Harmonic Wavenumbers Research Articles

Conformational, vibrational, and structural studies of 2,2,3,3,3‐pentafluoropropylamine from Raman and infrared spectra of gas, liquid, xenon solutions, and solid supported by ab initio calculations

AbstractThe Raman and infrared spectra (3500–50 cm−1) of the gas, liquid or solution, and solid were recorded of 2,2,3,3,3‐pentafluoropropylamine (CF3CF2CH2NH2) and the ND2 isotopomer. Variable temperature (−55 to − 100 °C) studies of the infrared spectra (3600–400 cm−1) of samples dissolved in liquid xenon have been carried out. From these data, two of the five possible conformers have been identified and their relative stabilities obtained. The enthalpy difference was determined between the more stable Tt conformer and the less stable Tg form to be 280 ± 14 cm−1 (3.35 ± 0.17 kJ/mol). The first indicator is the NCCC dihedral angle (G = gauche or T = trans), and the second one (g = gauche or t = trans) is the relative position of the lone pair of electrons on nitrogen with respect to the β‐carbon. The percentage of the Tg conformer at ambient temperature is estimated to be 34 ± 2%. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug‐cc‐pVTZ for both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been provided for most of the observed bands for both isotopomers, supported by MP2(full)/6‐31G(d) ab initio calculations to predict the harmonic force fields, wavenumbers, infrared intensities, Raman activities, and depolarization ratios for both conformers. Estimated r0 structural parameters were obtained from adjusted MP2(full)/6‐311 + G(d,p) calculations. The results are discussed and compared with the corresponding properties of some related molecules. Copyright © 2011 John Wiley & Sons, Ltd.

Structure and vibrational assignment of tautomerism of 4-hydroxyquinazoline in gaseous and aqueous phases

The tautomerizm and conformation of the 4-hydroxyquinazoline molecule were investigated, and its three tautomers (4-HQ1, 4-HQ2, 4-HQ3) and conformer of 4-HQ2 (4-HQ2A) were considered. The tautomeric and conformational equilibrium geometry of 4-hydroxyquinazoline have been studied using density functional theory (DFT) and Møller–Plesset second-order (MP2) methods in the gas phase and in water. The tautomerization processes in water ( ε = 78.39) were studied by using self-consistent reaction field theory with the polarized continuum model (PCM). Energetics and relative stabilities of the tautomers were compared and analyzed in both the gaseous and water. In agreement with experimental results, our calculations show that the 4-HQ1 was the most stable form in the gas phase and in water. Solvent effect induced slight changes in geometry of rings and the order of stability changed. The harmonic wavenumbers of 4-HQ1 were calculated in the gas phase and in water by the B3LYP/6-311++G ∗∗ DFT method and the wavenumbers were given. The infrared spectra of 4-hydroxyquinazoline were recorded in the regions 400–4000 cm −1. The variation of dipole moments and charges on atoms were studied in the gas phase and in water.

Slow Photoelectron Spectroscopy of δ‐Valerolactam and Its Dimer

We studied the single-photon ionization of gas-phase δ-valerolactam (piperidin-2-one) and of its dimer using vacuum-ultraviolet (VUV) synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer. The slow photoelectron spectrum (SPES) of the monomer is dominated by the vibrational transitions to the ͠X state. Moreover, several weaker and complex bands are observed, corresponding to the population of the vibrational bands (pure or combination) of the electronically excited states of the cation arising from their mutual vibronic interactions. For the dimer, we measure a unique large band. These spectra are assigned with the help of theoretical calculations dealing with the equilibrium geometries, electronic-state patterns and evolutions, harmonic and anharmonic wavenumbers of the monomer and dimer, either neutral or positively charged. The state energies of the [δ-valerolactam](+) cation in the ͠X ground, ͠A, ͠B, ͠C, excited electronic states, and of the [δ-valerolactam](2) (+) cation's lowest states are determined. After its formation, [δ-valerolactam](2) (+) is subject to intramolecular isomerization, H transfer and then unimolecular fragmentation processes. Close to the ionization thresholds, the photoionization of these molecules is found to be mainly dominated by a direct process whereas the indirect route (autoionization) contributes at higher energies.

CCSD(T)‐F12 investigations on HBNH and its isotopologues

AbstractCCSD(T)‐F12 ab initio computations are performed to investigate the isomerization path between HBNH and BNH2, and the six‐dimensional potential energy surface of the electronic ground state X̃1Σ+ of the linear isomer. The equilibrium geometries and harmonic wavenumbers obtained at the CCSD(T)‐F12a/aug‐cc‐pVTZ level of theory are nearly those computed with the CCSD(T)/aug‐cc‐pV5Z level, but with a smaller amount of CPU time for the evaluation of the total energy. The analytical representation of the potential energy surface is used in variational calculations of the rovibrational energy levels of H11BNH and isotopologues. The computed rovibrational energy levels are compared with the available experimental data, and a good agreement is generally noticed. We also propose an assignment of the rovibrational energy levels of H11BNH up to 3000 cm−1 above the zero point energy. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

Experimental and theoretical vibrational spectroscopic investigation of Zn(II) halide complexes of 3-aminopyridine and 3-chloropyridine

The aim of this study is to analyse the influence of the formation of metal–ligand bond through the ring nitrogen on the vibrational wavenumbers of pyridine derivatives, depending on the electron releasing (NH 2) or electron withdrawing (Cl) substituent, in the same position. As pyridine derivatives, 3-aminopyridine (3apy) and 3-chloropyridine (3Clpy) were used. Moreover, determination of the wavenumbers of metal–ligand bond vibrations has a separate interest. In order to investigate the influence of the counter ligand, halide, on pyridine derivative vibrations, calculations were carried out on both Zn(L) 2Cl 2and Zn(L) 2Br 2 (where L = 3-aminopyridine or 3-chloropyridine) compounds. Full assignment of the spectra is proposed and the analysis of the experimental data are supported by DFT calculations performed with B3LYP functional and the 6-311++G(d,p) basis set. The FT-IR (400–4000 cm −1) and Raman (100–3200 cm −1) spectra of compounds are recorded and are compared with that of the calculated spectra. Anharmonic corrections to the harmonic wavenumbers are done with the same method and level of theory. The coordination effects on vibrational wavenumbers of 3apy and 3Clpy were discussed by comparing the spectra of free and coordinated molecules.

Quantum chemical computational studies on 5-(4-bromophenylamino)-2-methylsulfanylmethyl-2H-1,2,3-triazol-4-carboxylic acid ethyl ester

The optimized molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) 1H and 13C NMR shift values of 5-(4-bromophenylamino)-2-methylsulfanylmethyl-2H-1,2,3-triazol-4-carboxylic acid ethyl ester have been calculated by using Hartree–Fock (HF) and density functional method (DFT/B3LYP) with 6-31G(d), 6-31G(d,p) and LANL2DZ basis sets. The optimized molecular geometric parameters were presented and compared with the data obtained from X-ray diffraction. In order to fit the calculated harmonic wavenumbers to the experimentally observed ones, scaled quantum mechanics force field (SQM FF) methodology was proceeded. Correlation factors between the experimental and calculated 1H chemical shift values of the title compound in vacuum and in CHCl 3 solution by using the conductor-like screening continuum solvation model (COSMO) were reported. The calculated results showed that the optimized geometry well reproduces the crystal structure. The theoretical vibrational frequencies and chemical shifts are in very good agreement with the experimental data. In solvent media the energetic behavior of the title compound was also examined by using the B3LYP method with the 6-31G(d) basis set, applying the COSMO model. The obtained results indicated that the total energy of the title compound decreases with increasing polarity of the solvent. Furthermore, molecular electrostatic potential (MEP), natural bond orbital (NBO) and frontier molecular orbitals (FMOs) of the title compound were performed by the B3LYP/LANL2DZ method, and also thermodynamic parameters for the title compound were calculated at all the HF and B3LYP levels.

Multiple scattering by cylinders randomly located in a fluid: Effective properties

We consider the interface between a homogeneous fluid and that same fluid with a random distribution of n0 cylinders per square meter inside. A harmonic plane wave, frequency v and wavenumber k, is incident upon that boundary under incidence angle α. The reflection coefficient obtained with the Fikioris and Waterman approach is expanded into powers of n0/K2 up to order 2, using Linton and Martin's expansion of the wavenumber of the coherent wave. This coefficient is then compared to that obtained when a homogeneous viscous fluid replaces the random medium. When the two reflection coefficients are equal, the random fluid is acoustically equivalent to the viscous one, which is called in that case the effective fluid. The coherent wave in the random medium is thus described as the acoustic mode in the effective fluid. Equating the two reflection coefficients provides expressions for the effective properties of the random medium: mass density ρeff, and coefficient of dilatation viscosity ρeff, as the shear viscosity is set to zero. Both depend on α and v, unless low frequencies only are considered, in which case the dependence on α vanishes.

Electronic Structure, Electric Moments and Vibrational Analysis of 3-(2-Methoxyphenoxy) Propane-1,2-Diol by Ab Initio and Density Functional Theory

The molecular properties and harmonic wavenumbers of 3-(2-methoxyphenoxy) propane-1,2-diol have been calculated using ab initio and density functional theory. The polarizability and first static hyperpolarizability of the title molecule have been calculated at different basis sets. In general a good agreement between experimental and calcu- lated normal modes has been observed. The frontier orbital and molecular electrostatic potential surface study has also been employed to understand the active sites of 3-(2- methoxyphenoxy) propane-1,2-diol.

Explicitly correlated coupled cluster calculations for the propargyl cation (H2C3H+) and related species

The vibrations of the propargyl cation (H(3)C(3)H(+)) have been studied by vibrational configuration interaction (VCI) calculations, using explicitly correlated coupled cluster theory at the CCSD(T*)-F12a level to determine the underlying 12-dimensional potential energy surface. The wavenumbers of the fundamental vibrations are predicted with an accuracy of ca. 5 cm(-1). Harmonic wavenumber shifts for three different energy minima of the complex H(2)C(3)H(+)·Ar are combined with the corresponding VCI values in order to provide a comparison with recent infrared photodissociation (IRPD) spectra (A. M. Ricks et al., J. Chem. Phys., 2010, 132, 051101). An excellent agreement between experiment and theory is obtained for bands ν(2) (symm. CH stretch), ν(3) (pseudoantisymm. CC stretch), and ν(4) (CH(2) scissoring). However, reassignments are suggested for the bands observed at 3238 cm(-1), the "doublets" around 3093 and 1111 cm(-1), and the band at 3182 cm(-1). The assignment of the latter to the asymmetric CH stretching vibration of c-C(3)H·Ar is certainly wrong; the combination tone ν(3) + ν(5) of H(2)C(3)H(+)·Ar is a more likely candidate. Furthermore, accurate proton affinities are predicted for the carbenes H(2)C(n) with n = 3-8, thereby providing data of interest for interstellar cloud chemistry.

Global spherical harmonic models of the internal magnetic field of the Moon based on sequential and coestimation approaches

Three new models of the global internal magnetic field of the Moon based on Lunar Prospector (LP) fluxgate magnetometer observations are developed for use in understanding the origin of the Moon's crustal magnetic field and for modeling its interaction with the solar wind. The models are at spherical harmonic degree 170, corresponding to 64 km wavelength resolution, from 30 km mean altitude LP observations. Coverage is complete except for a few areas near each pole. Original signal amplitudes are best preserved in the sequential approach map, whereas feature recognition is superior in the coestimation and harmonic wave number correlation maps. Spherical harmonic degrees less than 15, corresponding to 666 km wavelength, are largely absent from the Moon's internal magnetic field. We interpret this bound in terms of the Moon's impact history. A derived magnetization map suggests magnetizations may locally exceed 0.2 A/m in the lunar crust at the survey resolution if the magnetic crust is as thick as 40 km.

Molecular structure and vibrational spectra of three substituted 4-thioflavones by density functional theory and ab initio Hartree–Fock calculations

The vibrational frequencies of three substituted 4-thioflavones in the ground state have been calculated using the Hartree–Fock and density functional method (B3LYP) with 6-31G* and 6-31+G** basis sets. The structural analysis shows that there exists H-bonding in the selected compounds and the hydrogen bond lengths increase with the augment of the conjugate parameters of the substituent group on the benzene ring. A complete vibrational assignment aided by the theoretical harmonic wavenumber analysis was proposed. The theoretical spectrograms for FT-IR spectra of the title compounds have been constructed. In addition, it is noted that the selected compounds show significant activity against Shigella flexniri. Several electronic properties and thermodynamic parameters were also calculated.

Jet-cooled laser-induced dispersed fluorescence spectroscopy of ScN: Observation of a3Σ+ state

Laser-induced dispersed fluorescence spectra of ScN molecules, produced in a free-jet apparatus, have been studied. Low-energy first excited state, a3Σ+ predicted by ab initio calculations, has been observed for the first time. The relative term energies of the vibrational levels of the X1Σ+ ground, a3Σ+, and A1Σ+ states have been determined. The harmonic wavenumbers equal to 787.7(3) and 1044.8(1)cm−1, respectively for the X1Σ+ and A1Σ+ states and ΔG1/2=888(11)cm−1 for the a3Σ+ state have been measured. RKR potential energy curves of the X1Σ+ ground as well as a3Σ+ and A1Σ+ low-energy excited states have been constructed.

Structural and nonlinear optical properties of cross‐conjugated system benzophenone thiosemicarbazone: a vibrational spectroscopic study

AbstractThe nonlinear optical (NLO) compound of interest benzophenone thiosemicarbazone (BTSC) was grown and the molecular structure generated with the aid of density functional theory (DFT). FT‐Raman and IR spectra were recorded and analyzed. The harmonic wavenumbers and IR and Raman intensities were computed with the B3LYP method. The observed vibrational wavenumbers were compared with the calculated results. The assignments of the experimental spectra were made with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field (SQMFF) methodology. The electronic structure of the most important molecular fragments is described in terms of natural bond orbital (NBO) analysis. Copyright © 2010 John Wiley & Sons, Ltd.

DFT and MP2 based quantum mechanical calculations and a theoretical vibrational spectroscopic investigation on roscovitine, a potential drug to treat cancers

AbstractTheoretically possible stable conformers of free roscovitine molecule in its electronic ground state were searched by means of molecular dynamics and energy minimization calculations performed using the MM2 force field. Afterwards, geometry optimization and thermochemistry calculations were carried out at room temperature for each of the found minimum‐energy conformers using the MP2 and DFT based electronic structure methods and different Pople‐style basis sets. The results obtained from these calculations confirmed that the strong intramolecular hydrogen bonding between the purine‐nitrogen and hydroxyl‐hydrogen atoms plays an important role on the rigidity of roscovitine molecule and causes a dramatic reduction in the number of the possible stable conformers of this molecule at room temperature. Furthermore, the same calculation results also revealed that two of the found seven stable conformers are considerably more favorable in energy than the others and thus dominate the experimental room‐temperature spectra of the molecule. In the light of the theoretical vibrational spectral data obtained for these two conformers, a successful assignment of the fundamental bands observed in the experimental IR and Raman spectra recorded at room temperature for solid roscovitine and for its ethanol solution is given, and the effects of the substitution and intramolecular hydrogen bonding on the fundamental bands associated with purine and phenyl group vibrations are discussed in detail. In the fitting of the calculated harmonic wavenumbers to the corresponding experimental wavenumbers, two different scaling procedures, called ‘dual scale factors’ and ‘Scaled Quantum Mechanical Force Field (SQM FF) methodology’, were applied independently. Both procedures yielded results generally in good agreement with the experiment; however, the SQM FF methodology proved its superiority over the other. Copyright © 2010 John Wiley & Sons, Ltd.

Resonant third harmonic generation of an infrared laser in a semiconductor wave guide

AbstractAn infrared laser propagating through a semiconductor waveguide, embedded with a density ripple of wave number q, resonantly excites third harmonic radiation. The phase matching is achieved when q equals difference between third harmonic wave number and three times the wave number of the laser. The excited third harmonic is in higher order radial Eigen mode than the pump laser. The third harmonic efficiency increases with electron concentration and decreases with the frequency of the laser.

An experimental and theoretical vibrational spectroscopic study on niflumic acid, a non-steroidal anti-inflammatory drug

The theoretically possible stable conformers of niflumic acid (NFA) molecule in electronic ground state were investigated by means of potential energy surface scan and thermochemistry calculations carried out at room temperature using DFT-B3LYP method and different Pople-style basis sets. The data obtained from these calculations confirmed that the two planar conformers in which the carboxyl and fluoromethyl functional groups are located either in “trans” or in “cis” position to each other are the most favorable ones in energy among all the stable conformers of the free molecule. This conclusion was also confirmed by the energy values obtained from the higher-accuracy thermochemistry calculations carried out using G3MP2B3 composite method. For both conformers and also for their most favorable dimer forms in energy, the equilibrium geometry, force field and vibrational spectral data were calculated first at B3LYP/6-31G(d) and then at B3LYP/6-311++G(d,p) levels of theory. On the basis of these theoretical data, the effects of the conformation and dimerization on the corresponding experimental data of NFA molecule were discussed in detail. The overestimations of the calculated harmonic wavenumbers were corrected by the aid of two different empirical scaling procedures referred to as “scaled quantum mechanical force field (SQM FF) methodology” and “dual scale factors”. In the light of the improved theoretical data obtained in these two approaches applied independently from each other, a successful assignment of the fundamental bands observed in the room-temperature IR and Raman spectra of the molecule was given.

Buckling strength of cylindrical steel tanks under harmonic settlement

Large vertical cylindrical steel tanks for bulk and fluid storage are usually constructed in soft foundations, so it is not surprising that tank foundations are susceptible to various types of settlement beneath the tank wall, which is usually decomposed as a Fourier series in harmonics. In this paper, buckling strength of cylindrical fixed-roof steel storage tanks under harmonic settlement is investigated through great deal of numerical analyses by the FE computer package ANSYS. Three types of buckling analyses are carried out which are the LBA, GNA, GNIA proposed also by Eurocode 3. The results show that the equilibrium path from both GNA and GNIA is highly nonlinear, and it seems ungrounded to establish design criterion on the principle of superposition based on the linear elastic theory. The influences of the harmonic wave number n, the radius-to-thickness ratio r/ t, the height-to-radius ratio h/ r, and the geometric imperfection δ 0/ t on the buckling strength of the storage tanks are mainly investigated. The ultimate harmonic settlements for various tank geometries are addressed and plotted in each analysis together with the buckling modes. The buckling modes from GNA and GNIA agree well with the lowest linear bifurcation buckling modes from LBA, and take mainly two types of deformations: shearing buckling extending throughout the entire height for the lower wave number n=2–4 and the elephant's foot failure occurring at the upward settlement zone caused by the meridional compression for the higher wave number n>4. It is also indicated from the results that both the ultimate harmonic settlement and the buckling mode of the tank are closely correlative with the geometric parameters: the wave number n, the radius-to-thickness ratio r/ t, the height-to-radius ratio h/ r, and the initial geometric imperfection δ 0/ t.

FT-IR and Raman spectroscopic and DFT theoretical investigations on Zn(II) halide complexes of 2-aminopyrimidine

In this study the vibrational spectra of monomeric Zn(L) 2X 2 (X = Cl and Br; L = C 4H 5N 3 = 2APM, 2-aminopyrimidine) compounds are reported and discussed. Full assignment of the spectra is presented and the analysis of the experimental data is supported by DFT calculations performed with B3LYP functional and the 6-311++G(d,p) basis set. The FT-IR (400–4000 cm −1) and Raman (100–3200 cm −1) spectra of compounds are recorded and compared with that of the calculated spectra. Anharmonic corrections to the harmonic wavenumbers are done with the same method and level of theory. The coordination effects on vibrational wavenumbers of 2APM are discussed in detail by comparing the spectra of free and coordinated 2APMs. The geometry optimization of [Zn(L) 2X 2] calculated using the DFT/B3LYP method with a 6-311++G(d,p) basis set yields a slightly distorted tetrahedral environment around Zn ion and compound reveals the C2 symmetry. The 2APM ligand is coordinated to Zn atom via ring nitrogen atom as monodentate ligand. The computed C–N bond length in Zn(2APM) 2Br 2 complex is found to be slightly longer than the corresponding bond length in Zn(2APM) 2Cl 2 complex.

FT-IR, FT-Raman spectra, density functional computations of the vibrational spectra and molecular geometry of 2-hydroxyquinoxaline

With the purpose of finding predominant tautomer among seven possible isomers of 2-hydroxyquinoxaline 2-OHQ, its equilibrium geometry and harmonic wavenumbers were calculated by the B3LYP/6-311++G ∗∗ DFT method. The infrared and Raman spectra of 2-OHQ were recorded in the regions 400–4000 cm −1, and 50–3500 cm −1, respectively. Vibrational wavenumbers were compared with IR, and Ra experimental data. Computational calculations at B3LYP/6-31+G ∗∗, and 6-311G ∗∗ levels were also employed in the study of the predominant tautomeric form of 2-OHQ. To support our relative energy results we also used the QCISD method. In agreement with experimental results, our calculations show that the keto form of 2-OHQ is the most stable tautomer and the best results were obtained at B3LYP level using 6-311++G ∗∗ basis set. All the tautomeric forms of 2-OHQ were determined and optimized. Bond distances, bond angles and dihedral angles are presented. For two most stable tautomers, the calculated wavenumbers were given. In addition, two stable dimer forms of 2-hydroxyquinoxaline calculated at the B3LYP/6-31G ∗ level. The dimer A is by 15.57 kcal mol −1 more stable than dimer B.

Ab initio and density functional study of the geometrical, electronic and vibrational properties of 3,4′-bi-1,2,4-triazole

The conventional ab initio method at the closed restricted Hartree–Fock level (RHF) and the density functional theory (DFT) approach at the B3-LYP level, using the 6-31+G* basis set, are applied to predict the molecular structure and the energetic and the vibrational properties (harmonic wave numbers, force fields and potential energy distributions) of the 3,4′-bi-1,2,4-triazole and of two deuterated derivatives (ND and ND(CD) 3). The theoretical results are compared to the Raman and infrared vibrational data. Using both methods, there is a very good agreement between theory and experiment concerning not only the wave numbers but also the isotopic shifts. This accordance allows us to validate the calculated structure of bTA. This molecule is characterized by an aromatic structure in which two triazolic rings are linked by a CN bond, intermediary between a single and double bond, in a planar conformation. From a methodological point of view, the B3-LYP method predicts more accurate structure and harmonic vibrational wave numbers than the RHF method.