Vibrational Energy Research Articles

Investigation of the FrH+ Alkali Hydride Cation: Analysis of Potential Energies, Dipole Functions, and Radiative Lifetimes

This paper presents an extensive ab-initio investigation of the structural and spectroscopic properties of the FrH+ alkali hydride cation, utilizing non-empirical pseudo-potentials for Fr+ core. We determine the potential energy curves for 19 electronic states with symmetries of 2+, 2, and 2, which exhibit dissociation up to Fr (8p) + H+ and Fr+ + H (3d). We identify and interpret avoided crossings between higher 2+ and 2 states. Additionally, we calculate the spectroscopic parameters, transition dipole functions, and vibrational energies associated with 1-32+ states. Using accurate potential energies of X2+ and 22+ states, along with transition dipole functions between these states, we evaluate the radiative lifetimes for the vibrational states confined within the 22+ state. As far as we are aware, no experimental or theoretical data concerning this system have been published to date. Therefore, we discuss and compare our findings with those of analogous systems. Consequently, this study presents the first theoretical results for the alkali hydride cation FrH+.

Improved energy equations and thermal functions for diatomic molecules: a generalized fractional derivative approach.

This work presents analytical expressions for ro-vibrational energy models of diatomic molecules by introducing fractional parameters to improve molecular interaction analysis. Thermodynamic models, including Helmholtz free energy, mean thermal energy, entropy, and isochoric heat capacity, are formulated for diatomic molecules such as CO (X 1∑+), Cs2 (3 3∑g+), K2 (X 1∑g+), 7Li2 (6 1Πu), 7Li2 (1 3Δg), Na2 (5 1Δg), Na2 (C(2) 1Πu), and NaK (c 3∑+). The incorporation of fractional parameters improves predictive accuracy for vibrational energies, as shown by reductions in percentage average absolute deviations from 0.5511 to 0.2185% for CO. Findings indicate a linear decrease in Helmholtz free energy and an initial increase in heat capacity with rising temperature, providing valuable insights for characterizing materials and optimizing molecular processes in chemistry, material science, and chemical engineering. The results obtained show strong agreement with established theoretical predictions and experimental data, validating the robustness and applicability of the proposed models. The energy equations are derived by solving the radial Schrödinger equation for a variant of the Tietz potential using the generalized fractional Nikiforov-Uvarov (GFNU) method in addition to a Pekeris-type approximation for the centrifugal term. The canonical partition function is derived using the modified Poisson series formula, which serves as a basis for calculating other thermodynamic functions. All computations are carried out using MATLAB programming software.

Semi-analytical model and vibrational energy recovery efficiency of piezoelectric beams with quasi-periodic additional acoustic black holes

Semi-analytical model and vibrational energy recovery efficiency of piezoelectric beams with quasi-periodic additional acoustic black holes

Dual-mode arrayed vibration-wind piezoelectric energy harvester

Piezoelectric patches are extensively utilized in sensor technology and energy harvesting owing to their uncomplicated design. This research proposes a dual-mode arrayed piezoelectric energy harvester for the efficient harvesting of vibrational and wind energy from the environment. This research elucidates the structure and operational principle of the dual-mode arrayed vibration-wind piezoelectric energy harvester. The theoretical model of the proposed energy harvester was meticulously derived, followed by a Comsol simulation of its piezoelectric electrical performance, and a Fluent simulation study of the natural wind disturbance flow was established. The wind energy harvesting test bench was constructed to carry out the wind energy harvesting assessment. The vibration tests of the sinusoidal sweep frequency, fixed frequency, and railroad spectrum of the energy harvester were conducted using the shaker. The results indicate that the simulated resonance frequencies nearly align with the measured resonance frequencies, and the large voltage output of the harvester varies from 6 to 20 Hz, enhanced by the coupling effect of the magnet’s restoring force. The feasibility of the energy harvester for energizing low-power consumption devices was validated under the measured rail acceleration. The dual-mode arrayed vibration-wind piezoelectric energy harvester presented in this research offers a solution for the self-powered sensors used in freight train hook force detection and plateau intelligent agriculture.

Spectroscopic and Quantum Chemical Evidence of Amine-CO2 and Alcohol-CO2 Interactions: Confirming an Intriguing Affinity of CO2 to Monoethanolamine (MEA).

A recent broadband rotational spectroscopic investigation of the cross-association mechanisms of CO2 with monoethanolamine (MEA) in molecular beams [F. Xie et al., Angew. Chem. Int. Ed., 2023, 62, e202218539] revealed an intriguing affinity of CO2 to the hydroxy group. These findings have triggered the present systematic vibrational spectroscopic exploration of weakly bound amine··CO2 and alcohol··CO2 van der Waals cluster molecules embedded in inert "quantum" matrices of neon at 4.2 K complemented by high-level quantum chemical conformational analyses. The non-covalent interactions formed between the amino and hydroxy groups and the electron-deficient carbon atom of CO2 are demonstrated to lift the degeneracy of the doubly degenerate intramolecular CO2-bending fundamental significantly with characteristic observed spectral splittings for the amine··CO2 (≈35-45 cm-1) and alcohol··CO2 (≈20-25 cm-1) interactions, respectively, despite the almost identically predicted total association energies (≈12-14 kJ·mol-1) for these van der Waals contacts, as revealed by benchmark Domain-based Local Pair Natural Orbital Coupled Cluster DLPNO-CCSD(T) theory. These high-level theoretical predictions reveal significantly higher "geometry preparation energies" for the amine··CO2 systems leading to a more severe distortion of the CO2 linearity upon complexation in agreement with the infrared spectroscopic findings. The systematic combined spectroscopic and quantum chemical evidences for cross-association between CO2 and amines/alcohols in the present work unambiguously confirm an intriguing binding preference of CO2 to the hydroxy group of the important carbon capture agent MEA, with an accurate vibrational zero-point energy corrected association energy (D0) of 13.5 kJ·mol-1 at the benchmark DLPNO-CCSD(T)/aug-cc-pV5Z level of theory.

Electronic structure, spectroscopic constants, and transition properties of NaC [formula omitted] diatomic species: An ab initio investigation

Diatomic species play a pivotal role in complex media, such as the interstellar and circumstellar media. Furthermore, there is a notable lack of information regarding NaC and its ions, NaC+ and NaC−, despite the pervasiveness of the carbon element (C) and the validated role of Na-bearing molecules as organic reagents or in catalytic processes. In this study, ab initio multi-reference calculations, including core valence and complete basis set schemes, were employed to accurately determine the potential energy curves (PECs), dipole moment functions (DMFs) and transition dipole moments (TDMs) of ten, three and ten low-lying electronic states energies, respectively, for NaC, NaC+ and NaC− diatomics species. The obtained results permitted the accurate determination of spectroscopic constants and vibrational transition properties, including vibrational level energies, Franck–Condon factors (FCFs), Einstein coefficients, absorption band oscillator strengths, vibrational transition energies and radiative lifetimes of allowed transitions. The predicted adiabatic ionisation energy value for NaC is 6.659 eV, while the vertical ionisation energy value is 6.676 eV. Similarly, the predicted adiabatic electron affinity value for NaC is 0.614 eV, while the vertical electron affinity value is 0.613 eV.

Characterising vibration patterns of winter jujube trees to optimise automated fruit harvesting

Understanding jujube tree dynamic characteristics is crucial for the design and invention of a catch-and-shake machine for fruit harvesting. Currently, the study of vibration characteristics based on the finite element method is the mainstream method for different types of fruit trees. However, limited by the lack of an accurate 3D tree model, there are still gaps between existing simulation analysis and actual tests to explore vibration characteristics. Specifically, the vibration mechanism of winter jujube trees is still unclear in jujube orchards. To address the issue, a multi-view 3D reconstruction technique is employed to acquire precise 3D tree models for simulation analysis. The obtained results from experiments indicate that the determination coefficient R2 of the trunks and branches diameter are 0.96 and 0.91 between reconstructed and actual measurement results. Subsequently, material properties of jujube tree are measured to conduct model analysis and harmonic response analysis to find the optimal frequency range (10–20 Hz) in which a considerable vibration response can be obtained at low vibration energies. Moreover, transient analysis and test experiments are conducted to explore the energy transfer properties under different vibration frequency. Results showed that the acceleration response gradually increased from the bottom to the top of the branch on most branches at non-resonant frequencies. The proposed method can provide informative insights on the design of high-efficiency and low-energy jujube catch-and-shake harvesters.

Nonlinear phase velocities in tri-directional functionally graded nanoplates coupled with NEMS patch using multi-physics simulation

The nonlinear phase velocities analysis of tri-directional functionally graded (FG) nanoplates is crucial for optimizing their performance as nano-electro-mechanical systems (NEMS). By understanding the nonlinear phase velocities of various wave modes within the nanoplate, engineers can accurately predict and enhance the efficiency of NEMS. This analysis allows for the precise tuning of the piezoelectric patches to capture vibrational energy more effectively, ensuring maximum energy conversion efficiency. Moreover, it helps in identifying the optimal placement and orientation of the piezoelectric patches, minimizing energy loss and enhancing the reliability and durability of the NEMS. Ultimately, this leads to more efficient utilization of ambient vibrations in airplanes, providing a sustainable power source for various onboard sensors and monitoring systems, contributing to reduced reliance on external power sources, and improved overall energy management. For this issue, for the first time, nonlinear phase velocity in the tri-directional functionally graded nanoplate coupled with a piezoelectric patch via COMSOL multi-physics simulation, physics-informed deep neural networks (PIDNNs), and mathematics simulation are presented. In the mathematics simulation domain, nonlocal strain gradient theory for modeling both the hardening and softening behavior of the current nanoplate is presented. The electromechanical coupling effect and the abrupt change in material properties at the interfaces will have a major influence on the mechanical performance of tri-directional functionally graded (TD-FG) nanoplate coupled with a piezoelectric patch if transverse shear deformations cannot be well modeled. Thereby, in the current simulation, a quasi-3D refined theory with 10 variables is presented. Also, for coupling the composite structure with the piezoelectric patch, compatibility conditions are considered. An analytical solution procedure is presented for solving the nonlinear partial differential equations of the current electrical system.

A transparent multifunctional integrated meta-window with excellent sound insulation and vibration reduction performance

As the speed of transportation vehicles such as high-speed train continues to increase, there has been a significant rise in both noise and vibration levels, substantially compromising passenger comfort and overall travel experience. In transportation vehicles, the necessity for transparency in windows poses a challenge in incorporating high sound-insulating or vibration-damping materials, rendering windows vulnerable in sound isolation and vibration attenuation. This study employs an integrated material-structural design concept to develop a multifunctional meta-window, which ensures optimal lighting transmission while achieving outstanding sound-insulating and vibration-damping capabilities. Two distinct structures, named ultra-lightweight thin plate-type metamaterial and high-stability thick plate-type metamaterial, are precisely designed to adapt to varied application scenarios. Utilizing a gradient parameter multi-cell parallel synergetic coupling design method broadens the working bandwidth for sound insulation. The meta-window incorporates localized resonance units, enabling acoustic and vibrational energy dissipation through low-frequency resonance, effectively enhancing the window’s sound-insulating and vibration-damping capabilities. Comprising a composite of various transparent materials, the design amalgamates sound insulation, vibration reduction, and light transmission, eliminating the need for opaque sound-insulating or damping materials. Consequently, it holds substantial potential for applications across sectors, including train, aircraft, and architectural domains.

Temperature Dependence of Coherent versus Spontaneous Raman Scattering.

Because of their sub picosecond temporal resolution, coherent Raman spectroscopies have been proposed as a viable extension of spontaneous Raman thermometry, to determine dynamics of mode specific vibrational energy content during out of equilibrium molecular processes. Here we show that the presence of multiple laser fields stimulating the vibrational coherences introduces additional quantum pathways, resulting in destructive interference. This ultimately reduces the thermal sensitivity of single spectral lines, nullifying it for harmonic vibrations and temperature independent polarizability. We demonstrate how harnessing anharmonic signatures such as vibrational hot bands enables coherent Raman thermometry.

Cavity induced modulation of intramolecular vibrational energy flow pathways.

Recent experiments in polariton chemistry indicate that reaction rates can be significantly enhanced or suppressed inside an optical cavity. One possible explanation for the rate modulation involves the cavity mode altering the intramolecular vibrational energy redistribution (IVR) pathways by coupling to specific molecular vibrations in the vibrational strong coupling (VSC) regime. However, the mechanism for such a cavity-mediated modulation of IVR is yet to be understood. In a recent study, Ahn et al. [Science 380, 1165 (2023)] observed that the rate of alcoholysis of phenyl isocyanate (PHI) is considerably suppressed when the cavity mode is tuned to be resonant with the isocyanate (NCO) stretching mode of PHI. Here, we analyze the quantum and classical IVR dynamics of a model effective Hamiltonian for PHI involving the high-frequency NCO-stretch mode and two of the key low-frequency phenyl ring modes. We compute various indicators of the extent of IVR in the cavity-molecule system and show that tuning the cavity frequency to the NCO-stretching mode strongly perturbs the cavity-free IVR pathways. Subsequent IVR dynamics involving the cavity and the molecular anharmonic resonances lead to efficient scrambling of an initial NCO-stretching overtone state over the molecular quantum number space. We also show that the hybrid light-matter states of the effective Hamiltonian undergo a localization-delocalization transition in the VSC regime.

A high-throughput framework for lattice dynamics

We develop an automated high-throughput workflow for calculating lattice dynamical properties from first principles including those dictated by anharmonicity. The pipeline automatically computes interatomic force constants (IFCs) up to 4th order from perturbed training supercells, and uses the IFCs to calculate lattice thermal conductivity, coefficient of thermal expansion, and vibrational free energy and entropy. It performs phonon renormalization for dynamically unstable compounds to obtain real effective phonon spectra at finite temperatures and calculates the associated free energy corrections. The methods and parameters are chosen to balance computational efficiency and result accuracy, assessed through convergence testing and comparisons with experimental measurements. Deployment of this workflow at a large scale would facilitate materials discovery efforts toward functionalities including thermoelectrics, contact materials, ferroelectrics, aerospace components, as well as general phase diagram construction.

The characterization of electronic structures and spin-orbit couplings in the diatomic sodium arsenide cation

A high-level ab initio computation has been performed in order to determine the molecular structures, electronic characters and transition properties of a hitherto unknown diatomic cation of NaAs+. The electronic states associated with five dissociation channels, including both the Na++As and Na+As+ limits, are subjected to detailed analysis. The results of the potential energy functions, spectroscopic constants and vibrational energy levels of the relevant states are presented herewith. The impact of the spin-orbit coupling effect on the low-lying electronic states is evaluated as well. Additionally, predictions of transition features, such as Einstein coefficients, Frank-Condon factors, and radiative lifetimes, are considered. It is concluded that the direct laser cooling of NaAs+ is infeasible.

Isotope-dependent site occupation of hydrogen in epitaxial titanium hydride nanofilms

Hydrogen, the smallest and lightest element, readily permeates a variety of materials and modulates their physical properties. Identification of the hydrogen lattice location and its amount in crystals is key to understanding and controlling the hydrogen-induced properties. Combining nuclear reaction analysis (NRA) with the ion channeling technique, we experimentally determined the locations of H and D in epitaxial nanofilms of titanium hydrides from the analysis of the two-dimensional angular mappings of NRA yields. Here we show that 11 at% of H are located at the octahedral site with the remaining H atoms in the tetrahedral site. Density functional theory calculations revealed that the structures with the partial octahedral site occupation are stabilized by the Fermi level shift and Jahn-Teller effect induced by hydrogen. In contrast, D was found to solely occupy the tetrahedral site owing to the mass effect on the zero-point vibrational energy. These findings suggest that site occupation of hydrogen can be controlled by changing the isotope mixture ratio, which leads to promising manifestation of novel hydrogen-related phenomena.

Nonadiabatic Excited-State Molecular Dynamics with an Explicit Solvent: NEXMD-SANDER Implementation.

In this article, the nonadiabatic excited-state Molecular dynamics (NEXMD) package is linked with the SANDER package, provided by AMBERTOOLS. The combination of these software packages enables the simulation of photoinduced dynamics of large multichromophoric conjugated molecules involving several coupled electronic excited states embedded in an explicit solvent by using the quantum/mechanics/molecular mechanics (QM/MM) methodology. The fewest switches surface hopping algorithm, as implemented in NEXMD, is used to account for quantum transitions among the adiabatic excited-state simulations of the photoexcitation and subsequent nonadiabatic electronic transitions, and vibrational energy relaxation of a substituted polyphenylenevinylene oligomer (PPV3-NO2) in vacuum and methanol as an explicit solvent has been used as a test case. The impact of including specific solvent molecules in the QM region is also analyzed. Our NEXMD-SANDER QM/MM implementation provides a useful computational tool to simulate qualitatively solvent-dependent effects, like electron transfer, stabilization of charge-separated excited states, and the role of solvent reorganization in the molecular optical properties, observed in solution-based spectroscopic experiments.

Photodesorption of CO ices: Rotational and translational energy distributions.

This study investigates the translational and rovibrational energy of vacuum-ultraviolet (VUV) photodesorbed CO molecules from a CO polycrystalline ice (15K) at ∼8eV. The electronic excitation was produced by a pulsed VUV laser, and the photodesorption of CO molecules in their ground and first vibrational states was observed using resonance enhanced multiphoton ionization. Time-of-flight and rotationally resolved spectra were measured, and the kinetic and internal energy distribution were obtained. Vibrationally cold CO molecules were observed, with little energy in rotation and translation (≤300meV). Ab Initio Molecular Dynamics (AIMD) simulations focusing on the description of the vibrational energy redistribution within an aggregate of 50 CO molecules were performed. The measured energy distributions are in very good agreement with those predicted by AIMD simulations. The rotational energy was found to slightly increase with translational energy, a trend also predicted by theory. This confirms the validity of the indirect desorption mechanism triggered by the excitation of CO in a high vibrational state.

Ultrastrong coupling between molecular vibrations in water and surface lattice resonances.

We investigate the vibrational ultrastrong coupling between molecular vibrations of water molecules and surface lattice resonances (SLRs) sustained by extended arrays of plasmonic microparticles. We design and fabricate an array of gold bowties, which sustain a very high field enhancement, with its SLR resonated with the OH stretching modes of water. We measure a Rabi splitting of 567 cm-1 in the strongly coupled system, whose coupling strength is 8% of the OH vibrational energy, at the onset of the ultrastrong coupling regime (10%). These results introduce metallic microparticle arrays as a platform for the investigation of ultrastrong coupling, which could be used in polaritonic chemistry to modify the dynamics of chemical reactions that require high coupling strengths.

Energy relaxation of N2O in gaseous, supercritical, and liquid xenon and SF6.

Rotational and vibrational energy relaxation (RER and VER) of N2O embedded in xenon and SF6 environments ranging from the gas phase to the liquid, including the supercritical regime, is studied at a molecular level. Calibrated intermolecular interactions from high-level electronic structure calculations, validated against experiments for the pure solvents, were used to carry out classical molecular dynamics simulations corresponding to experimental state points for near-critical isotherms. The computed RER rates in low-density solvents of krotXe=(3.67±0.25)×1010 s-1 M-1 and krotSF6=(1.25±0.12)×1011 s-1 M-1 compare well with the rates determined by the analysis of two-dimensional infrared experiments. Simulations find that an isolated binary collision description is successful up to solvent concentrations of ∼4 M. For higher densities, including the supercritical regime, the simulations do not correctly describe RER, probably due to the neglect of solvent-solute coupling in the analysis of the rotational motion. For VER, the near-quantitative agreement between simulations and pump-probe experiments captures the solvent density-dependent trends.

Superstatistical functions of modified shifted Morse potential for diatomic molecules

The application of the molecular potential model to the study of different thermodynamic systems has been a focus of interest in recent time due to its importance in molecular and chemical physics. Hence, the asymptotic iteration method and the Laguerre polynomials are employed to obtain the eigensolutions of the Schrödinger equation with the modified shifted Morse potential model. Vibrational energy results for different diatomic molecules have been presented numerically, and these results are compared with experimental data and other results from available literature. The variation of normalised wave function and probability density of modified shifted Morse potential for some selected diatomic molecules at the ground- and first-excited states have been considered. Results obtained show that the equally spaced sinusoidal wave curves and varying nodes depend on the level of electron concentrations in the diatomic molecules considered. Partition function and other superstatistical function expressions of modified shifted Morse potential for some diatomic molecules within the modified Dirac delta distribution are obtained, using the Poisson summation formula. The superstatistical plots show a high level of dependence on the temperature parameter, maximum vibrational quantum number and deformation parameter. The superstatistical functions for a deformation parameter of zero correspond to the conventional thermodynamic functions.

Temperature-dependent vibrational energy relaxation of hydrogen-bonded and free OD groups at the air-water interface.

Water interfaces play a crucial role in regulating interactions and energy flow. Vibrational sum-frequency generation (vSFG) spectroscopy provides structural and dynamic information on water molecules at interfaces. It has revealed, for instance, the presence of the hydrogen-bonded and free OH groups at the air-water interface. Here, using temperature-dependent, time-resolved vSFG, we focus on the vibrational energy relaxation dynamics of interfacial heavy water (D2O). We reveal that while the relaxation timescale for hydrogen-bonded OD stretch modes is temperature-independent, the lifetime of the free OD stretch mode decreases with increasing temperature. Our data, supported by simulations, suggest that both intramolecular energy transfer and rotational reorientation mechanisms jointly contribute to the energy relaxation process of the free OD, with temperature influencing these mechanisms differently.