Raman spectroscopy spectral range

Since the vibrational spectra of sulfur allotropes are characteristic for their molecular and crystalline structure, vibrational spectroscopy has become a valuable tool in structural studies besides X-ray diffraction techniques. In particular, Raman spectroscopy on sulfur samples at high pressures is much easier to perform than IR spectroscopical studies due to technical demands (e.g., throughput of the IR beam, spectral range in the far-infrared). On the other hand, application of laser radiation for exciting the Raman spectrum may cause photo-induced structural changes. High-pressure phase transitions and structures of elemental sulfur at high pressures were already discussed in [1]. 

In either case, the information on the vibrational transition is contained in the energy difference between the excitation radiation and the inelastically scattered Raman photons. Consequently, the parameters of interest are the intensities of the lines and their position relative to the Rayleigh line, usually expressed in wavenumbers (cm 1). As the actually recorded emissions all are in the spectral range determined by the excitation radiation, Raman spectroscopy facilitates the acquisition of vibrational spectra through standard VIS and/or NIR spectroscopy. 

A spectroscopic technique that is associated with the enhancement of Raman line intensities upon photon absorption in the electronic spectral range corresponding to an absorption peak. See Raman Spectroscopy... 

With few exceptions, all investigations of matrix-isolated reactive intermediates are done by absorption spectroscopy, in the UV-vis and/or in the IR spectral range, or, in the case of open-shell species, by ESR. Occasionally, one also finds studies where emission or Raman scattering of reactive intermediates is probed in matrices, but these studies are few and far between, so we will focus in this section on the first group of techniques that can be easily implemented with commercially available equipment. 

Table 12.2 summarizes these and other selected Raman spectroscopy studies. Most published accounts utilize the same spectral range ( 300-l 800 cm-1), and thus specific ranges are not specified here. 

The same general principle that applies for intrinsic fluorescence should hold true for Raman spectroscopy as well. Unlike in fluorescence spectroscopy, spectral distortion owing to prominent absorbers is less of an issue in the NIR wavelength range. However, for quantitative analysis the turbidity-induced sampling volume variations become very significant and usually dominate over spectral distortions. 

UV-Visible and Raman Spectroscopies. In situ UV-visible absorption spectra of a 5000 A PPy-GOD film, which was formed on an ITO coated glass, were recorded in the PB solution (pH 7.4). The spectra recorded at both the oxidation (0.4 V) and the reduction (-1.0 V) potentials showed an absorption peak near 380 nm, which is due to the PPy. When the PPy was reduced at -1.0 V, the absorbance in the wavelength range of 500-800 nm decreased, and the absorbance at 380 nm increased. The observed spectral changes of the PPy-GOD film during the redox reaction were similar to those of the PPy film doped with C104" (PPy-C104) (27). 

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