Raman and infrared spectroscopy of the manganese arsenate mineral allactite

The mineral allactite [Mn(7)(AsO(4))(2)(OH)(8)] is a basic manganese arsenate which is highly pleochroic. The use of the 633 nm excitation line enables quality spectra of to be obtained irrespective of the crystal orientation. The mineral is characterised by a set of sharp bands in the 770-885 cm(-1) region. Intense and sharp Raman bands are observed at 883, 858, 834, 827, 808 and 779 cm(-1). Collecting the spectral data at 77K enabled better band separation with narrower bandwidths. The observation of multiple AsO(4) stretching bands indicates the non-equivalence of the arsenate anions in the allactite structure. In comparison the infrared spectrum shows a broad spectral profile with a series of difficult to define overlapping bands. The low wavenumber region sets of bands which are assigned to the nu(2) modes (361 and 359 cm(-1)), the nu(4) modes (471, 452 and 422 cm(-1)), AsO stretching vibrations at 331 and 324 cm(-1), and bands at 289 and 271 cm(-1) which may be ascribed to MnO stretching modes. The observation of multiple bands shows the loss of symmetry of the AsO(4) units and the non-equivalence of these units in the allactite structure. The study shows that highly pleochroic minerals can be studied by Raman spectroscopy.     

Thermal analysis and Hot-stage Raman spectroscopy of the basic copper arsenate mineral

The thermal analysis of euchroite shows two mass loss steps in the temperature range 100–105 °C and 185–205 °C. These mass loss steps are attributed to dehydration and dehydroxylation of the mineral. Hot-stage Raman spectroscopy (HSRS) has been used to study the thermal stability of the mineral euchroite, a mineral involved in a complex set of equilibria between the copper hydroxy arsenates: euchroite Cu₂(AsO₄)(OH)·3H₂O → olivenite Cu₂(AsO₄)(OH) → strashimirite Cu₈(AsO₄)₄(OH)₄·5H₂O → arhbarite Cu₂Mg(AsO₄)(OH)₃. HSRS inolves the collection of Raman spectra as a function of the temperature. HSRS shows that the mineral euchroite decomposes between 125 and 175 °C with the loss of water. At 125 °C, Raman bands are observed at 858 cm^?1 assigned to the ν₁ AsO₄ ^3? symmetric stretching vibration and 801, 822, and 871 cm^?1 assigned to the ν₃ AsO₄ ^3? (A₁) antisymmetric stretching vibrations. A distinct band shift is observed upon heating to 275 °C. At 275 °C, the four Raman bands are resolved at 762, 810, 837, and 862 cm^?1. Further heating results in the diminution of the intensity in the Raman spectra, and this is attributed to sublimation of the arsenate mineral. HSRS is the most useful technique for studying the thermal stability of minerals, especially when only very small amounts of mineral are available.     

Raman and infrared spectroscopy of arsenates of the roselite and fairfieldite mineral subgroups

Raman spectroscopy complimented with infrared spectroscopy has been used to determine the molecular structure of the roselite arsenate minerals of the roselite and fairfieldite subgroups of formula Ca(2)B(AsO(4))(2).2H(2)O (where B may be Co, Fe(2+), Mg, Mn, Ni and Zn). The Raman arsenate (AsO(4))(2-) stretching region shows strong differences between the roselite arsenate minerals which is attributed to the cation substitution for calcium in the structure. In the infrared spectra complexity exists with multiple (AsO(4))(2-) antisymmetric stretching vibrations observed, indicating a reduction of the tetrahedral symmetry. This loss of degeneracy is also reflected in the bending modes. Strong Raman bands around 450 cm(-1) are assigned to nu(4) bending modes. Multiple bands in the 300-350 cm(-1) region assigned to nu(2) bending modes provide evidence of symmetry reduction of the arsenate anion. Three broad bands for roselite are found at 3450, 3208 and 3042 cm(-1) and are assigned to OH stretching bands. By using a Libowitzky empirical equation hydrogen bond distances of 2.75 and 2.67 A are estimated. Vibrational spectra enable the molecular structure of the roselite minerals to be determined and whilst similarities exist in the spectral patterns, sufficient differences exist to be able to determine the identification of the minerals.     

Asbestos mineral analysis by UV Raman and energy-dispersive X-ray spectroscopy.

The applicability of a UV micro-Raman setup was assessed for the rapid identification of fibrous asbestos minerals using 257 and 244 nm laser light for excitation. Raman spectra were obtained from six asbestos reference standards belonging to two basic structural groups: the serpentines (chrysotile) and the amphiboles (crocidolite, tremolite, amosite, anthophyllite, and actinolite). The UV Raman spectra reported here for the first time are free from fluorescence, which is especially helpful in assessing the hydroxyl-stretching vibrations. The spectra exhibit sharp bands characteristic of each asbestos species, which can be used for the unambiguous identification of known and unknown asbestos fibres. Evident changes of the relative band intensities sensitively reflect the chemical substitutions that typically occur in asbestos minerals. The elemental composition of the asbestos reference samples was analysed by using a scanning electron microscope equipped with an energy-dispersive X-ray (EDX) spectrometer. The discussion of the experimental results in terms of EDX analysis sheds new light on the structural and vibrational consequences of cation distribution in asbestos minerals.     

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.     

Quantitative surface-enhanced Raman spectroscopy

The purpose of this tutorial review is to show how surface-enhanced Raman (SERS) and resonance Raman (SERRS) spectroscopy have evolved to the stage where they can be used as a quantitative analytical technique. SER(R)S has enormous potential for a range of applications where high sensitivity needs to be combined with good discrimination between molecular targets, particularly since low cost, compact spectrometers can read the high signal levels that SER(R)S typically provides. These advantages over conventional Raman measurements come at the cost of increased complexity and this review discusses the factors that need to be controlled to generate stable and reproducible SER(R)S calibrations.     

Raman spectroscopy in astrobiology

Raman spectroscopy is proposed as a valuable analytical technique for planetary exploration because it is sensitive to organic and inorganic compounds and able to unambiguously identify key spectral markers in a mixture of biological and geological components; furthermore, sample manipulation is not required and any size of sample can be studied without chemical or mechanical pretreatment. NASA and ESA are considering the adoption of miniaturised Raman spectrometers for inclusion in suites of analytical instrumentation to be placed on robotic landers on Mars in the near future to search for extinct or extant life signals. In this paper we review the advantages and limitations of Raman spectroscopy for the analysis of complex specimens with relevance to the detection of bio- and geomarkers in extremophilic organisms which are considered to be terrestrial analogues of possible extraterrestial life that could have developed on planetary surfaces.     

Filament-driven impulsive Raman spectroscopy

Vibrational Raman spectroscopy is performed in the gas phase using a femtosecond laser pulse undergoing filamentation as an impulsive excitation source. The molecular coherence induced by the filamentary pulse is subsequently probed using a narrowband, sub-picosecond laser pulse to produce Raman spectra of gas phase species in a few tens of milliseconds (~10 laser shots). Pulse shortening with concomitant spectral broadening during filamentation results in a pulse that is both sufficiently short and of sufficient spectral power density to impulsively excite the highest energy ground state vibrations (up to 4158 cm(-1) corresponding to H(2)). Gas phase detection of chloroform, methylene chloride, cyclohexane, toluene, pentane, triethylamine, ammonia, nitromethane, and gasoline is performed.     

Raman spectroscopy on zeolites

The zeolite Raman literature is reviewed, with an emphasis on zeolite structure and synthesis, adsorption and metal complex formation in zeolites     

Non-linear coherent Raman spectroscopy

A general introduction to several coherent Raman methods, which are based on the third-order non-linear susceptibility is given. These methods are described basically under a common point of view, which is the excitation of coherent molecular vibrations in the field of two strong laser beams operating at different frequencies. Most of these methods can be applied successfully also under electronic resonance conditions. As a particular example, studies of coherent anti-Stokes continuum resonance Raman scattering in iodine vapour will be presented and discussed in detail.     

Fourier transform Raman spectroscopy

The basic experimental aspects of Fourier transform Raman Spectroscopy are reviewed with an emphasis on detector technology. The sensitivity is comparable to dispersive Raman Spectroscopy using visible lasers. The ease of spectral subtraction is demonstrated and examples are given showing the elimination of fluorescence.     

Ionization-detected stimulated Raman spectroscopy

We report a new spectroscopic technique which we call “ionization-detected stimulated Raman spectroscopy” that combines the high sensitivity of resonant laser ionization methods with the high spectral resolution of stimulated Raman spectroscopy. A Q-branch spectrum of NO at 10 mTorr pressure illustrates an improvement in sensitivity of over 1000-fold compared to previous stimulated Raman methods.     

Frequency modulation Raman spectroscopy

A frequency modulation (FM) technique is described for elimination of the fluorescence background from Raman spectra of surfaces. The experimental apparatus is described, and theoretical considerations regarding the detection limits are presented and compared with experimental results.     

Raman spectroscopy in bioanalysis

Recent advances in instrument design have allowed researchers to use smaller, more efficient components in designing Raman spectrometers. Advances in instrumentation have increased the performance of Raman instruments and increased their usage in bioanalysis. This paper reviews recent improvements in instrument design and discusses several applications of Raman spectroscopy to diagnosis in biology, chemistry and medicine.     

Analytical applications of Raman spectroscopy

In this article interaction of transition metal complexes with DNA and its applications in electrochemical DNA biosensors as hybridization indicator or electroactive marker of DNA are reviewed. Special emphasis has been given to the efforts for the development of new transition metal complexes and their interaction to DNA. DNA and polymers covalently conjugated with transition metal complexes were also reviewed.