Microscopic Investigation of Ethylene Carbonate Interface: A Molecular Dynamics and Vibrational Spectroscopic Study

Ethylene carbonate(EC) liquid and its vapor-liquid interface were investigated using a combination of molecular dynamics(MD)simulation and vibrational IR, Raman and sum frequency generation(SFG)spectroscopies. The MD simulation was performed with a flexible and polarizable model of the EC molecule newly developed for the computation of vibrational spectra. The internal vibration of the model was described on the basis of the harmonic couplings of vibrational modes, including the anharmonicity and Fermi resonance coupling of C=O stretching. The polarizable model was represented by the charge response kernel(CRK),which is based on ab initio molecular orbital calculations and can be readily applied to other systems. The flexible and polarizable model can also accurately reproduce the structural and thermodynamic properties of EC liquid. Meanwhile, a comprehensive set of vibrational spectra of EC liquid, including the IR and Raman spectra of the bulk liquid as well as the SFG spectra of the liquid interface, were experimentally measured and reported. The set of experimental vibrational spectra provided valuable information for validating the model, and the MD simulation using the model comprehensively elucidates the observed vibrational IR, Raman, and SFG spectra of EC liquid. Further MD analysis of the interface region revealed that EC molecules tend to orientate themselves with the C=O bond parallel to the interface. The MD simulation explains the positive Im[χ~((2))](ssp) band of the C=O stretching region in the SFG spectrum in terms of the preferential orientation of EC molecules at the interface. This work also elucidates the distinct lineshapes of the C=O stretching band in the IR, Raman, and SFG spectra. The lineshapes of the C=O band are split by the Fermi resonance of the C=O fundamental and the overtone of skeletal stretching. The Fermi resonance of C=O stretching was fully analyzed using the empirical potential parameter shift analysis(EPSA) method. The apparently different lineshapes of the C=O stretching band in the IR, Raman, and SFG spectra were attributed to the frequency shift of the C=O fundamental in different solvation environments in the bulk liquid and at the interface. This work proposes a systematic procedure for investigating the interface structure and SFG spectra, including general modeling procedure based on ab initio calculations, validation of the model using available experimental data, and simultaneous analysis of molecular orientation and SFG spectra through MD trajectories. The proposed procedure provides microscopic information on the EC interface in this study, and can be further applied to investigate other interface systems, such as liquid-liquid and solid-liquid interfaces.     

Optical Characterization of 4H-,6H- and 15R-SiC Crystals

The optical absorption of 4H-,6H-and 15R-SiC single crystals has been measured at room temperature. The band gaps were calculated,and the reasons for band gap shrinking were discussed. Influence of free carrier concentration was considered. The first-and second-order Raman spectra of 4H-,6H- and 15R-SiC samples were analyzed. Raman spectra of disorder structure in 6H-SiC grown by Lely method were given and simulated. The low wave-number Raman spectrum is a reliable method to distinguish the SiC polytypes. We analyzed the similarity of the second-order Raman spectra of all polytypes.     

Ab Initio Calculations on Nitramide and Its Methyl Derivatives( Ⅱ )——The Harmonic Force Fields and Vibrational Spectra of Nitramide and Its Isotopic Derivatives

The harmonic force field and the vibrational spectrum of nitramide were calculated by using the ab initio gradient program TEXAS at the Hartree-Fock level with a 4-21G basis set. The directly computed theoretical harmonic force field was scaled by using empirical scale factors which are transferred from other molecules and provided an a priori prediction of fundamental frequencies and intensities. The average deviations between predicted vibrational frequencies of nitramide and experimental IR spectrum in an argon matrix are 63 cm-1 for symmetric vibrations and 41 cm-1 for antisymmetric modes. A new set of scale factors was optimized in this paper. These scale factors reduced the average deviations to 2. 3 cm-1 for symmetric modes and 0. 8 cm-1 for antisymmetric ones. The vibrational spectra of three isotopic derivatives of nitramide were predicted by using the force field resulted from the optimized set of scale factors, which are in good agreement with their experimental data in an argon matrix.     

Theoretical Study on the High Energy Density Compound Hexanitrohexaazatricyclotetradecanedifuroxan

Density functional theory （DFT） has been employed to study the molecular geometries, electronic structures, infrared （IR） spectra, and thermodynamic properties of the high energy density compound hexanitrohexaazatricyclotetradecanedifuroxan （HHTTD） at the B3LYP/6-31G^＊＊ level of theory. The calculated results show that there are four conformational isomers （α, β, γ and δ） for HHTTD, and the relative stabilities of four conformers were assessed based on the calculated total energies and the energy-gaps between the frontier molecular orbitals. The computed harmonic vibrational frequencies are in reasonable agreement with the available experimental data. Thermodynamic properties derived from the IR spectra on the basis of statistical thermodynamic principles are linearly correlated with the temperature. Detonation performances were evaluated by using the Kamlet-Jacobs equations based on the calculated densities and heats of formation. It was found that four HHTTD isomers with the predicted densities of ca. 2 g·cm^-3, detonation velocities near 10 km·s^-1, and detonation pressures over 45 GPa, may be novel potential candidates of high energy density materials （HEDM）. These results may provide basic information for the molecular design of HEDM.     

A Dodecahedrane-like Molecule C_（12）H_（12）B_8 with Uncommon T_h Symmetry

The molecule with Th symmetry is rare.A dodecahedrane-like molecule C12H12B8 with uncommon Th symmetry has been reported here.Density functional calculations and minimization techniques have been employed to characterize its structural and electronic properties.Its geometry,electronic properties,vibrational frequencies and heat of formation have been calculated at the B3LYP/6-311+G(d,p) level of theory.The absence of imaginary vibrational frequency confirms that it corresponds to true minimum on the potential energy hypersurface.Its vibrational bands in the IR intensity have been discussed and compared with future experimental identification.At the B3LYP/6-311+G(d,p) level,the heat of formation has been calculated to be 720.9 kJ mol-1 using the isodesmic reaction.According to this value,it is a potential high energy density molecule.     

Vibrational frequencies of hydrazoic acid and methyl azide: density functional theory study

Harmonic vibrational frequencies of HN3 and CH3N3 molecules and their several isotopomers are calculated using HF, MP2 and five popular density functional theory (DFT) methods. On the basis of the comparison between calculated and experimental results, assignments of fundamental vibrational modes arc examined. HF and MP2 results are in bad agreement with experimental values. Of the five DFT methods, BLYP reproduces the observed fundamental frequencies the most satisfactorily. Two hybrid DFT methods are found to yield frequencies generally higher than the observed fundamental frequencies. The results indicate that BLYP calculation is a very promising approach for understanding the observed spectral features.     

ab initio calculation study on vibrational spectra of C_2B_(10)H_(12),NB_(11)H_(12) and C_2B_(10)H_(11)Cl

Geometrical optimization and theoretical calculation of the vibrational frequencies have been performed for C2B10H12, NB11H12 and C2B10Cl by using Gaussian 92 program at 6-31G basis set. The results obtained in this work are in agreement with experimental ones. The optimized geometry and vibrational spectra show that the icosahedral configuration remains unchanged upon converting from B12H122- to the title compounds. The vibrational spectrum of C2B10H11Cl features the absence of C-Cl stretching vibration. But the (C2B10H11)-Cl vibration mode in the low frequency region is as the case for two-atom molecules if the group (C2B10H11) is considered as a pseudoatom     

NMR Parameters and Vibrational Investigation of 2-Dicyanovinyl-5-（4-ethoxyphenyl） thiophene by ab initio HF and DFT Calculations

Optimized geometry and harmonic vibrational frequency of 2-dicyanovinyl-5-(4- ethoxyphenyl)thiophene (C16H12N2OS) are calculated at the HF/6-31++G(d,p) and B3LYP/6- 311++G(d,p) levels. Mulliken charges in the ground state are also calculated. The research shows the presence of intermolecular interaction in the title compound. The scaled harmonic vibrational frequencies have been compared with experimental FT-IR spectra. A detailed interpretation of the infrared spectra of the title compound is reported. The theoretical spectrograms for IR spectra of the title compound have been constructed. The isotropic chemical shift computed by 13C and 1H NMR analyses also shows good agreement with the experimental observations.     

锂、钠、镁的乙酰丙酮配合物的核磁共振碳谱理论计算

In this paper, the geometric configurations of lithium、sodium and magnesium coordination compounds with acetylacetone were optimized with density functional B3LYP method of quantum chemistry at the bigger basis sets 6-31++G(d, p), vibrational analyses were made and there were not imaginary frequencies. Their ¹³C NMR spectra were calculated at the same basis sets with GIAO method. The results of calculation are essentially consistent with experimental values.     

Synthesis and Infrared Spectra Computation of Sterically Congested 2,2-Disubstituted Indane-1,3-dione Derivatives

Sterically congested 2,2-disubstituted indane-1,3-dione derivatives have been syn-thesized and characterized by 1H NMR,13C NMR,FT-IR and elemental analysis.The B3LYP/HF calculations for computation of IR spectra have been carried out for the title compounds at the 6-31G and 6-311++G basis set levels.Predicted vibrational frequencies have been assigned and compared with the experimental FT-IR spectra and they are supported each other.     

Surface enhanced Raman spectra of nucleic acid components adsorbed at a silver electrode

High-resolution vibrational spectra of nucleic acid components adsorbed on a silver electrode were obtained using a spectroelectrochemical method based on the large-intensity enhancement for Raman scattering at electrode surfaces.The laser surface Raman spectra of purine, adenine, adenosine, deoxyadenosine, adenine mononucleotides, adenylyl-3′, 5′-adenosine and polyriboadenylic acid were recorded in the range of 150–3500 cm^?1. The intensities of the vibrational bands were highly dependent upon the electrochemical preparation of the electrode, the applied potential and the nature of the adsorbate species. High-intensity spectra in rather dilute bulk solutions were obtained.The phosphate derivatives of adenosine exhibited strongly enhanced Raman scattering. Spectral band frequencies corresponded closely with normal Raman spectra of these molecules in solution. The adenine ring breathing mode at 740 cm^?1 and the adenine ring skeletal vibration at 1335 cm^?1 produced prominent Raman scattering. A strong band at about 240 cm^?1 for the adenine mononucleotides was attributed to silver/adsorbed phosphate group vibrations.     

FOURIER TRANSFORM INFRARED SPECTRAL STUDIES ON THE SCHIFF BASE MODE OF ALL-trans BACTERIORHODOPSIN and ITS PHOTOINTERMEDIATES,K and L*

Abstract– Difference Fourier transform infrared spectra were recorded for bacteriorhodopsin upon irradiation at 230, 170 or 77 K, which gave, respectively, the spectrum of the M, L or K intermediate minus unphotolyzed all-trans bacteriorhodopsin (denoted as BR). By replacement of the Schiff base nitrogen with ¹⁵N, or of either its hydrogen at N or C₁₅ with deuterium, the vibrational bands related to the Schiff base were identified and the isotope-shifts evaluated for BR, K and L. The 1348 cm^?l band of BR and K and the 1400 cm^?1 band of L were sensitive to each of these isotope substitutions. The 1254 cm^?1 band of BR, the 1245 cm^?1 band of K and the 1301 cm^?1 band of L were sensitive to either N- or C₁₅-deuteration but not to ¹⁵N-substitution. The N—D in-plane bending vibration of K and L appeared at 969 and 997 cm^?1, respectively, upon substitution with D₂O. All the results show that L is larger in frequencies related to the N—H in-plane bending vibration than K or BR and suggest that L has the strongest interaction with the protein. Among the bands containing an N—H bending vibration, the 1348 cm^?1 band of K was more intense than the corresponding band of L at 1400 cm^?1. The C₁₅-deuteration-induced upshift of the 1245 cm^?1 band of K was unobservable for the 1301 cm^?1 band of L. Such differences between L and K might be brought about by a distortion in the retinal moiety close to the protonated Schiff base of the 13-cis chromophore.     

Vibrational spectra of mixed (phthalocyaninato)(porphyrinato) yttrium(III) double-decker complexes: Density functional theory calculations

The vibrational (IR and Raman) spectra of neutral and reduced mixed (phthalocyaninato)(porphyrinato) yttrium(III) double-decker complexes Y(Pc)(Por) and [Y(Pc)(Por)]⁻ [the simplified models of mixed (phthalocyaninato)(porphyrinato) rare earth(III) complexes] are studied using density functional theory (DFT) calculations. The simulated IR and Raman spectra of Y(Pc)(Por) are compared with the experimental IR spectrum of Tb(Pc)(TClPP) and Raman spectrum of Y(Pc)(TClPP), respectively, and many bands can acceptably fit in spite of the different species. On the basis of comparison with the simulated spectra of PbPc and PbPor together with the assistance of normal coordinate analysis, the calculated frequencies in their IR and Raman spectra are identified in terms of the vibrational mode of different ligand for the first time. The calculated frequency at 1048 cm⁻¹ in the IR spectrum of [Y(Pc)(Por)]⁻ with contribution from both Pc and Por vibrational modes is the characteristic IR vibrational mode of the reduced double-decker, while the characteristic IR vibrational mode of Y(Pc)(Por) attributed from the vibration of phthalocyanine monoanion radical Pc⁻ appears at 1257 cm⁻¹. In line with our previous experimental findings that the Raman spectra of M(Pc)(TPP) and M(Pc)(TClPP) are dominated by the Pc vibrational modes, theoretical calculations indicate that most of the Raman vibrational modes contributed from Por ring are covered up by those of Pc ring and thus are hard to be recognized in the Raman spectra of [Y(Pc)(Por)]⁻ and Y(Pc)(Por) due to their much weaker intensity in comparison with that of Pc ligand. Comparison in the IR and Raman spectra between [Y(Pc)(Por)]⁻ and Y(Pc)(Por) also suggests the localization of hole on the Pc ring in the neutral double-decker Y(Pc)(Por). The present work, representing the first detailed DFT study on the vibrational spectra of mixed (phthalocyaninato)(porphyrinato) rare earth(III) double-decker complexes, is useful in helping to understand the vibrational spectroscopic properties of this series of mixed tetrapyrrole ring complexes.     

CN stretching and NO2 deformation vibrations and normal coordinate analysis of m-dinitrobenzene and m-dinitrobenzene-d4

Two bands appear for each CN stretching and nitro deformation vibration in the infrared and Raman spectra of m-dinitrobenzene and m-dinitrobenzene-d₄. The 907 cm^?1 bending mode in the vibrational spectra of m-dinitrobenzene undergo 30 cm^?1 upward shift upon d₄ substitution. A normal coordinate analysis pointed out that the 937 cm^?1 bending and 727 cm^?1 CN stretching vibrations as well as 18b CD in-plane deformation are mixed to a great extent. The other nitro bending mode undergo also an inverse isotopic effect (2 cm^?1 upward shift) due to coupling with the 18a CD in-plane deformation vibration.     

Some 1-substituted quaternary imidazolium compounds and related polymers: Qualitative and quantitative infrared analysis

It was found that 1-substituted quaternary imidazolium compounds show some characteristic infrared (IR) activity. On quarternization of 1-substituted imidazoles strong absorption bands appeared at about 1150 and 1550 cm^?1 in the IR spectra of these compounds. The band at 1150 cm^?1 was assigned to the position 2 C?H bending mode and the 1550 cm^?1 band was attributed to a ring vibration mode of the quaternary imidazolium compounds. The concentration of the quaternary imidazolium units in a polymer can be determined by measuring the intensity of the absorption bands at 1150 or 1550 cm^?1 in relation to another suitable absorption band of the spectrum.     

Vibrational spectra and noncovalent interactions of carbohydrates molecules

The differences between the vibrational spectra of carbohydrates of the same chemical structure caused by the noncovalent intra- and intermolecular interactions have been systematized. In the general case, these differences show up as the following specific features of changes in the bond intensities: change in the intensity ratio of closely spaced bands (IR and Raman spectra); selective change (increase, decrease) in intensities of individual bands (IR and Raman spectra); change (increase, decrease) in intensities of practically all bands (IR and Raman spectra); appearance of strong bands in the region of low frequencies from 50 to 200 cm⁻¹ (Raman spectra); appearance of strong diffuse bands in the low-frequency range with a simultaneous great reduction in the other bands (practical disappearance of the majority of bands) (Raman Spectra). The causes of such a kind of changes in the band intensities in the vibrational spectra of carbohydrates are discussed.     

Infrared and Raman spectroscopic characterization of the phosphate mineral kosnarite KZr2(PO4)3 in comparison with other pegmatitic phosphates

In this research, we have used vibrational spectroscopy to study the phosphate mineral kosnarite KZr₂(PO₄)₃. Interest in this mineral rests with the ability of zirconium phosphates (ZP) to lock in radioactive elements. ZP have the capacity to concentrate and immobilize the actinide fraction of radioactive phases in homogeneous zirconium phosphate phases. The Raman spectrum of kosnarite is characterized by a very intense band at 1,026?cm^?1 assigned to the symmetric stretching vibration of the PO₄ ^3? ??₁ symmetric stretching vibration. The series of bands at 561, 595 and 638?cm^?1 are assigned to the ??₄ out-of-plane bending modes of the PO₄ ^3? units. The intense band at 437?cm^?1 with other bands of lower wavenumber at 387, 405 and 421?cm^?1 is assigned to the ??₂ in-plane bending modes of the PO₄ ^3? units. The number of bands in the antisymmetric stretching region supports the concept that the symmetry of the phosphate anion in the kosnarite structure is preserved. The width of the infrared spectral profile and its complexity in contrast to the well-resolved Raman spectrum show that the pegmatitic phosphates are better studied with Raman spectroscopy.     

Vibrational spectra and reinvestigation of the crystal structure of a polymeric copper(II)-orotate complex, [Cu(μ-HOr)(H2O)2]n: The performance of new DFT methods, M06 and M05-2X, in theoretical studies

The crystal and molecular structure of a polymeric Cu(II)-orotate complex, [Cu(μ-HOr)(H₂O)₂]_n, has been reinvestigated by single crystal X-ray diffraction. It is shown that several synergistic interactions: two axial Cu-O interactions; intramolecular and intermolecular hydrogen bonds; and π-π stacking between the uracil rings contribute to the stability of the crystal structure. The Raman and FT-IR spectra of the title complex are reported for the first time. Comprehensive theoretical studies have been performed by using three unrestricted DFT methods: B3LYP; and the recently developed M06, and M05-2X density functionals. Clear-cut assignments of all the bands in the vibrational spectra have been made on the basis of the calculated potential energy distribution, PED. The very strong Raman band at 1219 cm⁻¹ is diagnostic for the N1-deprotonation of the uracil ring and formation of the copper-nitrogen bond, in this complex. The Cu-O (carboxylate) stretching vibration is observed at 287 cm⁻¹ in the IR spectrum, while the Cu-N (U ring) stretching vibration is assigned to the strong Raman band at 263 cm⁻¹. The molecular structure and vibrational spectra (frequencies and intensities) calculated by the M06 functional method are very similar to the results obtained by the B3LYP method, but M06 performs better than B3LYP in calculations of the geometrical parameters and vibrational frequencies of the interligand O-H?O hydrogen bonding. Unfortunately, the M05-2X method seriously overestimates the strength of interligand hydrogen bond.     

DFT and Raman spectroscopy of porphyrin derivatives: Tetraphenylporphine (TPP)

Raman spectrum of the meso tetraphenylporphine (TPP) deposited onto smooth copper surface as thin film were recorded in the region 200–1700 cm⁻¹. To investigate the effect of meso-phenyl substitution rings on the vibrational spectrum of free base porphyrin, we calculated Raman and infrared (IR) spectra of the meso-tetraphenylporphine (TPP), meso tetramethylporphine (TMP), copper (II)porphine (CuPr) and free base porphine (FBP) at the B3LYP/6-311+G(d,p) level of the density functional theory (DFT). The observed Raman spectrum of the TPP is assigned based on the calculated its Raman spectrum in connection with the calculated spectra of the TMP, CuPr and FBP by taking into account of their corresponding vibrational motions of the Raman modes of frequencies. Results of the calculations clearly indicated that the meso tetraphenyl substitution rings are totally responsible for the observed Raman bands at ∼1593, 1234 and 1002 cm⁻¹. The calculated and observed Raman spectra also suggested that the observed Raman band with a medium intense at 962 cm⁻¹ might result from the surface plasmon effect. Furthermore, the observed Raman bands with medium intense at ∼334 and ∼201 cm⁻¹ are as results of the dimerization or aggregation of the TPP or would be that related to intramolecular interaction. We also calculated IR spectra of these molecules at same level of the theory. To investigate the solvent effect on the vibrational spectrum of porphine, the Raman and IR spectra of the TPP and FBP are calculated in solution phase where water used as solvent. The results of these calculation indicated that there is no any significant effect on the vibrational spectrum of the TPP.     

Neutron inelastic scattering spectra of strongly hydrogen bonded acid oxalates NaHC2O4, KHC2O4 and LiHC2O4

Neutron inelastic scattering spectra of NaHC₂O₄, KHC₂O₄ crystals at 80 K have been recorded in the 2200-200 cm^?1 range. The lithium acid salt was also studied at different temperatures. NIS spectra are compared to the corresponding infrared and Raman spectra and an assignment is proposed. Two strong bands near 1500 and 1100 cm^?1 are assigned to δ(OH) and γ(OH) vibrations, respectively, while five weak bands below 900 cm^?1 are associated with skeletal modes, mainly bending vibrations. The OH stretching vibration is not observed and is believed to be hidden by other bands; the peak intensity must be low because of its band width which is of the order of a few hundreds wavenumbers.