Assignment Of Modes Research Articles

Structure, vibrational, electrical and optical study of [C2H10N2] (IO3)2·4HIO3

The iodate salt [C2H10N2](IO3)2·4HIO3 denoted as EBITIA, was synthesized at this first time by A. M. Petrosyan et al. during the investigation the system C2H8N2HIO3H2O. In their study authors, have characterized the compound using iodometric titration and IR spectroscopy to determine its stocheometric composition. Later, K. Saidi et al. have studied the structural properties of the EBITIA crystal using X-ray single crystal diffraction at room temperature. In this work, this iodate salt was reproduced and was analyzed using the X-ray powder diffraction showing that the crystal structure of this compound corresponds well to the structrural model of the EBITIA. Variable temperature X-ray powder diffraction (VT-XRPD), 13C NMR, DSC and complex impedance spectroscopy (CIS) investigation were undertaken and show that the EBITIA is stable at the temperature range 303–393 K. The temperature dependence of both bulk and DC conductivities follow the Arrhenius law and the impedance data were fitted to an adequate equivalent circuit model consisting of a parallel combination of a bulk resistance and CPE. The near values of activation energies obtained from the conductivity and impedance measurements suggested that the electrical conductivity in the EBITIA may be due to the ion hopping mechanism.Moreover, the DFT calculation of the optimized geometries, vibrational wavenumbers, FOM's and Mulliken charge were also reported and were in better agreement with experiments. The complete, precise and reliable assignments of the fundamental vibrational modes were performed with the aid of potential energy distribution (PED). The optical properties of the compound were also studied using diffuse reflectance (DRS) and fluorescence spectroscopy.

Assignment of the Abrasive-Jet Machining Mode of Si3N4-Ceramic Components Considering the Stress State of Various Surface-Layer Phases

The influences of mechanical and thermal actions specific to abrasive-jet machining on the distribution of stresses in various surface-layer phases of Si3N4 ceramic were investigated. An approach to selecting the operating modes during preliminary and finishing processes was proposed based on the established trends.

M-S Multiple Bond in HMSH, H2MS, and HMS Molecules (M = B, Al, Ga): Matrix Infrared Spectra and Theoretical Calculations.

Reaction products of B, Al, and Ga atoms with H2S have been identified in solid argon using matrix isolation infrared absorption spectroscopy. The results show that the ground state B atom reaction with H2S gives the H2BS molecule while for the Al atom the HAlSH molecule forms first, which then further isomerizes to H2AlS upon >500 nm irradiation. The reaction of the Ga atom with H2S only takes place upon photolysis to produce HGaSH in the matrix. The assignments of the major modes for these products were confirmed by appropriate 10B, 11B, D2S, and H234S isotopic shifts and theoretical frequency calculations. Topological analysis of the electron density suggests that both HBSH and H2BS molecules possess covalent B-S bond with significant double bond character, while the M-S bond in the heavier group 13 homologues (Al, Ga) was characterized as a polar covalent strong interaction.

Vibrational spectroscopy of a crystallographically unsettled uranyl carbonate: Structural impact and model

Room-temperature vibrational and photoluminescence (PL) spectra of a natural, rare hydrated calcium copper uranyl carbonate mineral, voglite (Ca2Cu(UO2)(CO3)4·6H2O) are recorded and discussed in details. Vibrational spectroscopy gives information about the structure of voglite, which is still missing due to its unknown crystallographic features. By comparison with other uranyl carbonates and sulfates, a strong Raman line occurring at 834 cm−1 is assigned to the ν1(UO2)2+ symmetric stretching vibration rather than to the ν2(CO3)2− out-of-plane bending vibration. The ν3(UO2)2+ antisymmetric stretching vibration is tentatively identified at 897 cm−1 from infrared (IR) spectroscopy. Several well resolved bands found at 1074,1092, 1381, 1566 cm−1 in the Raman and 1046, 1114, 1145, 1376, 1426, 1510, 1561 cm−1 in the IR are ascribed to symmetric and antisymmetric stretching motions of the carbonate units. The presence of all these intense vibrational bands points to different CO bond lengths. The infrared water band is well structured, suggesting a few different OH moieties in the crystal. Original micro-PL spectra show a manifold of vibronic features whose energy spacing is close to the frequency of the symmetric OUO stretching vibration and confirms the uranium origin of the most intense Raman band. The study suggests that voglite structure has no inversion centers, a low symmetry, and contains molecular units similar to those of the parent phases, andersonite or liebigite, like uranyl tricarbonate clusters (UTC). The existence of these UTCs in voglite is confirmed by density functional theory calculations. A new assignment of all vibrational modes is proposed.

Syntheses, X-ray structures and characterisation of luminescent chromium(III) complexes incorporating 8-quinolinato ligands

A series of six coordinate homoleptic and heteroleptic Cr(III) complexes have been formed that incorporate 8-quinolinato ligands. Three classes of complex have been synthesised and characterised: (i) [Cr(Q)3]; (ii) [Cr(Q)2(H2O)2]Cl; (iii) [Cr(Q)(N^N)2](PF6)2 (where Q is a ligand, 8-hydroxyquinoline, 8-hydroxy-2-methyl-quinoline, or 8-hydroxy-5-nitroquinoline; N^N = 1,10-phenanthroline or 2,2′-bipyridine). Single crystal X-ray structures were obtained for four complexes giving examples of [Cr(Q)2(H2O)2]Cl, two [Cr(Q)(bipy)2](PF6)2 and [Cr(Q)(phen)2](PF6)2. Each complex shows the ligands in the expected coordination mode with a distorted octahedral geometry evident at the metal centre. The UV–Vis. absorption data allowed assignments of the quinolinato-centred electronic transitions together with a much weaker spin allowed d–d transition (4A2 → 4T2) around 550 nm. Each complex was found to be luminescent in aerated MeCN solution at room temperature, which was attributed to a ligand-centred fluorescence based on the coordinated quinolinato ligand.

Investigating Raman spectra and density functional theory calculations on SrAl2O4 polymorphs

AbstractSrAl2O4 is a long‐lasting material that combines several favorable attributes in comparison with their inorganic luminescent predecessor. In addition, it is an intriguing material combining a structural polymorphism with potential application such as in solar cells, biological labeling and imaging, and security encode. Here, we unambiguously determinate the Raman spectra for hexagonal and monoclinic polymorphs. Specifically, the Raman mode assignment of phonon modes obtained experimentally is done for the first time by modeling these structures following the principle calculations within the framework of the density functional theory. Several functionals are evaluated, considering the agreement of the calculated modes with the experimental data. The optimized structure is obtained, first, on the basis of minimizing the total energy of the structure. The calculated vibrational modes show qualitative agreement with the experimental observation. This study offers a new insight to study the relationships between structural and optical behavior in this system, providing tools to design new technological applications.

Assignment of the electronic transitions in B4.3C boron carbide implies a specifically distorted crystal structure

The reversible high-pressure phase transition in boron carbide, making this opaque solid glasslike transparent, the visualization of actual structural distortions in the form of atomic arrangements replacing the three-atomic chain in the unit cell, and the electronic DOS calculated for realistic structure models require re-interpretation of the well-known electronic transitions. – The excellent correlation with a selected distorted structure model, proposed by Ektarawong, assuming that the polar C atoms are randomly distributed over all polar sites of the icosahedra, suggests this model to be close to the actual structure. Assignment between electronic properties and structural peculiarities enables solving some open problems, for example, the nature of the high-pressure phase transition. According to Rasim, some boron-rich components replacing a certain share of three-atomic exhibit negative energies; thus they reduce the total energy and make B4.3C the most stable structure.

Probing the Lowest-Lying Electronic States of Acrylic Acid by Experimental and Theoretical Methods.

We report a combined experimental and theoretical study of the electronic state spectroscopy of acrylic acid (C3H4O2) in the gas phase, by high-resolution vacuum ultraviolet (VUV) photoabsorption measurements in the 4.0-10.8 eV energy range, together with ab initio calculations (vertical energies and oscillator strengths), which were used in the assignment of the valence transitions. We also discuss the Rydberg transitions for this molecular target, obtained using the experimental ionization energies available in the literature. The experimental spectrum presented in this paper represents the highest resolution data yet reported for acrylic acid and reveals new features not previously reported in the literature. The dominant transitions have been assigned to (π*(4a″) ← π(3a″)) and (π*(4a″) ← π(2a″)), the latter exhibiting excitation of the ν5'( a') C = O stretching mode with mean energy of 0.155 eV. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of acrylic acid in the upper stratosphere (20-50 km).

Spectroscopic (FT-IR, FT-Raman) investigation, topology (ESP, ELF, LOL) analyses, charge transfer excitation and molecular docking (dengue, HCV) studies on ribavirin

Ribavirin, a triazole derivative has a wide application in the medical field as an antiviral drug. In the present work, a quantum chemical approach was followed to study the vibrational modes and the reactivity. Experimental techniques of FT-IR, FT-Raman were used to study the vibrational spectrum. A complete vibrational analysis was carried out and assignments of the fundamental modes were proposed. Molecular electrostatic potential, frontier molecular orbitals, electronic localization function and fukui functions were analyzed by using wavefunction analyser, Multiwfn 3.4.1 to study the chemical reactivity. Band gap energy of the title molecule is found to be 6.01 eV, as calculated from the HOMO-LUMO energies. The intermolecular charge transfer within the molecule was confirmed from the charge transfer interactions. Molecular docking studies were carried out to study the biological activity of the compound. Viral target proteins such as Dengue and Hepatitis C were chosen and the respective docking parameters were calculated.

On the structural and spectroscopic properties of the thienyl chalcone derivative: 3-(5-Bromo-2-thienyl)-1-(4-nitrophenyl)-prop-2-en-1-one

In this study, we investigate the structural and spectroscopic properties of the thienyl chalcone derivative 3-(5-Bromo-2-thienyl)-1-(4-nitrophenyl)-prop-2-en-1-one, C13H8BrNO3S, using nuclear magnetic resonance (1H and 13C NMR), UV–vis and Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy at room conditions combined with density functional theory (DFT) and time-dependent DFT (TD-DFT) augmented with B3LYP/6-311G(d,p) and CAM-B3LYP/6-311G(d,p) basis sets, yielding valuable information on the molecular conformational preferences, vibrational assignments, optical properties and electronic transitions. The vibrational mode assignments of the most stable conformer of C13H8BrNO3S are discussed based on potential energy distribution (PED) analysis and establishing a comparison with a similar chemical structure. The temperature dependence on the Raman spectra of the C13H8BrNO3S shows a reversible phase transition in the range 443–443 K pointed out by the discontinuity in the dω/dT of bands in the external and internal modes region. The UV–vis spectrum of the C13H8BrNO3S indicates a semiconductor behavior with an optical band gap of 2.6 eV, corresponding to the predicted value of 3.42 eV assigned as the electronic transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). TD-DFT calculations reveal that the electron donor and acceptor group substitution on the 1-phenyl-3-(thiophen-2-yl)prop-2-en-1-one affects its absorption and nonlinear activity.

Vibrational Spectra, NBO and NLO Analyses, and A Molecular Docking Study of 3a,8a-Dihydroxy-2-Thioxo-1,3,3a,8a-Tetrahydroindeno[1,2-d]Imidazol-8(2H)-One Using DFT

A detailed spectroscopic investigation along with quantum chemical studies on 3a,8a-dihydroxy-2-thioxo- 1,3,3a,8a-tetrahydroindeno[1,2-d]imidazol-8(2H)-one (dihydroxy-thioxo-tetrahydroindeno-imidazole) is carried out and shows the antimicrobial activity. The density functional method at the B3LYP/6-311++G(d,p) level is used to obtain the equilibrium geometries of the title compound. We have performed the vibrational analysis of the title compound at their equilibrium geometries and established the complete assignment of significant vibrational modes. The calculated vibrational frequencies are shown to be in perfect agreement with the experimentally observed FT-IR spectra of the molecule under study. The electronic properties of the molecule are discussed with the help of the descriptors such as HOMO-LUMO and MEPS, and several electronic and thermodynamic parameters are calculated which are closely related to the chemical reactivity and reaction paths. In addition, the molecular docking and NBO analyses are also carried out to get a better insight of the molecule.

Experimental and theoretical study of Raman scattering spectra of ternary chalcogenides Tl4HgI6, Tl4HgBr6, and TlHgCl3

AbstractThe results of a comprehensive experimental and theoretical study of Raman scattering of Tl4HgI6, Tl4HgBr6, and TlHgCl3 ternary chalcogenides are presented. Phonon mode assignment to the specific lattice eigenmodes is achieved via comparison of experimental data with the results of first principle lattice dynamics calculations. Both experimental data and theoretical calculations allow to confirm that Tl4HgBr6 crystals belong to the non‐centrosymmetric space group P4nc, whereas Tl4HgI6 to the centrosymmetric space group P4/mnc.

Conformational study of octopamine in gas phase and effect of hydrochloride.

This work deals with the molecular modeling and vibrational spectra of all the twenty conformers of an important biomolecule octopamine which have been investigated using the DFT/B3LYP level of theory in combination with the 6-31++g(d,p) as a suitable basis set. The experimental FTIR and FTRaman spectra of octopamine neurotransmitter were recorded in the spectral region 400-4000 cm-1 and 50-4000 cm-1 respectively and correlated with the calculated spectra of the most stable conformer. The effect of hydrochloride on the important geometrical parameters of most stable conformer of octopamine was also studied. The normal coordinate analysis was performed to scale the theoretical frequencies and to calculate potential energy distributions for precise normal mode assignment. Most of the frequencies were in good agreement with experimental one. However, some have been modified. Natural bond orbital analysis was performed in order to confirm the stability of electronic structure of octopamine molecule. HOMO-LUMO analysis for all the twenty conformers was also performed to give the transition profile and to study the chemical reactivity of octopamine.

Vibrational and structural properties of L-Alanyl-L-Phenylalanine dipeptide by Raman spectroscopy, infrared and DFT calculations

A study of vibrational and structural properties of l-Alanyl-l-Phenylalanine hydrophobic dipeptide (molecular formula C12H16N2O3) is reported. The l-alanyl-l-phenylalanine is formed by two hydrophobic amino acids, L-alanine and l-phenylalanine, through a peptide bond. Individually these compounds have many important properties, including increasing immunity and providing energy to muscle tissue, brain and central nervous system (l-alanine). We have performed measurements of Raman and Fourier transform infrared spectroscopy, between 3500-50 cm−1 and 4000-130 cm−1, respectively, at ambient conditions. To support the experimental results calculations using the density functional theory (DFT) with B3LYP functional, 6–31 G ++ (d, p) basis sets and the polarizable continuum model of solvatation in an isolated molecule in the zwitterionic form were done. The assignment of the normal modes was described by the potential energy distribution analysis. In this way, it was possible to analyze the vibrational and structural properties of L-alanyl-L-phenylalanine, allowing the assignment of each vibrational normal mode of the molecular structure, associating them with those results obtained experimentally.

Experimental (FT-IR, Laser-Raman and NMR) and theoretical comparative study on 2-benzylsulfanyl-4-pentyl-6-(phenylsulfanyl)pyrimidine-5-carbonitrile, a potential bioactive agent

In this paper, the experimental and theoretical vibrational frequencies of a potential bioactive pyrimidine derivative molecule named 2-benzylsulfanyl-4-pentyl-6-(phenylsulfanyl)pyrimidine-5-carbonitrile has been investigated. The experimental FT-IR and Laser-Raman spectra of the studied molecule are in the region (4000–400[Formula: see text]cm[Formula: see text] and (4000–100[Formula: see text]cm[Formula: see text], respectively, in gas phase. The vibrational modes and optimized ideal structure parameters(bond lengths, bond angles and selected dihedral angles) were calculated by using DFT/B3LYP, DFT/BHandHLYP and DFT/PBE1PBE methods with 6-311[Formula: see text]G(d,p) basis set. The theoretical mode assignments have been obtained by using potential energy distribution (PED) with the VEDA4 software program. Additionally, infrared and Raman intensities, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energies and their clouds, and other related molecular properties were calculated and evaluated. The proton (1H) and carbon-13 ([Formula: see text]C) nuclear magnetic resonance (NMR) chemical shifts have been investigated for the title molecule, both experimentally (in DMSO-d[Formula: see text] and theoretically (in vacuum and DMSO). The thermodynamic properties of the tile compound have been investigated using the mentioned theoretical computational methods. The results revealed that there isgood agreement between experimental and theoretical results and these results have supported the related literature.

Raman spectroscopy under high pressures and DFT calculations of the amino acid l-glutamine

l-glutamine crystal was obtained by the slow evaporation method and its crystallographic structure was verified by X-ray diffraction experiments and the Rietveld method. The vibrational modes of l-glutamine were investigated through Raman spectroscopy and the normal modes were obtained using the Density Functional Theory with the B3LYP functional and set of bases 6-31G++(d, p). With such approach, it was possible to make a theoretical-experimental comparison of the results obtained and to furnish a more precise assignment of the normal modes. The crystal was submitted to high pressure conditions and the Raman spectra between 3055 and 40 cm−1 were recorded for pressures up to 6.1 GPa in a diamond anvil cell. This study allowed us to understand that the crystal undergoes a reversible structural phase transition around 4.0 GPa, characterized mainly by spectral changes in the region of the external modes.

Solution-processed Ga–Cd–O thin-films with tunable bandgaps and their transistors

Ga–Cd–O (GCO) thin films with different Ga contents were fabricated based on a solution-processed method. The direct optical bandgap of GCO films is changed from 2.89 to 4.53 eV with the Ga-content from 30% to 100% and their relationship agrees well with a second-order equation. The Raman spectra of GCO are dominated by three main features: a relatively sharp peak at ~260 cm−1 and two broad features at ~405 and 949 cm−1, and their variations with the Ga-content are analyzed associated with their phonon mode assignment. Moreover, thin-film transistors using the GCO channels all exhibit n-type transistor characteristics and the evolution of their key electrical parameters with the Ga-content is well elucidated by the structural and morphological properties. A saturation field-effect mobility of 5.1 cm2 V−1 s−1, on/off current ratio of 2.1 × 107, subthreshold slop of 0.83 V/dec, and threshold voltage of −6.8 V were achieved by the 50% Ga-content device.

MOLECULAR STRUCTURE AND VIBRATION SPECTRA OF PIVALIC ACID

The metal carboxylates such as metal pivalates (salts of the pivalic acid (CH3)3CCOOH) attract a great interest as most promising precursors for chemical vapor deposition (CVD) technology. The possibility to use these substances in the CVD technology is specified by their good thermal stability and high volatility. For modeling of chemical reactions with metal pivalates in the gas-phase and the data on molecular structure will be very useful, in particularly information about effect of central metal ion to geometry of pivalic ligands. In the frame of this task the structures of metal pivalate molecules and pivalic acid (H(piv)) in a gas phase should be finding. The aim of present work is theoretical investigation of the geometry and IR-spectrum of H(piv) using density functional theory (DFT) methods. All calculations were performed using the Gaussian 03 program. The optimization of geometry and quadratic force field calculations were carried out using DFT functionals B3LYP, PBE, PBE0 and BP86 with correlation-consistent triple-ζ valence cc-pVTZ basis sets for O, C, and H. Appropriate assignment of vibrational modes was carried out by the potential energy distribution (PED) analysis among internal coordinates using the SHRINK program. According to DFT computations, the H(piv) molecule has an equilibrium structure of Cs symmetry with Гvib=26A'+19A''. The theoretical and experimental IR-spectra are satisfactorily agreed. The comparison of the ten intensities of highest bands in spectra allowed determining linear correlation between peaks position in experimental and modeling IR-spectra. It should be note the complicated composition of vibrational modes.

Structural and vibrational characteristics and vibronic coupling of tetramethyltetraselenafulvalene

The molecular, electronic and crystal structures of tetramethyltetraselenafulvalene (TMTSF) have been investigated. The experimental IR and Raman spectra and single crystal XRD for TMTSF have been interpreted. In order to facilitate this, computations have been carried out for the molecular structures and vibrational characteristics of the TMTSF molecule. Study of Molecular electrostatic potential surface of the TMTSF and its cation is also done. Normal mode assignments have been made on the basis of the computed potential energy distributions (PEDs). In addition, a comprehensive study of molecular geometries, atomic charges and vibrational fundamentals of TMTSF and its cationic molecule has been carried out. Vibronic coupling constants in TMTSF and TMTSF+ have been computed using the DFT/B3LYP results. The TMTSF molecule belongs to C2v point group symmetry. All the studied molecules exhibit partial double bond character as all the bond lengths are changed from their usual bond lengths. The partial double bond character has been found to be indicate that the conducting behaviour of these molecules. In the unit cell of TMTSF, some H atoms and all the Se atoms are interacting with the molecules of neighboring and its own cell. The major changes in frequencies from neutral to the cationic state for í (ring) and í(CC) are found for the both molecules. The vibronic coupling corresponding to a vibrational mode helps to transport charge along the stacks of a conducting organic molecules from a neutral molecule to an adjacent charged ion. The magnitude of the VCC is noticed to be maximum for the í (CC). The geometry of the neutral molecule under this mode resembles to that of the ion and vice-versa. The large VCC of this mode shows that removal of an electron is much easier during the vibrational modes. Thus from the present study i.e. the molecular, electronic and crystal structures and vibronic investigations confirm the conducting behaviour of the TMTSF molecule. From the MEP surface it is clear that the sites close to selenium atoms in TMTSF show region of most negative electrostatic potential.

Uniaxial compression behavior and spectroscopic properties of the explosive pentaerythritol tetranitrate from first-principles calculations

Using dispersion corrected density functional theory, we have investigated the uniaxial compression effect on pentaerythritol tetranitrate (PETN) crystal, which is an secondary high explosive. The principal stresses and shear stresses along different orientations exhibit considerable anisotropy. The Raman spectroscopy is used to explore the pressure effects on the vibrational properties of PETN. Several features are observed in selected Raman vibrational modes along different orientations. Especially, compression along the [0 0 1] orientation induces some anomalous changes of some vibrational modes. Through analyzing intermolecular hydrogen bonds, vibrational mode assignments and variation of the corresponding peak positions of PETN crystal, we propose that the changes between 15.8 and 17.6 GPa may be associated with a phase transformation. This present study has shed light on the anisotropic impact sensitivity and phase change of PETN under compression at atomistic scale.