Changes In Vibrational Frequencies Research Articles

NEGATIVE EFFECTIVE PRESSURES IN LIQUID MIXTURES

Ethanol was studied under hydrostatic pressure and in mixtures with water and with chloroform. High resolution Raman spectroscopy was used to monitor the change in vibrational frequency as a function of pressure and composition. Molecular dynamics (MD) simulations were carried out and were compared with experimental results. Results show that for mixtures the cohesive energy density (CED) acts like a real pressure. The CED of a mixture is different from the CED's of the components, and the differences result in effective pressures, negative and positive, on the components of the mixture. Other strong effects overshadow the working of this pressure in some cases. Nevertheless, it is possible to generate an effective negative pressure, which will have various applications in for example protein folding.

Electronic structure of the trimethylenemethane diradical in its ground and electronically excited states: Bonding, equilibrium geometries, and vibrational frequencies

Accurate equilibrium properties of the ground and the three lowest excited states of the trimethylenemethane (TMM) diradical are calculated by using the novel spin–flip electronic structure method. Changes in structures and vibrational frequencies upon excitation are analyzed. The bonding picture in different states of TMM is derived from wave function analysis and comparison of equilibrium structures with typical values of coupled-cluster (CC) bond lengths, e.g., a double CC bond in ethylene, a single CC bond in twisted ethylene, and a bond in the allyl radical.

Identification of bound water through infrared spectroscopy in methylcellulose

This paper describes the interaction of water with solid polymers. A portion of the water adsorbed in hydrophilic materials is strongly bound to individual sites (bound water), while an additional amount is bound less firmly to the polymeric chain (free water). Both, free and bound water, have been the subject of many studies that have uncovered, in some cases, qualitative evidence of the presence of bound water. In this paper we report a method to quantify the fraction of water adsorbed in the first layer in contact with an hydrophilic material. The measurement was carried out on infrared spectroscopy data of methylcellulose films exposed to several humid environments. The quantification was based on the determination of the change in the natural vibration frequency brought about by the interaction of water molecules with the solid.

A Quartz Crystal Microbalance (QCM) Sensor for the Detection of Bacillus cereus

Bacillus cereus is a common food pathogen and is often associated with food poisoning. In this report we demonstrate a rapid, label free QCM sensor for the specific detection of this pathogen. All assays were carried out directly in solution and analysis was performed in real time. A self-assembled monolayer of thiosalicylic acid was used for covalent immobilization of antibodies to the quartz crystal surface. The QCM is a very sensitive device that measures mass by detecting the change in vibrational frequency of the quartz crystal. The change in frequency of the crystal upon binding is proportional to mass of the binding material. A limit of detection of about 104 cells/mL was obtained.

Influence of High-Fluence Proton Irradiation on the Optical Absorption and Microstructure of Rutile

ABSTRACTRutile (TiO2) single crystals of (110) or (001) orientation were irradiated by high fluence protons with the energy of 0.5, 4.9 and 18 MeV and with the fluence of 1×1018 and 1.9×1022 m-2. UV-VIS-IR, LRS and HRTEM were used to analyze the optical absorption and microstructure of samples. The UV-VIS-IR results showed that proton irradiation induces two absorption peaks centered at 760 and 1700 nm respectively, even high fluence irradiation induces absorption plateau at 600∼2500 nm. LRS results showed that the related intensity of common vibration modes is different for different planes. Proton irradiation induces the vibration frequency and related intensity change for inherent LRS modes, and several new vibration modes also appear. High fluence proton irradiation induced large defect clusters, i.e. stacking faults, which is demonstrated by HRTEM observation. The optical absorption mechanism also has been discussed.

Adsorption of H2, H22, O2, and CO on ZrB2(0001)

Adsorption of H2, H22, O2, and CO on ZrB2(0001) was investigated by using high-resolution electron energy loss spectroscopy. In hydrogen and oxygen adsorption, a strong loss peak appears in the specular spectra, showing the dissociative adsorption on the threefold hollow site. The vibrational frequency shifts toward higher energy with increase in oxygen coverage, while little changes in vibrational frequencies were observed in the hydrogen or deuterium adsorption. This means that the interaction between the adsorbates is stronger in oxygen adsorption than in hydrogen adsorption. The initial stage of CO adsorption shows two vibrational peaks, one of which corresponds to the atomic oxygen described above, the other is therefore the atomic carbon, showing dissociative adsorption.

Resonance characteristics of a vibrated fluidized bed with a high bed hold-up

The changes of vibration amplitude, bed expansion and forces on a fluidized bed from distributor with the applied vibration frequency are investigated at different gas velocities. The results show that there exist two resonance frequencies in the system of a vibrated fluidized bed (VFB), which result from the elastic properties of the vibration base and the fluidized bed, respectively. The change of the force on the fluidized bed with the vibration frequency is consistent with the change of the vibration amplitude. When the gas velocity and the vibration frequency reach certain values, the bed expansion ratio reaches its maximum. For vibration frequencies above this value, as the vibration frequency and amplitude change, the fluidization state is stable and the expansion ratio remains constant. This is an ideal stable operation region. The frequency at which the bed expands most rapidly to the maximum is defined as the minimum stable operation frequency, which is approximately the resonance frequency of the fluidized bed when the gas velocity is lower than 2.10 mm/s and approximately the resonance frequency of the vibration base when the gas velocity is above 2.10 mm/s.

DFT study of inner-sphere electron transfer in a gas-phase SN2 reaction at the saturated carbon

The SN2 reaction is investigated from the point of view of an inner-sphere electron transfer reaction. Density functional theory (DFT) calculations are applied to investigate the intrinsic reaction pathway (IRP) of the symmetrical SN2 (inner-sphere electron transfer) reactions, Xa− + CH3Xb → XaCH3 + Xb− (X = F, Cl, Br, I). The geometries of the stationary points in the potential energy surface are compared with available experimental data and with calculations at the MP2 level. The changes in the geometrical parameters, the projected frequencies, charge distribution and dipole moment along the reaction coordinate are discussed. Some relationships between the amount of transferred electron density and the changes in geometrical parameters, vibrational frequencies and energies are given: the greater the amount of transferred electron density, the smaller the decrease in the frequency of the C–Xb stretching mode (from reactant to TS), and the lower the activation energy and the complexation energy. Moreover, the amount of transferred electron density is related to the electronegativity of the halogen atom. Two parameters in the electron transfer theory, the coupling interaction and the reorganization energy, which affect the reactivity are discussed. We conclude that the stronger the CH3–Xb bond, the worse the acceptor.

Theoretical studies of hydrogen bonding in water–cyanides and in the base pair Gu–Cy

Density-functional (DFT) and many-body-perturbation theories (MBPT/CC) are used to study the hydrogen bonding in the water–cyanide complexes H–CN⋯H 2O, H 3C–CN⋯H 2O and (CH 3) 3C–CN⋯H 2O. Structures, binding energies and changes in vibrational frequencies are analyzed. The calculated CN stretching frequency is found to shift to the blue upon complexation in H–CN⋯H 2O and H 3C–CN⋯H 2O. To investigate electron correlation effects on the binding energies of these complexes, single-point calculations are performed at the MBPT/CC (MP2, MP3, MP4, CCSD and CCSD(T)) levels using the optimized MP2 geometries. Binding energies are also obtained at different levels of DFT (B3LYP and PW91) and compared with the MBPT/CC results. All calculations include corrections for basis set superposition error (BSSE) and zero-point vibrational energies. Additionally, the triple hydrogen-bonded guanine–cytosine (Gu–Cy) base pair is analyzed. The binding energy of the Watson–Crick model for Gu–Cy is calculated using the Hartree–Fock calculations and DFT (B3LYP and BP86) methods. The results for the hydrogen bonding distances and binding energies are in good agreement with experimental and recent theoretical values. The calculated dipole moment of the Gu–Cy complex is compared with the direct vector sum of the isolated bases. After taking into account the BSSE effects we find that the electron polarization due to the hydrogen binding leads to an increase of ∼20% of the calculated dipole moment of the complex.

Calculation of the properties of acid sites of the zeolite ZSM-5 using ONIOM method

The performance of the ONIOM method was tested in reproducing the properties of the acid sites of the zeolite ZSM-5. The acid sites in three crystallographic locations (Al3–O19(H)–Si6, Al6–O18(H)–Si9 and Al7–O17(H)–Si4) have been modelled by three combinations of two-layer ONIOM method with varied size (two and eight T atoms) and calculation method (ab initio and DFT) used for the chemically important (active) part. The best correspondence with experimental data was achieved in case of Al6–O18(H)–Si9 site calculated with ONIOM(B3LYP/6-311+G ∗∗:MNDO) method using eight T atoms in model system for the following properties: stretching vibrational frequencies, 1H NMR chemical shifts of the bridged hydroxyl groups, vibrational frequency shifts and changes in 1H NMR chemical shifts of the hydroxyl groups upon adsorption of CO.

Transform method in resonance Raman scattering: effect of mode mixing

AbstractThe effect of mode mixing on resonance Raman scattering is examined on the basis of exact transform relations for the resonance Raman excitation profiles and absorption lineshape in the time domain. General transform relations are presented which hold for an arbitrary number of mixed modes. A detailed description of the excitation profiles of two mixed Raman modes is given, taking into account an arbitrary number of other modes. The dependence of the mixing parameters, change of vibrational frequencies and equilibrium positions in the excited state on the vibronic coupling parameters is found. It is shown that in the case of a substantial change in chemical bonds at the electronic transition, the mode mixing drastically changes the Raman cross‐sections/excitation profiles. Copyright © 2002 John Wiley & Sons, Ltd.

Ultrafast Intramolecular Electron Transfer Studied by Picosecond and Stationary Raman Spectroscopy

Abstract Ultrafast photoinduced intramolecular electron transfer (ET) of betaine-30 (B-30) is studied in different solvents by resonance Raman spectroscopy. We apply stationary and picosecond time-resolved Raman techniques combined with ab initio Hartree–Fock calculations. Picosecond Raman spectroscopy of the first excited singlet state allows to monitor changes of vibrational frequencies due to ET. From the intense Raman lines of the stationary resonance Raman spectra we predict relevant geometric changes of B-30 due to ET which are confirmed by calculations of geometrical changes between the ground and excited electronic states of B-30. The torsional motion between the phenolate and the pyridinium rings as well as nitrogen pyramidalization play an essential role in electron transfer. Vibrational modes accepting the bulk of excess energy after back-electron transfer are identified by time-resolved anti-Stokes resonance Raman spectroscopy. In particular, the highest-frequency mode of the resonance Raman spectrum exhibiting a large Franck–Condon factor is most effective in accepting energy. Mode specific excitation of B-30 after back-electron transfer results in nonequilibrium vibrational populations within the first few picoseconds and subsequent quasi-equilibrium populations of hot Raman active modes. The observed vibrational kinetics can be qualitatively understood by a solvent dependent interplay of direct vibrational excitation and intramolecular vibrational energy redistribution.

Mode mixing via resonance Raman excitation profiles

In the case of linear+quadratic vibronic coupling with an arbitrary number of configurational coordinates, the exact equation for the resonance Raman amplitude has been derived via the absorption Fourier transform. There are some actual cases when this equation has simple solutions: change of vibrational frequency at the electronic transition without mode mixing, mixing of two modes, mixing of modes with close frequency. The corresponding transform relations between Raman amplitudes (→excitation profiles) and the absorption are given, which allow to determine the mixing parameters, vibrational frequencies as well as the linear vibronic coupling parameters.

The Bubble Behavior in a New-type Horizontal Vibro-Fluidized Bed.

The bubble sizes and distribution were measured in a horizontally two-dimensional vibro-fluidized bed. Glass bead of group B particles was fluidized at varying gas velocities, while the bed was vibrated at different frequencies and amplitudes to study the effect on the bubble behavior. Experimental results show that the local average bubble sizes under the vibration field are generally smaller than those without vibration. The local average bubble sizes are hardly affected with the change of vibration frequency, but increase with an increase in the vibration amplitude. Few bubbles were observed in the both side-well of a bed in the experiment at a gas velocity of 0.0907 m/s. Due to horizontal vibration, bubbles were too small to measure the bubble size in the lower area (H < 50 mm). The ratio of the maximum diameter to the minimum diameter of a bubble is not correlated well with vibration, superficial gas velocity and bed height.

Structure and bonding of bisaquamercury(ii) and trisaquathallium(iii) trifluoromethanesulfonate

The structure and bonding in bisaquamercury(II) trifluoromethanesulfonate, [Hg(OH2)2(CF3SO3)2]∞, and trisaquathallium(III) trifluoromethanesulfonate, [Tl(OH2)3(CF3SO3)3], have been studied by means of single-crystal X-ray diffraction, EXAFS and vibrational spectroscopy. The crystal structure of bisaquamercury(II) trifluoromethanesulfonate shows an unusual connectivity pattern. The mercury(II) ion strongly binds two water molecules axially with the Hg–O bond distance 2.11 A, and four oxygen atoms from four trifluoromethanesulfonate ions complete a tetragonally compressed octahedral coordination geometry, at the mean Hg–O distance 2.53 A. Two trifluoromethanesulfonate ions form double bridges between the bisaquamercury(II) entities giving rise to infinite >Hg(OH2)2 Hg(OH2)2< chains. The parallel chains are held together in layers by relatively strong hydrogen bonds with O(–H)⋯O distances in the range 2.688(9)–2.735(9) A. The O–D stretching vibrational frequencies of the hydrogen bonds in the partly deuterated compound occur in a broad band at about 2400 cm−1, bandwidth ca. 170 cm−1. The layers are connected only via van der Waals interactions between the protruding CF3 groups, consistent with the fragile sheet-like structure of the crystalline compound. Trisaquathallium(III) trifluoromethanesulfonate crystallises as molecular complexes where each thallium(III) ion binds three water molecules and three oxygen atoms from trifluoromethanesulfonate ions, with Tl–O bond distances in the range 2.18–2.24 A. A hydrogen bond network between the water molecules and trifluoromethanesulfonate ions with O(–H)⋯O distances in the range 2.65(1)–2.80(1) A holds the structure together. Raman and infrared spectra have been recorded and analysed. The changes in force constants and vibrational frequencies have been correlated with bond lengths for the S–O bond in the coordinated trifluoromethanesulfonate ion and for the Hg–O and Tl–O bonds, also including the hexaaquaions in the comparisons.

Theoretical aspects of electron transfer reactions of complex molecules

Features of electron transfer involving complex molecules are discussed. This notion presently refers to molecular reactants where charge transfer is accompanied by large molecular reorganization, and commonly used displaced harmonic oscillator models do not apply. It is shown that comprehensive theory of charge transfer in polar media offers convenient tools for the treatment of experimental data for such systems, with due account of large-amplitude strongly anharmonic intramolecular reorganization. Equations for the activation barrier and free energy relationships are provided, incorporating vibrational frequency changes, local mode anharmonicity, and rotational reorganization, in both diabatic and adiabatic limits. Systems for which this formalism is appropriate are discussed.

Analysis of the water bound to a polymer matrix by infrared spectroscopy

This article focuses on the interaction of water with solid polymers. A portion of the water adsorbed in hydrophilic materials is strongly bound to individual sites (bound water), while an additional amount is bound less firmly to the polymeric chain (free water). Both free and bound water have been the subject of many studies that have uncovered, in some cases, qualitative evidence of the presence of water directly bound. In this article, we report a method to determine the different fractions of water adsorbed in hydrophilic materials. One fraction corresponds to the first layer in contact with the adsorbing solid and the other corresponds to the remaining water absorbed layers. We were able to determine said quantification by means of measuring the change in the natural vibration frequency brought about by the interaction of water molecules with the solid. The measurement was done on films of methylcellulose exposed to humid environments using infrared spectroscopy and gravimetric static microclime sorption methods. Theoretical predictions for bound water were developed using multilayer adsorption models. The experimental concentration of bound water as a function of relative humidity was compared with these predictions, allowing us to judge the applicability of different adsorption models employed in the study of gas condensation.

Hydrogen-bonding interactions in some benzopyranopyridine esters

Hydrogen bonds in benzopyranopyridine esters have been investigated by means of NMR and IR spectroscopy and quantum chemical calculations. Significant changes in vibrational frequencies, NMR chemical shifts and calculations have pointed towards the formation of different interactions in the solid state and in solution.

Olefinic vs. aromatic pi-H interaction: a theoretical investigation of the nature of interaction of first-row hydrides with ethene and benzene.

The nature and origin of the pi-H interaction in both the ethene (olefinic) and benzene (aromatic) complexes of the first-row hydrides (BH(3), CH(4), NH(3), H(2)O, and HF) has been investigated by carrying out high level ab initio calculations. The results indicate that the strength of the pi-H interaction is enhanced as one progresses from CH(4) to HF. Unlike conventional H-bonds, this enhancement cannot be simply explained by the increase in electrostatic interactions or the electronegativity of the atom bound to the pi H-bonded proton. The contributions of each of the attractive (electrostatic, inductive, dispersive) and repulsive exchange components of the total binding energy are important. Thus, the inductive energy is highly correlated to the olefinic pi-H interaction as we progress from CH(3) to HF. On the other hand, both electrostatic and inductive energies are important in the description of the aromatic pi-H interaction. In either case, the contribution of dispersion energies is vital to obtain an accurate estimate of the binding energy. We also elaborate on the correlation of various interaction energy components with changes in geometries and vibrational frequencies. The red-shift of the nu(Y-H) mode is highly correlated to the inductive interaction. The dramatic increase in the exchange repulsion energies of these pi complexes as we progress from CH(4) to HF can be correlated to the blue-shift of the highly IR active out-of-plane bending mode of the pi system.

加工性およびリサイクル性に優れたMnCuNiFe制振合金の開発

Control of noise and vibration remains to be solved for the lowering of environmental load in all the industrial fields. It is necessary to take account of the noise and vibration problem when designing machines or structures. Therefore the development of damping materials suitable for structural parts that are easy to process and recycle, is urgently required. Mn-Cu damping alloys show the most satisfactory mechanical properties and damping capacity among the developed damping alloys. The M2052 damping alloy, which has a nominal composition of Mn-20Cu-5Ni-2Fe (at%), shows both a high damping capacity and a high strength. The damping capacity of M2052 alloy increases to a high level below a certain temperature, and the damping level also varies sensitively to the changes in vibration frequency and strain amplitude. By the peak-shift method the thermal activation energy for the {101} twin boundaries responsible for the low-temperature damping peak is calculated to be 4.88×104 J/mol. The tensile strength of the alloy is 500 MPa, accompanied with a superior workability for practical applications. It is confirmed experimentally that M2052 damping alloy is quite effective in damping the intolerable vibrations when used as structural parts.