Electrolyte—formamide interactions studied by raman spectroscopy

The effects of dissolved electrolytes on the structure of liquid formamide have been investigated by Raman spectroscopy. The spectral features are dependent on the concentration and nature of the dissolved electrolyte and are discussed in terms of direct electrolyte formamide interactions. Two vN—H bands, arising from ion—formamide species, have been observed superimposed on the spectrum of residual liquid formamide. The results lend further support to the interaction model for electrolytes in liquid formamide previously proposed by us on the basis of nuclear magnetic resonance and infrared spectral data.     

Fourier-transform raman spectroscopy of minerals

The FTR spectra of a variety of minerals are reported, comprising carbonates, phosphates, arsenates, vanadates, sulphates, molybdates, tungstates, oxides and sulphides. It is shown that FTR can be a fast, non-destructive technique for the study of such minerals.     

Conformational study of the chromophore of C-phycocyanin by resonance raman and electronic absorption spectroscopy.

The conformation of the chromophore of C-phycocyanin (PC) was investigated by using electronic absorption and resonance Raman spectroscopy, and theoretical calculations. Using an A-dihydrobilindione as model compound, the syn, syn, syn conformation was established for the isolated chromophore in solution. For the native PC, the best results were obtained by considering the syn, syn, anti conformation, although the possibility of having a syn, anti, anti conformation could not be excluded.     

Physical gels from PVC: molecular structure of pregels and gels by low-angle neutron scattering

In this paper we report on investigations into the short-range molecular structure of pregels (aggregates formed in dilute solutions) and gels as a function of ageing time, temperature and solvent type. In some solvents (diethyl oxalate and bromobenzene) it is found that the structure of the pregels is cylinder-like or ellipsoid-like. The structure is seen to be the same for the gels and the pregels in the investigated range of transfer momentum which leads us to conclude that the gels are probably fiber-like, a statement in agreement with the morphology observed by Yang and Geil. The fiber section is also about the same order of magnitude as that reported by these authors. Also, further evidence is given for the existence of a second type of physical knot, different from those formed by the more syndiotactic sequences. The validity of the molecular structures deduced from these experiments is discussed in the light of macroscopic properties such as compression modulus and swelling.     

Coherent raman spectroscopy of HCN complexes

Photoacoustic Raman spectroscopy (PARS) is shown to be a sensitive technique for obtaining Raman spectra of hydrogen-bonded complexes in the gas phase. Coherent anti-Stokes Raman spectroscopy (CARS) provides analogous spectra in supersonic expansions. The effective resolution is higher in the latter case due to the cooling and collision-free conditions in the jet. The ability to “tune” complex size by changing expansion conditions is demonstrated in the case of HCN.     

浓度对电荷转移诱导的表面增强拉曼光谱的影响

银溶胶中加入具有双官能团的对氨基苯甲酸分子,功能分子PABA吸附到银粒子上形成Ag-PABA复合物,采用1064nm激发光对复合物进行SERS研究。研究发现,功能分子浓度较低时,b2振动得到极大增强,这是通过功能分子在银纳米粒子间电荷转移的直接结果。浓度较高时,SERS中a1振动占主导地位,因为在这样的体系中,银粒子被功能分子包围,彼此相距较远,跨越粒子的电荷转移被阻断的结果。     

Interference effects in resonance raman spectroscopy

We show that resonance Raman excitation profiles are not generally expected to superimpose on the profile of the absorption spectrum. The discrepancy is due to interference between transition amplitudes of preresonant and more nearly resonant states. Two cases are outlined: in the first the amplitudes have similar magnitudes, and in the second they are quite different. Examples discussed include hemeproteins, visual pigments and resonant scattering from triplet states of molecules. A main point is that qualitative aspects of these interferences may be used to assign states and vibrations. Some new experiments are reported for ferrocytochrome-c scattering.     

Fast resonance raman spectroscopy of short-lived radicals

We report the first application of pulsed resonance Raman spectroscopy to the study of short-lived free radicals produced by pulse radiolysis. A single pulse from a flash-lamp pumped tunable dye laser is used to excite the resonance Raman spectrum of the p-terphenyl anion radical with an initial concentration of 4 × 10^?5 moles per liter and a half life of 2 μs. The spectrum is recorded by an optical multichannel system consisting of an image intensifier coupled to a TV-camera.     

High-resolution nonlinear raman spectroscopy of small molecules

After a review of recent progress in nonlinear coherent Raman spectroscopy of gaseous small molecules we report on measurement by the techniques of intra- cavity cw CARS in Munich and inverse Raman spectroscopy in forward and backward scattering configuations in Dijon.     

Infrared and raman spectroscopy of stressed polyethylene

Polyethylene films were stressed in uniaxial tension at room temperature while the infrared (FTIR) or Raman spectra were simultaneously measured. The purpose of these experiments was to gain an understanding of the molecular origins of the stress-induced vibrational frequency shifts Δν and determine the mechanisms of molecular deformation and fracture of PE molecules with stress σ. The PE samples consisted of ultradrawn, high-density, ultrahigh-molecular-weight, solid-state-extruded films and the stress was applied parallel to the nearly perfectly oriented orthorhombic crystal c-axis direction. The experimental frequency shifting coefficients α = (?ν/?σ)_σ→0 were compared with calculated α values determined from a vibrational analysis of an isolated PE chain using conformational energy minimization methods in which both harmonic and anharmonic (Morse) potential energy functions were used for the C? C stretching modes in the valence force field. The following α values were obtained and are compared with theory (anharmonic case in parentheses, in cm^?1/GPa): C? C symmetric stretch, α(1127) = ?5.9 (?5.3); CC asymmetric stretch, α(1059) = ?11.2 to ?5.7 (?5.8); CH₂ rock, α(730/720) = ?2.0 to ?3.0 (?2.2); CH₂ scissors, α(1472/1462) = ?1.0 to ?1.2 (?1.1); CH₂ twist, α(1295) ? 0(0.8); CH₂ wag, α(1370) undetermined owing to weak bands (?4.6); CH₂ stretch α(3000) ≈ 0. The largest negative frequency shifts were observed for the C? C stretching modes, in agreement with the calculations using the Morse potential. The harmonic potential for C? C stretching resulted in small positive α values for both the CC stretching and CH₂ wagging modes, while the other modes were unaffected by this choice of potential. The relative contribution of C? C bond stretching and C?C valence angle bending to the c-axis strain was about 1:1, in agreement with experiment. The Young's tensile modulus of a PE chain was calculated as E_c = 267 GPa.     

The application of fourier transform raman spectroscopy to the study of paint systems

This paper describes the application of FT Raman spectroscopy to three fields of analytical interest in the coatings industry: (1) an emulsion polymerization is monitored; (2) it is used, in conjunction with FTIR, to characterize an alkyd resin, and to follow its curing reactions; (3) it is used, along with ATR-FTIR, to evaluate painted panels which have been subjected to a prolonged weathering cycle. Points of interest to the analyst are noted, and future developments briefly discussed.     

Microrheology of chemically crosslinked polymer gels by diffusing-wave spectroscopy

The Brownian motion of probe particles in aqueous solutions of poly(vinyl alcohol)(PVA) and in chemically crosslinked PVA gels has been studied by diffusing-wave spectroscopy (DWS). At long time scales the measurements allow us to determine the effect of the crosslinking ratio on the macroscopic viscosity of sols and the shear modulus of gels. The local shear modulus of gels as obtained from the characteristic length of the Brownian cage was found to agree with that measured by classical rheometry and dynamic light scattering (DLS). These microrheological techniques were applied to two polymer gel systems. Substrate induced gradient structure of hydrogels was studied from a microrheological point of view using DLS. It is clearly seen that hydrophobic substrate induces weakly crosslinked network formation at the interface region up to a few millimeters as expected from other experimental facts. Magnetic particle motion in gels under external magnetic field was investigated by DWS. The translational motion of the magnetic particles in gels due to the alternating magnetic force can be detected and found to be superimposed on the relaxation due to the thermal motion.     

Characterization of chemically modified silica gels by DRIFT spectroscopy

Chemically modified silica gels are investigated with respect to identity, purity and degree of surface coverage using diffuse reflectance FTIR (DRIFT) Spectroscopy. We report the results for two bonded HPLC phases, pyrene butyric acid propylamido- and octadecyl-groups grafted on irregular porous silica gel. For quantitative determination calibration standards are prepared by adsorbing structurally similar ligand compounds onto the surface of the silica gel; these coated materials give linear calibration curves up to a concentration of 1 mmol/g modified silica gel.     

Model aluminum-poly(p-phenylenevinylene) interfaces studied by surface raman spectroscopy

Polymeric organic light-emitting diodes (OLEDs) have emerged as inexpensive and versatile alternatives to traditional inorganic-based display technologies. Further advances in this field depend on extending device lifetimes and improving electroluminescence efficiencies, both of which are strongly coupled to the integrity of the electrode/organic contacts. Therefore, the deposition of low-work function metals on organic materials has been extensively studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), and near-edge X-ray adsorption fine structure (NEXAFS) to ascertain information about the chemical and electronic states within the interfacial region. However, to date, the only molecular structural information about metal-organic species formed in these regions has come from fits of theoretical models to existing XPS and UPS data. Very little direct structural information exists about the potential multitude of metal-organic species formed during cathode deposition. We report the use of surface Raman spectroscopy to study the interactions between aluminum and trans-stilbene, a model for poly(p-phenylenevinylene) (PPV). The Raman spectral data suggest preferential formation of covalent Al-C bonds at the vinylene carbons as opposed to the phenyl carbons of PPV.     

Micro and two-dimensional NIR FT raman spectroscopy

The former major problem in conventional Raman spectroscopy in the visible range, the disturbing fluorescence of impurities, has now been eliminated: Raman spectra can be excited by light quanta in the near-infrared range, the energy of which is too low to excite fluorescence spectra. An inherent disadvantage of this technique, the v ⁴-dependence of the intensity of the Raman radiation, is compensated for by using interferometers, which are more powerful, by a factor of several hundred, than grating spectrometers. Raman spectroscopy can now be applied to analyses of real world samples bio materials, food, paintings, micro electronics and new materials, as well as to quality control of raw materials, to production and product control without special sample preparation. By using fiber bundles, Raman spectra can be recorded on line at the sample site, in containers and in real time. For successful recording of NIR FT Raman spectra of small samples a compromise between large lateral resolution and a large signal/noise ratio has to be found. Its theoretical base and practical approach is discussed. Confocal microscopes allow recording of NIR FT Raman spectra of small particles or inclusions. They can be coupled to the spectrometer by fiber optics, so that they may be placed at some distance from the spectrometer. By using computer-driven x-y stages, systematic mapping of the distribution of specific compounds on the surface of different samples is possible with the FT Raman microscope, as well as with the ordinary sample arrangement.     

Quantitative analysis of topical gels and ointments by FT-Raman spectroscopy

A method for quantitative determination of ibuprofen (IBU), naproxen (NAP), methyl salicylate (MES) and menthol (MNT) in commercial topical gels and ointments using partial least squares (PLS) models based on FT-Raman spectra is described. The calculated relative standard errors of prediction (RSEP) were found to be in the range of 2.1–3.2% for the calibration and validation data sets. Two commercial topical gels containing 5.0% of IBU and 10% of NAP (w/w), as well as one ointment containing 15% of MES and 10% of MNT (w/w) as active pharmaceutical ingredients (APIs), were successfully quantified using the developed models with recoveries in the 99.2–101.5% range. The proposed procedure can be used as a fast, reliable and economic method for the quantification of APIs in topical gels and ointments.     

Structure of unsaturated polyester resins crosslinked with styrene as studied by raman spectroscopy

An unsaturated polyester resin and the styrene-crosslinked polyester were studied with laser Raman spectroscopy. Following the polyesterification reaction, Raman measurements showed that the polyester contained 55% fumarate and 45% maleate unsaturation. Additionally, the glycol fragment was indicated to exist as the gauche isomer. The 1213 cm^?1 line is assigned to the glycol-ester linkage and can be measured to follow the conversion to polymer. After the crosslinking reaction, styrene was found to copolymerize preferentially with the fumarate unsaturation. There was no evidence of forming long-chain polystyrene crosslinks. Our results indicate that, after crosslinking, 41% of the fumarates have reacted with styrene and there is an average of two styrene molecules in each link.