1064-nm-excited Fourier transform Raman studies of bacteriochlorophyll-a in solid films and in a blue-green mutant of Rhodobacter sphaeroides

1064-nm-excited Fourier transform Raman spectra of bacteriochlorophyll-a (BChl) in various solid films and in chromatophores from a blue-green mutant of Rhodobacter sphaeroides have been obtained. The observed Raman spectra are free from high fluorescence backgrounds and sample degradation. The observed intensities seem to be enhanced because of a pre-resonant effect between the exciting radiation at 1064 nm and the Q_y absorption at 770–870 nm of BChl. The spectral features are substantially different from the Soret and Q_x resonance Raman spectra extensively investigated so far; several bands in the wavenumber region lower than 1200 cm⁻¹ are particularly enhanced in the Q_y pre-resonance Raman spectra. Bands due to both the C₂O and C₉O stretches appear at 1700–1620 cm⁻¹, providing structural information on these carbonyl groups. In the CC stretching region (1620–1490 cm⁻¹), the correlation between band positions and the co-ordination number of central magnesium, which was previously found in the Soret-excited Raman spectra, is preserved in the Q_y, pre-resonance Raman spectra as well. The relative intensities of strong bands in the 1200–1000 cm⁻¹ region appear to be useful for characterizing the BChl state. By using these advantages of the Q_y, pre-resonance Raman spectra, molecular interactions and arrangements of BChl in hydrated films and in the B870 light-harvesting complex of R. sphaeroides are discussed.     

Gas phase UV and IR absorption spectra of CxF2x+1CHO (x = 1-4)

The UV and IR spectra of C_xF_2x+1CHO (x = 1-4) were investigated using computational and experimental techniques. C_xF_2x+1CHO (x = 1-4) have broad UV absorption features centered at 300-310 nm. The maximum absorption cross-section increases significantly and shifts slightly to the red with increased length of the C_xF_2x+1 group: CF₃CHO, 3.10 × 10⁻²⁰ (300 nm); C₂F₅CHO, 6.25 × 10⁻²⁰ (308 nm); C₃F₇CHO, 8.96 × 10⁻²⁰ (309 nm); and C₄F₉CHO, 10.9 × 10⁻²⁰ (309 nm). IR spectra for C_xF_2x+1CHO were recorded, calculated, and assigned. Results are discussed with respect to the literature data and to the atmospheric fate of CxF2x+1CHO.     

Spectra and structure of small ring compounds—LX. Raman and infrared spectra,conformational stability,normal coordinate analysis,and ab initio calculations of cyclobutyl acetylene

The Raman spectra (3400 to 10 cm⁻¹ of gaseous, liquid (with qualitative depolarization values) and solid cyclobutyl acetylene, c-C₄H₇CCH, have been recorded. Additionally, the infrared spectra (3500 to 90 cm⁻¹ of the gas and solid have been obtained. The spectra of the fluid phases are consistent with two stable conformers existing at ambient temperature. These data have been interpreted on the basis that the equatorial conformer is more stable than the high energy axial form in both the gas- and liquid-phases, and is the only conformer present in the solid. Two Q-branches are observed in the low frequency vibrational spectra of the gas at 133 and 118 cm⁻¹ and are assigned to the fundamental ring puckering vibration and an associated upper state transition of the low energy equatorial conformer. These data have been used to approximate the form of the potential function governing ring inversion. Experimental values for the enthalpy difference between the two conformers have been determined for both the gas, 282 ± 49 cm⁻¹, and the liquid, 181 ± 15 cm⁻¹, from relative intensities of a pair of Raman lines over 71 and 100°C temperature ranges, respectively. The structure, conformational stability, inversion barrier and vibrational frequencies have been determined by ab initio calculations using the 3-21G and/or 6-31G* basis sets. These calculated results are discussed in comparison to those determined from experiment and to corresponding quantities for some similar molecules.     

In-plane chemical pressure in (U1−yCey)O2 studied by Raman spectroscopy

We investigate the nature of bonding and charge states in (U_1−yCe_y)O₂ (y = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) by Raman spectroscopy. Raman spectrum of UO₂ exhibits two prominent bands below 1000 cm⁻¹, a F_2g mode at 446 cm⁻¹ and a F_1u LO mode at 578 cm⁻¹. As y is increased from 0 to 0.6, the F_1u exhibits a large blue shift of 90 cm⁻¹, and from y = 0.6 to 1.0, a red shift of 54 cm⁻¹. We show that our results can be interpreted as arising from anisotropic compression/relaxation of the lattice under Ce substitution and this can give an indication of its charge states. Alternate interpretations have been given in the literature on the effect of substituents and dopants to the Raman spectra of UO₂ and CeO₂. The present interpretation of chemical stress effects can be taken as another plausible explanation.     

Low frequency Raman spectra of barium borate glasses in the system (BaCl2)y[(BaO)x(B2O3)1-y-x]1-y for various x and y

Low frequency Raman spectra of glasses of the types (BaO)_x·(B₂O₃)_1−x and (BaCl₂)_y·[(BaO)_x·(B₂O₃)₁-_y-_x]₁-_y have been reported. The temperature reduced Raman spectra show peaks at 67, 116 and 140 cm⁻¹ for the binary glass. The bands at 116 and 140 cm⁻¹ are ascribed to the librational motions of the borate groups and the 67 cm⁻¹ band arises because of the limited structural correlation range (SCR) of the glass network, causing a maximum of the frequency dependent Raman coupling coefficient. Due to addition of BaO in v-B₂O₃, the oxygen are mostly incorporated in the formation of BO₄ units; however large Ba²⁺ ions also enhance the number of non-bridging oxygen at higher concentrations of dopant. These barium ions as well as chlorine ions are accomodated in the interstitial vacancies of the glass network which leads to an expansion of the network structure.     

Molecular structure and IR absorption spectra of perfluorinated aldehyde hydrates (n-CxF2x+1CH(OH)2, x = 1-4)

Structures and IR absorption spectra of the conformational isomers of perfluorinated aldehyde hydrates, n-C_xF_2x+1CH(OH)₂, (x = 1-4) have been calculated using density functional theory (DFT) and compared to experimental FT-IR measurements. Two absorption peaks around 3600-3700 cm⁻¹ were observed and are assigned to OH stretching modes of OH groups with, and without, intramolecular hydrogen bonding. For n-C₃F₇CH(OH)₂, two absorption bands around 900-1000 cm⁻¹ were observed in the experimental spectra, whereas only a single in-phase stretching mode of the (CF₃)(C₂F₄CH(OH)₂) and (C₃F₇)(CH(OH)₂) bonds was calculated for each conformer. The experimental spectra were well described by composite spectra of the thermal equilibrium mixture of different conformational isomers of n-C_xF_2x+1CH(OH)₂ calculated by DFT.     

Conformational analysis,barriers to internal rotation,vibrational assignment and ab initio calculations of chloroacetone

The infrared (3500-20 cm⁻¹) and Raman (3200-10 cm⁻¹) spectra have been recorded for gaseous and solid chloroacetone (1-chloro-2-propanone), CH₂ClC(O)CH₃. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. These data have been interpreted on the basis that the molecule exists predominantly in a gauche conformation having a “near cis” structure of C₁ symmetry (dih ClCCO=142°C) in the vapor but for the liquid a second conformer having a trans structure (chlorine atom oriented trans to the methyl group) with C_s point group symmetry is present. From a study of the Raman spectrum of the liquid at variable temperatures, the trans conformation has been determined to be more stable than the gauche form by 1042±203 cm⁻¹ (2.98±0.6 kcal mol⁻¹ and is the only conformer present in the spectrum of the annealed solid. From ab initio calculations at the 3-21G* and 6-31G* basis set levels optimized geometries for both the gauche and trans conformers have been obtained and the potential surfaces governing internal rotation of the symmetric and asymmetric rotors have been obtained. The observed vibrational frequencies and assignments to the fundamental vibrations for both the gauche and trans conformers are compared to those calculated with the 3-21G* basis set. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.     

Vibrational anharmonicity and Fermi resonances in CHF2Cl

The infrared spectrum of CHF₂Cl has been recorded between 15 000 and 350 cm⁻¹. The Fermi resonance between levels involving ν₄ and 2ν₆ is analysed in bands extending from 800 cm⁻¹ to 7000 cm⁻¹ leading to a best value of k₄₆₆ = ± 14.98 cm⁻¹. In conjunction with the recent results of Amrein, Dubal and Quack, Molec. Phys. 56,727 (1985); estimates are reported for 38 out of 45 possible x_ij constants. A variation in the relative intensity of the two Q branches associated with ν₁, on cooling the gas cell, indicates that a hot band contributes to the upper branch at 3024.55 cm⁻¹. However, other evidence suggests that the latter arises also from the combination ν₂ + ν₇ + ν₉, in a very weak, close resonance with ν₁ at 3021.27 cm⁻. A number of anomalous band contours are reported.     

Paramagnetic resonance of interstitial mo5+ in a tio2 lattice

Paramagnetic absorption of Mo⁵⁺ has been studied in a polycrystalline TiO₂ rutile lattice, The g tensor (g_x = 1.897, g_y = 1.920, g_z = 1.857) and the hyperfine tensor (A_x = 32.7, (A_y = 51.2, (A_z = 58.5 (in 10^?4 cm^?1)) are in agreement with those expected for an nd¹ ion in an interstitial position.     

Structure,chemical bonding and electrochemical behavior of heteroatom-substituted carbons prepared by arc discharge and chemical vapor deposition

The structural characteristics, chemical bonding and electrochemical properties of the heteroatom-substituted carbons synthesized by arc discharge and chemical vapor deposition have been investigated. C_xN was prepared only as a soot by arc discharge in nitrogen atmosphere; BC_x and B_xC_yN_z were obtained both as soot and cathode deposits by arc discharge of graphite rods having B₄C and boron nitride (BN) in argon and nitrogen atmospheres, respectively. Transmission electron microscopic study showed that C_xN, BC_x and B_xC_yN_z soots were composed of nanoparticles with diameters of 20–100 nm, while cathode deposits contained nanotubes with diameters of ca. 20 nm or less and nanoparticles with diameters less than 100 nm. It was found from XPS study that C_xN contained a large amount of pyridine type nitrogen atoms at the edge of graphene layer; the BBC₂ structure was dominant in BC_x; and B₃N, B₂NC and BNC₂ structures might exist in B_xC_yN_z. Carbon- and C_xN-coated graphite were prepared by deposition of carbon and C_xN onto natural graphite powder, respectively. The concentrations of coated C_xN layers were between C₂₁N and C₆₂N. Charge–discharge profiles of C_xN, BC_x and B_xC_yN_z soots prepared by arc discharge were similar to each other, giving linearly increasing potential with lithium ion deintercalation. C_xN soot heat-treated at 3000°C showed a similar profile for charge–discharge curves to that of graphite with a charge capacity of 334 mAh g⁻¹. On the other hand, C_xN-coated graphite exhibited as high as 397 mAh g⁻¹ larger than ∼365 mAh g⁻¹ for carbon-coated graphite and that of heat-treated C_xN soot.     

PE-CVD of Fluorocarbon/SiO Composite Thin Films Using C4F8 and HMDSO

Plasma copolymerization of hexamethyldisiloxane (HMDSO,(CH₃)₃-Si-O-Si-(CH₃)₃) and C₄F₈ was performed using an RF plasma enhanced chemical vapor deposition method for application to low dielectric constant intermetal dielectrics. Structure of the films was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The film composition was controlled gradually from fluorinated carbon to organic siloxane by changing the mixing ratio of HMDSO/Ar. Dielectric constant of the films ranged from 2–3.3. Thermal stability of the films, which was characterized by intensity loss of IR absorbance peak around 1000–1500 cm^–1 corresponding to C-F _n , Si-O-Si and Si-(CH₂)_n-Si bonds, was inferior to that from C₂F₄/HMDSO/Ar. In situ gasphase FT-IR spectroscopy revealed that there was a marked difference between the gas phase of C₄F₈/HMDSO/Ar and that of C₂F₄/HMDSO/Ar discharges. The IR spectrum of the former combination plasma contained a peak at 1250 cm^–1 with full width at half maximum as large as 150 cm^–1, which suggests that fluorocarbon particles and/or dusts are formed in the plasma. This suggests also that deposition precursors are not only CF _n (n = 1, 2, and 3) but also larger precursors such as C _x F _y (x > 1, y < 2x + 2) in C₄F₈/HMDSO/Ar discharges, which is presumably the cause of difference in thermal stability of the films prepared from C₄F₈/HMDSO/Ar and C₂F₄/HMDSO/Ar mixtures.     

Zirconium titanate ceramic pigments: Crystal structure, optical spectroscopy and technological properties

Srilankite-type zirconium titanate, a promising structure for ceramic pigments, was synthesized at 1400 °C following three main doping strategies: (a) ZrTi_1−xA_xO₄, (b) ZrTi_1−x−yA_xB_yO₄ and (c) Zr_1−xC_xTiO₄ where A=Co, Cr, Fe, Mn, Ni or V (chromophores), B=Sb or W (counterions) and C=Pr (chromophore); x=y=0.05. Powders were characterized by XRD with Rietveld refinements and DRS in the UV-visible-NIR range; technological properties were appraised in several ceramic matrices (frits, glazes and body). Zirconium titanate can be usefully coloured with first row transition elements, giving green and greenish yellow (Co and Ni); orange-buff (Cr and V); tan-brown hues (Mn and Fe). In industrial-like synthesis conditions, a disordered structure as (Zr,Ti)O₂, with both Zr and Ti randomly distributed in the octahedral site, is achieved. Doping with chromophores and counterions induces unit cell dimensions variation and causes an oversaturation in zirconium oxide. Optical spectroscopy reveals the occurrence of Co²⁺, Cr³⁺, Fe³⁺, Mn²⁺, Mn³⁺, Ni²⁺, V³⁺ and V⁴⁺. The zirconium titanate pigments fulfil current technological requirements for low-temperature applications, but exhibit a limited chemico-physical stability for higher firing temperature and in chemically aggressive media.     

Competitive Coordination of Chloride and Fluoride Anions Towards Trivalent Lanthanide Cations (La3+ and Nd3+) in Molten Salts

Molten salt electrolysis is a vital technique to produce high-purity lanthanide metals and alloys. However, the coordination environments of lanthanides in molten salts, which heavily affect the related redox potential and electrochemical properties, have not been well elucidated. Here, the competitive coordination of chloride and fluoride anions towards lanthanide cations (La³⁺ and Nd³⁺) is explored in molten LiCl-KCl-LiF-LnCl₃ salts using electrochemical, spectroscopic, and computational approaches. Electrochemical analyses show that significant negative shifts in the reduction potential of Ln³⁺ occur when F⁻ concentration increases, indicating that the F⁻ anions interact with Ln³⁺ via substituting the coordinated Cl⁻ anions, and confirm [LnCl_xF_y]^3−x−y (y_max=3) complexes are prevailing in molten salts. Spectroscopic and computational results on solution structures further reveal the competition between Cl⁻ and F⁻ anions, which leads to the formation of four distinct Ln(III) species: [LnCl₆]³⁻, [LnCl₅F]³⁻, [LnCl₄F₂]³⁻ and [LnCl₄F₃]⁴⁻. Among them, the seven-coordinated [LnCl₄F₃]⁴⁻ complex possesses a low-symmetry structure evidenced by the pattern change of Raman spectra. After comparing the polarizing power (Z/r) among different metal cations, it was concluded that Ln−F interaction is weaker than that between transition metal and F⁻ ions.     

Ionic Liquids with More than One Metal: Optical and Electrochemical Properties versus d-Block Metal Combinations

Thirteen N-butylpyridinium salts, including three monometallic [C₄Py]₂[MCl₄], nine bimetallic [C₄Py]₂[M_1−x^aM_x^bCl₄] and one trimetallic compound [C₄Py]₂[M_1−y-z^aM_y^bM_z^cCl₄] (M=Co, Cu, Mn; x=0.25, 0.50 or 0.75 and y=z=0.33), were synthesized and their structure and thermal and electrochemical properties were studied. All compounds are ionic liquids (ILs) with melting points between 69 and 93 °C. X-ray diffraction proves that all ILs are isostructural. The conductivity at room temperature is between 10⁻⁴ and 10⁻⁸ S cm⁻¹. Some Cu-based ILs reach conductivities of 10⁻² S cm⁻¹, which is, however, probably due to IL dec. This correlates with the optical bandgap measurements indicating the formation of large bandgap semiconductors. At elevated temperatures approaching the melting points, the conductivities reach up to 1.47×10⁻¹ S cm⁻¹ at 70 °C. The electrochemical stability windows of the ILs are between 2.5 and 3.0 V.     

Achieving high electrode specific capacitance with materials of low mass specific capacitance: Potentiostatically grown thick micro-nanoporous PEDOT films

Electrode materials for supercapacitors are at present commonly evaluated and selected by their mass specific capacitance (C_M, F g⁻¹). However, using only this parameter may be a misleading practice because the electrode capacitance also depends on kinetics, and may not increase simply by increasing material mass. It is therefore important to complement C_M by the practically accessible electrode specific capacitance (C_E, F cm⁻²) in material selection. Poly[3,4-ethylene-dioxythiophene] (PEDOT) has a mass specific capacitance lower than other common conducting polymers, e.g. polyaniline. However, as demonstrated in this communication, this polymer can be potentiostatically grown to very thick films (up to 0.5 mm) that were porous at both micro- and nanometer scales. Measured by both cyclic voltammetry and electrochemical impedance spectrometry, these thick PEDOT films exhibited electrode specific capacitance (C_E, F cm⁻²) increasing linearly with the film deposition charge, approaching 5 F cm⁻², which is currently the highest amongst all reported materials.     

Lithium electrochromism of atmospheric pressure plasma jet-synthesized NiO x C y thin films

Reversible lithium intercalation and deintercalation behavior of atmospheric pressure plasma jet (APPJ)-synthesized organonickel oxide (NiO _x C _y ) thin films under various substrate distances is testified in an electrolyte (1?M LiClO₄–propylene carbonate solution) at low driving voltages from ?0.5 to 1.5?V. Fast responses of 2?s bleaching at ?0.5?V and 6?s coloration at +1.5?V are accomplished for the nano-porous NiO _x C _y thin films. This study reveals that a rapid synthesis of electrochromic NiO _x C _y thin films in a single process via APPJ by 21?s is investigated. This study presents a noteworthy electrochromic performance in a light modulation with up to 43% of transmittance variation and a coloration efficiency of 36.3?cm²/C at a wavelength of 830?nm after 200?cycles of cyclic voltammetry measurements.     

Spectra and structure of phosphorus—boron compounds—XXVI. Infrared and Raman spectra,conformational stability and normal coordinate analysis of ethyldichlorophosphine-borane

The Raman (3500-10 cm⁻¹) and infrared (3500-50 cm⁻¹) spectra of solid ethyldichlorophosphine-borane, CH₃CH₂P(BH₃)Cl₂ and its deuterated analog, CH₃CH₂P(BD₃)Cl₂ have been recorded. Additionally, the infrared spectra of the gases and the Raman spectra of the liquids have been recorded and qualitative depolarization ratios have been obtained. Based on the fact that several distinct Raman lines disappear on going from the liquid to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers, with the trans conformer being more stable in the liquid phase, and the only one present in the solid phase. From a temperature study of the Raman spectrum of the liquid, the enthalpy difference between the gauche and trans conformers was determined to be nearly zero. Based on Raman depolarization data, group frequencies, isotopic shift factors and infrared band contours, a complete vibrational assignment has been proposed for the trans conformer. The assignment is supported by a normal coordinate calculation which was carried out utilizing a modified valence force field to obtain the frequencies of the normal modes and the potential energy distribution. The BH₃ torsion has been observed at 188 cm⁻¹, while the BD₃ torsion was not observed. The methyl torsions in the spectra of the solids have been observed at 209 and 202 cm⁻¹ for the “light” and deuterated species, respectively. From the torsional data, barriers to internal rotation have been calculated. The asymmetric torsional mode has been observed for the trans conformer in the infrared spectra of the gas phase at 108 and 104 cm⁻¹ for the BH₃ and BD₃ species, respectively. These results are compared with similar quantities for some corresponding organophosphine—borane compounds.     

Fullerite with intercalated freon Ch2F2

Fullerite C₆₀ with intercalated CH₂F₂ (Freon-32) was prepared for the first time. The sample was studied by elemental analysis, X-ray powder diffraction, mass spectrometry, and IR spectroscopy. The composition of the sample was found to be (CH₂F₂)C₆₀. The sample had a face-centered cubic lattice with the lattice parameter (1.4284 nm) much larger than that of pure fullerite (1.416 nm). The gas released from the sample during heating in a vacuum to 450°C largely consisted of initial Freon (mass spectrometry data); no Freon destruction products were observed at this temperature. The C-F stretching vibration frequency (1058 cm^?1) was shifted in (CH₂F₂)C₆₀ by 30 cm^?1 toward lower wave numbers compared with the gas phase. The absorption bands at 1182 and 1428 cm^?1 (IR active modes (F _1u ) of high-symmetry (I _h ) C₆₀ molecules) did not change their positions in the intercalate.     

La fluoration de l'hexachlorobenzene et de la pentachloropyridine en milieu de fluorure de potassium solide

The fluorinations of hexachlorobenzene and pentachloropyridine were carried out in sealed tubes with KF in presence of inert gas; the fluorinated derivatives C₆F_xCl_y x + y = 6 0?x?6 and C₅F_xCl_yN x + y = 5 0?x?5 are obtained. The influence of contact time, temperature and the concentration of the ion F^? are investigated and compared; the molar yield varied from 45% to 90%. It is possible to get directly and selectively some fluorinated derivatives as C₅Cl₂F₃N. The fluorinations in liquid KFKCl and solid KF are compared.     

The features of the Cu2+-entry into the structure of tourmaline

EPR and optical absorption spectra of Cu²⁺ ion were investigated in natural elbaites from Brazil and Zambia and in synthetic olenite single crystal. In elbaite from Zambia, the content of Cu²⁺ ions was found to be about 0.006 pfu, whereas in Brazilian elbaite the amount of this ion can approach up to 0.2 pfu. The rose color of elbaite from Zambia is mainly due to optical absorption at 515 nm related to Mn³⁺ ions. The blue color of Brazilian elbaite is related to Cu²⁺ absorption bands at 695 nm and 920 nm. Spin Hamiltonian parameters of Cu²⁺ calculated from the angular dependence of the EPR spectra are: g _x = 2.054, g _y = 2.092, g _z = 2.374; A _x = 27.8·10^?4 cm^?1, A _y = 59.3·10^?4 cm^{? 1}, A _z = 133.2·10^?4 cm^?1. We propose that Cu²⁺ ions enter into Y octahedra with common edges; the symmetry of these Y octahedra is lowered because of local disorder induced by occupancy of the Y site by cations of very different size and charge, such as Li⁺, Al³⁺, and Cu²⁺.