Harmonic Wavenumbers Research Articles

Raman and infrared, microwave spectra, conformational stability, adjusted r0 structural parameters, and vibrational assignments of cyclopentylamine

Fourier transform microwave spectrum of cyclopentylamine, c–C5H9NH2 has been recorded, and seven transitions have been assigned for the most abundant conformer, and the rotational constants have been determined: A = 4909.46(5), B = 3599.01(4), and C = 2932.94(4). From the determined microwave rotational constants and ab initio MP2(full)/6‐311 + G(d,p) predicted structural values, adjusted r0 parameters are reported with distances (Å): rCα–Cβ = 1.529(3), rCβ–Cγ = 1.544(3), rCγ–Cγ = 1.550(3), rCα–N = 1.470(3), and angles (°) ∠CCN = 108.7(5), ∠CβCαCβ = 101.4(5), and τCβCαCβ′Cγ′ = 42.0(5). The infrared spectra (4000–220 cm−1) of the gas have been recorded. Additionally, the variable temperature (−60 to −100 °C) Raman spectra of the sample dissolved in liquefied xenon was recorded from (3800–50 cm−1). The four possible conformers have been identified, and their relative stabilities obtained with enthalpy difference relative to t‐Ax of 211 ± 21 cm−1 for t‐Eq ≥ 227 ± 22 cm−1 for g‐Eq ≥ 255 ± 25 cm−1 for g‐Ax. The percentage of the four conformers is estimated to be 53% for the t‐Ax, 11 ± 1% for t‐Eq, 20 ± 2% for g‐Ax and 16 ± 2% for g‐Eq at ambient temperature. The conformational stabilities have been predicted from ab initio calculations by utilizing several different basis sets up to aug‐cc‐pVTZ from both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been provided for the observed bands for all four conformers, which are predicted by MP2(full)/6‐31G(d) ab initio calculations to predict harmonic force constants, wavenumbers, infrared intensities, Raman activities, and depolarization ratios for all of the conformers. The results are discussed and compared to the corresponding properties of some related molecules. Copyright © 2014 John Wiley & Sons, Ltd.

FT-IR, FT-Raman spectra, and DFT computations of the vibrational spectra and molecular geometry of chlorzoxazone

Far-IR, mid-IR, and FT-Raman spectra of the chlorzoxazone (CZX) were recorded. The observed vibrational wavenumbers were analyzed and assigned to different normal modes of vibration of the molecule. Density functional calculations were performed to support wavenumber assignments of the observed bands. The equilibrium geometry and harmonic wavenumbers of CZX were calculated by the DFT B3LYP method. All tautomeric forms and dimer form of CZX were determined and optimized. Additionally, experimental FT-IR spectrum in ethanol solution was recorded and compared with solid phase experimental data for the first time. The combination of the DFT B3LYP with polarized continuum model (PCM) was employed to characterize the solvent effects in ethanol solution.

Anharmonic Spectroscopic Investigation of Tellurophene and Its Perdeuterated Isotopomer: Application of Second-Order Perturbation Theory

Vibrational spectra of tellurophene and of its perdeuterated isotopomer were computed using the DFT-B3LYP functional with the LANL2DZ(d,p) basis set. The frequencies of fundamental and overtone transitions were obtained in vacuum under the harmonic approximation and anharmonic second-order perturbation theory (PT2). On the whole the anharmonic corrections reduce the harmonic wavenumber values, in many cases better reproducing the observed fundamental frequencies. The largest anharmonic effects are found for the C–H and C–D stretching vibrations, characterized by relatively high anharmonic coupling constants (up to ca. 120 cm−1). For the C–H/C–D stretches, the harmonic H→D isotopic frequency red-shifts overestimate the observed data by 47–63 cm−1 (5.9–8.1%), whereas the PT2 computations exhibit significantly better performances, predicting the experimental data within 1–19 cm−1 (0.1–2.4%).

Microwave, structural, conformational, vibrational studies and ab initio calculations of isocyanocyclopentane

The infrared and Raman spectra (3200–50cm−1) of the gas, liquid or solution, and solid have been recorded of isocyanocyclopentane, c-C5H9NC. FT-microwave studies have also been carried out and 23 transitions were recorded for the envelope-axial (Ax) conformer. Variable temperature (−65 to −100°C) studies of the infrared spectra (3200–400cm−1) dissolved in liquid xenon have been carried out. From these data, both the Ax and envelope-equatorial (Eq) conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 102±10cm−1 (1.21±0.11kJmol−1) with the Ax conformer the more stable form. The percentage of the Eq conformer is estimated to be 38±1% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations by utilizing several different basis sets up to aug-cc-pVTZ from both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been made for the observed bands for both conformers with initial predictions by MP2(full)/6-31G(d) ab initio calculations to obtain harmonic force constants, wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The structural parameter values for the Ax form are; for the heavy atom distances (Å): CN=1.176 (3); CαN=1.432 (3); CαCβ,Cβ′=1.534 (3); CβCγ,Cγ′=1.542 (3); CγCγ′=1.554 (3) and angles (°):∠CαNC=177.8 (5); ∠CβCαN=110.4 (5); ∠CβCαCβ′=102.9 (5); ∠CαCβCγ=103.6 (5); ∠CβCγCγ′=105.9 (5). The results are discussed and compared to the corresponding properties of some related molecules.

Jet-cooled laser-induced dispersed fluorescence spectroscopy of NiC: Observation of low-lying Ω = 0+ state

Laser-induced dispersed fluorescence spectra of 58Ni12C molecules, produced in a free-jet apparatus, have been studied. A new low-lying Ω=0+ state has been observed at Te=5178 (6)cm−1. Based on previous ab initio calculations this state is plausibly assigned as 0+ spin–orbit component of the first excited 3Π state. The term energies of vibrational levels up to v=10 for X1Σ+ ground and v=3 for Ω=0+ states have been determined. The harmonic and anharmonic wavenumbers respectively equal to 833 (4) and 6.7 (13)cm−1 for Ω=0+ state have been measured.

Theoretical and experimental study of solvent effects on the structure, vibrational spectra, and tautomerism of 3-amino-1,2,4-triazine

The structure, and vibrational spectra of an important heteroaromatic compound, 3-amino-1,2,4-triazine (3-atz), have been calculated by using B3LYP/6-311++G(d,p) method in the gas phase and in various solvents. Solvent effects have been analyzed by using the self-consistent reaction field (SCRF) method based on polarizable continuum model (PCM) in chloroform, acetonitrile (ACN), dimethyl sulfoxide (DMSO), and water. Tautomers and conformations of the 3-atz molecule were also investigated. Energies, relative stabilities, and dipole moments of all conformers were compared and analyzed in the gas phase and in solvents as well. Raman spectrum was recorded only in solid state, infrared spectra were recorded in solid state as well in DMSO and in water solutions. In accordance with experimental results, our calculations showed that 3-atz1 is the most stable form in the gas phase and in solution. Geometrical parameters of 3-atz1 were slightly affected. Some harmonic wavenumbers, especially the NH and CH modes of 3-atz1 were noticeably affected by the choice of medium. Moreover, solvent effects on infrared and Raman intensities are quite considerable, and they increase as one goes from lower to higher dielectric constant.

FT-IR, FT-Raman spectra and other molecular properties of 3,5-dichlorobenzonitrile: A DFT study

The IR and Raman spectra of 3,5-dichlorobenzonitrile (3,5-DCBN) molecule were recorded at room temperature and then the assignment of the observed fundamental bands were achieved by the aid of the theoretical vibrational spectral data obtained from a quantum chemical study carried out for the free molecule case. In the calculations performed to determine the molecular geometry, vibrational spectral data and thermodynamic parameters, Møller–Plesset second order perturbation theory (MP2) and hybrid Density Functional Theory (DFT) types of electronic structure methods, B3LYP and B3PW91, were used. The overestimations of the calculated harmonic wavenumbers were efficiently corrected by the aid of a specific scaling procedure. This empirical scaling process significantly increased the reliability of our assignments and analyses on the observed bands due to different vibrational normal modes of the molecule. For the majority of the normal modes, the deviations between the corresponding experimental and scaled theoretical wavenumbers have located in the expected range. A correct characterization of the normal modes is of vital importance in the assignment of the observed bands, and this was successfully done by the aid of the Potential Energy Distributions (PEDs) separately calculated for each normal mode of 3,5-DCBN.

Vibrational and conformational analysis on-N1-N2-bis((pyridine-4-yl)methylene) benzene-1,2-diamine

The molecule N1-N2-bis((pyridine-4-yl)methylene)benzene-1,2-diamine (NBPMB) was synthesized and characterized by FT-IR, FT-Raman and UV–Vis., spectra. To identify the stable structure of the molecule meticulous conformational analysis was performed. The observed (FT-IR and FT-Raman) spectral frequencies were compared with harmonic wavenumbers. The vibrational assignments were performed on the basis of the total energy distribution (TED). The optimized geometrical parameters are calculated and compared with experimental results. The non-linear optical behavior NBPMB molecule is analyzed using hyperpolarizability calculation. The charge transfer within the molecule and biological activity of NBPMB were calculated.

Effect of top stiffening rings of open top tanks on critical harmonic settlement

The purpose of this work is to investigate the effect of top stiffening rings of open top tanks on the critical harmonic settlement. First, the buckling behavior of a tank with a top stiffening ring is provided and the results are compared with that of the model with no stiffening ring. The results show that the critical harmonic settlement for the tank with a top stiffening ring is lower than that for the tank with no top stiffening ring. Moreover, the top stiffening ring plays a significant role on the critical harmonic settlement when the wave number is small, but plays a minor role on that when the wave number is large. Then, the imperfection sensitivity analysis is conducted to identify whether the top stiffening ring can decrease the sensitivity of imperfection. Meanwhile, the worst imperfection form for tanks subjected to harmonic settlement is reported. The results present that the weld depression has the most adverse effect on the settlement carrying capacity of tanks. Moreover, it is indicated that the top stiffening ring cannot always decrease the sensitivity of the imperfection. The sensitivity plots are related to harmonic wave numbers, as well as imperfection forms. Finally, the effect of top stiffening rings with different structure parameters on the critical harmonic settlement is reported, including the length and the thickness of the top stiffening ring. For the length of the top stiffening ring, the critical harmonic settlement versus the wave number decreases more and more slightly with the increasing length of the top stiffening ring. For the thickness of the top stiffening ring, the critical harmonic settlement versus the wave number decreases more and more mildly with the thickness of the top stiffening ring on the increase.

Slow Photoelectron Spectroscopy of 3-Hydroxyisoquinoline

We studied the single photon ionization of gas phase 3-hydroxyisoquinoline by means of VUV synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer. Near the ionization thresholds of 3-hydroxyisoquinoline, the photoionization is found to occur mainly via a direct process. The spectra are assigned with the help of theoretical calculations on the equilibrium geometries, electronic states patterns, harmonic and anharmonic wavenumbers of the lactim and lactam forms of 3-hydroxyisoquinoline and their cations. The slow photoelectron spectrum (SPES) of this lactim is dominated by vibrational transitions to the X̃ state of the cation. In addition, several weaker and complex bands are observed, corresponding to the population of the vibrational bands (pure or combination) of the à electronically excited state of the cation. The adiabatic ionization energy of 3-hydroxyisoquinoline and the lowest electronic state energetics of the lactim and lactam cationic forms are determined.

Infrared and Raman Spectra of C4H4Se and C4D4Se Isotopomers: A DFT‐PT2 Anharmonic Study

IR and Raman spectra of selenophene and of its perdeuterated isotopomer have been obtained in gas phase through density‐functional theory (DFT) computations. Vibrational wavenumbers have been calculated using harmonic and anharmonic second‐order perturbation theory (PT2) procedures with the B3LYP method and the 6‐311G∗∗ basis set. Anharmonic overtones have been determined by means of the PT2 method. The introduction of anharmonic terms decreases the harmonic wavenumbers, giving a significantly better agreement with the experimental data. The most significant anharmonic effects occur for the C–H and C–D stretching modes, the observed H/D isotopic wavenumber redshifts being satisfactorily reproduced by the PT2 computations within 6–20 cm−1 (1–3%). In the spectral region between 500 cm−1 and 1500 cm−1, the IR spectra are dominated by the out‐of‐plane C–H (C–D) bending transition, whereas the Raman spectra are mainly characterized by a strong peak mainly attributed to the C=C + C–C bonds stretching vibration with the contribution of the in‐plane C–H (C–D) bending deformation. The current results confirm that the PT2 approach combined with the B3LYP/6‐311G∗∗ level of calculation is a satisfactory choice for predicting vibrational spectra of cyclic molecules.

Structural, electronic, thermodynamical and charge transfer properties of Chloramphenicol Palmitate using vibrational spectroscopy and DFT calculations

The global problem of advancing bacterial resistance to newer drugs has led to renewed interest in the use of Chloramphenicol Palmitate (C27H42Cl2N2O6) [Palmitic acid alpha ester with d-threo-(-),2-dichloro-N-(beta-hydroxy-alpha-(hydroxymethyl)-p-nitrophenethyl)acetamide also known as Detereopal]. The characterization of the three polymorphic forms of Chloramphenicol Palmitate (CPP) was done spectroscopically by employing FT-IR and FT-Raman techniques. The equilibrium geometry, various bonding features, and harmonic wavenumbers have been investigated for most stable form A with the help of DFT calculations and a good correlation was found between experimental data and theoretical values. Electronic properties have been analyzed employing TD-DFT for both gaseous and solvent phase. The theoretical calculation of thermodynamical properties along with NBO analysis has also been performed to have a deep insight into the molecule for further applications.

Conformational and structural studies of cyclobutylsilane from temperature dependent infrared spectra of xenon solutions and ab initio calculations

The infrared spectra (3500–220cm−1) in the gas phase of cyclobutylsilane, c-C4H7SiH3 has been recorded. Variable temperature (−65 to −100°C) studies of the infrared spectra (3500–400cm−1) dissolved in liquid xenon have been carried out. From these data, both the equatorial and axial conformers have been identified and their relative stability obtained. The enthalpy difference has been determined from 15 band pairs to be 67±7cm−1 (0.81±0.08kJmol−1) with the equatorial conformer the more stable form. The percentage of the axial conformer is estimated to be 42±1% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug-cc-pVTZ from both MP2(full) and density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants along with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained for both conformers. The determined heavy atom distances (Å) for the equatorial [axial] form are Si–Cα=1.879(3) [1.884(3)], Cα–Cβ, Cβ′=1.562(3) [1.561(3)], Cγ–Cβ, Cβ′=1.551(3) [1.553(3)] and angles in degrees (°) ∠SiCαCβ=118.6(5) [113.2(5)], ∠CβCαCβ′=88.2(5) [88.4(5)], ∠CαCβCγ=87.8(5) [88.9(5)], ∠CβCγCβ′=88.9(5) [89.0(5)] and a puckering angle of 29.0(5) [23.5(5)]. Support for the vibrational studies have been provided from MP2(full)/6-31G(d) ab initio calculations to predict harmonic force constants, fundamental wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are discussed and compared to the corresponding properties of some related molecules.

Structure and conformation studies from temperature dependent infrared spectra of xenon solutions and ab initio calculations of cyclobutylgermane

The infrared spectra (3500–220cm−1) of cyclobutylgermane, c-C4H7GeH3 have been recorded of the gas. Also variable temperature (−65 to −100°C) studies of the infrared spectra (3500–400cm−1) of the sample dissolved in liquid xenon were recorded and both the equatorial and axial conformers were identified. The enthalpy difference has been determined from 10 band pairs 8 temperatures to give 112±11cm−1 (1.34±0.13kJmol−1) with the equatorial conformer the more stable form. The percentage of the axial conformer present at ambient temperature is estimated to be 37±1%. From ab initio calculations conformational stabilities have been predicted from both MP2(full) and density functional theory calculations from a variety of basic sets. The r0 structure parameters have been obtained for both conformers from the previously reported rotational constants from the three isotopologues. The determined heavy atom distances for the equatorial [axial] form are (Å) Ge–Cα=1.952(3) [1.950(3)], Cα–Cβ,Cβ′=1.557(3)[1.565(3)], Cγ–Cβ,Cβ′=1.551(3) [1.551(3)] and angles in degrees (°) ∠GeCαCβ=118.6(5) [113.4(5)], ∠CβCαCβ′=88.3(5)[88.0(5)], ∠CαCβCγ=87.8(5) [88.8(5)], ∠CβCγCβ′=88.7(5)[89.0(5)] and a puckering angle of 29.1(5) [25.1(5)]. Data from ab initio calculations were used to predict vibrational harmonic force constants, fundamental wavenumbers, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are compared to the corresponding properties of some related molecules.

Conformational and structural studies of n‐propylamine from temperature dependent Raman and far infrared spectra of xenon solutions and ab initio calculations

The Raman and infrared spectra (4000 to 50 cm–1) of the gas, liquid or solution, and solid have been recorded of n‐propylamine, CH3CH2CH2NH2. Variable temperature (−60 to −100 °C) studies of the Raman (1175 to 625 cm–1) and far infrared (600 to 10 cm–1) spectra dissolved in liquid xenon were carried out. From these data, the five possible conformers were identified and their relative stabilities obtained with enthalpy difference relative to trans–trans (Tt) for trans–gauche (Tg) of 79 ± 9 cm–1 (0.9 ± 0.1 kJ/mol); for Gg of 91 ± 26 cm–1 (1.08 ± 0.3 kJ/mol); for Gg′ of 135 ± 21 cm–1 (1.61 ± 0.2 kJ/mol); for Gt of 143 ± 11 cm–1 (1.71 ± 0.1 kJ/mol). The percentage of the five conformers is estimated to be 18% for the Tt, 24 ± 1% for Tg, 23 ± 3% for Gg, 18 ± 1% for Gg′ and 18 ± 1% for Gt at ambient temperature. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug‐cc‐pVTZ from both second‐order Møller–Plesset (MP2, full) and density functional theory calculations by the Becke, three‐parameter, Lee–Yang–Parr method. Vibrational assignments were provided for the observed bands for all five conformers, which are supported by MP2(full)/6‐31G(d) ab initio calculations to predict harmonic force constants, 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 © 2012 John Wiley & Sons, Ltd.

FTIR spectroscopic and quantum chemical studies on hydantoin

In this study the geometry optimization of monomeric and dimeric forms (D1, D2, and D3) of hydantoin molecule were done using DFT method employing 6–31++G(d, p) basis set. Harmonic and anharmonic wavenumbers and infrared intensities were computed at the same theory level. Experimental IR spectrum was recorded in the region 400–4000 cm−1. It has also been characterized by 1H and 13C NMR spectrum. The hydrogen bond (HB) interaction of hydantoin was analyzed via dimers of hydantoin. Detailed vibrational wavenumber shifts and all vibrational mode analyses were reported. Total energy distributions (TED, %) calculations were done to characterize the fundamentals.

Structural and vibrational studies on (E)-2-(2-hydroxy benzyliden amino)-3-phenyl propionic acid using experimental and DFT methods

The structural and spectroscopic properties of (E)-2-(2-hydroxy benzyliden amino)-3-phenyl propionic acid ((E)-2-HBAPPA) has been investigated by using theoretical and experimental methods. Using the computational studies the most stable conformer was identified. Density functional theory (DFT) calculations of 16 (E)-2-HBAPPA conformers have been performed to find the optimized structure and the computed vibrational wavenumbers of the most stable one. The FT Raman and FT-IR spectra of (E)-2-HBAPPA molecule have been recorded and analyzed. A detailed interpretation of the FT-IR, FT-Raman and harmonic wavenumbers obtained at B3LYP/6-311++G(d,p) level was reported. The vibrational assignments were studied using TED method. Intra-molecular charge transfer between nitrogen and hydroxyl hydrogen (CN⋯HO) has been studied. First order hyperpolarizability (β0) has been calculated. Electronic excitation of (E)-2-HBAPPA was recorded in the visible region and compared with calculated TD-DFT results.

Ab Initio Structural and Vibrational Investigation of Sulfuric Acid Monohydrate

We employ ab initio methods to find stable geometries and to calculate potential energy surfaces and vibrational wavenumbers for sulfuric acid monohydrate. Geometry optimizations are carried out with the explicitly correlated coupled-cluster approach that includes single, double, and perturbative triple excitations (CCSD(T)-F12a) with a valence double-ζ basis set (VDZ-F12). Four different stable geometries are found, and the two lowest are within 0.41 kJ mol(-1) (or 34 cm(-1)) of each other. Vibrational harmonic wavenumbers are calculated at both the density-fitted local spin component scaled second-order Møller-Plesset perturbation theory (DF-SCS-LMP2) with the aug-cc-pV(T+d)Z basis set and the CCSD-F12/VDZ-F12 level. Water O-H stretching vibrations and two highly anharmonic large-amplitude motions connecting the three lowest potential energy minima are considered by limiting the dimensionality of the corresponding potential energy surfaces to small two- or three-dimensional subspaces that contain only strongly coupled vibrational degrees of freedom. In these anharmonic domains, the vibrational problem is solved variationally using potential energy surfaces calculated at the CCSD(T)-F12a/VDZ-F12 level.

FT-IR, FT-Raman, vibrational assignments, and density functional studies of 1,2,4-triazole-3-carboxylic acid, and its tautomers, dimers

The molecular geometry, relative energy, and vibrational properties (harmonic wavenumbers, total energy distributions) of several plausible tautomers and homodimers of 1,2,4-triazole-3-carboxylic acid (TCA) molecule were analyzed by applying the density functional theory (DFT), with the B3LYP functional and the 6-311++G(d,p) basis set. FT-IR and FT-Raman spectra of the biomolecule TCA were recorded in the regions 4000–100 cm−1 and 3500–100 cm−1, respectively. The calculated vibrational wavenumbers were compared with IR and Raman experimental data. The atomic charges and the dimer forms of the most stable tautomer were also discussed.

FT-IR, FT-Raman spectra, density functional computations of the vibrational spectra and molecular conformational analysis of 2,5-di-tert-butyl-hydroquinone

The purpose of finding conformer among six different possible conformers of 2,5-di-tert-butyl-hydroquinone (DTBHQ), its equilibrium geometry and harmonic wavenumbers were calculated by the B3LYP/6-31G(d,p) method. The infrared and Raman spectra of DTBHQ were recorded in the region 400–4000 cm −1 and 50–3500 cm −1, respectively. In addition, the IR spectra in CCl 4 at various concentrations of DTBHQ are also recorded. The computed vibrational wavenumbers were compared with the IR and Raman experimental data. Computational calculations at B3LYP level with two different basis sets 6-31G(d,p) and 6-311++G(d,p) are also employed in the study of the possible conformer of DTBHQ. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes, calculated using VEDA 4 program. The general agreement between the observed and calculated frequencies was established.