Rotational Spectra Research Articles

Structural and Electronic Evolution of Ethanolamine upon Microhydration: Insights from Hyperfine Resolved Rotational Spectroscopy.

Ethanolamine hydrates containing from one to seven water molecules were identified via rotational spectroscopy with the aid of accurate quantum chemical methods considering anharmonic vibrational corrections. Ethanolamine undergoes significant conformational changes upon hydration to form energetically favorable hydrogen bond networks. The final structures strongly resemble the pure (H2O)3-9 complexes reported before when replacing two water molecules by ethanolamine. The 14N nuclear quadrupole coupling constants of all the ethanolamine hydrates have been determined and show a remarkable correlation with the strength of hydrogen bonds involving the amino group. After addition of the seventh water molecule, both hydrogen atoms of the amino group actively contribute to hydrogen bond formation, reinforcing the network and introducing approximately 21-27 % ionicity towards the formation of protonated amine. These findings highlight the critical role of microhydration in altering the electronic environment of ethanolamine, enhancing our understanding of amine hydration dynamics.

Rotational spectroscopy and structure of 1,1-dichloro-1-silacyclohex-2-ene

The ground state rotational spectrum of 1,1-dichloro-1-silacyclohex-2-ene has been recorded using a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer. Several isotopologues in their natural abundances have been observed in the free-jet expansion, and their spectra assigned, making it possible to present a partial heavy-atom substitution structure. Furthermore, the high resolution of this technique allows the complicated hyperfine splitting pattern to be largely deconvoluted. As a result, the on-diagonal nuclear quadrupole coupling constants for the two chlorine atoms have been determined for all observed isotopologues. Additionally, χbc is determined for both chlorine atoms of the parent species. The quadrupole coupling tensors for the parent species have been diagonalised, noting some assumptions have been made pertaining to the off-diagonal nuclear quadrupole coupling constants in the principal axis system, to yield reasonable values of χzz and η which are then compared.

Theoretical investigation of interstellar 3-pyrroline: formation and, rotational and vibrational spectroscopy

ABSTRACT The recent detection of CN-functionalized aromatics partly addresses the long-standing mystery of the apparent absence of five- and six-membered rings in interstellar environments. Nitrogen (N)-heterocycles, which are crucial as the fundamental structures of nucleobases, have been a focus of these aromatic searches due to their biological significance. Although N-heterocycles have not been conclusively detected in astrophysical environments, their presence in chondrites and meteorites signifies their interstellar and circumstellar connection. Precise spectral data identify the unique signatures of molecules, confirming their presence in space. In this light, this work reports an extensive computational investigation on interstellar 3-pyrroline, a five-membered ring N-heterocycle. This includes an alternative formation route in cold interstellar environments and highly accurate rotational and vibrational spectroscopy. The results indicate that 3-pyrroline can form on dust grain surfaces from vinyl cyanide, as its formation from pyrrole through double hydrogenation may lead to the formation of pyrrole itself via an H2-abstraction process. 3-Pyrroline’s rotational transition at 52.3 GHz offers a potential tool for its detection in cold interstellar regions. Additionally, the strongest infrared (IR) features of 3-pyrroline at 16.09 and $\sim$3.50 $\mu$m are observable with JWST. The provided data are crucial for laboratory identification and future interstellar observations of 3-pyrroline at both radio and IR wavelengths.

The carbonyl-sulfur chalcogen bonding interaction: Rotational spectroscopic study of the 2,2,4,4-tetrafluoro-1,3-dithietane···formaldehyde complex

The rotational spectrum of a binary molecular cluster consisting of 2,2,4,4-tetrafluoro-1,3-dithietane (C2S2F4) and formaldehyde (H2CO) was studied by means of high-resolution Fourier transform microwave spectroscopy in conjunction with quantum chemical calculations. One of the three isomers predicted at the B3LYP-D3(BJ)/def2-TZVP level of theory was successfully detected in the supersonic expansion. Theoretical analyses using the non-covalent interactions and natural bond orbital methods reveal that the observed isomer is primarily stabilized by one C=O⋯S chalcogen bond and two C−H⋯F hydrogen bonds. The distance between the oxygen atom of H2CO and the nearest sulfur atom of C2S2F4 within the observed isomer is 2.9260(1) Å and the angle ∠O⋯S−C is 161.83(1)°. The analysis utilizing the symmetry-adapted perturbation theory approach demonstrates that electrostatic interactions play a significant role in stabilizing the studied complex, with the contribution of dispersion interactions being comparable to that of electrostatic ones.

Femtosecond Terahertz Pulse Propagation Measurements and Simulations of Dewetting Kinetics in Real Time.

We report a terahertz time-domain study of dewetting kinetics on two time scales: femtoseconds and in real time (on the order of minutes). We recorded full electric field terahertz time domain signals with femtosecond time resolution during dewetting of water in cellulose. The femtosecond time-domain signals were analyzed with respect to the amplitude and signal emission times and how these two quantities changed over the course of dewetting kinetics. The femtosecond time-domain signals were modeled by a combination of finite-difference time-domain electromagnetic simulations of linear terahertz pulse propagation and an effective medium description of the dielectric permittivity. A logistic regression mechanism was incorporated into the electrodynamics simulations to account for the observed kinetics. In addition, analysis of the area-normalized, real-time time-dependent terahertz spectra was used to identify broad regions in the terahertz spectral range that correlated with the kinetic process. Real-time two-dimensional terahertz correlation maps were used to identify the pure rotational spectrum of water vapor, thus characterizing the evaporation part of the dewetting kinetics problem. We conclude with a kinetic model that accounts for our observations through a microscopic mechanism involving the interconversion among bulk water, water clusters, and individual water molecules in the gas phase. Overall, the approach presented here illustrates an application of femtosecond time-resolved experiments in the terahertz spectral range to the study of kinetic processes.

Rotational spectra of ten new fluoroethylene/CO2 clusters, (C2H3F)x(CO2)y: Application of data-centered methods to the assignment of spectra in complex mixtures

Chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy has been used to measure the spectra of ten previously unobserved fluoroethylene (FE)/CO2 clusters, (FE)x(CO2)y, with x from 1 to 4 and y from 0 to 4. Multiple spectra were recorded with varying concentrations of CO2 in the sample, and at least 400,000 free induction decays averaged per data set. This allowed implementation of data-centered approaches, using intensity variation, to identify subsets of transitions belonging to the same cluster species or those of similar composition, simplifying the assignment process for the complex mixture of clusters present. All spectra were fitted to Watson A-reduction Hamiltonians, including quartic distortion constants, with very few species requiring higher order distortion constants for satisfactory fits to be obtained. Computational data at MP2/6-311++G(2d,2p) and ωB97X-D/6-31+G(d,p) levels suggested FE:CO2 ratios and likely structural arrangements of each cluster based on comparisons with experimental rotational constants.

Rotational Spectroscopy of the Acetone-Water Complex: Large Amplitude Motions.

Acetone (CH3COCH3), the simplest ketone, has recently attracted considerable attention for its important role in atmospheric chemistry and in the formation of ices in extraterrestrial sources that contain complex organic molecules. In this study, we employed a combination of experimental rotational spectroscopy and quantum chemistry calculations to investigate the structure and dynamics of the acetone-water complex. Our aim was to understand how non-covalent interactions with water affect the methyl internal rotation dynamics of acetone, and how water-centered large amplitude motions alter the observed physical properties compared to those predicted at the equilibrium position. Detailed rotation-tunneling analyses of acetone-H2O and -D2O reveal that the interactions with water disrupt the equivalence of the two methyl rotors, resulting in a noticeably lower methyl rotor barrier for the top with the close-by water compared to that of free acetone. The barrier for the methyl group further from water is also lower, although to a lesser degree. To gain further insights, extensive theoretical modelling was conducted, focusing on the associated large amplitude motions. Furthermore, quantum theory of atoms in molecules and non-covalent interactions analyses were utilized to visualize the underlying causes of the observed trends.

Computation of rate coefficients in solutions based on transition state theory combined with a heuristically corrected polarizable continuum model: intermolecular Diels-Alder reactions as case studies.

Transition state theory (TST) based on activation parameters computed using quantum mechanics calculations combined with the polarizable continuum model (QM/PCM) is a fundamental tool for investigating reaction rates in the liquid phase. In conventional QM/PCM methods, thermodynamic data and partition functions for a solute are often derived from a quasi-ideal gas treatment (IGT) widely implemented in commercially available computation packages. This approach tends to overestimate entropy because calculations of thermodynamic parameters in the liquid phase ignore hindered translational and rotational modes in real solutions. The present work formulated partition functions for more realistic solutes hindered by surrounding solvent molecules in conjunction with the basic QM/PCM concept. In addition, a configuration partition function for solute molecules at a standard concentration of 1 mol dm-3 was incorporated using a simple lattice model. The canonical partition function and thermodynamic functions were derived based on statistical thermodynamics for localized systems. Expressions for rate coefficients within TST were also derived with a consistent formalism based on the standard state selected in partition function calculations. The performance of the proposed method was assessed by predicting rate coefficients for three different Diels-Alder reactions and comparing these with experimental results. QM/PCM calculations at the G4//ωB97X-D/6-311++G(d,p)/IEF-PCM level of theory with corrections for the dispersion and repulsion energies were performed to obtain the electronic structures of stationary points on potential energy surfaces as a means of finding activation enthalpy, entropy and Gibbs energy values based on revised partition functions as well as predicting rate coefficients. The activation Gibbs energies obtained from our proposed method were lower than those obtained from the IGT method due to reasonable entropy computations. The proposed method overestimated the rate coefficients by one to two orders of magnitude compared to the experimental values, whereas the IGT method underestimated them by the same amount. This discrepancy arises because the proposed method calculates the partition function from the viewpoint of a localized system, whereas the IGT method calculates it from the viewpoint of a non-localized system. Given that actual liquids exist in a state between non-localized and localized systems, it is essential to formulate the partition function in a way that more accurately represents the liquid state.

Development and Implementation of a Veterinary Spectrum of Care Clinical Rotation Aligned with the CBVE Model.

Spectrum of care (SOC) has recently been described in the literature, yet it is not an entirely new concept within the veterinary profession. Practitioners in general veterinary practice have long needed to provide a broad range of unique care options for their patients and clients, particularly those for whom referral is not possible. More recently, graduates and their employers have reported that new veterinarians often lack the competence and confidence to provide a broad array of care options, while training in ever more specialized tertiary-referral environments. To better prepare veterinary learners to cope with the variable nature of general veterinary practice and to better meet employer demands, The Ohio State University College of Veterinary Medicine purposefully backward designed learning experiences in a new outcomes-based curriculum so that SOC is emphasized and aligned with the foundation offered by the Competency-Based Veterinary Education (CBVE) model. A unique set of subcompetencies and educational goals were collaboratively developed and used to define a new final year rotation, with additional input provided by an advisory panel of practicing SOC veterinarians from private practice. Ideal caseload characteristics, case numbers, appointment length, daily activities, and other elements were defined, and final year student performance was monitored during implementation to assess progress in meeting key developmental milestones. Incorporating spectrum of care training at The Ohio State University shows promise for developing confidence and competence in new graduates, while also increasing their skills, and perhaps improving their mental health.

An optical measurement method of DC total electric field with space charges based on probe self-rotation modulation

Researching the measurement of DC total electric field with space charges (Poisson field) can help establish a monitoring system for the electromagnetic environment of UHVDC transmission lines and protect the health of the ecological environment. This paper proposes a DC total electric field optical measurement method based on the Pockels effect and probe self-rotation modulation. It can address the issues of internal charge drift and external charge accumulation in traditional optical probes when measuring DC electric fields with space charges. Theoretical analysis was conducted on measurement under probe rotation, and the optical modulation system was integrated into a probe with dimensions of 60 mm × 30 mm × 20 mm. A self-rotating platform for the probe was designed, and the influence of rotation mode on the results was analyzed. It was found that the sensitivity was higher when using the horizontal-horizontal mode. The signal processing system was tested, showing that the probe retained around 50 % of its original output when rotating at low speeds (frequency 1–3 Hz), fully meeting the measurement requirements. The test platform has been constructed, and the probe’s sensitivity was assessed under an AC electric field and validated under a DC electric field. Finally, the optical method proposed in this paper was used to measure the DC total electric field with space charges under a small model of a unipolar HVDC transmission line. Five locations under the line were selected as measurement points, and the results were compared with those obtained from a field mill probe and numerical simulation. This comparison indicates that the proposed method agrees with experimental and simulation results. The average sensitivity of the self-rotating optical probe was 3.71 mV/(kV/m). The error did not exceed 5 % in high-field strength areas (above 20 kV/m) and was also controlled within 15 % in low-field strength areas (below 20 kV/m).

Fiber Specklegram Sensor Based on Reflective Mode Rotation in Few-Mode Fiber

Fiber Specklegram Sensor Based on Reflective Mode Rotation in Few-Mode Fiber

Exploring the conformational landscape through rotational spectroscopy and computational modelling: The tunneling dynamics in 2,6-diethylphenol

Phenol and some of its derivatives exhibit interesting tunneling motions consisting of two groups of transitions separated by a few hundred MHz. Recently, one of its derivatives, 2,6-di-tert-butylphenol, has shown additional hyperfine tunneling components, the origin of which remains unclear. In this work, another member of the family, 2,6-diethylphenol, has been investigated through its rotational spectrum. The jet-cooled broadband chirped-pulse Fourier transform microwave spectra in the 2–8 GHz frequency region revealed the presence of two conformers. The comparison with the equilibrium structure obtained by computational calculations at the B3LYP-D3(BJ)/Def2-TZVP level validates the structural determination and the orientation of the lateral ethyl groups. Additional observation of all the singly-substituted 13C isotopologues for the most stable ones allowed the determination of the substitution structure by means of the Kraitchman equations. Both conformers exhibited tunneling that was reproduced using an advanced 1D model, which provides an estimate of the barrier height for both conformers.

Millimeter-Wave and High-Resolution Infrared Spectroscopy of the Ground and Seven Lowest Fundamental States of 1H-1,2,4-Triazole.

A combined analysis of millimeter-wave (70-700 GHz) and rotationally resolved infrared (400-1200 cm-1) spectra of the ground state and seven fundamental vibrational modes of 1H-1,2,4-triazole is reported. While the lowest-energy vibrationally excited state (ν18) is well-treated using a single-state distorted-rotor Hamiltonian, the second (ν17) and third (ν16) vibrationally excited states are involved in strong c-type Coriolis coupling and require an appropriate two-state Hamiltonian. The oblate nature of 1H-1,2,4-triazole is sufficiently close to the oblate symmetric-top limit that the analysis requires the use of A-reduced, sextic centrifugally distorted-rotor Hamiltonian models in the Ir representation in order to achieve low σfit values. The coupling between ν17 (A″) and ν16 (A″) resulted in many transitions with slightly perturbed frequencies, many highly displaced resonant intrastate transitions, and 165 nominal interstate transitions. Modeling the spectra of ν17 and ν16 required three c-axis Coriolis-coupling terms (Fab, FabJ, and FabK) to treat the interaction. Many of the nominal interstate transitions form clearly discernible Q-branch bands, comprising degenerate sets of a- and b-type transitions. The rotational spectra of four higher-energy vibrationally excited states (ν15, ν14, ν13, and ν12), which form a complex polyad involving Coriolis and anharmonic coupling interactions, were analyzed by single-state models, thus producing only effective spectroscopic constants. Inclusion of rotationally resolved infrared transitions enabled the accurate and precise determination of vibrational band origins for the four lowest-energy fundamental states: ν18 = 542.601 824 3 (28) cm-1, ν17 = 665.183 128 5 (43) cm-1, ν16 = 682.256 910 5 (43) cm-1, and ν15 = 847.557 400 (11) cm-1.

An experimental and numerical analysis of slit plate as replaceable fuse in moment resisting frame

This study contributes to the ongoing progress in developing cost-effective structural fuse solutions for steel structures, emphasizing enhanced strength, ductility, and energy dissipation capacity. These fuses are strategically placed to coincide with plastic hinge locations under lateral load. During minor seismic events, they provide substantial rotational stiffness, while during medium to large earthquakes, they leverage their post-yield strength for effective energy dissipation. Three varieties of beam-column sub-assemblages viz. single oval slit damper fuse (SOSDF), dual oval slit damper fuse (DOSDF) and single elliptical slit damper fuse (SESDF), featuring advanced replaceable fuses were evaluated using both experimental and numerical analyses under quasi-static loading conditions. The seismic performance of these specimens was comprehensively assessed, focusing on characteristics such as moment-carrying capacity concerning rotation, energy dissipation, ductility, and failure modes. The findings indicate that all specimens exhibited stable hysteresis, with connections utilizing SESDF and DOSDF showing slightly higher moment carrying capacities (19 % and 10 %, respectively) compared to those employing SOSDF. According to AISC 2016 standards, all three connections were classified as full-strength connections. Moreover, the ductility of specimens incorporating SESDF was notably higher as 3.5, marking a 28 % and 26 % increase over the ductility of SOSDF and DOSDF connections, respectively. In major seismic events, damage was confined solely to the fuse components, with no damage observed in the beam and column. Detailed finite element analysis using ABAQUS CAE further corroborated these findings, demonstrating good alignment between experimental and simulated results.

A multi-stable rotational energy harvester for arbitrary bi-directional horizontal excitation at ultra-low frequencies for self-powered sensing

A rotational multi-stable energy harvester has been presented in this paper for harnessing broadband ultra-low frequency vibrations. The novel design adopts a toroidal-shaped housing to contain a rolling sphere magnet which absorbs mechanical energy from bidirectional base excitations and performs continuous rotational movement to transfer the energy using electromagnetic transduction. Eight alternating tethering magnets are placed underneath its rolling path to induce multi-stable nonlinearity in the system, to capture low-frequency broadband vibrations. Electromagnetic transduction mechanism has been employed by mounting eight series connected coils aligned with the stable regions in the rolling path of the sphere magnet, aiming to achieve greater power generation due to optimized rate of change of magnetic flux. A theoretical model has been established to explore the multi-stable dynamics under varying low-frequency excitation up to 5 Hz and 3 g acceleration amplitudes. An experimental prototype has been fabricated and tested under low frequency excitation conditions. The harvester is capable of operating in intra-well, cross-well, and continuous rotation mode depending on the input excitation, and the validated physical device can generate a peak power of 5.78 mW with 1.4 Hz and 0.8 g sinusoidal base excitation when connected to a 405 Ω external load. The physical prototype is also employed as a part of a self-powered sensing node and it can power a temperature sensor to get readings every 13 s on average from human motion, successfully demonstrating its effectiveness in practical wireless sensing applications.

Analysis of the Effect of Slow-Varying Errors on Rotary Modulation Systems.

Rotation modulation is a technique that relies on the specific rotation of an inertial measurement unit (IMU) to achieve the self-compensation of device errors. Common rotation schemes are classified into two modes: continuous rotation and a rotation-stop combination. Aiming at the problem of the poor modulation of slow-varying errors in the rotation-stop combination mode, a detailed analysis is conducted on the modulation effects of slow-varying errors in three schemes employing different rotation modes. Firstly, a detailed mathematical analysis is performed on the influence of gyro slow-varying drifts on two rotation modes, and the analysis results are validated through simulations. Subsequently, simulation experiments are conducted on three schemes to analyze their modulation effects on the slow-varying errors of inertial devices. The simulation results reveal that the modified dual-axis rotation scheme exhibits superior modulation effects on the slow-varying errors of inertial devices compared to the dual-axis sixteen-position rotation scheme and the multi-axis alternating continuous rotation scheme.

Interference mechanism of trailing edge flap shedding vortices with rotor wake and aerodynamic characteristics

A robust Reynolds-Averaged Navier-Stokes (RANS) based solver is established to predict the complex unsteady aerodynamic characteristics of the Active Flap Control (AFC) rotor. The complex motion with multiple degrees of freedom of the Trailing Edge Flap (TEF) is analyzed by employing an inverse nested overset grid method. Simulation of non-rotational and rotational modes of blade motion are carried out to investigate the formation and development of TEF shedding vortex with high-frequency deflection of TEF. Moreover, the mechanism of TEF deflection interference with blade tip vortex and overall rotor aerodynamics is also explored. In non-rotational mode, two bundles of vortices form at the gap ends of TEF and the main blade and merge into a single TEF vortex. Dynamic deflection of the TEF significantly interferes with the blade tip vortex. The position of the blade tip vortex consistently changes, and its frequency is directly related to the frequency of TEF deflection. In rotational mode, the tip vortex forms a helical structure. The end vortices at the gap sides co-swirl and subsequently merge into the concentrated beam of tip vortices, causing fluctuations in the vorticity and axial position of the tip vortex under the rotor. This research concludes with the investigation on suppression of Blade Vortex Interaction (BVI), showing an increase in miss distance and reduction in the vorticity of tip vortex through TEF phase control at a particular control frequency. Through this mechanism, a designed TEF deflection law increases the miss distance by 34.7% and reduces vorticity by 11.9% at the target position, demonstrating the effectiveness of AFC in mitigating BVI.

Damage identification of simply-supported beams based on SD value method

Abstract Combining the relationships among the displacement mode, rotation mode, and curvature mode, this study proposes a structural curvature variance ratio (SD) method that can simplify the calculation and reduce the damage recognition error. Using beam structures in the western region as an example, a finite element model is established, and the impact of the displacement modulus on beam damage recognition is analyzed. The applicability of the SD method for damage recognition is also investigated. In the presence of measurement errors, the SD method and the curvature modulus difference method are compared and analyzed. The results show that this method can effectively identify structural damage, determine the location and quantity of local damage, and simplify calculations while reducing error transmission and amplification.

How Nonpolar CO2 Aggregates on Cycloalkenes: A Case Study with Cyclopentene-(CO2)1-3 Clusters.

This study explores the molecular clusters of cyclopentene (CPE) with one to three CO2 molecules (CPE-(CO2)1-3) through their jet-cooled rotational spectra using Fourier transform microwave spectroscopy with supplementary quantum chemical calculations. The assembly of CPE-(CO2)1-3 clusters is predominantly driven by tetrel bonding networks, notably C···π(C═C) and C···O interactions, with additional stabilization from weak C─H(CH2)···C═O hydrogen bonds. Critically, the dispersive forces play a pivotal role in stabilizing CO2 aggregation on CPE, eclipsing the effects of electrostatic and orbital interactions. This highlights the complex balance of forces that govern the formation and stabilization of these molecular clusters. Our findings offer precise insights into noncovalent interactions that could enhance atmospheric chemistry models and sustain climate science through informed environmental chemistry strategies.

Twins in rotational spectroscopy: Does a rotational spectrum uniquely identify a molecule?

Rotational spectroscopy is the most accurate method for determining structures of molecules in the gas phase. It is often assumed that a rotational spectrum is a unique "fingerprint" of a molecule. The availability of large molecular databases and the development of artificial intelligence methods for spectroscopy make the testing of this assumption timely. In this paper, we pose the determination of molecular structures from rotational spectra as an inverse problem. Within this framework, we adopt a funnel-based approach to search for molecular twins, which are two or more molecules, which have similar rotational spectra but distinctly different molecular structures. We demonstrate that there are twins within standard levels of computational accuracy by generating rotational constants for many molecules from several large molecular databases, indicating that the inverse problem is ill-posed. However, some twins can be distinguished by increasing the accuracy of the theoretical methods or by performing additional experiments.