Vibrational spectroscopic study of the arsenate mineral strashimirite Cu8(AsO4)4(OH)4·5H2O—Relationship to other basic copper arsenates

The basic copper arsenate mineral strashimirite Cu₈(AsO₄)₄(OH)₄·5H₂O from two different localities has been studied by Raman spectroscopy and complemented by infrared spectroscopy. Two strashimirite mineral samples were obtained from the Czech (sample A) and Slovak (sample B) Republics. Two Raman bands for sample A are identified at 839 and 856 cm⁻¹ and for sample B at 843 and 891 cm⁻¹ are assigned to the ν₁ (AsO₄³⁻) symmetric and the ν₃ (AsO₄³⁻) antisymmetric stretching modes, respectively. The broad band for sample A centred upon 500 cm⁻¹, resolved into component bands at 467, 497, 526 and 554 cm⁻¹ and for sample B at 507 and 560 cm⁻¹ include bands which are attributable to the ν₄ (AsO₄³⁻) bending mode. In the Raman spectra, two bands (sample A) at 337 and 393 cm⁻¹ and at 343 and 374 cm⁻¹ for sample B are attributed to the ν₂ (AsO₄³⁻) bending mode. The Raman spectrum of strashimirite sample A shows three resolved bands at 3450, 3488 and 3585 cm⁻¹. The first two bands are attributed to water stretching vibrations whereas the band at 3585 cm⁻¹ to OH stretching vibrations of the hydroxyl units. Two bands (3497 and 3444 cm⁻¹) are observed in the Raman spectrum of B. A comparison is made of the Raman spectrum of strashimirite with the Raman spectra of other selected basic copper arsenates including olivenite, cornwallite, cornubite and clinoclase.     

Vibrational spectra of π-olefin-transition metal complexes : (π-maleic anhydride)iron tetracarbonyl

The infrared and Raman spectra of solutions and solid samples of (π-maleic anhydride)iron tetracarbonyl have been studied. An assignment of the modes is suggested and the ligand vibrations in the complex are compared the data for maleic and succinic anhydrides. The C=C stretching frequency maleic anhydride shifts from 1595 to 1352 cm⁻¹ after coordination with the The essential decrease of the IR intensities of out-of-plane CH modes is for the complex and explained by the lowering of the effective charge on olefinic protons due to back-donation from metal to ligand.     

Conformational analysis and vibrational spectroscopic investigation of 3-phenylpropylamine

The possible stable forms of 3-phenylpropylamine (3-PPA) molecule were experimentally and theoretically studied by infrared and Raman spectroscopy. FT-IR and Raman spectra of 3-PPA were recorded in the regions of 4000–400 cm⁻¹ and 3700–60 cm⁻¹, respectively. The potential energy surface corresponding to the internal rotations of the molecule was investigated by semi-empirical quantum mechanical methods, and appropriate conformers defined with B3LYP hybrid density functional theory method along with the basis sets of different size and type. Results from experimental and theoretical data showed the trans–trans–gauche (TTG) to be the most stable form of a 3-PPA molecule.     

Microwave spectrum of bicyclo[2,2,1] hepta-2,5-dien-7-ol and spectroscopic evidence for an intramolecular (OH π) hydrogen bond

The microwave spectrum of bicyclo[2,2,1]hepta-2,5-dien-7-ol and of the deuteroxyl species have been recorded over 8–40 GHz. Rotational constants and centrifugal distortion constants were fitted to the measured rotational transitions for both species. The electric dipole components μm_a = 1.223(3) D, μm_b = 1.053(2) D and μm_total = 1.614(2) D were deduced from Stark splittings. Only a trans conformation of the OH group with respect to the hydrogen is compatible with the microwave data.Infrared spectra of bicyclo[2,2,1]hepta-2,5-dien-7-ol and the corresponding saturated compound have been recorded in the gas phase and in Ar matrix isolation. The difference of 77.4 cm⁻¹ in the O---H stretching frequencies between unsaturated and saturated compounds points towards a moderately strong intramolecular (OH π) hydrogen bond.     

Investigation of silicate mineral sanidine by vibrational and NMR spectroscopic methods

Sanidine, a variety of feldspar minerals has been investigated through optical absorption, vibrational (IR and Raman), EPR and NMR spectroscopic techniques. The principal reflections occurring at the d-spacings, 3.2892, 3.2431, 2.9022 and 2.6041 Å confirm the presence of sanidine structure in the mineral. Sanidine shows five prominent characteristic infrared absorption bands in the region 1200–950, 770–720, 590–540 and 650–640 cm⁻¹. The Raman spectrum shows the strongest band at 512 cm⁻¹ characteristic of the feldspar structure, which contains four membered rings of tetrahedra. The UV–vis–NIR absorption spectrum had strong absorption features at 6757, 5780 and 5181 cm⁻¹ due to the combination of fundamental OH– stretching. The bands at 11236 and 8196 cm⁻¹and the strong, well-defined band at (30303 cm⁻¹ attest the presence of Fe²⁺ and Fe³⁺, respectively, in the sample. The signals at g = 4.3 and 3.7 are interpreted in terms of Fe³⁺ at two distinct tetrahedral positions Tl and T2 of the monoclinic crystal structure The ²⁹Si NMR spectrum shows two peaks at −97 and −101 ppm corresponding to T2 and T1, respectively, and one peak in ²⁷Al NMR for Al(IV).     

UV–visible spectrum of the phenyl radical and kinetics of its reaction with NO in the gas phase

Pulse radiolysis transient UV–visible absorption spectroscopy was used to study the UV–visible absorption spectrum (225–575 nm) of the phenyl radical, C₆H₅(), and kinetics of its reaction with NO. Phenyl radicals have a strong broad featureless absorption in the region of 225–340 nm. In the presence of NO phenyl radicals are converted into nitrosobenzene. The phenyl radical spectrum was measured relative to that of nitrosobenzene. Based upon σ(C₆H₅NO)_{270 nm}=3.82×10⁻¹⁷ cm² molecule⁻¹ we derive an absorption cross-section for phenyl radicals at 250 nm, σ(C₆H₅())_{250 nm}=(2.75±0.58)×10⁻¹⁷ cm² molecule⁻¹. At 295 K in 200–1000 mbar of Ar diluent k(C₆H₅()+NO)=(2.09±0.15)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹.     

Cationic polyfluorene: Conformation and aggregation in a “good” solvent

The conjugated polyelectrolyte (CPE) poly{9,9′-bis[6″-(N,N,N-trimethylammonium)-hexylfluorene-alt-co-phenylene] dibromide} (PFPN⁺Br⁻) demonstrates a high solubility in methanol in comparison to other more hydrophilic or hydrophobic solvents. We have employed a combination of pulsed-field-gradient-NMR, photoluminescence (PL), and Raman spectroscopy to establish the conformation and aggregation behavior of PFPN⁺Br⁻ in methanol, with the aim to attain information on how to design CPEs with a high solubility in a preferred solvent. We find that the diffusion coefficient and PL spectrum of PFPN⁺Br⁻, as well as the Raman-active methyl rocking mode of methanol, all exhibit a strong dependence on PFPN⁺Br⁻ concentration. We rationalize our findings with a model in which PFPN⁺Br⁻ forms aggregates via π–π interactions between main-chain segments, while the ionic side chains are surrounded and electrostatically screened by the methanol solvent. Accordingly, the notably high solubility of PFPN⁺Br⁻ in methanol is rationalized by favorable interactions between the ionic side chains and the methanol molecules. We propose that an appropriate design of a high-solubility CPE should consider a matching of the mixed hydrophobic/hydrophilic character of the ionic side chain with that of the preferred solvent.     

Preparation and electrical properties of new oxide ion conductors Ce6−xDyxMoO15−δ (0.0 ≤ x ≤ 1.8)

Ce_6−xDy_xMoO_15−δ (0.0 ≤ x ≤ 1.8) were synthesized by modified sol–gel method. Structural and electrical properties were investigated by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The XRD patterns showed that the materials were single phase with a cubic fluorite structure. Impedance spectroscopy measurement in the temperature range between 350 °C and 800 °C indicated a sharp increase in conductivity for the system containing small amount of Dy₂O₃. The Ce_5.6Dy_0.4MoO_15−δ detected to be the best conducting phase with the highest conductivity (σ_t = 8.93 × 10⁻³ S cm⁻¹) is higher than that of Ce_5.6Sm_0.4MoO_15−δ (σ_t = 2.93 × 10⁻³ S cm⁻¹) at 800 °C, and the corresponding activation energy of Ce_5.6Dy_0.4MoO_15−δ (0.994 eV) is lower than that of Ce_5.6Sm_0.4MoO_15−δ (1.002 eV).     

A novel route to bicyclic iron tricarbonyl complexes involving π-allyl and σ-components

Nucleophilic attack of CN⁻ on bicyclo[3.2.1]octadienyl-, bicyclo[3.2.2]- nonadienyl-, and 6,7-benzobicyclo[3.2.2]nonadienyliron tricarbonyl tetrafluoroborates, results in mixed-type complexes containing both σ and π-allyl bonds. The cyano group in the products is located exo to the bicyclic ring.In contrast, the three cations react smoothly with I⁻; carbon monoxide is displaced to give iron complexes containing covalently-bound halogen.     

Spectra and Structures of Silicon-Containing Compounds. XXIV.* Raman and Infrared Spectra,r 0 Structural Parameters,Vibrational Assignment,Barriers to Internal Rotation,and Ab Initio Calculations of Ethylsilane

The infrared (3200 to 400 cm^–1) and Raman (3200 to 20 cm^–1) spectra of gaseous and solid ethylsilane, CH₃CH₂SiH₃, have been recorded. Additionally, the Raman spectrum of the liquid has been obtained with quantitative depolarization values. The SiH₃ torsional mode has been observed as sum and difference bands with the silicon-hydrogen stretching vibration. Utilizing the torsional fundamental frequency of 132 cm^–1 the threefold periodic barrier of 590 cm^–1 (7.06 kJ/mol) has been obtained. Utilizing the frequencies of the silicon-hydrogen stretches, Si-H bond distances of 1.485 and 1.484 Å have been obtained for the bonds gauche and trans to the methyl group, respectively. Using previously reported rotational constants from seven different isotopomers, the r ₀ parameters have been calculated and are compared to the corresponding r _s parameters. A complete vibrational assignment is proposed that is consistent with the predicted frequencies utilizing the force constants from ab initio MP2/6-31G(d) calculations. Both the infrared intensities as well as the Raman activities and depolarization values have been obtained from the ab initio calculations. Complete equilibrium geometries have been determined by ab initio calculations employing the 6-31G(d), 6-311 + G(d,p), and 6-311+G(2d,2p) basis sets at levels of restricted Hartree–Fock (RHF) and/or Moller–Plesset (MP) to second order. The results are discussed and the theoretical values are compared to the experimental values when appropriate.     

An optical, EPR and electrical conductivity study of blue barium titanate, BaTiO3−δ

The electronic UV–VIS–NIR absorption spectra of single crystalline BaTiO_3−δ (BTO) are studied in the temperature range of 102–1173 K in pure oxygen and at conditions of moderate and strong reduction of the material. The strongly reduced crystals are of deep blue colour. The optical spectra of blue BTO are characterised by a strong absorption in the NIR region at around 7000 cm⁻¹, which is attributed to polaronic defects associated with the formation of Ti³⁺ in the material. This assumption is supported by fits of the spectra using polaronic line shape functions appropriate for disordered systems and also by the electrical conductivity of blue BTO which, in agreement with results from the optical spectra, exhibits an activation energy of 0.20 eV. The EPR spectra of moderately reduced BTO powders show an anisotropic g-factor, which is compatible with the optical spectrum. The temperature dependence of the band gap energy of BTO was found to be given as dE_g/dT = −7.21 × 10⁻⁴ eV/K.     

Dielectric and Raman studies on the solid solution (1−x)BaTiO3/xNaNbO3 ceramics

In order to elucidate the correlation between the relaxor type of phase transition and the percent of the A and B site substitution in the Ba_1−xNa_xTi_1−xNb_xO₃ solid solution, the dielectric permittivity was carried out in the temperature range 80–600 K. All ceramics of these solid solutions present a ferroelectric–paraelectric phase transition with relaxor and classical character depending on the value of x. With increasing x the three phase transition of pure BaTiO₃ are pinched into one rounded dielectric peak, and there is evidence for Vogel–Fulcher type relaxational freezing. Raman spectra of the x=0.3 and x=0.7 compositions taken at various temperatures and measured over the wavenumber range 100–1200 cm⁻¹ confirm that the first order scattering is dominant in phonon bands resulting from both ordered region and disordered matrix.     

Analysis of the 4800-Å absorption band of Cs2 by the classical method

The broad absorption band in Cs₂ having peak intensity near 4800 Å is analyzed through computational simulation of the experimental spectrum using the classical method. The absorption, which terminates in a weak satellite at 5223 Å, can be interpreted in terms of a single transition from the ground state (R_e = 4.65 Å, ω_e = 42 cm⁻¹) to an upper state having T_e = 20 470 cm⁻¹, ω_e = 33 cm⁻¹ and R_e = 5.28 Å. The absolute absorption strength is roughly consistent with published lifetime data, but its reliability is limited by thermodynamic uncertainties stemming from the remaining uncertainty in the Cs₂ ground state dissociation enegy. The paper includes a summary of diatomic radiation relations pertinent to the analysis of low-resolution spectra, and a brief discussion of the reduced potential method applied to the alkali dimer ground states.     

Tetracene oxygenation caused by infrared excitation of molecular oxygen in air-saturated solutions: the photoreaction action spectrum and spectroscopic parameters of the transition in oxygen molecules

The action spectrum of tetracene photooxygenation was measured in air-saturated carbon tetrachloride in the wavelength range of 1220–1290 nm using a wavelength-tunable forsterite laser. The data show that the photoreaction occurs due to laser excitation of the transition in oxygen molecules. The molar absorption coefficient (₁₂₇₃) and the cross section of light absorption (σ₁₂₇₃) corresponding to the spectral maximum of this transition were calculated from the observed photoreaction rates. The obtained values ε₁₂₇₃ = 0.003 M⁻¹ cm⁻¹ and σ₁₂₇₃ = 10⁻²³ cm² (±20%) reasonably correlate with those extrapolated from the high-pressure oxygen absorption spectra.     

Infrared optical constants, dielectric constants, molar polarizabilities, transition moments, dipole moment derivatives and Raman spectrum of liquid cyclohexane

Previous studies have been done in this laboratory focusing on the optical properties of several liquid aromatic and aliphatic hydrocarbons in the infrared. The current study reports the infrared and absorption Raman spectra of liquid cyclohexane. Infrared spectra were recorded at 25 °C over a wavenumber range of 7400–490 cm⁻¹. Infrared measurements were taken using transmission cells with pathlengths ranging from 3 to 5000 μm. Raman spectra were recorded between 3700 and 100 cm⁻¹ at 25 °C using a 180° reflection geometry. Ab initio calculations of the vibrational wavenumbers at the B3LYP/6311G level of theory were performed and used to help assign the observed IR and Raman spectra. Extensive assignments of the fundamentals and binary combinations observed in the infrared imaginary molar polarizability spectrum are reported. The imaginary molar polarizability spectrum was curve fitted to separate the intensity from the various transitions and used to determine the transition moments and magnitudes of the derivatives of the dipole moment with respect to the normal coordinates for the fundamentals.     

The B1 ← A1 absorption system of NO2 in Xe matrices: evidence for Renner—Teller interaction

A tentative vibrational assignment of the ²B₁ ← ²A₁ absorption system of NO₂ in solid Xe is reported. About 65 bands were analysed, yielding normal vibration energies of ν₁ = 1230, ν₂ = 450 and ν₃ = 2040 cm⁻¹. The electronic transition energy can be estimated to be T₀₁₀ = 14160 cm⁻¹ (14220 cm⁻¹ for the gaseous phase). These observations are in good agreement with predictions made using ab initio calculations. Evidence for Renner—Teller interaction is documented by a systematic staggering of frequency intervals between successive bands in the ν₂ progression of the state.     

In vivo molecular evaluation of guinea pig skin incisions healing after surgical suture and laser tissue welding using Raman spectroscopy

The healing process in guinea pig skin following surgical incisions was evaluated at the molecular level, in vivo, by the use of Raman spectroscopy. After the incisions were closed either by suturing or by laser tissue welding (LTW), differences in the respective Raman spectra were identified. The study determined that the ratio of the Raman peaks of the amide III (1247 cm⁻¹) band to a peak at 1326 cm⁻¹ (the superposition of elastin and keratin bands) can be used to evaluate the progression of wound healing. Conformational changes in the amide I band (1633–1682 cm⁻¹) and spectrum changes in the range of 1450–1520 cm⁻¹ were observed in LTW and sutured skin. The stages of the healing process of the guinea pig skin following LTW and suturing were evaluated by Raman spectroscopy, using histopathology as the gold standard. LTW skin demonstrated better healing than sutured skin, exhibiting minimal hyperkeratosis, minimal collagen deposition, near-normal surface contour, and minimal loss of dermal appendages. A wavelet decomposition–reconstruction baseline correction algorithm was employed to remove the fluorescence wing from the Raman spectra.     

Vibrational spectra of halogen substituted cyclopropanes—V. Trans-1,2-dichlorocyclopropane

The i.r. spectra of gaseous trans-1,2-dichlorocyclopropane were measured from 4000 to 400 cm⁻¹ and to 200 cm⁻¹ in the liquid phase. The Raman spectrum of the liquid was obtained from 4000 to 50 cm⁻¹. An assignment of all 21 normal vibrations was proposed on the basis of i.r. vapour phase band contours, Raman depolarization ratios, expected group frequencies and comparison with closely related molecules. There is excellent agreement with the normal modes previously assigned for the cis and trans isomers of the chloro, bromo and iodo analogues. The data indicate little interaction between the two CHCl moieties.     

Redox features of β-VOPO4 catalyst using tracer and laser Raman spectroscopy

The oxygen ions of the β-VOPO₄ catalyst were exchanged with an tracer by a reduction–oxidation method and by a catalytic oxidation of but-1-ene using ₂. The bands at 992 and 900 cm⁻¹ were more shifted to lower frequencies than those at 1076 and 1002 cm⁻¹. Applying the correlation between the Raman bands and stretching vibrations in the literature, the exchanged oxygen species were estimated. The results suggest that the P–O–V vacancies corresponding to 992 and 900 cm⁻¹ were responsible for reoxidation and the V=O oxygen corresponding to the 1002 cm⁻¹ band of β-VOPO₄ was not. The (VO)₂P₂O₇ was oxidized to β-VOPO₄ by O₂ above 823 K. The insertion position of oxygen was determined at the bands at 992 and 900 cm⁻¹ of β-VOPO₄ using ₂, which is the same as the exchanged position.     

Spectrophotometric determination of cobalt(II) with 2-(3′-sulfobenzoyl)pyridine benzoylhydrazone

A simple method has been described for the Spectrophotometric determination of cobalt(II) with 2-(3′-sulfobenzoyl)pyridine benzoylhydrazone (SBPBH). In aqueous solution, cobalt(II) reacts with SBPBH to form a yellow complex, which is not destroyed even by the addition of 3.8 M perchloric acid. The absorption maximum of the complex in 1.5 M perchloric acid medium was found to be 400 nm; the molar absorptivity was 2.17 × 10⁴ liters mol⁻¹ cm⁻¹. The proposed method is fairly selective and has been applied to the determination of cobalt in standard alloy steel samples.