Far infrared spectra, conformational equilibria, vibrational assignments, ab initio calculations and structural parameters for 2-bromoethanol

The far infrared spectrum from 370 to 50 cm⁻¹ of gaseous 2-bromoethanol, BrCH₂CH₂OH, was recorded at a resolution of 0.10 cm⁻¹. The fundamental O–H torsion of the more stable gauche (Gg′) conformer, where the capital G refers to internal rotation around the C–C bond and the lower case g to the internal rotation around the C–O bond, was observed as a series of Q-branch transitions beginning at 340 cm⁻¹. The corresponding O–H torsional modes were observed for two of the other high energy conformers, Tg (285 cm⁻¹) and Tt (234 cm⁻¹). The heavy atom asymmetric torsion (rotation around C–C bond) for the Gg′ conformer has been observed at 140 cm⁻¹. Variable temperature (−63 to −100°C) studies of the infrared spectra (4000–400 cm⁻¹) of the sample dissolved in liquid xenon have been recorded. From these data the enthalpy differences have been determined to be 411±40 cm⁻¹ (4.92±0.48 kJ/mol) for the Gg′/Tt and 315±40 cm⁻¹ (3.76±0.48 kJ/mol) for the Gg′/Tg, with the Gg′ conformer the most stable form. Additionally, the infrared spectrum of the gas, and Raman spectrum of the liquid phase are reported. The structural parameters, conformational stabilities, barriers to internal rotation and fundamental frequencies have been obtained from ab initio calculations utilizing different basis sets at the restricted Hartree–Fock or with full electron correlation by the perturbation method to second order. The theoretical results are compared to the experimental results when appropriate. Combining the ab initio calculations with the microwave rotational constants, r₀ adjusted parameters have been obtained for the three 2-haloethanols (F, Cl and Br) for the Gg′ conformers.     

The effect of hydrogen bonding interactions between 2-[4-(dimethylamino)phenyl]-3-hydroxy-4H-chromene-4-one in the ground and excited states and dimethylsulfoxide or methanol on electronic absorption and emission transitions

The surface state of optically pure polydisperse TiO₂ (anatase and rutile) was determined by infra-red (IR) spectroscopy analysis in the temperature range of 100–453 K. Anatase A300 spectrum, contrary to rutile R300 one, has a broad three-component absorption band with peaks at 1048, 1137 and 1222 cm⁻¹ in the spectral range of δ(Ti–O–H) deformation vibrations. For rutile R300 we observed a very weak band at 1047 cm⁻¹, and for the thermal treated rutile R900 these bands were not appeared at all. The analysis of temperature dependencies for the mentioned absorption bands revealed the spectral shift of 1222 cm⁻¹ band towards the high frequencies, when the temperature increased, but the spectral parameters of 1137 and 1048 cm⁻¹ bands remained the same. The temperature of 1222 cm⁻¹ band maximum shift was 373–393 K and correlated with DSC data. Obtained results allowed to assign 1222 cm⁻¹ band to the deformation vibrations of OH-groups, bounded to the surface adsorbed water molecules by weak hydrogen bonds (5 kcal/mol). During the temperature growth these molecules desorbed, which also resulted in the intensity decreasing of stretching OH-groups vibration IR-bands at 3420 cm⁻¹. The destruction and desorption of surface water complexes led to Ti–O–H bond strengthening. IR bands at 1137 and 1048 cm⁻¹ were attributed to the stronger bounded adsorbed water molecules, which are also characterized with stretching OH-groups vibration bands at 3200 cm⁻¹. These surface structure were additionally stabilized by hydrogen bonds with the neighbouring TiO₂ lattice anions and other OH-groups, and desorbed at higher temperatures.     

Infrared matrix isolation studies of complexes formed between dimethylsulfide, dimethyldisulfide and nitrous acid

The complexes formed by dimethylsulphide (DMS) and dimethyldisulphide (DMDS) with two isomers of nitrous acid have been observed, and characterised in argon and nitrogen matrices. The ν₁ OH stretching vibration of the perturbed trans-HONO monomer is 425 and 294 cm⁻¹ red shifted, respectively, for the DMS and DMDS complex in solid argon, and 441 and 301 cm⁻¹ in solid nitrogen. A large blue shift is also observed for the ν₃ NOH in-plane deformation mode: 101 and 80 cm⁻¹ for DMS–HONO-trans in argon and nitrogen matrices and 46 cm⁻¹ for DMDS–HONO-trans in nitrogen matrix. The results indicate formation of strong hydrogen bonds in the studied DMS–HONO and DMDS–HONO systems. The origin of the complicated shape of the ν₁ OH absorption is discussed. Similarities and differences between argon and nitrogen matrices are considered.     

Spectroscopic and structural analysis of Ca substituted La orthoferrite

Samples of orthoferrites La_1−xCa_xFeO₃ (0.15≤x≤0.45) were synthesized by double sintering ceramic technique. X-ray diffraction and infrared spectroscopy experiments were carried out and discussed for the investigated samples. The data showed the formation of single-phase orthorhombic structure of space group Pbnm. The FTIR spectra were performed in the region (1200–200 cm⁻¹). Four main absorption bands were present with some side bands and shoulders in the range (1200–400 cm⁻¹). Another four bands were appeared in the range (400–200 cm⁻¹). The positions, intensities and values of the absorptions bands vary depending on the Ca content in the samples. The first absorption band appeared at about 920 cm⁻¹ was assigned to the La–O stretching vibration.     

A study of the Raman spectra of alkanes in the Fermi-resonance region

The experimental and theoretically predicted Raman spectra for the first few alkanes in the homologous series: methane, ethane, propane and butane are presented for the region 2700–3100 cm⁻¹. The structure of the spectra is rather complex. Analysis of the results obtained shows that Fermi resonance occurs between the CH stretching vibrations in the 3000 cm⁻¹ region and the 2ν overtones of deformation vibrations in the low frequency (1450–1500 cm⁻¹) region.     

Matrix isolation infrared studies of complexes formed between substituted phenols and trimethylamine

Infrared spectroscopy and matrix isolation technique have been used to study the 1 : 1 complexes formed between 2,4,5-trichlorophenol (TCP), pentachlorophenol (PCP) or 2-chloro-4,6-dinitrophenol (CNP) and trimethylamine (TMA) isolated in solid argon. The results were analyzed in relation to the type of complex formed. Depending on the proton-donor ability of the phenol three different types of hydrogen bonded complexes have been identified in argon matrices. The weakest phenol in the series, TCP (pK_a = 6.72), forms a strong molecular hydrogen bonded complex with TMA as indicated by the broad ν(OHN) absorption with a maximum at 2490 cm⁻¹ and a band at 811 cm⁻¹ due to the ν_s(C₃N) mode of the perturbed amine. The strongest phenol, CNP (pK_a = 2.01), interacts with TMA in an argon matrix to form ionic complex with the proton transferred to the base molecule. This is evidenced by the presence of the ν(NH⁺---O⁻) absorption between 3000−1800 cm⁻¹, by the ν_as(C₃N⁺) and ν_s(C₃N⁺) absorptions due to the protonated amine and by numerous product bands due to the relatively strongly perturbed modes of the phenol ring. The interaction between TMA and a phenol of intermediate strength, PCP (pK_a = 4.74), in solid argon probably leads to the formation of two types of hydrogen bonded complexes: an ionic complex with the proton transferred to the amine molecule and a pseudosymmetric one with the proton more or less equally shared between the phenol and amine molecules. In this case the protonic absorption consists of two broad features situated in the 3000–1600 cm⁻¹ and 950–400 cm⁻¹ regions due to the ν(NH⁺O⁻) and ν(OHN) modes, respectively.     

Infrared depletion spectroscopy of the doubly hydrogen-bonded aniline–(tetrahydrofuran)2 complex produced in supersonic jet

The vibrational frequencies of the N–H stretching modes of aniline after forming a strong doubly H-bonded complex with tetrahydrofuran (THF) are measured with infrared depletion spectroscopy that uses cluster-size-selective resonance-enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry. Two strong infrared absorption features observed at 3355 and 3488 cm⁻¹ are assigned to the symmetric and antisymmetric N–H stretching vibrations of the 1:2 aniline–THF complex, respectively. The red-shifts of the N–H stretching vibrations of aniline agree with the ab initio calculated (MP2/6-31G**) aniline-(THF)₂ structure in which both aniline N–H bonds interact with the oxygen atom of THF through two hydrogen bonds. The calculated binding energy is found to be 29.6 kJ mol⁻¹ after corrections for basis set superposition error (BSSE) and zero-point energy. The calculated structure revealed that the angle between the N–H bonds in the NH₂ group increased to 112.5° in the aniline–(THF)₂ complex from that of 109.8° in the aniline. The electronic 0–0 band origin for the S₁ ← S₀ transition is observed at 32,900 cm⁻¹ in the aniline–(THF)₂ complex, giving a red-shift of 1129 cm⁻¹ from that of the aniline molecule.     

Far infrared spectroscopy on hemoproteins: A model compound study from 1800–100 cm

Infrared spectroscopy measurements on different hemoproteins and models of the active side have been completed for the spectral range from 1800 to 100 cm⁻¹ giving an overview on the contributions expected in the low frequency range. Little is known of the low frequency contribution of proteins in infrared. In order to detect the contributions of heme centers and protein moiety, a systematic study of the infrared spectroscopic properties of the porphyrin ring, the ferric porphyrines with different ligands (hemine and hematine), a heme with 11 amino acids (microperoxidase-11), cytochrome c and cytochrome c oxidase are compared at different pD values and an overview on the relative contributions of hemes, their ligands and the protein site can be provided in the low frequency region. Beside the well know amide I and II modes, the low frequency range is found to be dominated by the amide IV and VI mode around 530/580 cm⁻¹ for cytochrome c and cytochrome c oxidase, as well as further proteins like ferrodoxin. Below 300 cm⁻¹ amide VII modes, doming modes of the heme site and hydrogen-bonding signatures overlap to a broad peak with covering 100–250 cm⁻¹. As clear markers for the iron ligands, bands can be depicted at 388/378 cm⁻¹ (FeN, histidine ligand) and 345 cm⁻¹ FeCl. Furthermore the ring vibration of the protonated histidine is determined at 623 cm⁻¹.     

Semi-quantitative trace analysis of nuclear fast red by surface enhanced resonance Raman scattering

The dye nuclear fast red has been detected and determined semi-quantitatively by means of surface enhanced resonance Raman scattering (SERRS) and surface enhanced Raman scattering (SERS), using laser exciting wavelengths of 514.5 and 632.8 nm, respectively, by employing a citrate-reduced silver colloid. A good linear correlation is observed for the dependence of the intensities of the SERRS bands at 989 cm⁻¹ (R=0.9897) and 1278 cm⁻¹ (R=0.9872) on dye concentration over the range 10⁻⁹ to 10⁻⁷ M, when using an exciting wavelength of 514.5 nm. At dye concentrations above 10⁻⁷ M, the concentration dependence of the SERRS signals is non-linear. This is almost certainly due to the coverage of the colloidal silver particles being in excess of a full monolayer of the dye. A linear correlation is also observed for the dependence of the intensities of the SERS bands at 989 cm⁻¹ (R=0.9739) and 1278 cm⁻¹ (R=0.9838) on the dye concentration over the range 10⁻⁸ to 10⁻⁶ M when using an exciting wavelength of 632.8 nm. Strong fluorescence prevented collection of resonance Raman scattering (RRS) spectra from powdered samples or aqueous solutions of the dye using an exciting wavelength of 514.5 nm, but weak bands were observed in the spectra obtained from both powdered and aqueous samples of the dye using an exciting wavelength of 632.8 nm. A study of the pH dependence of SERRS/SERS and UV–VIS absorption spectra revealed the presence of different ionisation states of the dye. The limits of detection for nuclear fast red by SERRS (514.5 nm), SERS (632.8 nm) and visible spectroscopy (535 nm) are 9, 89 and 1000 ng ml⁻¹, respectively.     

Conformational studies of cyclopropylmethyl isocyanate from temperature dependent FT-IR spectra of xenon solutions and ab initio calculations

Variable temperature (−55 to −100 °C) studies of the infrared spectra (3200 to 100 cm⁻¹) of cyclopropylmethyl isocyanate, c-C₃H₅CH₂NCO, dissolved in liquefied xenon, have been carried out. The infrared spectra (gas and solid) as well as the Raman spectrum of the liquid have been recorded from 3200 to 100 cm⁻¹. By analyzing six conformer pairs in xenon solutions, an enthalpy difference of 193 ± 19 cm⁻¹ (2.31 ± 0.23 kJ/mol) was obtained with the gauche–cis rotamer (the first designation indicates the orientation of the CNCO group with respect to the three-membered ring, the second designation indicates the relative orientation of the NCO group with respect to the bridging CC bond) the more stable form and the only form present in polycrystalline solid. The abundance of the cis–trans conformer present at ambient temperature is 16 ± 1%. The potential function governing the conformational interchange has been obtained from B3LYP/6-31G(d) calculations and the two-dimensional potential has been obtained. From MP2 ab initio calculations utilizing various basis sets with diffuse functions, the gauche–cis conformer is predicted to be more stable by 223 to 269 cm⁻¹, which is consistent with the experimental results. However, without diffuse functions the predicted conformational energy differences are much smaller (77–166 cm⁻¹). Similar diffuse function dependency affects density functional theory calculations by the B3LYP method to a lesser extent. A complete vibrational assignment for the gauche–cis conformer is proposed and several fundamentals for the cis–trans conformer have been identified. The structural parameters, dipole moments, conformational stability, vibrational frequencies, infrared intensities and Raman activities have been predicted from ab initio calculations and r₀ structural parameters are estimated. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.     

Characterization and decomposition mechanism of an unusual nickel, thiocyanate and 4-methylpyridine polymeric complex

The synthesis, characterization, and thermal decomposition of the [Ni(SCN)₂(H⁺SCN)₂(4-mepy)₂] compound with an octahedral structure in polymeric chain were reported, in which SCN groups form bridges among Ni(II) ions. The compound decomposes in water resulting in a pH<4 solution. The FT-IR spectrum presented doublet bands at 2117; 2128 cm⁻¹, 788; 773 cm⁻¹ assigned to ν(C---N) and ν(C---S) stretching modes, respectively, and δ(SCN) deformation modes at 468; 476 cm⁻¹. The Raman spectrum of the compound presented the ν(C---N) stretching as a strong doublet at 2122; 2128 cm⁻¹, ν(C---S) at 783; 770 cm⁻¹, and δ(SCN) at 468; 477 cm⁻¹. No significant changes were observed in the 4-mepy ligand bands compared with the vibrational frequencies of the pure compound or the compound in aqueous solution 0.2 mol l⁻¹. The crystal UV–vis reflectance spectrum presented two bands centered in 626 and 424 nm tentatively assigned to the d→d type transitions, ³A_2g→³T_1g and ³A_2g→³T_1g, for a symmetry close to O_h. The TG curve showed a mass loss between 120 and 200 °C assigned to the loss of the two 4-mepy molecules; from 200 to 265 °C, the loss of the two H⁺SCN groups; and from 265 to 450 °C, the loss of the two SCN groups that formed the bridges among the nickel atoms. Based on these mass loss data, a mechanism of thermal decomposition for the compound was proposed.     

Vibrational predissociation of OCS clusters excited near the ν3 vibration of the monomer

OCS clusters have been produced in a supersonic beam. Dissociation spectra for these clusters have been measured with a diode laser and a bolometer detector. Two sets of results are presented: (1) Results for large clusters with discrete sampling through a range of 80 cm⁻¹ around the ν₃ monomer absorption. In this group the size distribution of the clusters is varied with the stagnation pressure in the source. Broad spectra are obtained (between 20 and 40 cm⁻¹ depending on the pressure) with a maximum blueshift of 12 cm⁻¹ from the monomer absorption. (2) Results for small clusters with a continuous scan. Here narrow (≈ 50 MHz) dissociation lines are observed, if the beam parameters are chosen so as to produce dimers preferentially.     

Infrared and Raman spectra, conformational stability, ab initio calculations of structure, and vibrational assignment of 2-hexyne

The infrared spectra (3500–50 cm⁻¹) of the gas and solid and the Raman spectra (3500–50 cm⁻¹) of the liquid and solid have been recorded for 2-hexyne, CH₃–CC–CH₂CH₂CH₃. Variable temperature studies of the infrared spectrum (3500–400 cm⁻¹) of 2-hexyne dissolved in liquid krypton have also been recorded. Utilizing four anti/gauche conformer pairs, the anti(trans) conformer is found to be the lower energy form with an enthalpy difference of 74±8 cm⁻¹ (0.88±0.10 kJ/mol) determined from krypton solutions over the temperature range −105 to −150 °C. At room temperature it is estimated that there is 42% of the anti conformer present. Equilibrium geometries and energies of the two conformers have been determined by ab initio (HF and MP2) and hybrid DFT (B3LYP) methods using a number of basis sets. Only the HF and DFT methods predict the anti conformer as the more stable form as found experimentally. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH₃ group exhibits almost completely free rotation which is in agreement with the observation of sub-band structure for the degenerate methyl vibrations from which values of the Coriolis coupling constants, ζ, have been determined. The results are compared to similar properties of some corresponding molecules.     

Collective dynamics of sub- and supercritical methanol by inelastic X-ray scattering

Inelastic X-ray scattering experiments have been performed on methanol as a function of density from ambient to the supercritical state. Positive dispersion of the sound velocity, as compared to the hydrodynamic values, is 50% in the ambient condition and decreases to zero at 0.50 g cm⁻³ over the momentum transfer Q = 1–10 nm⁻¹ with lowering density; however, it increases again with a further decrease in density down to 0.20 g cm⁻³in the supercritical state only in the Q-range above 5 nm⁻¹. These results have been interpreted as the formation of small oligomers in the low-density supercritical methanol.     

Intramolecular hydrogen bonding. Spectroscopic and theoretical studies of vibrational transitions in dibenzoylmethane enol

The vibrational structure of the title compound (DBM) was investigated by FTIR spectroscopy in liquid solutions, by FTIR linear dichroism (LD) measurements, and by Raman spectroscopy. The results were supported by the application of theoretical model calculations and analyzed with particular attention to the possible origin of the broad, very strong, and irregularly shaped absorbance band observed in the 1700–1400 cm⁻¹ region. The orientation factors derived from the observed LD data indicate that rotational dynamics of the phenyl groups do not contribute significantly to the broadening of the band. The position of the two sharp Evans transmission windows near 1580 and 1500 cm⁻¹ is unaffected by deuteration of the reactive protons in DBM. The transmissions coincide with prominent peaks in the Raman spectrum and can be assigned to combinations of phenylic modes (9a, 18a) with low IR intensity, but large Raman scattering activity.     

High-field EPR investigation of a series of mononuclear Mn(II) complexes doped into Zn(II) hosts

The five-coordinate mono-halide mononuclear Zn(II) complexes [Zn(tpa)X]⁺ (tpa = tris(2-pyridylmethyl)amine; X = I ([Zn(tpa)I]I; 1a), Br ([Zn(tpa)Br](ZnBr₄)_0.5; 2a) and Cl ([Zn(tpa)Cl](ZnCl₄)_0.5; 3a)) and the six-coordinate mononuclear complex [Zn(tpa)(NCS)₂] (4a) have been synthesized and characterized by X-ray crystallography. The [Zn(tpa)X]⁺ complexes doped with the corresponding [Mn(tpa)X₂] complexes (X = I (1b), Br (2b) and Cl (3b)) have been synthesized and their electronic properties investigated by multifrequency high field EPR (HF-EPR) (95–285 GHz). The magnetically diluted conditions allow the determination of the hyperfine coupling constant A (A = 68.10⁻⁴ cm⁻¹ for 1b–3b). The zero-field splitting parameters (D and E) found for 1b–3b are comparable to those found for neat samples of the [Mn(tpa)X₂] complexes (1b: D = 0.635 cm⁻¹, E/D = 0.189; 2b: D = 0.360 cm⁻¹, E/D = 0.192; 3b: D = 0.115 cm⁻¹, E/D = 0.200). The efficacy of using multifrequency EPR under dilute conditions to precisely determine spin Hamiltonian parameters is discussed.     

Strong antiferromagnetism in the dinuclear 2-pyridone complex with N–C–O bridges: A paddle-wheel analogue of the dinuclear tetracarboxylates

A novel dinuclear complex [Cu₂(μ-L)₄(HL)₂] (1) was isolated from starting 2-pyridone (HL) via a resonance and a tautomeric transformation. Each copper centre is in a square-pyramidal coordination sphere, defined by two oxygen atoms (Cu–O4 1.978(5), Cu–O11 1.964(4) Å) and two nitrogen atoms (Cu–N2 2.003(5), Cu–N3 2.007(5) Å) of four bridging deprotonated pyridin-2-olates and an oxygen atom on the top from a neutral 2-pyridone (Cu–O2 2.227(5) Å), analogous to tetracarboxylate paddle-wheel complexes. Compound 1 was compared with mixed pyridin-2-olato/methanoato analogues [Cu₂(μ-HCO₂)₂(μ-L)₂(HL)₂] · 2CH₃CN (2) and [Cu₂(μ-HCO₂)₂(μ-L)₂(HL)₂] (2a) (2a is an air stable form obtained from 2 outside mother-liquid). The EPR spectra of air stable 1 and 2a show three signals H_z1, H₂ and H_z2, typical for the binuclear systems with spin S = 1, both revealing strong antiferromagnetism 2J = −334 (1) and −324 cm⁻¹ (2a). Interestingly, only for 1 additional H₁ signal at 100 mT is noticed (D(1) = 0.293 cm⁻¹ < hν = 0.320 cm⁻¹ < D(2a) = 0.347 cm⁻¹). On the other hand, several broad signals in the 100–450 mT region, only in the high temperature spectrum for 2a are observed. These results are in agreement with the magnetic susceptibility analysis.     

Monitoring of technical oils in supercritical CO(2) under continuous flow conditions by NIR spectroscopy and multivariate calibration

Metal parts and residues from machining processes are usually polluted with cutting or grinding oil and have to be cleaned before further use. Supercritical carbon dioxide can be used for extraction processes and precision cleaning of metal parts, as developed at Forschungszentrum Karlsruhe. For optimizing and efficiently conducting the extraction process, in-line analysis of oil concentration is desirable. Therefore, a monitoring method using fiber-optic NIR spectroscopy in combination with PLS calibration has been developed. In an earlier paper we have described the instrumental set-up and a calibration model using the model compound squalane in the spectral range of the CH combination bands from 4900 to 4200 cm⁻¹. With this model only poor prediction results were obtained if applied to technical oil samples in supercritical CO₂. In this paper we describe a new calibration model, which was set up for the squalane/carbon dioxide system covering the 323–353 K temperature and the 16–35.6 MPa pressure range. Here, calibration data in the spectral range from 6100 to 5030 cm⁻¹ have been used. This range includes the 5100 cm⁻¹ CO₂ band of the Fermi triad as well as the hydrocarbon 1st overtone CH stretching bands, where spectral features of oil compounds and squalane are more similar to each other.

The root mean-squared error of prediction obtained with this model is 4 mg cm⁻³ for carbon dioxide and 0.4 mg cm⁻³ for squalane, respectively. The utilizability of the newly developed PLS calibration model for predicting the oil concentration and CO₂ density of solutions of technical oils in supercritical carbon dioxide has been tested. Three types of “real world” cutting and grinding oil formulations were used in these experiments. The calibration proved to be suitable for determining the technical oil concentration with an error of 1.1 mg cm⁻³ and the CO₂ density with an error of 6 mg cm⁻³. Therefore, it seems possible to apply this in-line analytical approach on the basis of a cost-effective and time-saving model compound calibration for the surveillance of real world de-oiling and other extraction process based on supercritical carbon dioxide, and furthermore to establish an automated process termination criterion based on this technique.     

Quantitative aqueous attenuated total reflectance Fourier transform infrared spectroscopy : Part II. Integrated molar absorptivities of alkyl carboxylates

A quantitative attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopic method is developed for the analysis of total carboxylate concentration, [COO⁻], in aqueous solution. The short (12–13 μm) and highly reproducible pathlength of the ATR cell permits quantitative subtraction of the water peak at 1640 cm⁻¹. Carboxylate quantitation is based on the area of the asymmetric stretching peak, which is nearly independent of compound structure. The molar absorptivity of alkyl carboxylates in water is 438 ± 58 l mol⁻¹ cm⁻¹, and the integrated molar absorptivity is 2.95 ± 0.08 × 10⁴ l mol⁻¹ cm⁻² (n = 15 compounds, 0.1 M ≤ [COO⁻] ≤ 1.5 M). The [COO⁻] in solutions of mixed carboxylates is measured with a root mean square error of 2.4% and a small (+1.5) positive bias. The accuracy of the method is limited by the assumption that integrated absorbance is constant for all COO⁻ groups.     

A study on the formation mechanism of graphite fluorides by Raman spectroscopy

Raman spectra were measured of highly fluorinated graphite samples prepared at room temperature, 380 and 515 °C. C_xF prepared at room temperature showed a novel downshifted band at 1555–1542 cm⁻¹ along with G band at 1593–1583 cm⁻¹. Similar behavior is also observed for samples prepared at 380 and 515 °C at early stages of fluorination, after which the Raman shifts completely disappeared. Raman spectra as well as X-ray diffraction (XRD) analysis suggest that graphite fluorides, (CF)_n and (C₂F)_n are formed via fluorine-intercalated phase with planar graphene layers.