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1.
Two new methods based on FT–Raman spectroscopy, one simple, based on band intensity ratio, and the other using a partial least squares (PLS) regression model, are proposed to determine cellulose I crystallinity. In the simple method, crystallinity in cellulose I samples was determined based on univariate regression that was first developed using the Raman band intensity ratio of the 380 and 1,096 cm?1 bands. For calibration purposes, 80.5% crystalline and 120-min milled (0% crystalline) Whatman CC31 and six cellulose mixtures produced with crystallinities in the range 10.9–64% were used. When intensity ratios were plotted against crystallinities of the calibration set samples, the plot showed a linear correlation (coefficient of determination R 2 = 0.992). Average standard error calculated from replicate Raman acquisitions indicated that the cellulose Raman crystallinity model was reliable. Crystallinities of the cellulose mixtures samples were also calculated from X-ray diffractograms using the amorphous contribution subtraction (Segal) method and it was found that the Raman model was better. Additionally, using both Raman and X-ray techniques, sample crystallinities were determined from partially crystalline cellulose samples that were generated by grinding Whatman CC31 in a vibratory mill. The two techniques showed significant differences. In the second approach, successful Raman PLS regression models for crystallinity, covering the 0–80.5% range, were generated from the ten calibration set Raman spectra. Both univariate-Raman and WAXS determined crystallinities were used as references. The calibration models had strong relationships between determined and predicted crystallinity values (R 2 = 0.998 and 0.984, for univariate-Raman and WAXS referenced models, respectively). Compared to WAXS, univariate-Raman referenced model was found to be better (root mean square error of calibration (RMSEC) and root mean square error of prediction (RMSEP) values of 6.1 and 7.9% vs. 1.8 and 3.3%, respectively). It was concluded that either of the two Raman methods could be used for cellulose I crystallinity determination in cellulose samples. 相似文献
2.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1993,49(5-6):801-807
The Fourier transform (FT) Raman and IR spectra of the shed dorsal skin of the snake Elaphe obsoleta (American black rat snake) are reported. Vibrational spectroscopic assignments are proposed for the first time. Although good quality Raman spectra were obtained from the hinge regions using an FT Raman microscope, the dorsal scale regions fluoresced even with 1064 nm IR excitation. This was ascribed to pigmentation markings on the scales. 相似文献
3.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1994,50(4):765-795
Vibrational spectroscopic studies, including IR vapor, Raman vapor and Raman liquid spectra, have been made to obtain the complete set of fundamental vibrational frequencies in the vapor and liquid states for furan, pyrrole and thiophene. For furan, vapor values have been determined for the two previously ambiguous fundamentals, ν11 and ν18. Also determined is the vapor frequncy of two fundamentals of furan for which only the liquid value had been known. The fundamental vibrational frequencies of pyrrole have been completely determined in the gas and liquid states. The thiophene results confirm the assignment of Rico et al. [Spectrochim. Acta 21, 689 (1965)], although for several of the fundamental modes the vapor frequency is now measured. The Raman vapor spectra are conclusive concerning the refinements in vibrational assignment for furan and pyrrole, where virtually every binary combination band involving the out-of-plane fundamentals that yield an A1 transition is observed. The Raman vapor results establish two significant Fermi resonances affecting fundamental vibration levels in pyrrole. Also, 13C and 34S isotopomers are identified in the Q-branches of the Raman vapor spectra at natural abundance. A comparison of the spectroscopic and calorimetric ideal-gas thermodynamic properties is made. The differences are negligible in the region where the calorimetric data are most reliable. 相似文献
4.
Spontaneous Raman spectra in the BaWO4 were measured in the temperature range from 4 K to 280 K, and the temperature dependence of the linewidth of the Ag (191 cm−1) Raman mode was analyzed using the lattice dynamical perturbative approach and one-phonon density of states (PDOS). The linewidth slope for the 191 cm−1 peak for an external mode is 7.2 times larger than that for the 926 cm−1 peak for a breathing mode. The different behaviors of these two modes in the case of temperature broadening could be attributed to the large energy band gap in the one-phonon density of states (PDOS) resulting in different anharmonic interactions. The origin may be that the ratio of up-conversion TDOS to down-conversion TDOS for Eg mode (191 cm−1) is more than that for Ag (926 cm−1). The peak of the Eg mode (191 cm−1) is attributed to the coupling mode both a rotation of the Barium and an out-of-phase rotation of the oxygen in x–y plane as a librational mode. 相似文献
5.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1994,50(3):399-419
The Raman spectra (3200–10 cm−1) of ethyl methyl selenide in the gas, liquid and solid phases and the infrared spectra (3200–30 cm−1) of the gas and solid have been recorded. Qualitative depolarization ratios have been obtained for the lines in the Raman spectrum of the liquid. By a variable temperature Raman study of the liquid, it has been determined that the gauche conformer is more stable than the trans rotamer by 158±16 cm−1 (452±46 cal mol−1), and the gauche conformer is the rotamer present in the solid. A complete vibrational assignment for the gauche conformer is presented. All of these data are compared to the corresponding quantities obtained from ab initio Hartree—Fock gradient calculations employing the STO-3G* and 4–31G*/MIDI-4* basis sets. Complete equilibrium geometries have been calculated for both rotamers and the results are discussed and compared with the corresponding quantities for some similar molecules. 相似文献
6.
The molecular structure of glassy polystyrenes with different stereoregularity was investigated by infrared, Raman, and solid state high resolution 13C NMR spectroscopies. The characteristic bands observed in infrared spectrum closely relates to the regular sequence length of conformational arrangement. The out-of-plane mode of phenyl ring in 500-600 cm−1 region, which is one of the most conformational sensitive bands for polystyrene, provided no characteristic peaks concerned with longer regular sequence than four monomers. Raman spectrum showed that most of the bands providing different peaks among polystyrenes with different stereoregularity are assumed local phenyl ring modes. Solid state high resolution 13C NMR is available to estimate the gauche content in terms of analysis based on γ-gauche effect. We determined that the gauche content takes 25.0, 27.9, and 34.3% for glassy state of syndiotactic, atactic, and isotactic polystyrenes, respectively. This indicates that the conformational structure of sPS tends to take trans sequence. Since a large content of trans sequence would make the molecular dimension wide, the glassy sPS provided the smallest density for polystyrenes with different stereoregularity. 相似文献
7.
《Vibrational Spectroscopy》2001,25(2):197-204
The crystal structure of the polymorphic form III (hemihydrate) of sulfamethoxazole (SMZ) was determined to exist in both the E- and Z-forms by X-ray analysis and was compared with the polymorphic forms I and II which are known to exist in the E-form. IR spectra of I–III and their corresponding forms ID–IIID which contain the deuterated amino and amido groups and D2O and Raman spectra of I–III have been measured. For I–III, assignment of the stretching vibration [ν(NH) and ν(CH)] bands of amino and amido groups and the CH bond of the isoxazole ring involved in the inter-molecular hydrogen bonds has been proposed based on consideration of the IR and Raman spectra and the results of X-ray analysis. A relationship was established between the relative intensity and wavenumbers for the ν(CH) band in the inter-molecular C(sp2)H⋯X hydrogen bond of the E-form. 相似文献
8.
Steffen Fischer Karla Schenzel Klaus Fischer Wulf Diepenbrock 《Macromolecular Symposia》2005,223(1):41-56
FT Raman spectroscopy and micro spectroscopy were used for the investigation of cellulose, cellulose derivatives and cellulosic plant fibres. Lattice structures of cellulose, polymorphic modifications I and II, as well as amorphous structure, were clearly identified by means of FT Raman vibrational spectra. Chemometric models were developed utilizing univariate calibration as well as methods of multivariate data analyses of FT Raman spectral data for the fast prediction of cellulose properties. Cellulose properties like the degree of crystallinity XcRaman, the degree of substitution DSCMC, DSAC and cellulose reactivity were determined. In situ/ in vivo FT Raman micro spectroscopy was used for the characterization of cellulose structures of flax and hemp fibres. Orientational and stress dependent FT Raman experiments were carried out. 相似文献
9.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1991,47(9-10):1389-1393
Fourier transform (FT)-Raman spectroscopy, utilizing a near-infrared (Nd:YAG laser, at 1.064 μm) source was used to characterise the three anhydrous polymorphic forms A, B and C of the drug cimetidine (N″-cyano-N-methyl-N′ -[2-[(5-methyl-1H-imidazol-4-yl) methylthio]ethyl]guanidine). The FT-Raman spectra were free from fluorescence interference and had good signal-to-noise ratios. Each polymorph has a distinct spectrum, characterised by two regions, 1250-1050 cm−1 and 1500-1350 cm−1. This work demonstrates that it is possible to use FT-Raman spectroscopy to differentiate between polymorphic forms of the same compound. 相似文献
10.
Annamma John Daizy Philip Keith R. Morgan S. Devanarayanan 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(14):386
The FT IR and FT Raman spectra of Co(en)3Al3P4O16 · 3H2O (compound I) and [NH4]3[Co(NH3)6]3[Al2(PO4)4]2 · 2H2O (compound II) are recorded and analysed based on the vibrations of Co(en)33+, Co(NH3)63+, NH4+, Al---O---P, PO3, PO2 and H2O. The observed splitting of bands indicate that the site symmetry and correlation field effects are appreciable in both the compounds. In compound I, the overtone of CH2 deformation Fermi resonates with its symmetric stretching vibration. The NH4 ion in compound II is not free to rotate in the crystalline lattice. Hydrogen bonding of different groups is also discussed. 相似文献
11.
Reikichi Iwamoto Masaru Miya Seiichi Mima 《Journal of Polymer Science.Polymer Physics》1979,17(9):1507-1515
Laser Raman spectra of atactic poly(vinyl alcohol) (PVA) after heat treatment and/or swelling in water have been obtained. An amorphous Raman band is observed at 1124 cm?1, while a crystalline Raman band is found at 1147 cm?1. A new method for crystallinity determination is proposed, in which the amorphous band is used instead of the crystalline band. The method is superior to others for water-swollen PVA samples. Laser Raman spectra of swollen PVA revealed that swelling causes destruction of a major fraction of the crystalline regions and the remaining intact crystalline part increases with increasing temperature of heat treatment. 相似文献
12.
An unpolarized, differential technique is described for obtaining the dichroic spectra of uniaxial liquid crystals from a single spectral scan. Using this method, we investigate the near infrared dichoic spectrum of n-heptyl cyanobiphenyl (7CB). The temperature dependence of the orientational order parameter has been derived close to the nematic-isotropic transition and this is in good agreement with earlier Raman data. The differential method is also advantageous for dichroic studies on oriented guest molecules in liquid crystals. Illustrative results are presented for p-nitrotoluene dissolved in a nematic medium. 相似文献
13.
《Vibrational Spectroscopy》2010,52(2):218-225
Plausible structures of the titanium tetramethoxide trimer were optimized at the B3LYP/6-31+G* level. From the four types of structures of the Ti3O12 cage found earlier for the Ti(OH)4 trimer only two isomers were found as energy minima on the Ti3(OMe)12 potential energy surface. One isomer (I), belonging to the Ci point group, is built from three interconnected titanium oxide tetrahedra with a linear arrangement of titanium atoms. This structure have a titanium oxide skeleton similar to that of Ti3(OH)12. The other isomer (II), of C2 symmetry, is built by edge sharing TiO6 groups. Theoretical IR spectra of these isomers are compared with reported experimental IR spectra of solid titanium tetramethoxide and newly obtained Raman spectra of commercial powders. It was shown that the number and position of observed bands in the CO stretching region of the IR spectra of the so-called modification A of solid titanium tetramethoxide are in a good agreement with the predicted vibrational spectrum of trimer I. The equilibrium structure and IR and Raman spectra were also obtained for the Ti4(OMe)16 tetramer. The comparison of the predicted vibrational spectrum with the experimental IR spectra of modification B as well as of the Raman spectrum of solid titanium tetramethoxide allows us to confirm the tetrameric structure of this modification and to propose the similar structure for commercial samples. 相似文献
14.
In this study a novel polymer composite electrolytes (PCEs) based on poly (vinyl alcohol) (PVA): Ce(III)-complex:NH4SCN plasticized with glycerol are prepared by solution cast technique. XRD and FTIR routes are used to study the film structure. The crystalline and amorphous areas are determined through the deconvolution of XRD spectra and their values were used to calculate the degree of crystallinity. The deconvolutions of the FTIR of asymmetric C≡N stretching mode are carried out to establish the bands coupled with free ions, contact ion pairs and ion aggregates. The maximum ambient temperature DC conductivity of 2.07 × 10−3 S cm−1 is recorded for the sample with the lowest degree of crystallinity. It was found that the number density (n), mobility (μ) and diffusion coefficient (D) of ions are increased with the glycerol concentration. Field emission scanning electron microscopy (FESEM) is used to examine the effect of plasticizer on film morphology. The DC conductivity trend is interpreted in detail with the help of dielectric properties. It is found that the transference numbers of ions (tion) and electrons (tel) are 0.965 and 0.035, respectively. It is shown by the linear sweep voltammetry (LSV) that the potential window of the PCE is 2.1 V. A shape, which is nearly rectangular at lower scan rates, is identified from cyclic voltammetry (CV). Specific capacitance and energy density are exhibited by EDLC with average of 161.5 F/g and 18.17 Wh/kg, respectively within 400 cycles. The initial power density is shown by EDLC to be 2.825 × 103 W/kg. 相似文献
15.
János Rétey William E. Hull Feliska Snatzke Günther Snatzke Ulrich Wagner 《Tetrahedron》1979,35(15):1845-1849
The pH-dependence of the 1H NMR and Circular Dichroism (CD) spectra of 2-methylsuccinic acid was investigated. Both spectra undergo dramatic changes between pH 4 and 6, where both carboxylic groups become ionized. From the coupling constants of the tertiary proton with the assigned1 diastereotopic methylene protons, it is concluded that below pH 4 the syn-clinal (2) and above pH 6 the anti-periplanar (1) conformation of methylsuccinic acid prevail. The diesters of methylsuccinic acid also assume mainly the syn-clinal conformation (2). The pH-dependence of the CD spectra is discussed in terms of conformation and/or ionization effects. 相似文献
16.
《Vibrational Spectroscopy》2007,43(1):125-139
Complete (full) set of the polarised Raman spectra for the α-glycine single crystal at room temperature are presented. For the strongest bands arising from the νsCH2, νaCH2, δCH2, τCH2, νCOO−, δCOO and νsCCN vibrations effective local Raman tensors are determined applying the Tsuboi approach. The obtained results are compared to literature data available on this problem. Unfortunately, significant differences are observed between our data and other published results. This is due to the improper single crystal sample preparation for polarised Raman spectra measurements in the past. The obtained results are presented in forms which allow to apply these data for the polarised Raman spectra of other crystals of glycine compounds. 相似文献
17.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1981,37(5):305-314
Rotational isomerism associated with internal rotation about the ring carbon(3)-ester carbonyl carbon single bond in a series of 3-ethoxycarbonyl-4(1H)-quinolones have been investigated spectroscopically in the solid state using Fourier transform i.r. and laser Raman spectroscopy. Particular attention is given to the 1700, 1300 and 1100 cm−1 spectral regions related primarily to the vibrations of the CO2C2H5 group. Within these regions rotational isomerism appeared in the compounds examined. The conformational changes are discussed and evidence is reported for occurrence of the unsubstituted compound 1 itself in the solid state at ambient temperature as an equilibrium mixture of both the s-trans (1a) and s-cis (1b) rotamers (this is in contrast to previous findings), and of its Bz-substituted derivatives. 相似文献
18.
Hidetsura Cho Yoshio Nishimura Hiroshi Ikeda Mitsuhiro Asakura Shinji Toyota 《Tetrahedron》2018,74(20):2405-2413
Experimental and theoretical studies on the thermodynamics and properties of 2-substituted 6(4)-methyl-1,4(1,6)-dihydropyrimidine-5-carboxylates were undertaken by 1H NMR measurements and DFT (density functional theory) calculations. The ratios of tautomers a/b of dihydropyrimidines (DPs) 1, 2, and 3 were determined under various conditions to reveal the effects of temperature, solvent, and concentration on the thermodynamic data. The observed results, the free energy differences (ΔG), enthalpy differences (ΔH), and entropy differences (ΔS), are discussed in terms of the molecular structures, dipole moments (DM), and the electrostatic potential maps calculated by the DFT to clarify the nature of the DPs. 相似文献
19.
The IR (50–3500 cm?1) and Raman (20–3500 cm?1) spectra have been recorded for gaseous and solid dimethylethylamine. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values have been obtained. Due to the fact that three distinct Raman lines disappear on going from the fluid phases to the solid state, it is concluded that the molecule exists as a mixture of the gauche and trans conformers in the fluid phases with the gauche conformer being more stable and the only one present in the spectra of the unannealed solid. From the temperature study of the Raman spectrum of the liquid a rough estimate of 3.9 kcal mol?1 has been obtained for ΔH. Relying mainly on group frequencies and relative intensities of the IR and Raman lines, a complete vibrational assignment is proposed for the gauche conformer. The potential functions for the three methyl rotors have been obtained, and the barriers to internal rotation for the two CH3 rotors attached to the nitrogen atom have been calculated to be 3.51 and 3.43 kcal mol?1, whereas the barrier for the CH3 rotor of the ethyl group has been calculated to be 3.71 kcal mol?1. The asymmetric torsional mode for the gauche conformer has been observed in both the IR and Raman spectra of the gas at 105 cm?1 with at least one hot band at a lower frequency. Since the corresponding mode has not been observed for the trans conformer, it is not possible to obtain the potential function for the asymmetric rotation although estimates on the magnitudes of some of the terms have been made. Significant changes occur in the low-frequency IR and Raman spectra of the solid with repeated annealing; several possible reasons for these changes are discussed and one possible explanation is that a conformational change is taking place in the solid where the trans form is stabilized by crystal packing forces. These results are compared to the corresponding quantities for some similar amines. 相似文献