Microanalysis of clay‐based pigments in painted artworks by the means of Raman spectroscopy

FT Raman spectroscopy and micro‐Raman spectroscopy with lasers of three different wavelengths (1064 nm, 785 nm and 532 nm) were used for analysis of reference samples of natural clay pigments including white clay minerals (kaolinite, illite, montmorillonite), green earths (glauconite and celadonite) and red earths (natural mixtures of white clay minerals with hematite). In addition, eight micro‐samples obtained from historical paintings containing clay pigments in ground and colour layers have been examined. Powder X‐ray diffraction and micro‐diffraction were used as supplementary methods. It was found that laser operating at 1064 nm provided the best quality Raman spectra for distinguishing different white clay minerals, but the spectra of green and red earths were affected by strong fluorescence caused by the presence of iron. Green earth minerals could be easily distinguished by 532 or 785 nm excitation lasers, even in small concentrations in the paint layers. On the other hand, when anatase (TiO₂) or iron oxides (such as hematite) were present as admixtures (both are quite common, particularly in red earths), the collection of characteristic spectra of clay minerals which form the main component of the layer was hindered or even prevented. Another complicating factor was the fluorescence produced by organic binders when analysing the micro‐samples of artworks. In those cases, it is always necessary to use powder X‐ray micro‐diffraction to avoid misleading interpretations of the pigment's composition. Copyright © 2013 John Wiley & Sons, Ltd.     

Infrared versus light scattering techniques to monitor the gel to liquid crystal phase transition in lipid membranes

In this study, Fourier transform infrared, Raman and Brillouin spectroscopy have been used to study lipid phase behavior of hydrated as well as dried multilamellar l ‐α‐phosphatidylcholine assemblies, in order to compare limitations and potentials of the different techniques. Dried lipid samples have been studied in the presence and absence of trehalose, which is known to affect the phase behavior of these systems. The methylene C‐H stretching (2800–3000 cm⁻¹) region in infrared (IR) and Raman spectra provided mutually consistent information on the rearrangement of lipid acyl chains occurring at the lipid melting temperature. IR spectra have a higher signal‐to‐noise ratio, thus permitting a more precise evaluation of the melting temperature. In the hydrated lipid samples, the C‐H stretching region in the Raman spectra is less affected by the contribution of water compared with that in the IR spectra. Raman spectra are particularly suitable to simultaneously study both lipid and water contributions allowing to distinguish ice from non‐frozen water below 0 °C. Brillouin light scattering was used to probe the collective dynamics, i.e. the propagation velocity and the attenuation of longitudinal acoustic modes in the lipid samples. Lipid phase transitions are evident from a change in the temperature behavior of the acoustic velocity. Moreover, a strong relaxation process with a characteristic time of 14 ps was observed in the sample dried without trehalose with a maximum in acoustic attenuation at about 45 °C, which likely reflects the rearrangement of acyl chains. Copyright © 2015 John Wiley & Sons, Ltd.     

The use of Raman microscopy and laser desorption ionization mass spectrometry in the examination of synthetic organic pigments in modern works of art

Synthetic organic pigments are widely used in modern and contemporary works of art. They have been examined by a variety of techniques including spectroscopic methods such as Fourier transform infrared spectroscopy, Raman, and X‐ray powder diffraction as well as chromatographic or mass spectrometric techniques such as pyrolysis‐gas chromatography/mass spectrometry and laser desorption ionization mass spectrometry (LDI–MS). Often, a combination of techniques has been used to examine these pigments. This paper describes use of Raman spectroscopy to create a database of colorants including two pigments not previously reported, PO1 and PO2. Then, using Raman spectroscopy in combination with LDI–MS, samples from modern works of art by artists including Mark Rothko, Barnett Newman, and José de Rivera were examined in order to identify the pigments present. One finding was that Rothko used a variety of red pigments over the course of his career including PR11 which has not been previously reported in artwork, and PO2 found with its positional isomer PR1. Knowledge of the colorants serves to inform conservators about display and treatment decisions. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

CW measurements of resonance Raman profiles,line‐widths,and cross‐sections of fluorescent dyes: application to Nile Blue A in water and ethanol

The aim of this work is to illustrate the power of recently developed methods for measuring resonance Raman scattering (RRS) spectra of efficient fluorophores (using a standard continuous wave excitation and a charge‐coupled device (CCD)‐based Raman spectrometer), by applying them to a detailed study of a specific fluorophore: Nile Blue A. A combination of methods are used to measure the RRS properties of Nile Blue A in water (quantum yield (QY) of 4%) and ethanol (QY of 22%) at excitation wavelengths between 514 and 647 nm, thus covering both pre‐resonance and RRS conditions. Standard Raman measurements are used in situations where the fluorescence background is small enough to clearly observe the Raman peaks, while the recently introduced polarization‐difference RRS and continuously shifted Raman scattering are used closer to (or at) resonance. We show that these relatively straightforward methods allow us to determine the Raman cross‐sections of the most intense Raman peaks and provide an accurate measurement of their line‐width; even for broadenings as low as ∼ 4 cm ^{− 1}. Moreover, the obtained Raman excitation profiles agree well with those derived from the optical absorption by a simple optical transform model. This study demonstrates the possibility of routine RRS measurements using standard Raman spectrometers, as opposed to more complicated time‐resolved techniques. Copyright © 2013 John Wiley & Sons, Ltd.     

SERS of the anti‐inflammatory drug piroxicam adsorbed on the surface of silver or gold colloids as nanocarrier model

Piroxicam is a non‐steroidal anti‐inflammatory drug actually used with limitations because of serious side effects. It is poorly soluble in pure water and exhibit a minimum of four conformers according to the pH conditions of the solution, but not all of them are medically active. In this study, we present, firstly, the Raman characterization of piroxicam in different organic solvents (dimethyl sulfoxide, 1,4‐dioxane, ethanol, 1‐propanol). These results have permitted us to analyze surface‐enhance Raman scattering spectra of piroxicam adsorbed on gold or silver nanoparticles surface at several pHs (1, 2, 4, and 7), imitating the environment of the drug in the body, either in the gastrointestinal tract or in healthy and disease tissues. Results indicate that, below pH = 7, piroxicam is mainly in the zwitterionic conformer, and molecules are oriented parallel to the noble metal surface; however at pH ≥ 7, the main specie detected is the anionic one, differently oriented with respect to the nanoparticle surface. The metal‐piroxicam systems here characterized by surface‐enhance Raman scattering spectroscopy could constitute nanocarriers in future projects of transporting and releasing of the drug in the body. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparison of the discriminating power of Raman and surface‐enhanced Raman spectroscopy with established techniques for the examination of liquid and gel inks

The ability to discriminate between inks is important for forensic document analysis. Here, Raman spectroscopy (RS) and surface‐enhanced RS have been compared to the traditional document examination techniques of video spectral comparison and thin layer chromatography on a population of blue and black‐coloured liquid and gel inks. It was found that in most cases, the Raman techniques provided a similar or better discriminating power than the conventional methods. Importantly, this study allowed us to determine whether the same underlying changes in composition were being exploited by the different methods to discriminate between samples. It was found that there was indeed a high degree of commonality in the sample pairs being discriminated by the various techniques. This work can therefore underpin introduction of Raman methods into standard operating procedures for ink analysis since it not only measures the extent of discrimination between samples but can also explain the origin of the spectral changes that are used to distinguish between them. © 2013 John Wiley & Sons Ltd and Crown copyright     

XANES speciation of mercury in three mining districts – Almadén,Asturias (Spain), Idria (Slovenia)

The mobility, bioavailability and toxicity of mercury in the environment strongly depend on the chemical species in which it is present in soil, sediments, water or air. In mining districts, differences in mobility and bioavailability of mercury mainly arise from the different type of mineralization and ore processing. In this work, synchrotron‐based X‐ray absorption near‐edge spectroscopy (XANES) has been taken advantage of to study the speciation of mercury in geological samples from three of the largest European mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). XANES has been complemented with a single extraction protocol for the determination of Hg mobility. Ore, calcines, dump material, soil, sediment and suspended particles from the three sites have been considered in the study. In the three sites, rather insoluble sulfide compounds (cinnabar and metacinnabar) were found to predominate. Minor amounts of more soluble mercury compounds (chlorides and sulfates) were also identified in some samples. Single extraction procedures have put forward a strong dependence of the mobility with the concentration of chlorides and sulfates. Differences in efficiency of roasting furnaces from the three sites have been found.     

Raman and infrared studies of synthetic Maya pigments as a function of heating time and dye concentration

Maya Blue is a famous indigo‐based pigment produced by the ancient Mayas. The organic/inorganic complexes inspired by Maya Blue have led to a new class of surface compounds that have novel applications to pigment industries. Materials analyzed in the present work are made by a synthetic route, and demonstrate chemical stability similar to that of the ancient Maya Blue samples. However, we have learned that stable complexes can be synthesized at much higher dye concentrations than used by the Mayas. Analysis by FT‐Raman and FT‐IR spectroscopy demonstrates the partial elimination of the selection rules for the centrosymmetric indigo, indicating distortion of the molecule. This distortion accounts for the observed color changes, as the molecular orbital structure is modified, allowing the complex to stabilize. The spectroscopic data also shows the disappearance of the indigo N H bonding, as the organic molecules incorporate into palygorskite material. A structural change of indigo to dehydroindigo during heating is suggested by this result. Infrared data confirm the loss of zeolitic water and a partial removal of structural water after the heating process. Evidence of bonding between cationic aluminum and dehydroindigo through oxygen and nitrogen is revealed by FT‐Raman measurements at higher dye concentrations. Copyright © 2007 John Wiley & Sons, Ltd.     

Rapid outdoor non‐destructive detection of organic minerals using a portable Raman spectrometer

Raman spectral signatures have been obtained for a series of organic minerals using a compact portable Raman instrument equipped with 785‐nm laser excitation. Well‐resolved Raman spectra of crystalline salts of carboxylic acids, whewellite and mellite, as well as of the aromatic mineral idrialite were recorded. For comparative purposes, an amorphous fossil resin, baltic amber, was also investigated. The results obtained confirm that portable Raman instruments can be considered as excellent tools for field geological applications, including the detection of organic minerals in the frame of outcrops of sedimentary rocks or coal beds. Organic minerals can be added to the list of established biomarkers, including porphyrins, hydrocarbons and organic acids, which are important for the study with regard to future exobiological missions such as the ESA ExoMars mission to detect the presence of extinct or extant life on Mars. Copyright © 2009 John Wiley & Sons, Ltd.     

Approximate chemical analysis of volcanic glasses using Raman spectroscopy

The effect of chemical composition on the Raman spectra of a series of natural calcalkaline silicate glasses has been quantified by performing electron microprobe analyses and obtaining Raman spectra on glassy filaments (~450 µm) derived from a magma mingling experiment. The results provide a robust compositionally‐dependent database for the Raman spectra of natural silicate glasses along the calcalkaline series. An empirical model based on both the acquired Raman spectra and an ideal mixing equation between calcalkaline basaltic and rhyolitic end‐members is constructed enabling the estimation of the chemical composition and degree of polymerization of silicate glasses using Raman spectra. The model is relatively insensitive to acquisition conditions and has been validated using the MPI‐DING geochemical standard glasses 1 as well as further samples. The methods and model developed here offer several advantages compared with other analytical and spectroscopic methods such as infrared spectroscopy, X‐ray fluorescence spectroscopy, electron and ion microprobe analyses, inasmuch as Raman spectroscopy can be performed with a high spatial resolution (1 µm²) without the need for any sample preparation as a nondestructive technique. This study represents an advance in efforts to provide the first database of Raman spectra for natural silicate glasses and yields a new approach for the treatment of Raman spectra, which allows us to extract approximate information about the chemical composition of natural silicate glasses using Raman spectroscopy. We anticipate its application in handheld in situ terrestrial field studies of silicate glasses under extreme conditions (e.g. extraterrestrial and submarine environments). © 2015 The Authors Journal of Raman Spectroscopy Published by John Wiley & Sons Ltd     

可见光-近红外、中红外光谱的土壤有机质组分反演

土壤有机质是土壤肥力的物质基础,其含量的高低是评价土壤肥力的重要标志。土壤有机质组分根据其溶解性可分为胡敏素(HM)、胡敏酸(HA)、富里酸(FA),不同组分的肥力特性差异显著,因此,土壤有机质组分数据可更加全面、客观的反映土壤肥力状况。传统土壤土壤有机质及组分的测定工序繁杂,效率低下且时效性差,大量研究表明高光谱技术能有效提高土壤属性的检测效率并降低测试成本,但关于可见光-近红外、中红外光谱检测土壤有机质组分的报道鲜见。为了探索中红外光谱及可见光-近红外-中红外组合光谱对土壤有机质组分检测的可行性,并对比有机质单一光谱模型与有机质不同组分的组合光谱模型的预测精度,以南疆地区农田土壤为例,在阿克苏及和田地区共采集93个土样,进行有机质、胡敏素、胡敏酸、富里酸含量及光谱数据的测定。其次,利用可见-近红外(VNIR)、中红外(MIR)及其组合光谱(VNIR-MIR)三种光谱数据集,采用偏最小二乘(PLSR)、支持向量机(SVM)、随机森林(RF)三种建模方式对土壤有机质、胡敏素、胡敏酸、富里酸含量进行组合模型分析预测。结果表明：(1)土壤有机质及各组分均与光谱反射率有较好的相关性,土壤有机质及组分在MIR谱段的特征波段数量明显多于VNIR谱段。(2)有机质最优预测模型的模式为VNIR-MIR-RF,该模型的决定系数R2为0.90;胡敏素与胡敏酸最优预测模型的模式均为VNIR-RF模型,R2均为0.92;富里酸最优预测模型的模式为MIR-RF模型,R2为0.94。(3) 基于胡敏素、胡敏酸和富里酸的有机质组合光谱模型的预测精度明显高于有机质单一光谱模型,两种模型的R2分别为0.93和0.90。实现了土壤有机质组分的高效快速反演,且基于有机质组分的组合模型提高了土壤有机质预测精度,为南疆地区大尺度土壤肥力的鉴定与精准施肥提供重要的参考价值。     

Laser wavelength dependence of background fluorescence in Raman spectroscopic analysis of synovial fluid from symptomatic joints

Gout is a disease process where the nucleation and growth of crystals in the synovial fluid of joints elicit painful arthritis‐like symptoms. Raman spectroscopy is evolving as a potential diagnostic tool in identifying such crystals; however, attainment of sufficient Raman signal while overcoming the background fluorescence remains as a major challenge. The current study focused on assessing whether excitation in 532–700 nm range will provide greater signal intensity than the standard 785 nm while not being impeded by background fluorescence. We characterized the fluorescence spectra, absorption spectra and Raman spectra of synovial fluid from patients who presented ‘gout‐like symptoms’ (symptomatic) and controls (asymptomatic). A digestion and filtration method was developed to isolate crystals from synovial fluid while reducing the organic burden. Spectral profile and photobleaching dynamics during Raman spectroscopy were observed under an excitation wavelength range spanning 532 to 785 nm. Absorbance and fluorescence profiles indicated the digestion and filtration worked effectively to extract crystals from symptomatic synovial fluid without introducing additional fluorescence. Raman spectral analyses at 532 nm, 660 nm, 690 nm and 785 nm indicated that both asymptomatic and symptomatic samples had significant levels of fluorescence at excitation wavelengths below 700 nm, which either hindered the collection of Raman signal or necessitated prolonged durations of photobleaching. Raman‐based diagnostics were more feasible at the longest excitation wavelength of 785 nm without employing photobleaching. This study further demonstrated that a near‐infrared (NIR) OEM‐based lower‐cost Raman system at 785 nm excitation has sufficient sensitivity to identify crystals isolated from the synovial fluid. In conclusion, while lower excitation wavelengths provide greater signal, the fluorescence necessitates NIR wavelengths for Raman analysis of crystal species observed in synovial aspirates. Copyright © 2013 John Wiley & Sons, Ltd.     

SERS detection of red organic dyes in Ag‐agar gel

Micro‐Raman spectroscopy has been widely employed in the last few years for the study of artworks, allowing for the characterization of a high class of pictorial materials. However, the detection of organic dyes by conventional Raman spectroscopy is quite difficult, due to the high fluorescence provided by these compounds. Recently, remarkable improvements have been achieved by the introduction of the surface enhanced Raman spectroscopy (SERS) technique for the analysis of organic dyes. In the present work, a new method is presented, based on the use of a SERS probe made of agar‐agar coupled with silver nanoparticles, for a non‐destructive and minimally invasive micro‐extraction of dyes from textiles. Ag‐agar gel has been tested first on textile mock‐ups dyed with alizarin, purpurin and carminic acid. SERS measurements have been performed adopting laser light excitations at 514.5 and 785 nm of a micro‐Raman setup. Highly structured SERS band intensities have been obtained. After having verified the safety of the method by colorimetric, X‐ray fluorescence and attenuated total reflectance Fourier transform infrared techniques, a real case, a pre‐Columbian piece of textile, have been investigated by Ag‐agar gel. This cutting‐edge method offers new possibilities for a sensitive and non‐destructive analysis of fluorescent materials. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman spectroscopic investigations on intermolecular interactions in aggregates and crystalline forms of trans‐astaxanthin

Astaxanthin is a carotenoid naturally found in microbial organisms, microalgae, and many crustaceans. Its consumption has led to beneficial effects such as pigmentation of marine animals, and it favorably addresses several human health issues as a result of its high important antioxidant property. Several companies produce synthetic trans‐astaxanthin for dietary purposes in aquaculture, where it is mainly used for pigmentation. It is known that trans‐astaxanthin manifests itself as a monomer in organic solvents, as aggregates in aqueous solutions of organic solvents, or as crystalline solids. These forms display unique optical and structural properties, which have an impact on biological systems. In this work, we report on detailed Raman investigations, in conjunction with optical absorption spectroscopy, of monomer, aggregates, and crystalline forms of trans‐astaxanthin. The Raman and optical absorption spectroscopic investigations of trans‐astaxanthin aggregates were performed as a function of time, showing the formation of card‐packed aggregates after 2 h, and head‐to‐tail aggregates after 24 h in a 10% acetone–water astaxanthin solution. For the crystalline trans‐astaxanthin, a pointwise Raman mapping evidenced the presence of two distinct crystal structures. The Raman modes of these crystal structures (A and B) were correlated with the intermolecular interactions present in chloroform solvated (AXT‐Cl) and unsolvated (un‐AXT) trans‐astaxanthin single crystals. Both crystal structure A and the card‐packed aggregates have similar intermolecular π stacking interactions as AXT‐Cl. The crystal structure B and the head‐to‐tail aggregates showed linear chain features as in un‐AXT. This work also clearly demonstrates that Raman spectroscopy is a powerful tool to distinguish the crystal structures present in crystalline powder of trans‐astaxanthin. Copyright © 2012 John Wiley & Sons, Ltd.     

Applications of Raman and Surface-Enhanced Raman Scattering Techniques to Humic Substances

This paper highlights the use of Raman, FT-Raman and surface-enhanced Raman scattering (SERS) techniques for the study of humic substances. In contrast to other technologies which reveal information only about the average compositions and the kinds of functional groups present in humic substances, Raman and especially FT-Raman spectroscopies characterize the building blocks of humic substances and their changes in derivation and separation processes. Furthermore, surface-enhanced Raman scattering (SERS) techniques are able to readily detect humic substances and co-existing organic species at low concentrations typically found in natural environments and reveal definitive information about the specific groups in humic substances that bind on metal electrodes. Further applications of both Raman and SERS techniques can be extended to complicated systems as well as real environmental samples. Experiments have demonstrated: (1). the backbones of humic substances are structurally disordered carbon networks in most cases; (2). The backbones of humic substances from different sources and types are similar to each other; (3). Normal Raman spectroscopic study of humic substances should concentrate on the use of near-IR laser(s) resulting from strong fluorescence background and self-adsorption under the excitation with visible laser irradiation; (4). FT-Raman spectroscopy is the required analytical method to assess the effectivity of fractionation methods; (5). SERS spectra of humic substances on metal colloids and films are in most aces very similar to the corresponding Raman spectra of neutralized samples; (6). SERS techniques are very sensitive and highly selective, also both visible lasers and near-IR lasers can be used for SERS study; (7). SERS spectra on metal electrodes may provide additional information about the binding sites and adsorption mechanisms of humic substances on metal surfaces.     

Plasmonic effects and the morphology changes on the active material P3HT:PCBM used in polymer solar cells using Raman spectroscopy

There is no consensus yet that the enhancement effects of plasmonic device are predominantly caused by plasmonic effects or induced morphology changes in the optoelectronic `materials. Herein, we present a detailed Raman characterization of a typical organic P3HT:PCBM system comprising silver nanowires (Ag NWs) with different size, which can simultaneously study the plasmonic effects and the morphology changes. The direct comparison of the Raman spectra of non‐annealed and annealed samples indicates that the morphology of plasmonic samples has changed before annealing and the morphology of plasmonic samples and reference sample after annealing is not distinguishable. This indicates that the interaction between P3HT and Ag NWs with different size can be explained by plasmonic effects after annealing. Moreover, in‐situ Raman spectroscopy is used to study the morphology changes in plasmonic samples with different diameters of Ag NWs during heating process. This method can distinguish the plasmonic effects and morphology changes of plasmonic device. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of grain size distribution on Raman analyses and the consequences for in situ planetary missions

Raman spectroscopy can be used for analysing both mineral and organic phases, thus allowing characterisation of the microbial‐scale geological context as well as the search for possible traces of life. This method is therefore very useful for in situ planetary exploration missions. Compared with the myriad of sample preparation techniques available in terrestrial laboratories, the possibilities for sample preparation during in situ missions on other planetary bodies are extremely limited and are generally restricted to abrasion of rock surfaces or crushing of the target samples. Whereas certain techniques need samples to be prepared in powder form, such as X‐ray diffraction, this kind of preparation is not particularly suitable for optical microscopy and/or Raman spectroscopy. In this contribution, we examine the effects of powdering rock and mineral samples on optical observations and Raman analyses. We used a commercial Raman spectrometer, as well as a Raman laser spectrometer that simulates the instrument being developed for the future ExoMars 2018 mission. The commercial Raman spectrometer documents significant modifications to the spectra of the powdered samples, including broadening of the peaks and shifts in their position, as well as the appearance of new peaks. These effects are caused by localised heating of the sample under the laser beam and amplification of nominal surface effects due to the increase in surface area in finer grain sizes. However, most changes observed in the Raman spectra using the Raman laser spectrometer system are negligible because the relatively large (50 µm diameter) laser spot size produces lower irradiance. Furthermore, minor phases were more easily detectable in the powdered samples. Most importantly, however, this sample preparation method results in the loss of the textural features and context, making identification of potential fossilized microbial remains more problematic. Copyright © 2013 John Wiley & Sons, Ltd.     

Do formalin fixation and freeze‐thaw affect near‐infrared Raman spectroscopy of cartilaginous tissue? A preliminary ex vivo analysis of native human articular cartilage

Near‐infrared (NIR) Raman microprobe spectroscopy has been applied to the non‐invasive characterization of the biochemical structure of extracellular matrix in articular cartilage, a step forward along the path of in vivo diagnostic application of chondropathy. In most studies handling ex vivo cartilage specimens, formalin fixation or freeze‐thaw treatments have been applied in order to stabilize tissue and cell constituents prior to spectroscopic measurements. However, these pre‐processing manipulations might significantly affect certain target bands of the cartilage spectra, thus introducing biases in the characterizations, and potentially leading to data misinterpretation. In this study, we evaluated how formalin fixing and freeze‐thaw processes affect Raman spectra from human femur cartilage. Healthy cartilage specimens were fixed/stored either in a 10% neutral buffered formalin solution or in a deep freezer set at −80 °C. The results of this study show that formalin fixation significantly affects the NIR Raman spectra of cartilage specimens due to concurrent formalin absorption and water dehydration within both collagen and glycosaminoglycan macromolecules. Water dehydration was also confirmed in the amide I structure in the frozen‐thawed specimen, but to a much lesser extent. Furthermore, soaking the tissues in phosphate‐buffered saline solution minimized the storage‐induced Raman artifacts, but its immersion had limited effectiveness in formalin‐fixed specimens, predominantly due to an overlap of signals from the formalin liquid (i.e. emitting at 1046 and 1492 cm⁻¹). Therefore, to provide a highly accurate biochemical evaluation of extracellular matrix using NIR Raman spectroscopy, freeze‐thaw processes are more suitable for ex vivo samples of human cartilage than formalin fixation. Copyright © 2015 John Wiley & Sons, Ltd.     

Investigation of inter-molecular hydrogen bonding in the binary mixture (acetone + water) by concentration dependent Raman study and ab initio calculations

This paper reports that vibrational spectroscopic analysis on hydrogen-bonding between acetone and water comprises both experimental Raman spectra and ab initio calculations on structures of various acetone/water complexes with changing water concentrations. The optimised geometries and wavenumbers of the neat acetone molecule and its complexes are calculated by using ab initio method at the MP2 level with 6-311+G(d,p) basis set. Changes in wavenumber position and linewidth (fullwidth at half maximum) have been explained for neat as well as binary mixtures with different mole fractions of the reference system, acetone, in terms of intermolecular hydrogen bonding. The combination of experimental Raman data with ab initio calculation leads to a better knowledge of the concentration dependent changes in the spectral features in terms of hydrogen bonding.