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1.
Ab initio simulation of the IR spectra of pyrope, grossular, and andradite   总被引:1,自引:0,他引:1  
IR spectra of pyrope Mg(3)Al(2)Si(3)O(12), grossular Ca(3)Al(2)Si(3)O(12) and andradite Ca(3)Fe(2)Si(3)O(12) garnets were simulated with the periodic ab initio CRYSTAL code by adopting an all-electron Gaussian-type basis set and the B3LYP Hamiltonian. Two sets of 17 F(1u) Transverse Optical (TO) and Longitudinal Optical (LO) frequencies were generated, together with their intensities. Because the generation of LO modes requires knowledge of the high frequency dielectric constant epsilon(infinity) and Born effective charges, they were preliminary evaluated by using a finite field saw-tooth model and well localized Wannier functions, respectively. As a by-product, the static dielectric constant epsilon(0) was also obtained. The agreement of the present calculated wavenumbers (i.e. peak positions) with the available experimental data is excellent, in that the mean absolute difference for the full set of data smaller than 8 cm(-1). Missing peaks in experimental spectra were found to correspond to modes with low calculated intensities. Correspondence between TO and LO modes was established on the basis of the overlap between the eigenvectors of the two sets and similarity of isotopic shifts; as result, the so called LO-TO splitting could be determined. Animation of the normal modes was employed to support the proposed pairing.  相似文献   

2.
The splitting of the ν(C=O) absorption band (AB) of about 12 cm−1 is found in the IR spectra of diphenylphthalide (DPP) in the crystalline phase and CCl4 solution. In the crystalline phase, this splitting is likely to be caused by the inequivalence of DPP molecules in the crystallographic cell, while in the solution, by the dimerization of DPP molecules via dipole-dipole and/or hydrogen bonds. A theoretical low-frequency shift of the ν(C=O) AB for a complex of two DPP molecules (in comparison with a single molecule) is 14 cm−1 in the PBE/3ξ approximation, which is close to the experimentally observed splitting. In two quantum chemical approximations (B3LYP/6-311G(d,p) (I) and PBE/3ξ (II)) the optimal structure and vibrational spectrum of DPP are calculated. Approximation I better reproduces the intensities, whereas approximation II better reproduces the IR frequencies of the DPP spectrum. Almost all 48 ABs of the IR spectrum of DPP are assigned to theoretical normal vibrations (modes). Based on the potential energy distribution over natural coordinates and the visualization of vibrations, experimental ABs (and the corresponding modes) are assigned to the stretching and bending vibrations of certain bonds in the DPP molecule. In particular, ABs at 1107 cm−1 and 970 cm−1 are assigned to the ν(-OC-O-) and ν(-C-O-) stretching vibrations, respectively, of the DPP lactonic ring, which differs from the previously accepted assignment. The results of the interpretation of the DPP spectrum are used to assign a number of ABs in the IR spectrum of polydiphenylenephthalide (PDP), for which DPP is a model compound. According to the calculations in approximation II of the vibrational spectrum of a model valence-bonded dimeric molecule, the intense complex AB at 800–870 cm−1 in the IR spectrum of PDP is mainly due to the out-of-plane bending vibrations of C-H bonds in the 1,4-substituted benzene rings of polymer biphenyl moieties and the bending vibrations of the lactonic ring.  相似文献   

3.
The equilibrium structural parameters, high‐ and low‐frequency dielectric tensors, Born effective charges, and Γ‐point vibrational frequencies of bulk Al2O3 corundum are calculated by using the periodic, ab initio program CRYSTAL, which adopts an all‐electron Gaussian‐type basis set. The effect of basis set and the performance of three different functionals, i.e., LDA, PW91, and B3LYP, are discussed. The mean absolute deviation from the measured frequencies is as small as 7 cm?1 for both the LDA and B3LYP functionals, indicating that these functionals perform extremely well in this case. The mean absolute deviation increases to 18 cm?1 when the PW91 functional is used. All three functionals reproduce the equilibrium geometry of corundum to a high level of accuracy, with LDA and B3LYP outperforming PW91 slightly. The comparison of the current all‐electron calculations with previous plane‐wave, pseudo‐potential calculations shows an overall similar performance. The results of isotopic substitution for both Al and O are also presented. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006  相似文献   

4.
The antimalarial agent mefloquine was investigated using Fourier transform near-infrared (FT NIR) Raman and FT IR spectroscopy. The IR and Raman spectra were calculated with the help of density functional theory (DFT) and a very good agreement with the experimental spectra was achieved. These DFT calculations were applied to unambiguously assign the prominent features in the experimental vibrational spectra. The calculation of the potential energy distribution (PED) and the atomic displacements provide further valuable insight into the molecular vibrations. The most prominent NIR Raman bands at 1,363 cm−1 and 1,434 cm−1 are due to C=C stretching (in the quinoline part of mefloquine) and CH2 wagging vibrations, while the most intense IR peaks at 1,314 cm−1; 1,147 cm−1; and 1,109 cm−1 mainly consist of ring breathings and δCH (quinoline); C–F stretchings; and asymmetric ring breathings, C–O stretching as well as CH2 twisting/rockings located at the piperidine moiety. Since the active agent (mefloquine) is usually present in very low concentrations within the biological samples, UV resonance Raman spectra of physiological solutions of mefloquine were recorded. By employing the detailed non-resonant mode assignment it was also possible to unambiguously identify the resonantly enhanced modes at 1,619 cm−1, 1,603 cm−1 and 1,586 cm−1 in the UV Raman spectra as high symmetric C=C stretching vibrations in the quinoline part of mefloquine. These spectroscopic results are important for the interpretation of upcoming in vitro and in vivo mefloquine target interaction experiments.  相似文献   

5.
This paper reports on a computer simulation of the vibrational spectra of C59B, C59N, C59BN, and C59HN. The modes whose frequencies are most sensitive to carbon substitution by heteroatoms are revealed. It is shown that the new bands at 818, 839, and 845 cm−1 in the experimental IR spectrum of C59HN arise from changes in selection rules and by removal of degeneracies due to a reduction in the symmetry of the molecule and force field perturbation. In the Raman spectrum of C59HN, the shifts of the 1460 and 491 cm−1 bands to the low-frequency region by 7 and 3 cm−1, respectively, relative to two Ag modes of C60 are explained by the perturbation induced by the N and C(H) atoms in the force field of adjacent CC bonds not containing these atoms. Institute of Spectroscopy, Russian Academy of Sciences (Troitsk, Moscow Region). Scientific and Production Association “Complex.” Scientific and Production Association “Tekhon.” Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 401–411, May–June, 1998.  相似文献   

6.
An industrial raw material taken from Sivrihisar (Eskişehir, Turkey) region was heat-treated at different temperatures in the range of 100–1000°C for 2 h. The volumetric percentage of the particles having a diameter below 2 μm after staying in an aqueous suspension of the material was determined as 67% by the particle size distribution analysis. The mineralogical composition of the material was obtained as mass% of 32% palygorskite, 10% metahalloysite, 35% magnesite, 20% dolomite and 3% interparticle water by using the acid treatment, X-ray diffraction and thermal analysis (TG, DTA) data. The temperature ranges were determined for the endothermic dehydrations for the interparticle water as 25–140°C, for the zeolitic water as 140–320°C, and for the bound water as 320–480°C, in the palygorskite. The temperature range for the endothermic dehydroxylation and exothermic recrystalization of the palygorskite is 780–840°C. The temperature range for the endothermic dehydroxylation of the metahalloysite and calcinations of magnesite are coincided at 480–600°C. Dolomite calcined in the temperature range of 600–1000°C by two steps. The zig-zag changes in the specific surface area (S/m2 g−1) and specific micro and mesopore volume (V/cm3 g−1) as the temperature increases were discussed according to the dehydrations in the palygorkskite, dehydroxylation of palygorskite and metahalloysite, and calcinations in magnesite and dolomite.  相似文献   

7.
Near-infrared (NIR) and IR spectroscopy have been applied for the characterisation of three complex Cu–Zn sulphate/phosphate minerals, namely ktenasite, orthoserpierite and kipushite. The spectral signatures of the three minerals are quite distinct in relation to their composition and structure. The effect of structural cation substitution (Zn2+ and Cu2+) on band shifts is significant both in the electronic and in the vibrational spectra of these Cu–Zn minerals. The variable Cu:Zn ratio between Zn-rich and Cu-rich compositions shows a strong effect on Cu(II) bands in the electronic spectra. The Cu(II) spectrum is most significant in kipushite (Cu-rich) with bands displayed at high wavenumbers, 11,390 and 7,545 cm−1. The isomorphic substitution of Cu2+ for Zn2+ is reflected in the NIR and IR spectroscopic signatures. The multiple bands for ν3 and ν4 (SO4)2− stretching vibrations in ktenasite and orthoserpierite are attributed to the reduction in symmetry of the sulphate ion from Td to C2V. The IR spectrum of kipushite is characterised by strong (PO4)3− vibrational modes at 1,090 and 990 cm−1. The range of IR absorption is higher in ktenasite than in kipushite, while it is intermediate in orthoserpierite.  相似文献   

8.
Spectra of coincidence of CH3F IR absorption with CO2-laser emission at pressures of 2, 10 and 60 Torr were recorded by the use of a photoacoustic detection method in the whole range of CO2-laser emission. The spectra show that CH3F absorbs many CO2-laser lines in the range 1084–1071 cm−1 with the strongest absorption at 1046.80cm−1, laser line P(20). Absorption is predominantly due to the fundamental of v3, which is well spread over the whole laser emission range. The intensities of all absorptions rise with increasing pressure, but some absorptions change their relative intensity with respect to one another. In addition, the fine structure of the line spectrum, characteristic of lower pressure samples, disappears as pressure is increased.  相似文献   

9.
Spectra of coincidence of SO2 IR absorption with CO2-laser emission at pressure of 50,100 and 450 Torr were recorded by the use of a photoacoustic detection method in the whole range of CO2-laser emission. The spectra show that SO2 absorbs many CO2-laser lines in the range 1084–1071 cm−1 with the strongest absorption at 1082.29cm−1, laser line R(26). The intensities of all absorptions rise with increasing pressure, but some absorptions change their relative intensity with respect to one another. In addition, the fine structure of line spectra, characteristic of lower pressure samples, disappear as pressure is increased.  相似文献   

10.
The interactions of a 6O2 + (H2O)50 system with two, four, or six Cl ions are studied by the molecular dynamics method. The integral intensity of IR and Raman spectra decreases with an increase in the number of Cl ions surrounding the system. The values of real and imaginary parts of dielectric permittivity increase with the rise in the frequency reaching maxima in the 850 ≤ ω ≤ 950 cm−1. As a result of interactions between ions and the formed (O2)6 (H2O)50 cluster, the pattern of the reflection spectrum of IR radiation becomes smoother. The interaction between 6O2 + (H2O)50 system and Cl ions leads to the substantial increase in the power of emitted radiation. With time, Cl ions gradually leave the interaction zone with the system. Maximum residence time of the last ion near the system boundary does not exceed 3 ps. Cl ions located closer to O2 molecules do not penetrate into the depth of an (O2)6 (H2O)50 cluster.  相似文献   

11.
s-trans, s-cis and gauche conformers of 1,3-butadiene have been studied using density functional theory and the coupled-cluster method using double substitutions (CCD). Matrix isolation Raman and IR data for the minor conformer were obtained and are used in combination with the theoretical results to resolve earlier ambiguities in vibrational assignments. Based on high-quality Hessians, new harmonic stretching force constants are reported for the carbon backbone of s-trans-1,3-butadiene. For the minor conformer the best unscaled root mean square error of the calculated frequencies for the s-cis and gauche geometries are 17.5 cm−1 and 7.4 cm−1, respectively, primarily due to a better agreement of the gauche results for the vibrations at 983 cm−1, 596 cm−1 and 470 cm−1 which depend strongly on the torsional angle. Although this points towards the gauche form rather than the s-cis form, the calculated transition dipole moment directions at the CCD/6-311G(d,p) level confirm the earlier conclusion that the minor conformer has C 2 v symmetry in the matrix. It is concluded that either the better agreement between the frequencies calculated for the gauche form and the observed values is coincidental, or that the molecule is indeed nonplanar in the matrix and tunnels very rapidly between the two mirror-image forms (or its lowest vibrational level lies above the barrier). Received: 1 July 1998 / Accepted: 26 October 1998 / Published online: 15 February 1999  相似文献   

12.
The structures and energies of formation of α-cyclodextrin (α-CD) dimers formed according to the “head-to-head” (HH), “head-to-tail” (HT), and “tail-to-tail” (TT) modes, harmonic vibrational frequencies, and intensities of IR bands of the IR transitions were calculated by the DFT/PBE density functional method with full geometry optimization without symmetry restrictions. The spectral data were transformed into spectral patterns. An α-CD molecule can exist in two isomeric forms close in energy, namely, α-CD and α-CD+, with different directions of the ring intramolecular hydrogen bonds. Among the three α-CD dimers, the highest dimerization energy (E d/kcal mol−1) belongs to the HH (68.9), TT (43.4), and HT (24.8) dimers. The strength of the α-CD+ dimers decreases in the series: TT+ (56.7), HT+ (49.4), and HH+ (42.4). The energies E H of hydrogen bonds were calculated from the low-frequency shifts of bands of stretching vibrations of the OH groups involved in the formation of these hydrogen bonds. The E H value for each dimer correlates with E d. A possibility of formation of intermolecular hydrogen bonds is a driving force of association of α-CD molecules in aqueous solutions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1289–1296, August, 2006.  相似文献   

13.
The oxidation of d-panthenol by MnO4 was studied in the absence and in the presence of ruthenium(III) catalyst in alkaline medium at 298 K and at constant ionic strength of 0.50 mol dm−3 by spectrophotometry. The stoichiometry in both the cases was [panthenol]: [MnO4 ] = 1:4. The oxidation products were identified by IR and GC–MS. The reaction was first-order with respect to both MnO4 and ruthenium(III), while the orders with respect to both panthenol and alkali varied from first order to zero order as the concentrations increased. The effects of added products, ionic strength and dielectric constant were studied. The reaction constants, activation parameters and thermodynamic quantities were calculated for both the uncatalysed and catalysed reactions.  相似文献   

14.
Near-infrared and mid-infrared spectra of three tellurite minerals have been investigated. The structures and spectral properties of copper bearing xocomecatlite and tlapallite are compared with an iron bearing rodalquilarite mineral. Two prominent bands observed at 9,855 and 9,015 cm−1 are assigned to 2B1g → 2B2g and 2B1g → 2A1g transitions of Cu2+ ion in xocomecatlite. The cause of spectral distortion is the result of many cations of Ca, Pb, Cu and Zn in the tlapallite mineral structure. Rodalquilarite is characterised by ferric ion absorption in the range 12,300–8,800 cm−1. Three water vibrational overtones are observed in xocomecatlite at 7,140, 7,075 and 6,935 cm−1 whereas in tlapallite bands are shifted to lower wavenumbers at 7,135, 7,080 and 6,830 cm−1. The complexity of rodalquilarite spectrum increases with the number of overlapping bands in the near-infrared. The observation of intense absorption feature near 7,200 cm−1 confirms hydrogen bonding water molecules in xocomecatlite. Weak bands observed near 6,375 and 6,130 cm−1 in tellurites are attributed to the hydrogen bonding between (TeO3)2− and H2O. A number of overlapping bands at low wave numbers 4,800–4,000 cm−1 are caused by combinational modes of tellurite ion. (TeO3)2− stretching vibrations are characterised by three main absorptions at ~1,070, 780 and 665 cm−1. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

15.
Simultaneous interaction of the (H2O)50 cluster with O3 molecules and Cl ions was studied by the molecular dynamics method. Six O3 molecules located near the cluster were absorbed by the aqueous aggregate, and Cl ions in turn left the zone of the interaction with the cluster. Some of Cl ions penetrated inside the formed (O3)6(H2O)50 cluster and come into collision with O3 molecules that split the ozone molecule into atoms. When Cl ions were removed sufficiently far away from the cluster, the water cluster with absorbed O3 molecules and O atoms was observed for 15.6 ps. The interaction of water molecules with Cl ions gives rise to an increase in the integral intensity of absorption and emission IR spectra, and also to an essential decrease in the analogous characteristics of the Raman spectrum in the frequency range of 0 ≤ ω ≤ 1000 cm−1. The presence of Cl ions did not affect essentially the location of the main band in the IR spectra, but considerably changed the shape of the bands in the Raman spectrum.  相似文献   

16.
A new ternary ion-association complex of tungsten(VI), 4-nitrocatechol (NC), and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (Thiazolyl Blue, MTT) was obtained and studied using an extraction-spectrophotometric method. The optimum pH, reagent concentrations, and extraction time were determined. The composition of the complex was found to be W(VI): NC: MTT = 1: 2: 2. The extraction process was investigated quantitatively and the key constants were calculated. The molar absorptivity of the chloroform extract at λmax = 415 nm was 2.8 × 104 dm3 mol−1 cm−1, and the Beer’s law was obeyed up to 8.8 μg cm−3 tungsten(IV). The limit of detection and limit of quantification were calculated to be 0.27 μg cm−3 and 0.92 μg cm−3, respectively. The effect of foreign ions and reagents was studied and a competitive method for determination of tungsten in products from ferrous metallurgy was developed. The residual standard deviation and the relative error were 0.53 % and 0.2 %, respectively.  相似文献   

17.
The geometrical structure and the vibrational spectrum of the LiClO3 molecule are studied by the Hartree-Fock-Roothaan (HF) and configurational interaction (CI) methods taking into account single and double excitations and Davidson's correction for quadruple excitations. Double-zeta basis sets of Huzinaga-Dunning and McLean-Chandler complemented with polarization and diffuse functions are used. Potential surface sections corresponding to migration of the Li+ cation around the ClO 3 fragment are investigated. It was found that the LiClO3 molecule has a single stable configuration of Cs symmetry with the bidentate coordination of the Li+ cation by the ClO 3 anion. The cyclic fragment is nonplanar (the dihedral angle θ(LiO2Cl)=173°). The tridentate configuration of C3v symmetry lies higher than the equilibrium configuration by 24.5 (HF) or 18.3 (CI) kJ/mole and is not an isomer. The ab initio force field of the molecule was refined by the scaling method. Some assignments of the IR bands of the matrix-isolated molecular forms existing in vapor over lithium chlorate are corrected. The vibration frequencies (cm−1) and IR intensities (km/mole; in parentheses) are calculated with the refined force field: A′ type 1099(236), 856(81), 630(73), 557(119), 481(87), 156(66); A″ type 887(229), 459(35), 367(23). Ivanovo State Chemical Technological Academy. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 3, pp. 440–449, May–June, 1996.  相似文献   

18.
BaZr0.2Ti0.8O3 thin films on Pt/Ti/SiO2/Si substrates have been fabricated under low temperature conditions by a sol–gel-hydrothermal technique. The dielectric constant is 247–83 in the frequency range of 1 kHz–1 MHz. The corresponding dielectric loss is ~10−2. The capacitance–voltage curve shows strong non-linear dielectric behavior leading to a high tunability, up to ~30% at 1 kHz. The remanent polarization and coercive field at room temperature are measured to be ~1.5 μC/cm2 and ~90 kV/cm. The infrared optical properties of the thin films are investigated using an infrared spectroscopic ellipsometry in the wave number range of 800–4,000 cm−1. Optical constants of the thin films are simultaneously obtained.  相似文献   

19.
Interactions of (Br) i (H2O)50−i clusters (0 ≤ i ≤ 6) with molecular oxygen is studied by the molecular dynamics method using flexible molecule model. Values of real and imaginary parts of permittivity decrease in the 0 ≤ ω ≤ 3500 cm−1 frequency range with increasing number of bromine ions in a cluster. The ability of cluster to absorb IR radiation decreases, whereas the reflectance and Raman light scattering remains nearly unchanged. An increase in the content of Br ions in the cluster lowers the power of emitted IR radiation and decreases the amount of active electrons participating in the interaction with IR radiation. However, when the concentration of Brions becomes substantially higher (at i = 5 and 6), the values of emitted power and the number of active electrons are restored to the values that are typical for water cluster in the absence of Br ions. At i ≥ 3, repelling Br ions acquire kinetic energy, which is sufficient to remove molecular oxygen from the system.  相似文献   

20.
The transition of cubic indium hydroxide to cubic indium oxide has been studied by thermogravimetric analysis complimented with hot-stage Raman spectroscopy. Thermal analysis shows the transition of In(OH)3 to In2O3 occurs at 219 °C. The structure and morphology of In(OH)3 synthesised using a soft chemical route at low temperatures was confirmed by X-ray diffraction and scanning electron microscopy. A topotactical relationship exists between the micro/nano-cubes of In(OH)3 and In2O3. The Raman spectrum of In(OH)3 is characterised by an intense sharp band at 309 cm−1 attributed to ν1 In–O symmetric stretching mode, bands at 1137 and 1155 cm−1 attributed to In-OH δ deformation modes, bands at 3083, 3215, 3123 and 3262 cm−1 assigned to the OH stretching vibrations. Upon thermal treatment of In(OH)3, new Raman bands are observed at 125, 295, 488 and 615 cm−1 attributed to In2O3. Changes in the structure of In(OH)3 with thermal treatment is readily followed by hot-stage Raman spectroscopy.  相似文献   

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