C–H⋯O/N–O⋯H type of hydrogen -bond intermolecular interactions. Moreover, Reactive site, inter/intra interactions are calculated, the optical behaviors for monomer structure of PNO were investigate by using UV–Vis spectroscopy in oxygenated solvents.

Highly Stable and Moisture-Immune Monocomponent White Perovskite Phosphor by Trifluoromethyl (-CF3) Regulation.

Halide perovskites are emerging as promising candidates for white light solid state lighting. Nevertheless, there are still challenges of a high water stability, a tunable color temperature, and a high photoluminescence quantum yield (PLQY). Herein, we report hydrophobic, electron-withdrawing trifluoromethyl (-CF3)-modified phenethylamine lead bromide (PEA2PbBr4) with ultrahigh stability in water for >2 months, and the broadband white light emission is illustrated by self-trapped excitons attributed to exciton-phonon coupling that coordinate molecular vibration, lattice distortion, and electrostatic interaction. In particular, by Mn2+ doping, the emission color can be tuned from cold (10237 K) to warm (2406 K), and a greatly enhanced PLQY of ≤87.93% can be achieved. Furthermore, the perovskites also possess an excellent color rendering index (the highest is 94). A monocomponent white light-emitting diode with amazing CIE 1931 coordinates of (0.33, 0.32) is further assembled, demonstrating a luminance of 471.5 cd m-2 at 50 mA and good long-term operation stability after >2 months. This study of highly efficient and stable perovskites with high-quality white light emission will open up new opportunities in solid state lighting.

Conduction band structure of high-mobility organic semiconductors and partially dressed polaron formation.

The energy band structure provides crucial information on charge transport behaviour in organic semiconductors, such as effective mass, transfer integrals and electron-phonon coupling. Despite the discovery of the valence (the highest occupied molecular orbital (HOMO)) band structure in the 1990s, the conduction band (the lowest unoccupied molecular orbital (LUMO)) has not been experimentally observed. Here we employ angle-resolved low-energy inverse photoelectron spectroscopy to reveal the LUMO band structure of pentacene, a prototypical high-mobility organic semiconductor. The derived transfer integrals and bandwidths from the LUMO are substantially smaller than those predicted by density functional theory calculations. To reproduce this bandwidth reduction, we propose an improved (partially dressed) polaron model that accounts for the electron-intramolecular vibrational interaction with frequency-dependent coupling constants based on Debye relaxation. This model quantitatively reproduces not only the transfer integrals, but also the temperature-dependent HOMO and LUMO bandwidths, and the hole and electron mobilities. The present results demonstrate that electron mobility in high-mobility organic semiconductors is indeed limited by polaron formation.

Correlation Between Tribological and Vibration Behaviors in Sliding Lubricated Contacts

Abstract The tribological and vibration behaviors of a lubricated system are often studied separately. However, in recent years, the combination of tribology and mechanical vibration significantly contributes in analyzing and solving many practical problems. The main objective of this study is to establish empirical equations that describe friction–-vibration interactions under dynamic (sliding) lubricated contacts. The effects of operating conditions on the tribological and vibration behaviors of lubricating oils having different viscosities were experimentally investigated using a four-ball wear test machine. The results indicated that the vibration velocity tends to increase with the sliding velocity. With a lower combination of ratio of the vibration velocity to the sliding velocity and the specific film thickness, lower friction coefficients were observed in the boundary and mixed lubrication regimes. The mean wear scar diameters exhibited positive correlations with the amplitudes of vibration accelerations. The empirical equations provide basic information for the prediction of friction variation by measuring vibration signals.

Molecular Optomechanics Approach to Surface-Enhanced Raman Scattering.

ConspectusMolecular vibrations constitute one of the smallest mechanical oscillators available for micro-/nanoengineering. The energy and strength of molecular oscillations depend delicately on the attached specific functional groups as well as on the chemical and physical environments. By exploiting the inelastic interaction of molecules with optical photons, Raman scattering can access the information contained in molecular vibrations. However, the low efficiency of the Raman process typically allows only for characterizing large numbers of molecules. To circumvent this limitation, plasmonic resonances supported by metallic nanostructures and nanocavities can be used because they localize and enhance light at optical frequencies, enabling surface-enhanced Raman scattering (SERS), where the Raman signal is increased by many orders of magnitude. This enhancement enables few- or even single-molecule characterization. The coupling between a single molecular vibration and a plasmonic mode constitutes an example of an optomechanical interaction, analogous to that existing between cavity photons and mechanical vibrations. Optomechanical systems have been intensely studied because of their fundamental interest as well as their application in practical implementations of quantum technology and sensing. In this context, SERS brings cavity optomechanics down to the molecular scale and gives access to larger vibrational frequencies associated with molecular motion, offering new possibilities for novel optomechanical nanodevices.The molecular optomechanics description of SERS is recent, and its implications have only started to be explored. In this Account, we describe the current understanding and progress of this new description of SERS, focusing on our own contributions to the field. We first show that the quantum description of molecular optomechanics is fully consistent with standard classical and semiclassical models often used to describe SERS. Furthermore, we note that the molecular optomechanics framework naturally accounts for a rich variety of nonlinear effects in the SERS signal with increasing laser intensity.Furthermore, the molecular optomechanics framework provides a tool particularly suited to addressing novel effects of fundamental and practical interest in SERS, such as the emergence of collective phenomena involving many molecules or the modification of the effective losses and energy of the molecular vibrations due to the plasmon–vibration interaction. As compared to standard optomechanics, the plasmonic resonance often differs from a single Lorentzian mode and thus requires a more detailed description of its optical response. This quantum description of SERS also allows us to address the statistics of the Raman photons emitted, enabling the interpretation of two-color correlations of the emerging photons, with potential use in the generation of nonclassical states of light. Current SERS experimental implementations in organic molecules and two-dimensional layers suggest the interest in further exploring intense pulsed illumination, situations of strong coupling, resonant-SERS, and atomic-scale field confinement.

Numerical modeling of noise and vibration due to discharge in hermetic compressors

The pulsive and intermittent nature of the operation of a hermetic refrigeration compressor leads to the generation of noise and vibration during the operation. Specifically, in hermetic compressors, gas pulsation induced by refrigerant discharge is a major source of NVH effects. The generation of noise and vibration due to refrigerant gas discharge is a process that involves thermo-mechanical operation within compressor cylinder, cavity acoustic resonance, valve opening/closing, hermetic shell vibration, and exterior sound radiation. In the presented study, a numerical simulation model was developed to address the multi-physical process of noise generation due to refrigerant gas discharge. The thermodynamics aspects of the compression process and the vibro-acoustics aspects are coupled together. The thermo-mechanical submodel is based on a compressor mechanistic model based on control volume analysis with lumped parameters. The vibro-acoustics submodel is based on finite element analysis, and it describes the two-way coupled interaction of compressor cavity acoustic resonances and hermetic shell vibration. Meanwhile, the acoustics response in the cavity is coupled with the thermodynamics submodel through proper modeling dynamics of discharge valves. Numerical simulations were conducted to demonstrate how simulation models work and how they can potentially help compressor manufacturers to gain a better understanding of the physical reasons behind NVH effects of compressors.

Anharmonic Coupling of Stretching Vibrations in Ice: A Periodic VSCF and VCI Description.

The anharmonicity of O-H stretching vibrations of water ice is characterized by use of a periodic implementation of the vibrational self-consistent field (VSCF) and vibrational configuration interaction (VCI) methods, which take phonon-phonon couplings explicitly into account through numerical evaluation of high-order terms of the nuclear potential. The low-temperature, proton-ordered phase of water ice (namely, ice XI) is investigated. The net effect of a coupled anharmonic treatment of stretching modes is not just a rigid blue-shift of the respective harmonic spectral frequencies but rather a complex change of their relative spectral positions, which cannot be captured by simple scaling strategies based on harmonic calculations. The adopted techniques allow for a hierarchical treatment of anharmonic terms of the nuclear potential, which is key to an effective identification of leading factors. We show that the anharmonic independent-mode approximation─only describing the "intrinsic anharmonicity" of the O-H stretches─is unable to capture the correct physics, and that couplings among O-H stretches must be described. Inspection of harmonic normal coordinates allows identification of specific features of the O-H stretching motions which most likely enable strong mode-mode couplings. Finally, by coupling O-H stretches to all other possible modes of ice XI (THz collective vibrations, molecular librations, bendings), we identify specific types of motion which significantly affect O-H stretching states: in particular, molecular librations are found to affect the stretching states more than molecular bendings.

Calculation of absolute Raman scattering cross-sections using vibrational self-consistent field/vibrational configuration interaction wave functions.

In the present study, the differential scattering cross-sections, depolarization ratios and Raman shifts of small molecular systems are obtained from configuration iteration wave functions of vibrational self-consistent field (VSCF) states. The transition polarizabilities were modeled using the Placzek approximation, neglecting those contributions not arising from the electric dipole mechanism. This theoretical approach is considered a good approximation for samples that absorb in the UV range if the excitation radiation falls in the visible region, as is the case of the molecules selected for the present study, namely: water, methane, and acetylene. Potential energy and electronic polarizability surfaces are calculated by the CCSD(T) and CC3 methods with aug-cc-p(C)V(T,Q,5)Z basis sets. The vibrational Hamiltonian includes the vibrational angular momentum contribution of the Watson kinetic energy operator. As expected, due to the variational nature of the VSCF and vibrational configuration interaction (VCI) methods, the Raman transition wavenumbers are substantially improved over the harmonic predictions. Surprisingly, the scattering cross-sections obtained using the harmonic approximation or the VSCF method better agrees with the experimental values than those cross-sections predicted using VCI wave functions. The more significant deviations of the VCI results from the experimental reference may be related to the significant uncertainties of the measured cross-sections. Still, it may also indicate that the VCI Raman transition moments may require a more accurate description of the electronic polarizability surface. Finally, the depolarization ratios calculated for H2 O and C2 D2 using harmonic and VCI wave functions have similar accuracy, whereas, for C2 H2 and C2 HD, the VCI results are more accurate.

Universal anharmonic potential energy surfaces for XY2-type molecules

An approach to generate anharmonic potential energy surfaces for both linear and bent XY2-type molecules from their equilibrium geometries, Hessians, and total atomization energies alone is presented. Two key features of the potential energy surfaces are that (a) they reproduce the harmonic behavior around the equilibrium geometries exactly and (b) they have the correct limiting behavior with respect to total bond dissociation. The potentials are constructed from two diatomic potentials, for which both the Morse or Varshni potentials are tested, and a triatomic potential, for which modified forms of the Anderson-n potential are tested. Potential energy surfaces for several linear and bent molecules are constructed from ab initio data, and the third-order derivatives of these surfaces at their equilibrium geometries are compared to the results of finite difference computations. For bent molecules, the vibrational spectra predicted by vibrational configuration interaction calculations on these surfaces are compared to experiment. A modified version of the Anderson-n potential, in combination with the Varshni potential, is demonstrated to predict vibrational frequencies associated with bond angle bending an average of 20 cm−1 below the harmonic oscillator approximation and with a fourfold reduction in the root-mean-square deviation from experiment compared to the harmonic oscillator approximation.