Experimental and computational studies on the solvation of lithium tetrafluorobrate in dimethyl sulfoxide

Solvation structures of the lithium cation and tetrafluorobrate anion in dimethyl sulfoxide (DMSO) were investigated by Raman spectroscopy and ab initio calculations at various salt concentrations. The SO and C S stretching bands were used to monitor the structural change of the solvation shell. It has been shown that the solvation number of Li⁺, calculated by the changes in intensities of the C S asymmetric and symmetric stretching bands, is consistent with the value predicted by ab initio calculations. The wavenumber shift of the C H stretching band is suggested to be the result of the anion solvation and the dissociation of the associated DMSO molecules. Copyright © 2007 John Wiley & Sons, Ltd.     

Investigation of inter-molecular hydrogen bonding in the binary mixture (acetone + water) by concentration dependent Raman study and ab initio calculations

This paper reports that vibrational spectroscopic analysis on hydrogen-bonding between acetone and water comprises both experimental Raman spectra and ab initio calculations on structures of various acetone/water complexes with changing water concentrations. The optimised geometries and wavenumbers of the neat acetone molecule and its complexes are calculated by using ab initio method at the MP2 level with 6-311+G(d,p) basis set. Changes in wavenumber position and linewidth (fullwidth at half maximum) have been explained for neat as well as binary mixtures with different mole fractions of the reference system, acetone, in terms of intermolecular hydrogen bonding. The combination of experimental Raman data with ab initio calculation leads to a better knowledge of the concentration dependent changes in the spectral features in terms of hydrogen bonding.     

Binary mixture of p‐methylbenzaldehyde with polar and nonpolar solvents

In this work, a combined theoretical and experimental study of binary mixture of liquid p‐methylbenzaldehyde (PMBz) is reported using ab initio calculations as well as Raman and IR spectroscopies. The purpose of this study was twofold: firstly, to describe the interaction of PMBz in terms of bonding energies and preferred geometries; and secondly, to characterize the spectroscopic effects on the vibrational modes of PMBz in the binary mixture of different polar and nonpolar solvents. The three vibrational modes, namely, carbonyl stretching, ν(C CH₃) and aldehydic (C H) vibrations have been analyzed in all the three solvents in different concentrations. The dependence of Raman linewidth on the concentration of PMBz of these modes was also taken into account. By analyzing the peak position and linewidth of these modes, it is seen that the solute–solvent interaction is stronger in BuOH and 1,2 dichloroethane (DCE) because of the hydrogen‐bonding interaction between these molecules. The formation of C H···O hydrogen bonds in liquid p‐methylbenzaldehyde is also investigated by Gaussian fitting. The ab initio calculations suggest several possible dimer configurations. Copyright © 2008 John Wiley & Sons, Ltd.     

Calculation of spectroscopic parameters and vibrational overtones of methanol

A high-level quartic ab initio potential energy surface of methanol has been used to calculate spectroscopic constants of the ¹²CH₃OH molecule. These include coefficients of quartic anharmonic resonance terms, Darling-Dennison constants, for stretching states. A model expressed in terms of dimensionless normal coordinates has been employed in the calculation of O—H and C—H stretching vibrational states in high-overtone regions. Both cubic Fermi and quartic Darling-Dennison anharmonic coupling terms have been included in the model in order to take into account strong resonances between different states. The nonlinear least-squares method has been used to optimize some of the model parameters employing experimental term values of ¹²CH₃OH as data. Vibrational assignments are suggested for the first C—H stretching overtone region.     

Experimental and theoretical structure and vibrational analysis of ethyl trifluoroacetate,CF3CO2CH2CH3

The molecular structure and conformational properties of ethyl trifluoroacetate, CF₃CO₂CH₂CH₃, were determined in the gas phase by electron diffraction, and vibrational spectroscopy (IR and Raman). The experimental investigations were supplemented by ab initio (MP2) and DFT quantum chemical calculations at different levels of theory. Experimental and theoretical methods result in two structures with C_s (anti–anti) and C₁ (anti–gauche) symmetries, the former being slightly more stable than the latter. The electron‐diffraction data are best fitted with a mixture of 56% anti–gauche and 44% anti–anti conformers. The conformational preference was also studied using the total energy scheme, and the natural bond orbital scheme. Also, the infrared spectra of CF₃CO₂CH₂CH₃ are reported for the gas, liquid and solid states, as is the Raman spectrum of the liquid. The comparison of experimental averaged IR spectra of C_s and C₁ conformers provides evidence for the predicted conformations in the IR spectra. Harmonic vibrational wavenumbers and scaled force fields have been calculated for both conformers. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman and infrared spectra,conformational stability,ab initio calculations and vibrational assignment of dimethylsilylisocyanate

The Raman (3200‐30 cm⁻¹) and/or infrared spectra (3500 to 400 cm⁻¹) of gaseous, liquid and solid dimethylsilylisocyanate, (CH₃)₂ Si(H)NCO, have been recorded. The MP2(full) calculations, employing a variety of basis sets with and without diffusion functions, have been used to predict the structural parameters, conformational stability, vibrational fundamental wavenumbers, Raman activities, depolarization values and infrared intensities to support the vibrational assignment. The low wavenumber Raman spectrum of the gas with a significant number of Q‐branches for the SiNC(O) bend is consistent with an essentially linear SiNCO moiety. The ab initio calculations supported this conclusion as all possible orientations of the NCO moiety lead to nearly the same energy. This result is at variance with the conclusion from the electron diffraction study that the heavy atom skeleton was bent with an angle of 152(5)° with one stable cis conformer. It is believed that this reported angle difference from 180° is due to the shrinkage effect. The SiH distance of 1.486 Å has been obtained from the isolated SiH stretching wavenumber. From the adjustment of the ab initio MP2(full)/6‐311+G(d,p) predicted structural parameters, a proposed structure is reported, which is expected to give rotational constants within a few megahertz of the actual ones. These experimental and theoretical results are compared with the corresponding quantities of similar molecules. Copyright © 2009 John Wiley & Sons, Ltd.     

Ab initio NMR parameters of BrCH3 and ICH3 with relativistic and vibrational corrections

This study is focused on two effects identified when NMR parameters are calculated based on first principles. These effects are 1. vibrational correction of properties when using ab initio optimized equilibrium geometry; 2. relativistic effects and limits of using the Flygare equation. These effects have been investigated and determined for nuclear spin-rotation constants and nuclear magnetic shieldings for the CH₃Br and CH₃I molecules. The most significant result is the difference between chemical shieldings determined based on the ab initio relativistic four-component Dirac-Coulomb Hamiltonian and chemical shieldings calculated using experimental values and the Flygare equation. This difference is approximately 320 ppm and 1290 ppm for ⁷⁹Br and ¹²⁷I in the CH₃X molecule, respectively.     

Theoretical studies of vibrational spectra of [N(CH3)4]2ZnCl4−yBry compounds with y = 0, 2 and 4

The infrared and Raman spectra of [N(CH₃)₄]₂ZnCl_4?yBr_y, where y = 0, 2 and 4, have been analyzed with ab initio calculations of the vibrational characteristics of constitutive polyhedra, tetramethylammonium [N(CH₃)₄]⁺ and [ZnCl_4?xBr_x]^2? (x = 0, 1, 2, 3 and 4) tetrahedra. The optimized geometries, calculated vibrational frequencies, infrared intensities and Raman activities are calculated using Hartree–Fock and density functional theory B3LYP methods with 3-21G, 6-31G(d) and 6-311G⁺(d,p) basis sets. Calculation of the root mean square difference δ_rms between the observed and calculated frequencies allows to give scaling factors and to deduce that the best agreements are obtained by B3LYP/6-311G⁺(d,p) for [N(CH₃)₄]⁺ and B3LYP/3-21G for [ZnCl_4?xBr_x]^2?. The present study establishes a strongly reliable assignment of the vibrational modes of [ZnCl_4?xBr_x]^2? tetrahedra based on comparison between experimental and ab initio calculations, both of the frequencies and the intensities of the Raman signals.     

Raman spectroscopy of acetic acid monomer and dimers isolated in solid argon

Acetic acid (AA) monomer and its dimers were studied by means of Raman spectroscopy combined with the matrix isolation technique. All fundamental bands of CH₃COOH monomer were identified, including the CH₃ torsional mode. Additionally, three overtone or combination modes were observed as a result of their enhanced intensities by Fermi resonance (FR). Twenty bands of the cyclic dimer (C_2h) were identified and assigned, among which appear all intermolecular modes. Bands due to two different higher energy forms of the dimer were also identified. The experimental assignments are supported by ab initio calculations. Copyright © 2011 John Wiley & Sons, Ltd.     

A study on the GVFF of CHF3, CH2F2, and CH3F

The complete GVFF of CHF₃, CH₂F₂, and CH₃F has been calculated from self-consistent-field ab initio energies, using a 4–31 G basis set. The larger part of the interaction force constants is close to those of the best available force fields from experimental data. Only one interaction term in CH₃F and the interaction force constants of the A₁ species in CH₂F₂ differ appreciably from the experimental ones. Using constraints from the ab initio studies we have improved the GVFF of CH₃F and CH₂F₂. It is shown that all comparable stretch-stretch interaction terms are of the same order of magnitude in the three molecules. The sign of all stretch/bend force constants are in accordance with those predicted by the hybrid orbital force field.     

On the application of the theory of the brownian movement in a periodic potential to the study of inertial effects and dipole coupling

For a series of ten electron molecules (HF, H₂O, NH₃, CH₄) the molecular polarizability tensor and the derivatives with respect to the symmetry coordinates have been calculated from ab initio SCF wavefunctions using the finite field method as well as perturbation theory approaches. Raman intensities and degrees of depolarization derived from the finite field results agree well with the available experimental data.

The zeroth order bond polarizability model and the atom dipole interaction model have been analysed. Both models can be used to describe the computed static polarizabilities and the derivatives with respect to bond stretching, but fail for the derivatives with respect to the bending coordinates.     

CALCULATIONS OF STRETCHING VIBRATIONAL ENERGY LEVELS OF THE CH3I MOLECULE BY A NONLINEAR MODEL

A nonlinear model, i.e. the quantized discrete self-trapping equation, is applied to calculate the highly excited CH stretching vibrational energy levels of the CH₃I molecule in the liquid phase at the electronic ground state up to n=8. The obtained results agree well with the experimental data and with those obtained from local mode model calculations. We note that the dominant feature of the methyl CH stretching vibrational energy levels of the CH₃I molecule is a pattern of local mode pairs. When n≥7, all the vibrational energy of the CH₃ group can nearly be localized on a single CH bond.     

Calculation of dipole moment functions with density functional theory: application to vibrational band intensities

We have calculated fundamental and overtone XH stretching vibrational band intensities for H₂O, benzene, cyclohexane, 1,3-butadiene, and HCN. The band intensities were calculated with a simple harmonically coupled anharmonic oscillator local mode model and a series expanded dipole moment function. The dipole moment functions were obtained from local, non-local and hybrid density functional theory calculations with basis sets ranging from 6–31G(d) to 6–311++G(3df,3pd). The calculated band intensities have been compared with intensities calculated with conventional ab initio methods and with experimental results. Compared with conventional correlated ab initio methods, a carefully chosen density functional method and basis set seems to give better fundamental and overtone intensities with far less resources used. We have found that the density functional methods appear to be less sensitive to the choice of basis set, with little difference between the results obtained with a non-local or hybrid density functional method.     

Vibrational studies of polar aprotic molecule in aromatic chemical and isotropic solvents: experimental and quantum chemical investigations

Raman spectroscopic technique has been used to study the intermolecular interactions and dynamics of SO, C―H and CSC stretching modes of dimethyl sulfoxide (DMSO) in binary mixtures using methyl benzene (MBN) and deuterated methyl benzene (MBNd) aromatic solvents. The Raman band of SO stretching mode has been deconvoluted into four distinct bands for neat DMSO as well as in binary mixtures. Deconvoluted bands in neat DMSO were assigned as monomer, cyclic out‐of‐phase, cyclic in‐phase and chain dimers having peak wavenumbers 1069.10, 1056.60, 1041.50 and 1027.30 cm⁻¹ respectively. Peak wavenumber of SO stretching mode shows red shift, while peak wavenumbers of C―H and CSC stretching modes show blue shift with the increase in solvent concentration. The vibrational relaxation phenomena for all the stretching modes have been studied as a function of solvent concentration. Quantum‐chemical calculations have been carried out to gain more insight into the self‐association of DMSO and in interacting environment with the solvents using ab initio and density functional theory method. The ab initio basis set is HF/6‐31 + G (d, p) for the interacting system. The hydrogen bond complexes of DMSO with MBN and MBNd using IEF‐PCM model have been calculated using B3LYP functional and 6‐31 + G(d,p) basis sets. Theoretical calculations have been compared with the experimental findings and we obtained good coherence of the results. Copyright © 2015 John Wiley & Sons, Ltd.     

Raman spectrum of vanadium pentoxide from density‐functional perturbation theory

We present ab initio calculation within the framework of the density‐functional theory (DFT) on band structure and vibrational properties of bulk V₂O₅. The structure of V₂O₅ comes from optimization of the experimental data with lattice parameters fixed. The band structure of the optimized structure has been calculated, and the result fits the experimental data very well and also gives similar results as those calculated by other methods. The phonon eigenwavenumbers of the Γ‐ point of V₂O₅ bulk have been calculated ab initio in density‐functional perturbation theory (DFPT). The calculated vibrational wavenumbers are in good agreement with observed infrared and Raman wavenumbers, and the predictive full phonon dispersion of bulk V₂O₅ has also been obtained. Further we calculated the Raman spectrum of vanadium pentoxide (V₂O₅) powder sample using the obtained Raman susceptibility. Calculated and measured intensities show overall good agreement. Copyright © 2008 John Wiley & Sons, Ltd.     

NIR‐FT Raman and FT‐IR spectral investigations of the nonlinear optical chromophore p‐bromoacetanilide

Vibrational spectral analysis of the hydrogen‐bonded nonlinear optical (NLO) material p‐bromo acetanilide (PBA) was carried out using NIR‐FT‐Raman and FT‐IR spectroscopy. Ab initio molecular orbital computations were performed at HF/6‐31G (d) level to derive equilibrium geometry, vibrational wavenumbers, intensities and first hyperpolarizability. The lowering of the imino stretching wavenumbers suggests the existence of strong intermolecular N H···O hydrogen bonding, which was substantiated by the natural bond orbital (NBO) analysis. The vibrational spectra confirm that the charge‐transfer interaction between the  NHCOCH₃ group and—Br through phenyl ring is responsible for simultaneous strong IR and Raman activation of the ring mode 8a. Vibrational analysis indicates that the lowering of stretching wavenumbers of methyl group due to electronic effects simultaneously caused by induction and hyperconjugation is due to the presence of the oxygen atom. The presence of blue‐shifting H‐bonds of CH stretching wavenumbers, simultaneous activation of carbonyl stretching mode, the strong activity of low‐wavenumber H‐bond stretching vibrations and the role of intramolecular charge transfer in making the molecule NLO active have been analyzed on the basis of the vibrational spectral features. Copyright © 2007 John Wiley & Sons, Ltd.     

FT‐Raman and FT‐IR spectral and quantum chemical studies on some flavonoid derivatives: Baicalein and Naringenin

In this study, the experimental and theoretical results on the molecular structures of some flavonoid derivatives (Baicalein and Naringenin) are presented. The FT‐IR and FT‐Raman spectra of the compounds have been recorded together for the first time between 4000–400 cm⁻¹ and 3500–5 cm⁻¹ regions, respectively. The molecular geometry and vibrational wavenumbers of the compounds have been also calculated in their ground states by using ab initio HF and DFT/B3LYP functional with 6‐31G(d,p) basis set used in calculations. The calculations were utilized to the C₁ symmetries of the molecules. All calculations were performed with Gaussian 98 software. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Scale factors have been used in order to compare how the calculated and experimental data are in agreement. Theoretical infrared intensities were also reported. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental and theoretical studies of Raman spectroscopy on 4‐mercaptopyridine aqueous solution and 4‐mercaptopyridine/Ag complex system

Raman scattering and surface‐enhanced Raman scattering (SERS) have been used to study the behavior of 4‐mercaptopyridine (4‐Mpy) dissolved in water and adsorbed on silver mirrors. In order to gain the actual structure and the theoretical modes of the 4‐Mpy dissolved in water and adsorbed on the surface of silver mirror, ab initio calculation at the Hartree–Fock (HF) level and density functional theory (DFT) at Beck's three‐parameter Lee‐Yang‐Parr (B3LYP) level were performed to calculate the vibrational modes and wavenumbers. 4‐Mpy/2H₂O and 4‐Mpy/Ag complex systems were optimized, and then the corresponding Raman spectra were calculated and analyzed. Compared with the experimental results, the calculated results of 4‐Mpy and 4‐Mpy/2H₂O complex systems obtained from DFT method were more accurate. Among the results calculated with HF method, the one with three Ag atoms was economical, which took less computer time but gave equivalent results to those with more noumber of Ag atoms. Copyright © 2007 John Wiley & Sons, Ltd.     

An ab initio calculation of the vibrational energies and transition moments of HSOH

We report new ab initio potential energy and dipole moment surfaces for the electronic ground state of HSOH, calculated by the CCSD(T) method (coupled cluster theory with single and double substitutions and a perturbative treatment of connected triple excitations) with augmented correlation-consistent basis sets up to quadruple-zeta quality, aug-cc-pV(Q+d)Z. The energy range covered extends up to 20 000 cm⁻¹ above equilibrium. Parameterized analytical functions have been fitted through the ab initio points. Based on the analytical potential energy and dipole moment surfaces obtained, vibrational term values and transition moments have been calculated by means of the variational program TROVE. The theoretical term values for the fundamental levels ν_SH (SH-stretch) and ν_OH (OH-stretch), the intensity ratio of the corresponding fundamental bands, and the torsional splitting in the vibrational ground state are in good agreement with experiment. This is evidence for the high quality of the potential energy surface. The theoretical results underline the importance of vibrational averaging, and they allow us to explain extensive perturbations recently found experimentally in the SH-stretch fundamental band of HSOH.     

Ionic liquid structure: the conformational isomerism in 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate ([bmim][BF4])

As a probe of local structure, the vibrational properties of the 1‐butyl‐3‐methylimidazolium tetrafluoroborate [bmim][BF₄] ionic liquid were studied by infrared (IR), Raman spectroscopy, and ab initio calculations. The coexistence of at least four [bmim]⁺ conformers (GG, GA, TA, and AA) at room temperature was established through unique spectral responses. The Raman modes characteristic of the two most stable [bmim]⁺ conformers, GA and AA, according to the ab initio calculations, increase in intensity with decreasing temperature. To assess the total spectral behavior of the ionic liquid both the contributions of different [bmim]⁺ conformers and the [bmim]⁺− [BF₄]⁻ interactions to the vibrational spectra are discussed. Copyright © 2008 John Wiley & Sons, Ltd.