Matrix Raman spectroscopy

Matrix Raman spectroscopy allows detection of some additional vibrations which are inactive in IR spectra (e.g. symmetrical vibrations vi in AB3 molecules having 3 symmetry) or which tie in the far infrared region. In practice, matrix-isolated organic intermediates have not been studied by Raman spectroscopy the main objects of these investigations are inorganic molecules (AICI3, PbS, Gep2, SiO, etc.) which are evaporated from solids in effusion cells. 

The experimental setup for matrix Raman spectroscopy is essentially the same as that for matrix IR spectroscopy. The major difference lies in optical geometry. Namely, backscattering geometry must be employed in Raman spectroscopy since the matrix gas and sample vapor are deposted on a cold metal (Cu, Al) surface. Figure 3-27 shows the optical arrangement... 

A subsequent investigation using matrix Raman spectroscopy confirmed the submillisecond timescale for tautomer interconversion but led to the conclusion that even this was slow compared to theoretical expectations.It was therefore suggested that the matrix environment, including the CO and COj... 

The 24 (10 + 14) electron systems cannot be of geomet. Honea et al. [12] prepared and isolated Si by low-energy deposition into a solid nitrogen matrix, and showed by Raman spectroscopy that the octahedron is distorted, in agreement with... 

Raman spectroscopy of matrix-isolated molecules carries some difficulties conneeted with the possibility of local heating of the matrix under laser irradiation. Besides, because of the relatively low intensity of Raman bands, higher concentrations of the species to be studied are needed in the matrix (the ratio of matrix gas to reagent = 100-500). As a result, the effective isolation of reactive intermediates is prevented. 

When investigating opaque or transparent samples, where the laser light can penetrate the surface and be scattered into deeper regions, Raman light from these deeper zones also contributes to the collected signal and is of particular relevance with non-homogeneous samples, e.g., multilayer systems or blends. The above equation is only valid, if the beam is focused on the sample surface. Different considerations apply to confocal Raman spectroscopy, which is a very useful technique to probe (depth profile) samples below their surface. This nondestructive method is appropriate for studies on thin layers, inclusions and impurities buried within a matrix, and will be discussed below. 

A recently developed field of research is matrix isolation laser Raman spectroscopy 214a)-d) which allows the study of vibrational Raman spectra with high resolution. Even small isotopic frequency shifts or the influence of crystal structure on the vibrational frequencies may be determined with high precision. This provides an effective constraint on intermolecular forcefields. 

In natural melts, the presence of high field strength ions such as Fe , TF, and P, which, like silicon, preferentially assume a tetrahedral coordination with oxygen, complicates the structure, and the constitution of the anion matrix may not be deduced on the basis of the equations in section 6.1.2. Structural parameters valid for compositionally complex melts were proposed by Mysen et al. (1980) and Virgo et al. (1980) on the basis of the results of Raman spectroscopy. These parameters are NBO/Si and NBO/T (NBO = Non-Bridging Oxygen T groups all tetrahedrally coordinated cations—i.e., Fe ", TF, P ", ... 

One of the greatest advantages of matrix isolation IR (or Raman) spectroscopy is that vibrational bands are inherently very narrow, because rotations are largely suppressed, which means that much more detailed information can be obtained than in the liquid phase at room temperature. However, this additional information can only be obtained if the spectrometer offers high enough resolution, which in the case of interferometers translates into sufficient displacement of the movable mirror. For most practical purposes, a resolution of 1 cm is adequate for matrix work, altough it is good to have 0.5-cm resoution available in case one needs it, say, for the elucidation of site structures. 

For appropriate comprehension of morphology and the concomitant structure-property correlations in nanocomposites, knowledge of the state and extent of nanofiller dispersion in the matrix is of paramount importance. Numerous methods have been reported in the literature in this regard, for instance, WAXD [6, 38], SAXS [8, 39], SANS [40], SEM, [6, 41], AFM [7, 42], HRTEM, STEM, EELS [43], SSNMR [44], EPRS [45], UV/vis/NIR, FTIR [46], Raman spectroscopy... 

Raman spectroscopy is well suited for examining calcified tissues such as bones and teeth owing to its ability to probe both the inorganic and organic constituents of the tissue. The frequency and band shape of the symmetric and asymmetric phosphate stretching vibrations provide critical information on the crystallinity and orientation of the hydroxyapatite matrix. The analysis of a Raman spectrum of dental enamel provides features that are highly characteristic of the health and integrity of the tissue. 

The first subsurface bone tissue Raman spectroscopic measurements were performed using picosecond time-resolved Raman spectroscopy on excised equine cortical bone [56, 57], In these experiments it was shown that a polystyrene backing could be detected through 0.3 mm of bone. The same picosecond technology was used to perform the first transcutaneous Raman spectroscopic measurements of bone tissue [58]. In this study, the cortical bone mineral/matrix ratios of excised limbs of wild type and transgenic (oim/oim) mice were compared and the differences demonstrated. 

Abstract Raman spectroscopy can potentially offer a non-invasive, information rich biochemical snap-shot of living human cells, tissues or material-cell tissue constructs rapidly (seconds-minutes), without the need of labels or contrast enhancers. This chapter details the exciting potential and challenges associated with the use of this analytical technique in tissue engineering (TE). The use of Raman spectroscopy in three intricately linked areas of TE will be considered (1) the characterisation of the various scaffolds and smart materials, (2) the biochemical analysis of cellular behaviour important in TE (e.g. differentiation) and (3) the use of Raman spectroscopy for the analysis of tissue/extra-cellular matrix (ECM) formation in vitro or possibly in vivo. 

A clever way to minimize the unwanted background from the cover plate or the environment is combining laser tweezers and confocal Raman spectroscopy (LTRS) [73, 74], While the single cells are levitated well off the surface and held in the focus of the laser beam the Raman spectral patterns of these cells are recorded with high sensitivity. Another appealing fact is the usage of one laser for both Raman excitation and optical trapping to keep the instrumental efforts as low as possible. Additionally the trapped cells can also be micro-manipulated and moved from one place to another, e.g., from the native matrix to a clean collection chamber. 

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