A theoretical and experimental study of Sb4O6: vibrational analysis, infrared, and Raman spectra

The first ab initio theoretical study of tetraantimony hexoxide (Sb4O6) is reported. The normal mode frequencies, intensities, and the corresponding vibrational assignments of Sb4O6 in T(d) symmetry were calculated using the GAUSSIAN 98 set of quantum chemistry codes at the Hartree-Fock (HF)/CEP-121G, M?ller-Plesset (MP2)/CEP-121G, and density functional theory (DFT)/B3LYP/CEP-121G levels of theory. By comparison to experimental data deduced by our laboratory and others, correction factors for the calculated vibrational frequencies were determined and compared. Normal modes were decomposed into three non-redundant motions (Sb-O-Sb stretch, Sb-O-Sb bend, and Sb-O-Sb wag). Percent relative errors found for the HF, DFT, and MP2 corrected frequencies when compared to experiment are 5.8, 6.1, and 5.7 cm(-1), respectively. Electron distributions for selected molecular orbitals are also considered.     

Theoretical Raman and infrared spectra, and vibrational assignment for para-halogenoanilines: DFT study

The theoretical IR and Raman spectra of para-halogenoanilines, 4-XC(6)H(4)NH(2) (X=F, Cl and Br) were calculated by using the density functional B3LYP method with the 6-311++G(df,pd) basis set. The theoretical spectra show very good agreement with experiment. The rigorous normal coordinate analyses have been performed, and the detailed vibrational assignment has been made on the basis of the calculated potential energy distributions (PEDs). Several ambiguities and contradictions in the previously reported vibrational assignments have been clarified. The "marker bands" and the effects of the halogen substituent on the characteristic aniline bands in the IR and Raman spectra are discussed.     

Molecular structures and infrared spectra of SiZrH4: A theoretical study

Molecular structures of the SiZrH₄ complex were investigated at BPW91, BPW91/IEF-PCM, B3LYP, and MP2 levels of theory with substantial basis sets. Relative stability of the stable conformers is fairly dependent on the methods, solvent effects, and zero-point energy corrections. All the four levels of calculations indicated that the singlet HSi(μ-H)ZrH₂, trans-Si(μ-H)₂ZrH₂, cis-Si(μ-H)₂ZrH₂, and the triplet Si(μ-H)₃ZrH are stable and comparable in energy. The energy of these four isomers is well below that of the Zr(³F₂) + SiH₄ system. The trans-dibridged, rather than the tribridged, isomer was always predicted to be the most stable one by all the four levels of calculations. For the two dibridged isomers, the two SiH₂ stretching modes are highly coupled with the two ZrH₂ stretching modes. And such coupling cannot be removed by the full deuteration.     

A combined theoretical and experimental study of the structure and vibrational absorption, vibrational circular dichroism, Raman and Raman optical activity spectra of the L-histidine zwitterion

A combined theoretical and experimental study of the vibrational absorption (VA)/IR, vibrational circular dichroism (VCD), Raman and Raman optical activity (ROA) spectra of l-histidine in aqueous solution has been undertaken to answer the questions (i) what are the species present and (ii) which conformers of the species are present under various experimental conditions. The VA spectra of l-histidine have been measured in aqueous solution and the spectral bands which can be used to identify both species (cation, zwitterion, anion) and conformer of the species have been identified and subsequently used to identify the species (zwitterion) and conformer (gauche minus minus, gauche minus plus for the side chain dihedral angles) present in solution at pH 7.6. The VCD spectral intensities have been used subsequently in combination with further theoretical studies to confirm the conclusions that have been arrived at by only analyzing the VA/IR spectra. Finally a comparison of measured Raman and ROA spectra of l-histidine with Raman and ROA spectral simulations for the conformers and species derived from the combined VA/IR and VCD experimental and theoretical work is presented as a validation of the conclusions arrived at from VA/IR and VCD spectroscopy. The combination of VA/IR and VCD with Raman and ROA is clearly superior and both sets of experiments should be performed.     

Experimental and theoretical study of the vibrational spectra of free 12-crown-4

The Raman and IR spectra of free 12-crown-4 (12c4) were measured in the solid, liquid, and solution phases. In the three phases, IR active modes were Raman inactive and IR inactive modes were Raman active. According to the exclusion rule, this is consistent with a conformation with a center of inversion. This indicates that 12c4 in the above-mentioned three phases exists in the C(i) conformation. Harmonic force fields were calculated for five of the lowest energy conformations of 12c4 of C(i), S(4), C(4), C(2), and C(s) symmetries at the corresponding optimized geometries at the B3LYP/6-31+G level. The five force fields were scaled using a six-scale-factor scaling scheme. The scale factors were varied to minimize the difference between the calculated and experimental fundamental frequencies, except that corresponding to the C-H stretching mode that was held fixed. The root-mean-square (rms) deviation of the experimental to the calculated vibrational frequencies was 6.2, 12.0, 10.8, 13.2, and 13.5 cm(-1), for C(i)(), S(4), C(4), C(2), and C(s) conformations, respectively. This supports the above conclusion that 12c4 in the solid, liquid, and considered solution phases exists in the C(i) conformation.     

A theoretical study of the vibrational spectra,geometry and force field of thiourea

A theoretical force field for the molecular vibrations of thiourea has been determined from ab initio calculations at the Hartree-Fock level using the 3-21G* basis set. The reliability of the force field is analyzed by calculating the vibrational frequencies for the deuterated and ¹⁵N isotopomers. Frequencies calculated from the force field are utilized to critically examine the experimental assignments for thiourea and deuterated thiourea. Theoretical geometry, the calculated IR and Raman band intensifies are analyzed.     

An SCF study of P4O6 and P4O10

The electronic structures of the oxides P₄O₆ and P₄O₁₀ are calculated by the self-consistent molecular orbital method including all valence electrons and the 3d orbitals on phosphorus. It is found that the former molecule appears to be virtually non-polar whilst in the latter, the P-O (terminal) bonds are highly polar. The bond order matrix shows that the internal P-P bonding in the P₄ unit is not marked.     

Solid-state vibrational spectra and theoretical study of alaninamide acetate

Solid-state IR and Raman spectroscopic elucidation of alaninamide acetate is preformed by means of the possibilities of linear-polarized IR and Raman methods. The experimental assignment is compared with theoretical vibrational analysis with the intention to explain the influence of intermolecular interactions in solid phase on the spectroscopic properties of the compound studied. The 1H and ¹³C NMR spectra in solution are compared with the corresponding ones of alanine, studying the amidation effect on the chemical shift signals in the alanine moieties.     

Theoretical anharmonic Raman and infrared spectra with vibrational assignments for monofluoroaniline isomers

The ortho-meta-, and para-fluoro substituted anilines are prototype molecules for investigation of the interactions of both the amino group and the fluorine atom with the aromatic ring. The molecular structures, natural atomic charges and theoretical anharmonic Raman and infrared spectra of the three fluoroaniline isomers have been calculated by using the density functional B3LYP method with the extended 6-311++G(df,pd) basis set. The Raman and infrared spectra of 2FA, 3FA, and 4FA have been recorded. The detailed vibrational assignments of the experimental spectra have been made on the basis of the calculated potential energy distributions, PEDs. The effect of fluorine substituent on the aniline ring geometry and charge distribution, the nature of the characteristic “marker bands” and a quenching of intensities of some bands are discussed. It is shown that the frequencies of the NH₂ stretching vibrations depend on the degree of pyramidalization of the C-NH₂ group, in the isomers. In 2FA and 3FA, the NH₂ stretching frequencies are higher than those in 4FA. This corresponds to a more flattened structure of the amino group in 2FA and 3FA, in comparison to 4FA.     

FT-IR, FT-Raman vibrational spectra and molecular structure investigation of 2-chloro-4-methylaniline: A combined experimental and theoretical study

In this work, the experimental and theoretical vibrational spectra of 2-chloro-4-methylaniline (2Cl4MA, C₇H₈NCl) were studied. FT-IR and FT-Raman spectra of 2Cl4MA in the liquid phase have been recorded in the region 4000–400 cm⁻¹ and 3500–50 cm⁻¹, respectively. The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree-Fock (HF) and density functional method (B3LYP) with the 6-31G(d), 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p) and 6-311G(d), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p) basis sets. The vibrational frequencies have been calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The DFT-B3LYP/6-311++G(d,p) calculations have been found more reliable than the ab initio HF/6-311++G(d,p) calculations for the vibrational study of 2Cl4MA. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of aniline and p-methylaniline molecules.     

Fourier transform infrared and Raman spectra, vibrational assignment and density functional theory calculations of naphthazarin

FT Raman and FTIR spectra of Naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) and its deuterated analogue are recorded. Comparison between the spectra obtained by two techniques, a series of density functional theory (DFT) calculations and the spectral behavior upon deuteration were used for the assignment of the vibrational spectra of this compound. The calculated vibrational frequencies by the B3LYP, B3PW91, G96LYP, G96P86, and MPWLYP density functionals are generally consistent with the observed spectra. Infrared and Raman vibrational transitions predicted by B3LYP/6-311++G** are reported for the titled compound and its deuterated analogous and the assignments are discussed. All experimental and theoretical results support a relatively weak hydrogen bond in naphthazarin (NZ), compared with that in the enol form of normal beta-diketones. The observed nuOH/nuOD and gammaOH/gammaOD appear at about 3060/2220 and 790/560 cm(-1), respectively, which are consistent with the calculated hydrogen bond geometry and proton chemical shift results. Two bands at about 350 and 290 cm(-1) are assigned to the O...O stretching modes belong to A1 and B2 species, respectively.     

Density of vibrational states in trans-polyene: comparison with the infrared,Raman and neutron spectra of trans-polyacetylene

The density of states has been calculated for the in-plane and out-of-plane vibrations in the infinite trans polyene chains. Comparison of the density of states spectra with the IR and Raman spectra of trans-polyacetylenes, (CH)_x, (¹³CH)_x and (CD)_x, shows that most of the weak bands as well as the strong bands arise from the trans polyene segments in the polymer films. The IR bands newly assigned to the trans segments include the 740 cm⁻¹ band, which was previously assigned to remnant cis CC bonds. The IR spectra of (¹³CH)_x and (CD)_x clearly indicate that the amount of remnant cis bonds in thermally isomerized trans films is much smaller than that proposed previously. The hydrogen-amplitude-weighted density of states calculated for the infinite polyene chain also shows satisfactory agreement with a neutron inelastic scattering spectrum of trans-(CH)_x.     

Raman and infrared spectra, ab initio and DFT calculations, and vibrational assignments for 2,3-cyclopentenopyridine

The structural properties of 2,3-cyclopentenopyridine (pyrindan) have been investigated using several spectroscopic and computational techniques. The Raman and infrared spectra of the molecule have been recorded and a full vibrational assignment was proposed on the basis of experimental and theoretical results. The vapor-phase Raman spectrum was successfully obtained at 260 degrees C without sample decomposition. Density functional theory (DFT) and M?ller-Plesset (MP2) calculations predict that the presence of the nitrogen atom in the six-membered ring has almost no effect on the barrier to inversion (587 cm(-1)) and puckering frequency (139 cm(-1)) as compared to the values previously determined (488 cm(-1) and 143 cm(-1)) for the indan molecule.     

Raman and infrared spectra of6Li2C2O4 and7Li2C2O4

Raman and infrared spectra of polycrystalline⁶Li₂C₂O₄ and⁷Li₂C₂O₄ have been investigated in the wavenumber region from 1,800 to 40 cm^–1. The internal C₂O₄ ^–2 vibrations have been studied on the basis of a D_2h molecular structure and the correlation field splittings have been found to be about 40 cm^–1 for the stretching modes and about 15 cm^–1 for the bending modes. The external vibrations of the Li⁺ and C₂O₄ ^–2 sites have been discussed by considering the results of the factor group analysis and the⁶Li/⁷Li isotope effect on the normal vibrations.

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Raman- und Infrarot-Spektren von⁶Li₂C₂O₄ und⁷Li₂C₂O₄

Zusammenfassung Es wurdenRaman- und IR-Spektren von polykristallinem⁶Li₂C₂O₄ und⁷Li₂C₂O₄ im Bereich der Wellenzahlen von 1800 bis 40 cm^–1 untersucht. Die internen Schwingungen wurden auf der Basis einer D_2h Molekülstruktur analysiert. Für die Streckschwingungen wurde eine Korrelationsaufspaltung von etwa 40 cm^–1 gefunden, für die Deformationsschwingungen etwa 15 cm^–1. Die Diskussion der externen Schwingungen von Li⁺ und C₂O₄ ^–2 erfolgte unter Berücksichtigung der Resultate der Faktorgruppenanalyse und des⁶Li/⁷Li Isotopeneffekts auf die Normalschwingungen.

     

Far infrared spectra,vibrational assignment and normal coordinate analysis of the tricyanomethanideion

Far infrared spectra of the tricyanomethanide ion C(CN)₃^? in solution and in the solid state have been investigated. The results allow a complete vibrational assignment to be made. A normal coordinate analysis has been carried out, the results of which are compatible with the existence of some double bond character in the C-C bonds of C(CN)₃^?.     

Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignments for 2-chloroethyl silane

The infrared (3500–30 cm⁻¹) spectra of gaseous and solid and the Raman (3500–10 cm⁻¹) spectra of liquid with quantitative depolarization ratios and solid 2-chloroethyl silane, ClCH₂CH₂SiH₃, have been recorded. Similar data have been recorded for the Si–d₃ isotopomer. These data indicate that two conformers, trans and gauche, are present in the fluid states but only one conformer, trans, is present in the solid. The mid-infrared spectra of the sample dissolved in liquified xenon as a function of temperature (−55 to −100°C) has been recorded. The enthalpy difference between the conformers has been determined to be 181±12 cm⁻¹ (2.17±0.14 kJ/mol) with the trans rotamer the more stable form. From the isolated Si–H frequencies from the Si–d₂ isotopomer the r_o Si–H distances of 1.484 and 1.483 Å for the trans and 1.481 for the gauche conformers have been obtained. Ab initio calculations have been carried out with several different basis sets up to MP2/6-311+G** from which structural parameters and conformational stabilities have been determined. With all the basis sets the trans form is predicted to be the more stable conformer which is consistent with the experimental results. These results are compared to the corresponding quantities for the carbon analogue.     

An experimental and theoretical study of vibrational spectra of picolinamide, nicotinamide, and isonicotinamide

The molecular structures and vibrational spectra of the three isomers of pyridinecarboxamide (picolinamide, nicotinamide, isonicotinamide) were calculated with the Density Functional Theory (DFT) method using the B3LYP function and the 6-31++G(d,p), Z2PolX, Z3PolX basis sets. The calculations were performed by using the Gaussian98W packet program set. The total energy distributions (TED) of the vibrational modes of these molecules were calculated by using the Scale 2.0 program and the vibrational modes of the molecules were determined. The Scaled Quantum Mechanical (SQM) method was used in the scaling procedure. In the experimental part of the study, the solid phase FT-IR and Micro Raman spectra of the three isomers of pyridinecarboxamide have been recorded in the range of 4000-650 and 1200-100 cm⁻¹, respectively. The calculated wavenumbers were compared to the corresponding experimental values. As a result, the observed bands of the three isomers of pyridinecarboxamide were assigned with good accuracy.     

A theoretical study on the ionization of tetrafluoroethylene with analysis of vibrational structure of the photoelectron spectra

Ab initio calculations have been performed to study on the molecular structures and the vibrational levels of the low-lying ionic states (²B_2u,²A_g,²B_2g,²B_3u,²A_u,²B_1g,²B_1u, and²B_3g) of tetrafluoroethylene. The equilibrium molecular structures and vibrational modes of these states are presented. The theoretical ionization intensity curves including the vibrational structures of the low-lying eight ionic states are also presented and compared with the photoelectron spectrum. Some new assignments of the photoelectron spectra are proposed.     

A theoretical study on the ionization of furan with analysis of vibrational structure of the photoelectron spectra

Summary Ab initio calculations have been performed to study on the molecular structures and the vibrational levels of the low-lying ionic states (²A₂ and²B₁) of furan. The equilibrium molecular structures and vibrational modes of these states are presented. The theoretical ionization intensity curves including the vibrational structures of the low-lying two ionic states are also presented and compared with the photoelectron spectrum. A number of new assignments of the photoelectron spectra are proposed.     

Raman,resonance Raman and infrared spectra of potassium uranyl croconate

The Raman, resonance Raman and IR spectra of potassium uranyl croconate, UO₂(H₂O)K₂(C₅O₅)₂ were obtained and interpreted. Several croconate modes are split indicating a substantial decrease in the oxocarbon symmetry, as is to be expected from a recent crystallographic investigation, revealing the coordination of the oxocarbon to be two non-equivalent UO²⁺₂ moieties in a monodentate fashion. In terms of vibrational frequency shifts it can be concluded that the UO²⁺₂ moiety behaves as an isolated oscillator.The resonance Raman results suggest that the strong band centered around 450 nm in the UV—vis spectrum should be assigned to a charge transfer transition from the oxocarbon to the uranyl ion. In fact, as resonance is approached, both uranyl and croconate modes are enhanced. It can also be inferred that the chromophore is rather delocalized into the oxocarbon ring, rather than localized in the carbonyl groups as previously observed for other croconate complexes.