Assignment Of Fundamental Modes Research Articles

Computational Study on Piperazine‐1,4‐Diium Acetate Using Dft Investigations: Structural Aspects, Topological and Nonlinear Optical Properties

AbstractThe work aims to investigate the nonlinear optical (NLO) activity of piperazine‐1,4‐diium acetate (PAA) molecule utilizing computational techniques. The computational calculations are performed using density functional theory (DFT) to explore the vibrational modes, electronic and NLO properties of PAA by comparing them with piperazine and acetic acid molecules. The natural bond orbital analysis is performed to identify hydrogen bonding and charge transfer interaction. A vibrational analysis is carried out and the assignment of fundamental modes is done using the vibrational energy distribution analysis (VEDA) program. Molecular electrostatic potential, frontier molecular orbital, electron localization function, localized orbital locator and Fukui analysis are carried out to identify chemical reactivity and charge transfer interaction. The UV–visible analysis is performed to obtain the electronic absorption spectrum. The hole–electron analysis is performed for the first five excitations to identify the type of excitation. The atoms in molecules, reduced density gradient and independent gradient model are performed to identify the hydrogen bonding, steric and van der Waals interactions. Hirshfeld analysis is performed to explore the intermolecular interactions within the PAA molecule. The NLO calculation is performed to evaluate the NLO parameters. The obtained results show that the PAA molecule is suitable for NLO applications.

IR and Raman spectra with Gaussian-09 molecular analysis of some other parameters and vibrational spectra of 5-fluoro-uracil

Recorded IR and Raman spectra of 5-fluoro-uracil have been analyzed with the carried out theoretical computation by Gaussian-09 [DFT/B3LYP/6-311 ++G**] and GAR2PED software. In the assignment of fundamental modes, the GAR2PED software has been used to calculate the PEDs. HOMO–LUMO energy gap study supports the possibility of charge transfer in biomolecule. Electrostatic potential plotting with iso-surface plot and the mappings of electron density with molecular electrostatic potential have been made for the concept of charge distribution in molecules as the sites of nucleophilic reactions and electrophilic effect. The DFT calculations have been employed to yield the atomic polarizability tensor charges, Mulliken atomic charges, molecular structure and thermodynamic functional properties of the biomolecule. The assignment has been made in the two species for the normal mode of the fluoro group substituent on pyrimidine ring.

Raman, Mid-IR, and NIR spectroscopic study of calcium sulfates and mapping gypsum abundances in Columbus crater, Mars

Calcium sulfates, including gypsum, bassanite, and anhydrite, have been identified on Mars by orbital and in situ remote sensing observations. A comprehensive spectroscopic study of three calcium sulfates in laboratory was performed. Raman, mid-infrared (mid-IR), and near infrared (NIR) spectra of the samples were acquired. The assignments for fundamental modes are made in the Raman and the mid-IR spectra and for overtones and combinational modes in the NIR spectra. Finally, we performed a case study to derive the abundance of gypsum in Columbus crater on Mars using the spectral unmixing analysis method. Our results show high abundance of gypsum and moderate abundance of hydrated sulfate without any basaltic glass or amorphous weathering products, which indicates these deposits could have formed through precipitation and evaporation and is consistent with the deep lake hypothesis proposed by previous studies.

Spectroscopic and QSAR analysis on Antibiotic drug; 2-amino-4,6- dimethylpyrimidine using Quantum Computational Tools

The antibiotic activity of 2-amino-4,6-dimethylpyrimidine has been analyzed using molecular spectroscopy tools. The biological activity was interpreted and drug likeness was evaluated by calculating biological parameters. The activeness of the internal molecular parts was assessed by the assignment of fundamental modes of vibrations. The chromophores action for the inducement of the antibiotic activity of the compound was analyzed from the electronic excitation absorption peaks. The σ-bond, π-bond and δ-bond interaction lobes were identified and the exchange of energy between the orbitals was investigated from frontier molecular orbital profile. The asymmetrical charge distribution among different entities of the molecule for the perseverance of anti-tuberculosis mechanism was recognized. The NMBO interaction profile was evaluated by the NBO calculation adapted with Gaussian and the exchange of maximum energy transaction among various functional groups for the incentive of antibiotic were determined. The second order Polarizability of the compound emphasized the consistency of the antibiotic activity of the molecule. Thermodynamic activity of the molecule with respect to the temperature was stressed the decomposition rate and Gibbs free energy helped to determine the steadiness of the compound. The inhibition catalytic efficiency of the title molecule was fully tested by molecular docking study.

Vibrational and UV spectroscopic studies of 2-coumaranone by experimental and density functional theory calculations

The vibrational and electronic properties of 2-coumaranone have been reported in the ground state using experimental techniques (FT-IR, FT-Raman, UV spectra and fluorescence microscopic imaging) and density functional theory (DFT) employing B3LYP correlation with the 6-31G(d, p) basis set. The theoretically reported optimized parameters, vibrational frequencies etc., were compared with the experimental values, which yielded good concurrence between the experimental and calculated values. The assignments of the vibrational spectra were done with the help of normal co-ordinate analysis (NCA) following the Scaled Quantum Mechanical Force Field(SQMFF) methodology. The whole assignments of fundamental modes were based on the potential energy distribution (PED) matrix. The electric dipole moment and the first order hyperpolarizability of the 2-coumaranone have been computed using quantum mechanical calculations. NBO and HOMO, LUMO analyses have been carried out. UV spectrum of 2-coumaranone was recorded in the region 100–300 nm and compared with the theoretical UV spectrum using TD-DFT and SAC-CI methods by which a good agreement is observed. Fluorescence microscopic imaging study reflects that the compound fluoresces in the green-yellow region.

DFT calculation and assignment of vibrational spectra of aryl and alkyl chlorophosphates

Abstract DFT calculations of vibrational spectra of chlorophosphates using wide range of basis sets and hybrid functionals were performed. Good agreement between calculated and experimental vibrational spectra was reached by the combination of non-empirical functional PBE0 with both middle and large basis sets. The frequencies of the stretching vibrations of the phosphate group calculated using semi-empirical functional B3LYP for all basis sets deviate significantly from the experimental values. The number of polarization functions on heavy atoms was shown to be a key factor for the calculation of vibrational frequencies of organophosphates. The importance of consideration of all the stable rotamers for a complete assignment of fundamental modes was shown.

Study of molecular structure and assignments of fundamental modes of 2-ethylpyridine-4-carbothioamide by density functional methods

The FT-IR and UV spectra of 2-ethylpyridine-4-carbothioamide have been recorded. The structure and spectroscopic data of the molecule in ground state have been calculated using AM1, PM3 semi-empirical methods, ab initio Hartree–Fock and density functional theory (B3LYP, B3PW91) methods by employing 6-31+ G (d, p) basis sets. The optimized geometry, vibrational frequencies in the ground state is calculated. The scaled vibrational frequencies are found to coincide with the experimentally observed values. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energies show that charge transfer occurs within these molecules. In this work, we have calculated 1H and 13C nuclear magnetic resonance chemical shifts of the molecules using the gauge-including atomic orbital method matches with the experimental values. The natural localized molecular orbital analysis has been made to study the atomic hybrid contribution of the title molecule. Molecular electrostatic potential and total density distribution are constructed to understand the electronic properties and to study the most stable geometry of the compound from the potential energy scan.

Infrared Spectra of Dimethylquinolines in the Gas Phase: Experiment and Theory

Infrared spectra of atmospherically important dimethylquinolines (DMQs), namely 2,4-DMQ, 2,6-DMQ, 2,7-DMQ, and 2,8-DMQ in the gas phase at 80 degrees C were recorded using a long variable path-length cell. DFT calculations were carried out to assign the bands in the experimentally observed spectra at the B3LYP/6-31G* level of theory. The spectral assignments particularly for the C-H stretching modes could not be made unambiguously using calculated anharmonic or scaled harmonic frequencies. To resolve this problem, a scaled force field method of assignment was used. Assignment of fundamental modes was confirmed by potential energy distributions (PEDs) of the normal modes derived by the scaled force fields using a modified version of the UMAT program in the QCPE package. We demonstrate that for large molecules such as the DMQs, the scaling of the force field is more effective in arriving at the correct assignment of the fundamentals for a quantitative vibrational analysis. An error analysis of the mean deviation of the calculated harmonic, anharmonic, and force field fitted frequencies from the observed frequency provides strong evidence for the correctness of the assignment.

Analysis of structure and vibrational spectra of 2,5‐dihydroxybenzoicacid based on density functional theory calculations

AbstractThe spectra of 2,5‐dihydroxybenzoic acid (DHBA) have been recorded using Fourier transform‐infrared spectroscopy (FT‐IR) and FT‐Raman measurements. The total energy calculations of DHBA were evaluated for various possible conformers. The spectra were interpreted with the help of normal coordinate analysis based on density functional theory (DFT) using standard B3LYP/6–31G* method for the most optimized geometry. The effect of intramolecular hydrogen bonding was discussed. Normal coordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors, yielding fairly good agreement between observed and calculated frequencies. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined. Copyright © 2009 John Wiley & Sons, Ltd.

A joint FTIR, FT‐Raman and scaled quantum mechanical study of 1,3‐dibromo‐2,4,5,6‐tetra‐fluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB)

AbstractThe liquid phase FTIR and FT‐Raman spectra of 1,3‐dibromo‐2,4,5,6‐tetrafluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB) were recorded in the regions 4000–400 cm−1 and 4000–50 cm−1, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure opti1mization and force field calculations based on the density functional theory using the standard B3LYP/6‐31G* method and basis set combination. The scaled force field reproduced the experimental wavenumbers of the molecule for DTFB and PFB, respectively. The effects of halogen substituents on the structure and vibrational wavenumbers have been investigated. Assignments of fundamental modes were made based on the comparison between calculated and experimental results. Copyright © 2009 John Wiley & Sons, Ltd.

Density functional theory study of vibrational spectra, and assignment of fundamental vibrational modes of 1-bromo 4-fluoronaphthalene

The FTIR and FT-Raman spectra of 1-bromo 4-fluoronaphthalene have been recorded in the regions 4000–100 cm −1 and 3500–100 cm −1, respectively. The spectra were interpreted with the aid of normal coordinate analysis based on DFT (density functional theory) using standard B3LYP/6-311+G** basis set combination for the most optimized geometry. Normal coordinate calculations performed with the DFT force field and subsequently corrected by a recommended set of scale factors, yielded fairly good agreement between observed and calculated frequencies. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined.

Single-crystal, polarized, Raman scattering study of the molecular and lattice vibrations for the energetic material cyclotrimethylene trinitramine

The single-crystal, polarized, Raman spectra for cyclotrimethylene trinitramine (RDX) have been studied at room temperature and pressure over the region of 5–3400cm−1. While the observed Raman bands agree well with a previous Raman study, this work provides a consistent interpretation of the Raman spectra by assignment of fundamental modes, overtones, and combination bands. A total of 56 internal vibrations were observed, 36 of which were labeled as fundamental molecular vibrations. In addition, all 24 lattice optical phonons are identified. All six possible polarizations were probed to obtain the Ag, B1g, B2g, and B3g symmetry modes for both the lattice and molecular modes. Finally, the importance of these phonons for coupling with “doorway” Raman-active modes of RDX is discussed in relation to proposed mechanisms for detonation initiation.

Single-Crystal, Polarized Raman-Scattering Study of the Molecular and Lattice Vibrations for the Energetic Material Cyclotetramethylenetetranitramine, β-Polymorph (β-HMX)

The single-crystal polarized Raman spectra for cyclotetramethylenetetranitramine, /3-polymorph (/3-HMX), are reported over the region of 10 to 3150 cm -1 . While the agreement with previous Raman studies is quite good, a consistent interpretation of the Raman spectra is provided through assignment of fundamental modes, overtones, and combination bands. This affords the first assignment of all six Raman-active optical phonons of β-HMX. It was found that three Ag symmetry librations are accidentally degenerate with three Bg optical phonons. The importance of these phonons for coupling with doorway Raman-active modes of β-HMX is discussed in relation to proposed vibrational mechanisms for the initiation of detonation.

DFT studies, vibrational spectra and conformational stability of 4-hydroxy-3-methylacetophenone and 4-hydroxy-3-methoxyacetophenone

The FT-IR and FT-Raman spectra of 4-hydroxy-3-methylacetophenone (HMA) and 4-hydroxy-3-methoxyacetophenone (HMOA) have been recorded. The total energy calculations of HMA and HMOA were tried for various possible conformers. The spectra were interpreted with the aid of normal coordinate analysis based on density functional theory (DFT) using standard B3LYP/6-31G * and B3LYP/6-311 + G ** methods and basis sets combinations for the most optimized geometries. Normal coordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors yielding fairly good agreement between observed and calculated frequencies. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined.

Raspite and studtite: Raman spectra of two unique minerals

AbstractThe Raman and IR spectra of monoclinic naturally occurring raspite, α‐PbWO4 (space group P21/a) were measured; it is irreversibly transformed to the tetragonal stolzite, β‐PbWO4, by heating to 450°C, and this process was followed by Raman spectroscopy. Assignments of fundamental modes are proposed. New data are also presented on single crystals of stolzite (space group I41/a), and it is shown that raspite and stolzite can easily be distinguished by their Raman spectra. We also present Raman and IR spectroscopic data on natural and synthetic studtite, UO4·4H2O, and its synthetic dehydration product metastudtite, UO4·2H2O, the only two naturally occurring peroxide‐containing minerals, and on partially deuterated synthetic forms of these materials. Assignments of fundamental modes are proposed and both TGA and DSC data are presented for studtite. Copyright © 2004 John Wiley & Sons, Ltd.

Vibrational spectra of the hydrated carbonate minerals ikaite, monohydrocalcite, lansfordite and nesquehonite

The Raman (200–4000 cm −1) and infrared (600–4000 cm −1) spectra of four rare carbonate hydrate minerals are reported. These are naturally occurring and synthetic ikaite CaCO 3 · 6H 2O, and nesquehonite MgCO 3 · 3H 2O; natural monohydrocalcite CaCO 3 · H 2O, and synthetic lansfordite MgCO 3 · 5H 2O. The spectra of synthetic ikaite partially substituted with 2H 2O and also with 13C were measured, as were those of synthetic deuteriated nesquehonite. Spectra of ikaite and lansfordite, both of which decompose at room temperatures, were measured below 0 °C. Assignments of fundamental modes are proposed.

Structures and vibrational frequencies of ethylphosphine: post-Hartree–Fock and density functional theory study

The molecular structure and conformational stability of ethylphosphine have been investigated using ab initio and density functional theory methods. The molecular geometries are optimized employing HF, MP2, BLYP and B3LYP methods implementing 6-31G ∗ and 6-311++G ∗∗ basis sets. From the calculations, the molecule is predicted to exist in two stable conformers with the trans (methyl group oriented trans to the lone pair on the phosphorus atom) being slightly lower in energy than the gauche rotamers. The optimized structural parameters for both conformations are compared to the structures obtained from microwave spectroscopy. Potential surfaces for both the methyl and PH 2 moiety internal rotation are determined at B3LYP and MP2 levels of theory. The vibrational frequencies are computed at different levels and compared to the fundamental values. The results indicate that the scaled B3LYP frequencies reproduce the experimental values satisfactorily with the mean absolute deviation about 19.9 cm −1. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes are examined. It is conclude that at these levels of calculations, the structure, potential surface and vibrational frequencies for ethylphosphine are well determined.

Vibrational spectra of 1,2-benzenedithiol, 2-aminothiophenol and 2-aminophenol and their SER spectra

The Raman and infra-red spectra of 1,2-benzenedithiol, 2-aminothiophenol and 2-aminophenol are reported and assignments of fundamental modes are proposed. The Surface-Enhanced Raman Spectra (SERS) of these three ortho-disubstituted benzenes and 2-aminophenoxazone on gold and silver colloids are recorded.

Vibrational spectra of catechol, catechol- d2 and - d6 and the catecholate monoanion

The Raman and infrared spectra of normal and deuterated catechol in the solid and aqueous solution phases are reported, together with data for the catecholate monoanion at high pH. Assignments of fundamental modes are proposed.

Pentanitrosyl Molybdenum Pentakis (Tetrafluoroborate)

Preparation and properties of pentanitrosyl molybdenum pentakis (tetrafluoroborate) are descfibed. The structure was determined by IR and Raman spectroscopy methods. Assignments of fundamental modes were proposed. The applicability of the complex under study as the precatalyst of olefin metathesis reaction was investigated. The homogeneous system Mo(NO) 5(BF 4) 5/EtA1C1 2 proved to be a highly active catalyst for 2-pentene meta- thesis.