Frequencies Of Normal Vibrations Research Articles

Friction and wear of non-ferrous materials under artificially created vibration for machine design

In this study, variations of friction and wear with the variation of the amplitude and frequency of normal vibrations were observed experimentally when mild steel pin slides on copper, aluminium and gunmetal using pin on disc test rig. The background of the study was to find the way of reduction of friction and wear under vertical vibration using artificially created external vibration mechanisms. The test parameters included the sliding speed (1 m/s), normal force (10 N), relative humidity (70%), amplitude (10-200 µm), and frequency (50-250 Hz). Results reveal that the friction coefficient decreases with increased in amplitude and frequency of vibration within the observed range. The reduction rate of friction coefficients and wear rate are different for different tested materials. Roughness affected the friction in conjunction with vibration. The results can be used in the selection of the most appropriate nonferrous material in mechanical and tribological applications.

Calculation of IR-spectra of structural fragments of lignins

To study structure of softwood lignins the experimental and theoretical IR-spectra in middle IR-diapason were analyzed. To interpret these data the quantum chemical calculations of IR-spectra of general dimmer fragments of softwood lignins by method of density functional theory (DFT/B3LYP) with 6-31G(d,p) as basis set were carried out. These calculations showed that frequencies of normal vibrations of fragment with β-alkyl-aryl linkage are close to the experimental values of the IR absorption bands of lignin, and infrared spectrum of this structure is similar to the experimental spectrum of lignin. The calculations with accounting for the solvent showed a strong increase in the intensity of the majority of the bands and the solvent effect on the frequencies of vibrations.

DFT Analyses of Reaction Pathways and Temperature Effects on various Guaiacol Conversion Reactions in Gas Phase Environment

AbstractGuaiacol component represents the phenolic fraction of bio‐oil. In this numerical study, six reaction pathways originating from guaiacol and yielding anisole, phenol, cyclopentanone and cyclohexanone as the major end products with various intermediates, are carried out. The transition state optimizations, normal mode vibrational frequencies, and intrinsic reaction coordinate calculations are performed under the density functional theory (DFT) framework at B3LYP/6‐311+g(d,p) level of theory. The thermochemistry calculations are carried out at 1 atm pressure and at a wide range of temperature between 298–898 K with an interval temperature of 100 K. Results indicate that all six reactions are both exothermic and spontaneous at each temperature point, however, pathways 1, 2, and 3 show increase in exothermicity and spontaneity with increase in temperature but pathways 4, 5, and 6 show the increase in exothermicity only with increase in temperature while decrement in reaction free energies with increasing temperature.

Bisboronic Acids for Selective, Physiologically Relevant Direct Glucose Sensing with Surface-Enhanced Raman Spectroscopy.

This paper demonstrates the direct sensing of glucose at physiologically relevant concentrations with surface-enhanced Raman spectroscopy (SERS) on gold film-over-nanosphere (AuFON) substrates functionalized with bisboronic acid receptors. The combination of selectivity in the bisboronic acid receptor and spectral resolution in the SERS data allow the sensors to resolve glucose in high backgrounds of fructose and, in combination with multivariate statistical analysis, detect glucose accurately in the 1-10 mM range. Computational modeling supports assignments of the normal modes and vibrational frequencies for the monoboronic acid base of our bisboronic acids, glucose and fructose. These results are promising for the use of bisboronic acids as receptors in SERS-based in vivo glucose monitoring sensors.

The normal modes of lattice vibrations of ice XI.

The vibrational spectrum of ice XI at thermal wavelengths using the CASTEP code, a first-principles simulation method, is investigated. A dual-track approach is constructed to verify the validity for the computational phonon spectrum: collate the simulated spectrum with inelastic neutron scattering experiments and assign the photon scattering peaks according to the calculated normal vibration frequencies. The 33 optical normal vibrations at the Brillouin center are illustrated definitely from the ab initio outcomes. The depolarizing field effect of the hydrogen bond vibrations at frequencies of 229 cm−1 and 310 cm−1 is found to agree well with the LST relationship. It is a convincing evidence to manifest the LO-TO splitting of hydrogen bonds in ice crystal. We attribute the two hydrogen bond peaks to the depolarization effect and apply this viewpoint to ordinary ice phase, ice Ih, which is difficult to analyse their vibration modes due to proton disorder.

Quantum-chemical simulation of the gas-phase molecular, thermodynamic, and kinetic parameters of CF, CF2, and CF3 radicals and CF4, C2F2, C2F4, and C2F6 molecules

Enthalpy of formation of gaseous CF, CF2, CF3, CF4, C2F2, and C2F4 molecules in the ground state have been simulated via the ab initio method in the CCSD(T) approximation with extrapolation to full basis and correlation energy. Equilibrium geometry, frequency of normal vibrations, and other parameters of these molecules have been determined; their thermodynamic functions at 0–2000 K were calculated from these data. Constants of the C2F6←→ 2CF3, C2F2←→ 2CF, C2F4←→ 2CF2, CF4←→ CF3 + F, CF4←→ CF2 + F2, and CF3←→ CF2 + F equilibriums have been calculated, and the data on the rate constants in the high-pressure limit have been obtained.

Geometric structure, electronic structure, and some thermodynamic properties of C13H22 trimethyl- and ethylmethyladamantanes

The structure of perhydrofluorene and its isomerization products 1,3,5-trimethyladamantane, 1,3,6-trimethyladamantane, cis-1,3,4-trimethyladamantane, trans-1,3,4-trimethyladamantane, 1-ethyl-3-methyladamantane, cis-1-ethyl-4-methyladamantane, trans-1-ethyl-4-methyladamantane, 1,2,6-trimethyladamantane, and 1,2,8-trimethyladamantane of the general formula C13H22 has been studied using the Becke—Lee—Yang—Parr (B3LYP) hybrid energy functional of electron density with the 6-31G* basis set. The geometric and electronic characteristics of the compounds and their total energy, transformation energies, entropies of transformations, and normal vibration frequencies have been calculated. It has been shown that the calculated Gibb free energies of formation for the perhydrofluorene isomerization products are in qualitative agreement with the experimental product composition of the isomerate.

Benchmark thermochemistry of N-methylaniline.

In this work, the standard molar enthalpy of formation in the gaseous state of highly pure N-methylaniline, Δ(f)H(m)°(g, 298.15 K) = 90.9 ± 2.1 kJ·mol⁻¹, has been obtained from the calorimetrically measured energy of combustion converted into the enthalpy of formation, Δ(f)H(m)°(liq, 298.15 K) = 35.9 ± 2.1 kJ·mol⁻¹, and from the molar enthalpy of vaporization, Δ(l)(g)H(m) = 55.0 ± 0.2 kJ·mol⁻¹, derived from vapor pressure measurements by transpiration method. The enthalpy of formation of N-methylaniline calculated using the quantum chemical G4 method was in excellent agreement with the experimental value. The frequencies of normal vibrations were obtained from the experimental and calculated spectra. Thermodynamic properties of N-methylaniline in the ideal gas state were calculated from molecular and spectral data in the temperature range 100-1500 K.

Temperature dependence of the heat capacity and times of the establishment of vacancy equilibrium in simple crystals

The concentration range of vacancies that affect the temperature dependence of the heat capacity at constant volume C v has been determined. The times of the establishment of vacancy equilibrium in spherical samples of simple crystals with different radii due to the thermal motion of atoms have been calculated for the process as close as possible to the equilibrium one with a decrease in the temperature from the melting point to the current value T. The free energy of an imperfect crystal has been determined taking into account contributions from interatomic interactions in terms of the Lennard-Jones potential functions and vibrational energies. The properties of an imperfect crystal have been calculated within the Lifshitz approximation linear in the density of vacancies with the frequency distribution function of the perfect crystal with the corresponding corrections, which reflect local vibrations of atoms around vacancies. The free energy of a defect-free perfect crystal has been determined from the calculated frequencies of normal vibrations with the inclusion of up to four nearest neighbors. It has been shown that disregard of acoustic (out-of-phase) parts of the spectrum in the calculation of the heat capacity C v with increasing temperature leads to a decrease (increase) in C v from the values calculated for the total vibrational spectrum. A nonequilibrium state of the imperfect crystal can lead to negative values of the heat capacity at constant volume.

Quantum-chemical calculations of the structure and vibration spectrum of methyl nitrate

Methyl nitrate vibration spectra theoretical analysis data within the B3LYP density functional theory method in the 6 -31G (d) basis are represented. When optimizing the geometry of the molecule it was found out that methyl nitrate is characterized by one stable conformation: trans – form. Frequency, intensity and forms of normal vibrations are calculated, their comparative analysis with well-known from the literature experimental data is given.

Calculating the effect of vacancies on the thermodynamic functions and frequencies of normal vibrations of a Lennard-Jones monoatomic crystal

Four main functions of a Lennard-Jones defect argon crystal with an FCC lattice are considered in the context of the lattice gas model: Helmholtz free energy, entropy, internal energy, and heat capacity at a constant volume (allowing for normal vibrations of a solid). Properties of the defect crystal are calculated from the distribution function of the frequencies of an ideal crystal, and corrections to it that reflect local atomic vibrations around vacancies, in the context of the Lifshits linear approximation according to vacancy density. To find the free energy of a defect-free ideal crystal, frequencies of normal vibrations of the crystal are calculated with allowance for the interactions of the four nearest neighbors. The nonlocality of the chemical potentials of the atoms of a solid is discussed, and the influence of contributions from various segments of the vibrational spectrum to the values of thermodynamic functions is investigated. It is shown that ignoring the acoustic or antiphase segments of the spectrum when calculating the free energy leads to increasing of its deviation from the one calculated using the full vibrational spectrum with an increase in temperature. It is concluded that the nonequilibrium state of the defect crystal can lead to negative values of heat capacity at a constant volume.

Calculation of geometric structure, electronic characteristics, vibration frequencies, and thermodynamic properties of C12H20 alkyladamantanes

The structure of perhydroacenaphthene (I) and its conversion products 1,3-dimethyladamantane (II), trans-1,4-dimethyladamantane (III), cis-1,4-dimethyladamantane (IV), 1,2-dimethyladamantane (V), 1-ethyladamantane (VI), and 2-ethyladamantane (VII) of the general formula C12H20 has been studied using the Becke-Lee-Yang-Parr (B3LYP) hybrid method for the energy functional of the electron density with the 6–31G* basis set. Geometric and electronic characteristics of the compounds and their total energy, trans-formation energies, transformation entropies, and normal vibration frequencies have been calculated. The equilibrium constants determined for the isomerization of perhydroacenaphthene into products II-VII are consistent with experimental data.

Hole hopping rates in single strand oligonucleotides

The rates of hole transfer between guanine and adenine in single strand DNA have been evaluated by using Fermi’s golden rule and Kubo’s generating function approach for the Franck–Condon weighted density of states. The whole sets of the normal modes and vibrational frequencies of the two nucleobases, obtained at DFT/B3LYP level of calculation, have been considered in computations. The results show that in single strand the pyramidalization/planarization mode of the amino groups of both nucleobases plays the major role. At room temperature, the Franck–Condon density of states extends over a wide range of hole site energy difference, 0–1eV, giving some hints about the design of oligonucleotides of potential technological interest.

Adsorption Characteristics and Structure of 4,4'-Bis(mercaptomethyl)biphenyl on Silver by Surface-enhanced Raman Scattering and Density Functional Theory Calculations

Adsorption of 4,4'-bis(mercaptomethyl)biphenyl (44BMBP) on silver nanoparticles has been investigated by surface-enhanced Raman scattering (SERS) spectroscopy. In addition, the Raman spectra of 44BMBP in solid state and in basic condition have been obtained for comparative study to elicit the characteristics of adsorption. The observed Raman and SERS spectra were analyzed comparing with the normal modes and vibrational frequencies from density functional theory (DFT) calculations performed for the feasible structures of 44BMBP molecule. On the basis of excellent agreement between the calculated and the experimental results, the molecule is found to have both the cis- and trans-forms for the mercaptomethyl groups in the solid state as well as in the basic condition. In contrast, the molecule is found to be chemisorbed on the silver surface by forming two Ag-S linkages only in the cis-form but not in the trans-form due to the steric interruption, which indicates the parallel orientation of molecules on the surface. Particularly, the spectral features in the SERS spectra such as the absence of the C-H stretching band and enhancement for the out-of-plane skeletal modes are confirmatory for the parallel geometry through <TEX>${\pi}$</TEX> interaction between the phenyl rings and the metal surface, based on the electromagnetic surface selection rule.

Manifestation of Intermolecular Interactions in Raman Spectra and ab Initio Calculations of Molecular Aggregation in Liquid Ethylene Glycol

We present the results of a study of intermolecular interactions in ethylene glycol by Raman spectra. For a more reasonable assumptions about the possibility of the existence of aggregated intermolecular complexes and monomeric molecules of ethylene glycol in the liquid, as well as manifestations of these formations in spectra, we carried out ab initio calculations of the normal vibration frequencies, depolarization ratios of bands, formation energy, and other physical and optical characteristics for aggregated complexes of molecules. Calculations were carried out in the framework of a self-consistent field (RHF) using the basis 6-31G++(d, p) with full optimization of the geometry of molecules. Calculations showed a possibility of the formation of an intermolecular H-bond between the H atom of the O–H group of one molecule and the O atom of another molecule. For a dimeric aggregate, the intermolecular H-bond length is 1.986 ˚ A. In molecules of the dimer, there is a slight change of bonds’ lengths, but also there is a significant change of the charge distribution between atoms. The energy of dimer formation is 4.6 kcal/mole, the dipole moment of an aggregate is 6.35 D (in the monomeric molecule, the dipole moment is 2.73 D). In Raman spectra, there are some features of the manifestation of the H-bonding between molecules: asymmetry of bands and splitting of bands that are the features that accompany the H-bond formation.

Electronic structures of organometallic complexes of f elements LXXXII: Comparison of assigned experimental and calculated (on the basis of density functional theory) frequencies of normal vibrations of the first homoleptic organometallic complex of the lanthanides: Tris(η5-tetramethylcyclopentadienyl)lanthanum

The far and mid infrared spectra of powdered La(η5-C5Me4H)3 as well as polarized Raman spectra of an oriented single crystal (where the principal axes of the two molecules per unit cell are uniformly oriented) have been recorded. Applying the selection rules of C3h symmetry to the experimental data, numerous signals were assigned which agree well with the predictions of a calculation based on density functional theory. Neglecting νC–H and γCp–H (out of plane) modes, an r.m.s. deviation of 21.9cm−1 for 71 assignments was achieved. Skeletal and intra-ligand vibrations were separated and an inspection of the vibronic sidebands of the purely electronic hypersensitive absorption transitions 4I9/2→4G5/2 of Nd(η5-C5Me4H)3 showed that mainly the latter are coupled.

New Approach to Tolman’s Electronic Parameter Based on Local Vibrational Modes

Tolman's electronic parameter (TEP) derived from the A1-symmetrical CO stretching frequency of nickel-phosphine-tricarbonyl complexes, R3PNi(CO)3, is brought to a new, improved level by replacing normal with local vibrational frequencies. CO normal vibrational frequencies are always flawed by mode-mode coupling especially with metal-carbon stretching modes, which leads to coupling frequencies as large as 100 cm(-1) and can become even larger when the transition metal and the number of ligands is changed. Local TEP (LTEP) values, being based on local CO stretching force constants rather than normal mode frequencies, no longer suffer from mode coupling and mass effects. For 42 nickel complexes of the type LNi(CO)3, it is shown that LTEP values provide a different ordering of ligand electronic effects as previously suggested by TEP and CEP values. The general applicability of the LTEP concept is demonstrated.

Computer simulation of the structure and raman spectra of GaAs polytypes

The structure, energy of formation, and Raman spectra of several polytypes (3C, 2H, 4H, and 8H) of gallium arsenide GaAs have been investigated using quantum mechanical calculations based on the local density functional theory. It has been found that the energy of the formation of hexagonal polytypes increases with an increase in the length of the periodicity and approaches the value corresponding to the ground state, i.e., to the structure of the 3C polytype. It has been shown that the calculated frequencies of normal vibrations of different polytypes are consistent, with good accuracy (±6 cm−1), with the scheme of folding of the phonon branches. In the calculated Raman spectra of the polytypes, there are new lines (forbidden in the spectrum of the 3C polytype) which can serve as characteristic lines of other polytypes. Similar lines can be found in the Raman spectra of GaAs nanowhiskers. This result has opened up new prospects for the application of Raman spectroscopy to the characterization of the structure of these nano-objects.

Calculated Vibrational Properties of Ubisemiquinones

Density functional theory has been used to calculate harmonic normal mode vibrational frequencies for unlabeled and isotope-labeled ubisemiquinones in both the gas phase and in several solvents. It is shown that four methoxy group conformations are likely to be present in solution at room temperature. Boltzmann weighted infrared and Raman spectra for the four conformers were calculated, and composite spectra that are the sum of the Boltzmann weighted spectra were produced. These composite spectra were compared to experimental FTIR and resonance Raman spectra, and it is shown that the calculated band frequencies, relative band intensities, and C13 and O18 isotope-induced band shifts are in excellent agreement with experiment. The calculations show that the C=O and C=C modes of ubisemiquinone strongly mix with methoxy methyl CH bending vibrations, and that the degree of mixing is altered upon isotope labeling, resulting in complicated changes in mode frequencies, intensities, and composition upon isotope labeling. Upon consideration of the calculated potential energy distributions of the normal modes of ubisemiquinone, and how they change upon isotope labeling, an explanation of some puzzling features in previously published Raman spectra is provided.

Experimental (IR) and theoretical (LDA) studies of the structure and vibrational-reorientational dynamics of ferroelastic 1-aminopyridinium iodide

Calculations of the molecular structure and normal vibration frequencies have been performed using ADF (Amsterdam Density Functional) program package for initial structural data of 1-aminopyridinium iodide, (1-NH2C5H5N)+I−, low temperature phase (110K). Cambridge Structural Database survey has been carried out in order to explore hydrogen bond patterns of 1-aminopyridinium ring and to analyze the strength of intermolecular N–H⋯I− interactions. Infrared spectra of powdered (1-NH2C5H5N)+I− in a frequency range 4000–400cm−1 in a wide temperature region (from 300 to 413K), covering ferroelastic-paraelastic phase transition at 384/383K (heating/cooling), are presented and analyzed. The mechanism of the phase transition is discussed.