Excited Bending Research Articles

Vibrational Relaxation of D2O Induced by Collision with He: A Rigid Bender Close Coupling Study.

The vibrational relaxation of the first excited bending state of D2O induced by collision with He is studied at the close coupling level and using the Rigid Bender approximation. A new 4D potential energy surface is calculated and reported for this system. It is then used to determine the low-lying bound states of the D2O-He van der Waals complex and to perform scattering calculations. Collision rates are determined for pure rotational transitions as well as for rovibrational transitions within the first excited bending state. The results are compared with those obtained for the collision of D2O with other noble gases such as Ne and Ar. We also analyse the differences observed with respect to the H2O+He collisions and compare our results with experiment.

Vibrationally Mode-Specific Molecular Energy Transfer to Surface Electrons in Metastable Formaldehyde Scattering from Cesium-Covered Au(111).

Nonadiabatic interaction of adsorbate nuclear motion with the continuum of electronic states is known to affect the dynamics of chemical reactions at metal surfaces. A large body of work has probed the fundamental mechanisms of such interactions for atomic and diatomic molecules at surfaces. In polyatomic molecules, the possibility of mode-specific damping of vibrational motion due to the effects of electronic friction raises the question of whether such interactions could profoundly affect the outcome of chemistry at surfaces by selectively removing energy from a particular intramolecular adsorbate mode. However, to date, there have not been any fundamental experiments demonstrating nonadiabatic electron-vibration coupling in a polyatomic molecule at a surface. In this work, we scatter excited metastable formaldehyde and formaldehyde-d2 from a low work function surface and detect ejected exoelectrons that accompany molecular relaxation. The exoelectron ejection efficiency exhibits a strong dependence on the vibrational mode that is excited: out-of-plane bending excitation (ν4) leads to significantly more exoelectrons than does CO stretching excitation (ν2). The results provide clear evidence for mode-specific energy transfer from vibration to surface electrons.

The tunneling splittings of the ground state and some excited vibrational states for the inversion motion in H3C− anion and H3Si[rad] radical

Splitting of the ground state and some excited symmetric bending vibrational states due to inversion tunneling in the H3C− anion and H3Si radical is analyzed by numerically solving the vibrational Schrödinger equation of restricted (2D) dimensionality. We used the following two vibrational coordinates for the H3X structure (X = C, Si): the distance of the X atom from the plane of a regular triangle formed by three hydrogen atoms (1) and a symmetry coordinate composed of three distances between chemically non-bonded hydrogen atoms (2). The kinetic energy operator in this case takes the simplest form. The 2D potential energy surface (PES) in the given coordinates was calculated for H3C− at the CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ, CCSD(T)/aug-cc-pV5Z, CCSD(T)/CBS(TQ5), CCSD(T)/d-aug-cc-pVTZ, CCSD(T)/t-aug-cc-pVTZ, and CCSD(T)/q-aug-cc-pVTZ levels of theory, based on recommendations from recently published work [M.C. Bowman, B. Zhang, W.J. Morgan, H.F. Schaefer III, Mol.Phys., 117 (2019) 1069–1077]. The same 2D PES for the H3Si radical was calculated at the CCSD(T)/aug-cc-pVDZ CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ, and CCSD(T)/CBS(D,T,Q) as well as at the CCSD(T)/d-aug-cc-pVTZ, CCSD(T)/un-aug-cc-pVTZ, CCSD(T)/un-aug-cc-pVQZ levels of theory. The tunneling splittings for the D3C− anion and D3Si radical were calculated as well. The results of calculations demonstrate good agreement with available experimental data on umbrella vibration frequencies and inversion splittings for the title molecules.

Lifetimes and decay mechanisms of isotopically substituted ozone above the dissociation threshold: matching quantum and classical dynamics.

Energies and lifetimes of vibrational resonances were computed for 18O-enriched isotopologue 50O3 = {16O16O18O and 16O18O16O} of the ozone molecule using hyperspherical coordinates and the method of complex absorbing potential. Various types of scattering resonances were identified, including roaming OO-O rotational states, the series corresponding to continuation of bound vibrational resonances of highly excited bending or symmetric stretching vibrational modes. Such a series become metastable above the dissociation limit. The coupling between the vibrationally excited O2 fragment and rotational roaming gives rise to Feshbach type resonances in ozone. Different paths for the formation and decay of symmetric 16O18O16O and asymmetric species 16O16O18O were also identified. The symmetry properties of the total rovibronic wave functions of the 18O-enriched isotopologues are discussed in the context of allowed dissociation channels.

The CN(X 2Σ+) + C2H6 reaction: Dynamics study based on an analytical full-dimensional potential energy surface.

The hydrogen abstraction reaction of the cyano radical with molecules of ethane presents some interesting points in the chemistry from ultra-cold to combustion environments especially with regard to HCN(v) product vibrational distribution. In order to understand its dynamics, a new analytical full-dimensional potential energy surface was developed, named PES-2023. It uses a combination of valence bond and mechanic molecular terms as the functional form, fitted to high-level abinitio calculations at the explicitly correlated CCSD(T)-F12/aug-cc-pVTZ level on a reduced and selected number of points describing the reactive process. The new surface showed a continuous and smooth behavior, describing reasonably the topology of the reaction: high exothermicity, low barrier, and presence of intermediate complexes in the entrance and exit channels. Using quasi-classical trajectory calculations (QCT) on the new PES-2023, a dynamics study was performed at room temperature with special emphasis on the HCN(v1,v2,v3) product stretching and bending vibrational excitations, and the results were compared with the experimental evidence, which presented discrepancies in the bending excitation. The available energy was mostly deposited as HCN(v) vibrational energy with the vibrational population inverted in the CH stretching mode and not inverted in the CN stretching and bending modes, thus simulating the experimental evidence. Other dynamics properties at room temperature were also analyzed; cold rotational energy distribution was found, associated with a linear and soft transition state, and backward scattering distribution was found, associated with a rebound mechanism.

Energy relaxation pathways and their isotope effects of water bending mode in liquid phase: A nonequilibrium ab initio molecular dynamics simulation study

Vibrational energy relaxation pathways and the rates of excited bending mode of water molecules (H2O) in bulk liquid water (H2O), and the rates of the excited bending mode of HOD molecules in D2O (isotopically diluted water) were examined via non-equilibrium ab initio molecular dynamics (NE-AIMD) simulation. The NE-AIMD simulation showed a significantly fast relaxation of the bend vibration, at the timescale of 127 fs in pure water and 144 fs in isotopically diluted water. The main relaxation pathway for pure and isotopically diluted water was found to be driven by intramolecular bend–libration coupling (84% in pure water and 96% in isotopically diluted water). In the case of pure water, intermolecular coupling between bend–bend vibrations was small but non-negligible (11%), whereas such intermolecular coupling was negligible in isotopically diluted water owing to a large frequency mismatch between the excited bend vibration and the surrounding bend vibrations.

Recent Advances in Vibro-Acoustics and Noise Control Of Aerospace Composite Structures

Composite structures are widely used in a variety of industrial applications due to their excellent mechanical properties, such as high stiffness-to-weight ratio, etc. The same characteristics that impart excellent mechanical efficiency, however, also result in efficient transmission and radiation of acoustic noise, posing serious vibro-acoustical problems for a variety of engineering systems in which composite structures are used. The composite structures are efficient radiators of noise mainly due to excitation and propagation of supersonic bending and/or shear waves in the structures. Composite skin-stringer structures mostly support supersonic flexural or bending waves propagating in the laminated structure whereas noise radiation by sandwich structures is dominated by supersonic shear waves in the core. Noise control of composite structures presents a significant technical challenge as the main advantages afforded by these structures, such as low weight and high strength, must not be compromised by added treatments. Recently, research has also been conducted to improve attenuation of vibration and noise radiation from such structure using nano-technology. This paper presents state-of-the-art review of the vibro-acoustics and noise control technology for aerospace composite structures.

Characterization of the intermolecular vibrational levels bound within the Ar + I2(E, v) potential energy surfaces

Two-color, two-photon laser-induced fluorescence experiments were performed to probe the intermolecular interactions within the Ar + I2(E, vE = 0–3) potential energy surfaces. Spectra were recorded using the lowest-energy T-shaped level and an excited intermolecular vibrational level with bending excitation within the Ar + I2(B, vB = 23) potential as intermediate levels to guide the spectral assignments. Progressions of intermolecular stretching and bending levels bound within the Ar + I2(E, vE) potentials were identified, and their vibrational frequencies were determined. The harmonic frequency and anharmonic constant for the bending vibrational mode were determined to be ωe(b) ∼ 34.8 cm−1 and ωeχe(b) ∼ 0.3 cm−1. The frequency and anharmonic constant for the stretching mode were found to be the same as reported previously [V.V. Baturo, et al. Chem. Phys. Lett. 647 (2016) 161], ωe(s) = 37.2(1.1) cm−1 and ωeχe(s) = 1.8(2) cm−1.

Optical Trapping of a Polyatomic Molecule in an ℓ-Type Parity Doublet State.

We report optical trapping of a polyatomic molecule, calcium monohydroxide (CaOH). CaOH molecules from a magneto-optical trap are sub-Doppler laser cooled to 20(3) μK in free space and loaded into an optical dipole trap. We attain an in-trap molecule number density of 3(1)×10^{9} cm^{-3} at a temperature of 57(8) μK. Trapped CaOH molecules are optically pumped into an excited vibrational bending mode, whose ℓ-type parity doublet structure is a potential resource for a wide range of proposed quantum science applications with polyatomic molecules. We measure the spontaneous, radiative lifetime of this bending mode state to be ∼0.7 s.

A convenient set of vibrational coordinates for 2D calculation of the tunneling splittings of the ground state and some excited vibrational states for the inversion motion in H3O+, H3O−, and H3O[rad

Splitting of the ground state and some excited symmetric bending vibrational states due to inversion tunneling of the oxygen atom in the H3O+, H3O− ions and in the H3O radical are analyzed by numerically solving the vibrational Schrödinger equation of restricted (2D) dimensionality. As two vibrational coordinates, we used 1) the distance of the oxygen atom from the plane of a regular triangle formed by three hydrogen atoms and 2) a symmetry coordinate composed of three distances between chemically non-bonded hydrogen atoms. The kinetic energy operator in this case takes the simplest form. The 2D potential energy surface (PES) in the given coordinates was calculated for H3O+ at the CCSD(T)/aug-cc-pVTZ and CCSD(T)-F12/cc-pVTZ-F12 levels of theory. The same 2D PES for the H3O− anion and H3O radical were calculated at the CCSD(T)/aug-cc-pVQZ, CCSD(T)/d-aug-cc-pVQZ and UCCSD(T)/aug-cc-pVQZ, UCCSD(T)/d-aug-cc-pVQZ levels of theory, respectively. The tunneling splittings were calculated for the cations H316O+, D316O+, T316O+, H318O+, D318O+, T318O+. The tunneling splittings for the H3O−, D3O−, T3O− anions and H3O, D3O, T3O radicals were calculated for the first time. The results of calculations demonstrate good agreement with experimental values of the tunneling splittings in the ground state and in some excited vibrational states of the H316O+ and D316O+ cations.

Computing excited OH stretch states of water dimer in 12D using contracted intermolecular and intramolecular basis functions.

Due to the ubiquity and importance of water, water dimer has been intensively studied. Computing the (ro-)vibrational spectrum of water dimer is challenging. The potential has eight wells separated by low barriers, which makes harmonic approximations of limited utility. A variational approach is imperative, but difficult because there are 12 coupled vibrational coordinates. In this paper, we use a product contracted basis whose functions are products of intramolecular and intermolecular functions computed using an iterative eigensolver. An intermediate matrix F facilitates calculating matrix elements. Using F, it is possible to do calculations on a general potential without storing the potential on the full quadrature grid. We find that surprisingly many intermolecular functions are required. This is due to the importance of coupling between inter- and intra-molecular coordinates. The full G16 symmetry of water dimer is exploited. We calculate, for the first time, monomer excited stretch states and compare P(1) transition frequencies with their experimental counterparts. We also compare with experimental vibrational shifts and tunneling splittings. Surprisingly, we find that the largest tunneling splitting, which does not involve the interchange of the two monomers, is smaller in the asymmetric stretch excited state than in the ground state. Differences between levels we compute and those obtained with a [6+6]D adiabatic approximation [Leforestier et al. J. Chem. Phys. 137 014305 (2012)] are ∼0.6 cm-1 for states without monomer excitation, ∼4 cm-1 for monomer excited bend states, and as large as ∼10 cm-1 for monomer excited stretch states.

INVESTIGATION OF THE PASSAGE OF VIBRATIONS THROUGH A FIXED SECTION OF AN ELONGATED PLATE CAUSED BY THE ACTION OF THE AXIAL FORCE AT THE END

A method has been developed for the experimental study of forced elastic vibrations of a cantilevered thin-walled structural element in the form of a rod-strip, excited due to the passage of vibrations through the section of a finite length fixed along one of the surfaces caused by axial loading by a harmonic force applied to the end of the fixed section. The experimental dependence of the amplitude values of the vibration accelerations of the point at the end of the console on the frequency of the excited bending vibrations of the end of the rod is obtained, indicating the passage of vibrations through the fixing section of the finite length, which occurs due to the transformation of longitudinal vibrations in the loading zone into longitudinal-transverse-shear vibrations of the rod-strip in the fixing zone, followed by their transformation into predominantly bending vibrations of the cantilever part of the rod. For the theoretical study of the described phenomenon, a transformational model of deformation of the rod-strip is constructed, taking into account the deformability of the fastening section of finite length on the basis of the refined model of S. Timoshenko. The cantilever part of the rod is represented by the classical Kirchhoff-Love model, taking into account geometric nonlinearity in determining axial deformations. The kinematic conditions of coupling of the fixed and cantilever parts of the rod are formulated. On the basis of the Hamilton-Ostrogradsky variational equation, the equations of motion of the non-fixed and fixed parts of the rod, as well as the boundary conditions for them and the force condition of conjugation of the marked parts of the rod are obtained. Numerical experiments have been carried out for a rod-strip made of aluminum alloy D16AT, showing a noticeable passage of vibrations through the fixing section of the final length into the cantilever part of the rod with a decrease in the dynamic shear modulus of the material to a certain value.

Thermal fluctuations and osmotic stability of lipid vesicles.

Biological membranes constantly change their shape in response to external stimuli, and understanding the remodeling and stability of vesicles in heterogeneous environments is therefore of fundamental importance for a range of cellular processes. One crucial question is how vesicles respond to external osmotic stresses, imposed by differences in solute concentrations between the vesicle interior and exterior. Previous analyses of the membrane bending energy have predicted that micron-sized giant unilamellar vesicles (GUVs) should become globally deformed already for nanomolar concentration differences, in contrast to experimental findings that find deformations at much higher osmotic stresses. In this article, we analyze the mechanical stability of a spherical vesicle exposed to an external osmotic pressure in a statistical-mechanical model, including the effect of thermally excited membrane bending modes. We find that the inclusion of thermal fluctuations of the vesicle shape changes renders the vesicle deformation continuous, in contrast to the abrupt transition in the athermal picture. Crucially, however, the predicted critical pressure associated with global vesicle deformation remains the same as when thermal fluctuations are neglected, approximately six orders of magnitude smaller than the typical collapse pressure recently observed experimentally for GUVs. We conclude by discussing possible sources of this persisting dissonance between theory and experiments.

Quantum study of the bending relaxation of H2O by collision with H

ABSTRACT Vibrationally excited levels of the H2O molecule are currently detected in various environments of the interstellar medium (ISM), and collisional data for H2O, including vibration with the main colliders of the ISM, are needed. The present study focuses on the bending relaxation of H2O by collision with H when taking bending–rotation coupling explicitly into account with the rigid-bender close-coupling (RB-CC) method. With this aim, a new four-dimensional potential energy surface including the H2O bending mode is developed from a large grid of ab initio energies computed using a high level of theory. For purely rotational transitions, our RB-CC rates show very good agreement with rigid-rotor calculations performed using our new potential energy surface (PES) and with those available in the literature. Calculations for pure rotational transitions inside the excited bending level ν2 = 1 of H2O are performed and compared with their equivalents inside ν2 = 0. Vibrational quenching of H2O is also calculated and found to be much more efficient through collision with H rather than with He.

Characterization of the Coriolis Coupled Far-Infrared Bands of syn-Vinyl Alcohol.

Rotational emission from vibrationally excited molecules are responsible for a large fraction of lines in the spectra of interstellar molecular clouds. Vinyl alcohol (VA) has two rotamers that differ in energy by 6.4 kJ/mol, both of which have been observed toward the molecular cloud, Sagittarius B2(N) [Turner and Apponi, Astrophys. J. 2001, 561, 207]. Previously, we reported an analysis of the far-infrared spectrum of the higher energy rotamer, anti-VA [Bunn et al. Astrophys. J. 2017, 847, 67], yielding rotational and higher order distortion constants in the first excited vibrational state, and here, we report an analysis of the far-infrared spectrum of the lower energy rotamer, syn-VA, whose spectrum is significantly more complicated on account of Coriolis interactions that result in perturbations to the rovibrational spectrum. We account for those perturbations with the inclusion of Coriolis coupling constants in the fit, which couples the first excited OH torsional (ν15) and CCO bending (ν11) states. Inclusion of them resulted in more physically meaningful rotational and centrifugal distortion constants, and allows for accurate pure rotational line predictions to be made up to high energies. These will be particularly useful in searches for vibrationally excited syn-VA toward warm regions of interstellar molecular clouds, where we predict that it may be significantly abundant.

Reactions of OH and OD radicals with ethanethiol and diethylsulfide: Branching ratio and vibrational energy disposal for the product water molecules

Reactions of OH and OD radicals with C 2 H 5 SH and (C 2 H 5 ) 2 S were studied by Fourier-transform infrared emission spectroscopy of the water product molecules from a fast-flow reactor. Vibrational excitation of the H 2 O, HOD and D 2 O product molecules was determined by computer modeling of the chemiluminescence spectra. Spectra of the abstraction of H-atom from the ethyl group (C-H) and sulfur atom (S-D) were separated using deuterated reactant, C 2 H 5 SD. The branching ratio was found to be 0.24 ± 0.05 (C-H):0.76 (S-D) both for OH and OD reactants. For the OH + C 2 H 5 SH reaction the branching fraction for the (C-H) channel of 0.25 ± 0.06 was obtained. Vibrational energy disposal for S-H abstraction is similar to that for the reaction with CH 3 SH, whereas abstraction from the ethyl group demonstrates higher bending excitation than abstraction from the methyl group of CH 3 SH. A similar trend was found for abstraction from the ethyl and methyl groups of (C 2 H 5 ) 2 S and CH 3 SCH 3 .

Ten-dimensional quantum dynamics study of H+CH3D → H2+CH2D reaction

The mode selectivity of the H+CH3D→H2+CH2D reaction was studied using a recently developed ten-dimensional time-dependent wave packet method. The reaction dynamics are studied for the reactant CH3D initially from the ground state, the CH3 symmetry and asymmetry stretching excitation, the CD stretching excitation and the fundamental and the first overtone of the CH3 bending mode. The calculated reaction probabilities show that exciting either of the CH3 stretching modes enhances the reactivity in the collision energy range below 1.0 eV, while the CD stretching excitation does not obviously prompt the reaction. Fundamental CH3 bending excitation has nearly no effect on promoting reactivity. However, a significant enhancement is observed for the first overtone excitation of the CH3 bending mode, resulting from the Fermi resonance between the fundamental state of the CH3 symmetry stretching mode and the first overtone state of the CH3 bending mode.

Probing the Exit Channel of the OH + CH3OH → H2O + CH3O Reaction by Photodetachment of CH3O-(H2O).

Transition state dynamics of bimolecular reactions can be probed by photodetachment of a precursor anion when the Franck-Condon region of the corresponding neutral potential energy surface is near a saddle point. In this study, photodetachment of anions at m/z = 49 enabled investigation of the exit channel of the OH + CH3OH → H2O + CH3O reaction using photoelectron-photofragment coincidence spectroscopy. High-level coupled-cluster calculations of the stationary points on the anion surface show that the methoxide-water cluster CH3O-(H2O) is the stable minimum on the anion surface. Photodetachment at a 3.20 eV photon energy leads to long-lived H2O(CH3O) complexes and H2O + CH3O products consistent with both direct dissociative photodetachment and resonance mediated processes on the neutral surface. The partitioning of total kinetic energy in the system indicates that water stretch and bend excitation is induced in dissociative photodetachment and evidence for long-lived complexes consistent with vibrational Feshbach resonances is reported.

Water vapor absorption in the region of the oxygen A-band near 760 nm

The oxygen A-band near 760 nm is used to determine the air-mass along the line of sight from ground or space borne atmospheric spectra. This band is located in a spectral region of very weak absorption of water vapor. The increased requirements on the determination of the air columns make suitable to accurately characterize water absorption spectrum in the region. In the present work, we use a cavity ring down spectrometer newly developed in Tomsk, to measure with unprecedented sensitivity and accuracy the water spectrum in the 12969 - 13172 cm−1 region. While about fifty transitions were previously detected in the region, a total of about 580 water lines are measured by CRDS and rovibrationally assigned, leading to the determination of 103 new levels and correction of 134 levels of H216O. Spectroscopic line lists available in the region (HITRAN, W2020 and theoretical line lists) show some important deviations compared to observations. In particular, line intensities are poorly predicted by available ab initio calculations for transitions involving a highly bending excitation.

Creasing of flexible membranes at vanishing tension.

The properties of freestanding tensionless interfaces and membranes at low bending rigidity κ are dominated by strong fluctuations and self-avoidance and are thus outside the range of standard perturbative analysis. We analyze this regime by a simple discretized, self-avoiding membrane model on a frame subject to periodic boundary conditions by use of Monte Carlo simulation and dynamically triangulated surface techniques. We find that at low bending rigidities, the membrane properties fall into three regimes: Below the collapse transition κ_{BP} it is subject to branched polymer instability where the framed surface is not defined, in a range below a threshold rigidity κ_{c} the conformational correlation function are characterized by power-law behavior with a continuously varying exponent α,2<α≤4 and above κ_{c},α=4 characteristic for linearized bending excitations. Response functions specific heat and area compressibility display pronounced peaks close to κ_{c}. The results may be important for the description of soft interface systems, such as microemulsions and membranes with in-plane cooperative phenomena.