Raman and Surface-enhanced Raman Scattering of Chlorophenols

Raman spectrum is a powerful analytical tool for determining the chemical information of compounds. In this study, we obtained analytical results of chlorophenols(CPs) molecules including 4-chlorophenol(4-CP), 2,6-dich- lorophenol(2,6-DCP) and 2,4,6-trichlorophenol(2,4,6-TCP) on the surface of Ag dendrites by surface-enhanced Raman scattering(SERS) spectra. SEM images indicate that the SERS substrate of Ag dendrites is composed of a large number of polygonal nanocrystallites, which self-assembled into a 3D hierarchical structure. It was found that there were distinct differences for those three molecules from Raman and SERS spectra. This indicates that SERS could be a new tool of detection technique regarding trace amounts of CPs.     

Raman and surface-enhanced Raman study of insecticide cyromazine

Surface-enhanced Raman scattering (SERS) spectroscopy is applied to the study of the adsorption of the insecticide cyromazine on Ag colloid. The influence of pH and the aggregation inductors, sodium chloride, potassium nitrate and sodium hydroxide on the adsorption mechanism was investigated. Two different adsorption mechanisms are deduced depending on the experimental conditions: via the N atom bounded to the cyclopropyl (cP) group or through an ionic pairing of protonated amino groups with the chloride adsorbed on the metal. An important contribution of the chemical mechanism was inferred when the interaction with the metal occurs through the N lone pair.     

Stimulated Raman laser excitation of spontaneous resonance Raman scattering

The efficient conversion of the second and third harmonics of a Nd YAG laser to near UV radiation in the 395–500 nm range by stimulated Stokes (and anti-Stokes) Raman scattering (SRS) in a 1 m Raman oscillator containing compressed H₂ or D₂ is used as an excitation source for spontaneous resonance Raman spectroscopy (RRS). SRS excited RR spectra are shown for the anion radical of tetracyanoquinodimethane (TCNQ).     

Polymer-capped fiber-optic Raman probe for non-invasive Raman spectroscopy

Advances in fiber optic probe design are moving Raman spectroscopy into the clinic, although there remain important practical problems. While much effort has been devoted to minimizing Raman and fluorescence background from fibers, less attention has been given to the need to generate reference Raman signals that can correct for variations in tissue albedo, which is important in quantifying changes in tissue composition. To address this shortcoming, we have developed a fiber optic probe that incorporates a fluorinated ethylene-propylene copolymer (FEP) cap at the end of each excitation fiber. Transmission of laser light through the transparent cap generates a 732 cm(-1) Raman band whose intensity scales linearly with the laser power delivered to the tissue of interest. In our first design, the FEP cap functions as a waveguide with only a small insertion loss (~5%). Laser transmission through 1 mm of the polymer is sufficient to generate a usable reference Raman signal. We show the application of the probe to quantitative non-invasive Raman spectroscopy of animal tissues using rat leg phantoms as models. Ex-vivo Raman spectroscopy of excised rat tibia supports the use of the probe for spectroscopy of various tissues. These results provide proof of principle that the Raman probe can be used in multiple spectroscopic applications.     

硒化镉量子点膜的拉曼光谱及拉曼成像分析

研究了CdSe量子点膜的Raman光谱,发现CdSe量子点的横模(TO)振动活性较强,表面模(SO)、纵模(LO)振动不明显。比较了量子点、氧化三辛基膦及十六胺的Raman光谱,证明量子点表面大部分区域被十六胺及二辛胺修饰。在此基础上,对量子点膜的TO模振动及C-H弯曲振动峰进行了Raman成像分析,并与明场图像进行了对比,表明拉曼成像信号对量子点膜的表面变化非常敏感。     

Inverse Raman bands in ultrafast Raman loss spectroscopy

Ultrafast Raman loss spectroscopy (URLS) is equivalent to anti-Stokes femtosecond stimulated Raman spectroscopy (FSRS), using a broadband probe pulse that extends to the blue of the narrow bandwidth Raman pump, and can be described as inverse Raman scattering (IRS). Using the Feynman dual time-line diagram, the third-order polarization for IRS with finite pulses can be written down in terms of a four-time correlation function. An analytic expression is obtained for the latter in the harmonic approximation which facilitates computation. We simulated the URLS of crystal violet (CV) for various resonance Raman pump excitation wavelengths using the IRS polarization expression with finite pulses. The calculated results agreed well with the experimental results of S. Umapathy et al., J. Chem. Phys. 133, 024505 (2010). In the limit of monochromatic Raman pump and probe pulses, we obtain the third-order susceptibility for multi-modes, and for a single mode we recover the well-known expression for the third-order susceptibility, χ(IRS) ((3)), for IRS. The latter is used to understand the mode dependent phase changes as a function of Raman pump excitation in the URLS of CV.     

Raman,surface-enhanced Raman scattering and DFT study of para-nitro-aniline

Raman spectra of para-nitro-aniline (pNA), a molecule with high applicability potential in molecular electronics, were recorded in solid state and in ethanol solution. Complete assignment of the experimental spectra was made by using the B3LYP/6-31G(d) theoretical results. The calculated molecular electrostatic potential shows a high negative charge localized on the nitro group of pNA and the surface-enhanced Raman scattering (SERS) spectrum of pNA adsorbed to colloidal silver particles denote the molecule interaction with the silver surface mainly through the nitro group. However, theoretical results obtained by modeling the pNA–4Ag complex also suggest the adsorption of pNA through the amino group or a flattened orientation of pNA with respect to the silver surface.     

Raman and surface Raman spectroscopy with ultraviolet excitation

We record the accurate and reliable Raman spectra of benzoic acid (BA), p-nitrobenzoic acid (PNBA) and o-nitrobenzoic (ONBA) in aqueous solution with ultraviolet excitation. And we find that the ultraviolet (UV) Raman spectrum of aqueous BA solution has one-to-one correspondence to that of BA solid whereas the others are less resemble to the solid counterparts. We also report surface Raman spectroscopy of them in silver colloid without any enhancement in UV region and call it surface-unenhanced Raman spectroscopy (SUERS) while the surface-enhanced Raman scattering (SERS) effects are perfect in near infrared or visible regions. It demonstrates the SERS effects are strongly dependent on the excitation wavelength. On the basis of the experiments, we discuss the mechanism of SERS excited in different regions.     

Fast Raman spectroscopy of cytochrome c using intracavity resonance Raman amplification

The resonance Raman spectrum of cytochrome c (5 × 10^?4 M) was obtained using the method of resonance Raman amplification (RRA) in a dye laser resonator in 30 ns. The second harmonic of a Q-switched Nd glass laser was used as an excitation source and the spectra were recorded using a photographic plate.     

Rapid monitoring of antibiotics using Raman and surface enhanced Raman spectroscopy

Comparatively few studies have explored the ability of Raman spectroscopy for the quantitative analysis of microbial secondary metabolites in fermentation broths. In this study we investigated the ability of Raman spectroscopy to differentiate between different penicillins and to quantify the level of penicillin in fermentation broths. However, the Raman signal is rather weak, therefore the Raman signal was enhanced using surface enhanced Raman spectroscopy (SERS) employing silver colloids. It was difficult by eye to differentiate between the five different penicillin molecules studied using Raman and SERS spectra, therefore the spectra were analysed by multivariate cluster analysis. Principal components analysis (PCA) clearly showed that SERS rather than the Raman spectra produced reproducible enough spectra to allow for the recovery of each of the different penicillins into their respective five groups. To highlight this further the first five principal components were used to construct a dendrogram using agglomerative clustering, and this again clearly showed that SERS can be used to identify which penicillin molecule was being analysed, despite their molecular similarities. With respect to the quantification of penicillin G it was shown that Raman spectroscopy could be used to quantify the amount of penicillin present in solution when relatively high levels of penicillin were analysed (>50 mM). By contrast, the SERS spectra showed reduced fluorescence, and improved signal to noise ratios from considerably lower concentrations of the antibiotic. This could prove to be advantageous in industry for monitoring low levels of penicillin in the early stages of antibiotic production. In addition, SERS may have advantages for quantifying low levels of high value, low yield, secondary metabolites in microbial processes.     

Raman,resonance Raman and infrared spectra of potassium uranyl croconate

The Raman, resonance Raman and IR spectra of potassium uranyl croconate, UO₂(H₂O)K₂(C₅O₅)₂ were obtained and interpreted. Several croconate modes are split indicating a substantial decrease in the oxocarbon symmetry, as is to be expected from a recent crystallographic investigation, revealing the coordination of the oxocarbon to be two non-equivalent UO²⁺₂ moieties in a monodentate fashion. In terms of vibrational frequency shifts it can be concluded that the UO²⁺₂ moiety behaves as an isolated oscillator.The resonance Raman results suggest that the strong band centered around 450 nm in the UV—vis spectrum should be assigned to a charge transfer transition from the oxocarbon to the uranyl ion. In fact, as resonance is approached, both uranyl and croconate modes are enhanced. It can also be inferred that the chromophore is rather delocalized into the oxocarbon ring, rather than localized in the carbonyl groups as previously observed for other croconate complexes.     

Raman and surface-enhanced Raman spectra of chrysin,apigenin and luteolin

The FT-Raman and surface-enhanced Raman (SER) spectra of three flavonoids, namely chrysin, apigenin and luteolin, have been obtained. The SERS spectra were obtained on citrate reduced Ag colloids. Assignments of the experimentally obtained normal vibrational modes were aided by density functional theory (DFT) calculations using the B3LYP functional and the 6-31+G* basis set. Excellent fits were obtained for the observed spectra with little or no scaling. The most intense lines in the three flavonoids SERS spectra are those in the CO stretching region and around 1250 cm^?1. The first ones are often weakened by proximity of the metal surface, whereas the latter are not affected by the Ag. On the other hand, the lines at lower wavenumbers, assigned to in-plane ring deformation, are strongly enhanced by the surface, indicating a perpendicular orientation of the flavonoids on the Ag surface. The spectra of the flavonoids are compared, and a case study of application to detect weld, a mixture of apigenin and luteolin, in a textile is presented.     

Raman Spectra of Carbohydrates

The Raman spectra of 13 different carbohydrates are investigated by a laser Raman spectrometer. It is found the C—H stretching vibrations around 3000 cm⁻¹ is the best region for qualitative analysis of these compounds. All compounds show an O—H stretching vibration around 3370 cm⁻¹ which was not mentioned by earlier works. Excessive background noise appears in many spectra, probably due to their amorphous stuctures.     

Raman spectroscopy of thiosulphates

The narrow line-width of Fourier transform Raman spectroscopy has been utilized to produce spectra of various simple thiosulphates. The accuracy of the technique has enabled us to show wide frequency shifts and splitting from counter ion to counter ion, and has thrown doubt on the use of vibrational spectra to indicate ion interactions.     

Raman spectroscopy of diamondoids

A selection of diamondoid hydrocarbons, from adamantane to [121321] heptamantane, have been analysed by multi-wavelength laser Raman spectroscopy. Spectra were assigned using vibrational frequencies and Raman intensities were calculated by employing the B3LYP functional and the split valence basis set of Schafer, Horn and Ahlrichs with polarisation functions on carbon atoms. The variation of the spectra and associated vibrational modes with the structure and symmetry of the molecules are discussed. Each diamondoid was found to produce a unique Raman spectrum, allowing for easy differentiation between molecules. Using the peak assignments derived from the calculations we find that the low frequency region of the spectra, corresponding to CCC-bending/CC-stretching modes, is particularly characteristic of the geometric shape of the diamondoid molecules.     

Raman and surface enhanced Raman microscopy of microstructured polyethylenimine/DNA multilayers

We analyze microstructured multilayer films of poly(ethyleneimine) (PEI) and DNA by employing Raman and surface enhanced Raman spectroscopy (SERS). The microstructuring of the samples allows a simultaneous measurement of signal and reference in a single analytic process. Silver nanoparticles are implemented in the microstructured multilayers for SERS measurements. The recorded SERS spectra of PEI/DNA are dominated by the Raman bands of the DNA bases which show a larger mean enhancement than bands belonging to DNA backbone vibrations. Our results show that the combination of SERS and microstructured multilayer films provides an adapted way to characterize the polyelectrolytes as well as to measure the enhancement factor and the distance dependence for the SERS active silver nanoparticles. Furthermore, microstructured polyelectrolyte films containing SERS active nanoparticles are used for sensing molecules.     

Development of Novel Substrates for Surface-enhanced Raman and Surface-enhanced Hyper Raman Spectroscopy

Since its discovery two decades ago, surface-enhanced Raman scattering (SERS) has been explored extensively as a useful technique in the study of molecular behaviors at interfaces and in chemical and biochemical analysis. At solid-liquid interface, SERS has been practiced mainly in aqueous solution on either aggregated metal colloids or roughened metal electrodes. However, both aggregated metal colloids and roughened electrodes have their own problems as SERS substrates. One of the intriguing questions in exploring SERS application in chemistry is that can SERS-activity be gained and regulated from the dispersed metal nanoparticles immobilized on a SERS-inactive smooth electrode surface. The very essence of this question is to explore the effect on SERS-activity when the main features of two conventional SERS-surfaces, namely metal colloids and electrode, are combined. Same question can also be asked for the nonlinear three-photon surface-enhanced hyper Raman scattering (SEHRS).     

钕的电子拉曼光谱和一种新的拉曼增强机理

拉曼光谱是研究分子体系微观结构的一种有力工具 [1] ,由于拉曼信号弱 ,在一定程定上影响了拉曼光谱的应用 .为解决此问题 ,人们一方面采用各种先进的光谱测试技术 ,另一方面广泛运用各种拉曼增强机理 ,以提高拉曼光谱的灵敏度 .到目前为止 ,公认的拉曼增强机理只有共振拉曼增强和表面拉曼增强两种 .最近 ,文献报道了一种称为聚集增强的拉曼增强机理[2 ] .众所周知 ,f电子使稀土具有极丰富的电子能级结构 ,使得稀土元素在发展各种高性能的功能材料方面具有巨大的潜在价值 [3～ 5] .人们利用稀土的能级结构发展各种探针技术以表征分子体系在…