Variable temperature Raman cell

Raman spectroscopy has been used frequently to investigate the chemisorption of probe molecules (Cooney et al., 1975 Weber, 2000). Several groups reported variable Raman cells in which the temperature of the sample and the environment can be controlled so that catalytic reaction conditions can be simulated (Abdelouahab et al., 1992 Brown et al., 1977 Chan and Bell, 1984 Cheng et al., 1980 Lunsford et al., 1993 Mestl et al., 1997a Vedrine and Derouane, 2000). In these investigations, conversion and selectivity values were not measured simultaneously with the spectra. The developments of these Raman experiments have been reviewed elsewhere (Banares, 2004 Knozinger and Mestl, 1999 Vedrine and Derouane, 2000). 

Abdullah and Sherman (1980) have described a variable temperature one-window high pressure cell. Raman spectra of four different phases of NH4Br illustrate the applicability of this cell for 180 ° Raman scattering studies. 

The formation of peroxide and superoxide on Fe,H/MFI compared with Fe/MFI also shows two distinguishing features. First, the amount of peroxide on Fe,H/MFI at room temperature is significantly greater than on Fe/MFI, as determined by the peroxide peak intensity relative to the intensities of the zeolite bands (52). Second, on Fe,H/MFI, peroxide is converted to superoxide when the sample temperature is lowered to 93 K, and then restored when the temperature is returned to 300 K. Figure 8 shows an overlay of Raman spectra characterizing Fe,H/MFI measured at 300 and at 93 K using 2. The band at 703 cm ( 02 ) decreases at 93 K relative to its intensity at 300 K, whereas the intensity near 1090cm ( Oj) shows the opposite behavior with temperature. In the spectrum of Fe/MFI, the relative peak intensities of peroxide and superoxide remain constant with temperature between 93 and 300 K. (A specialized variable-temperature fluidized-bed Raman cell was constructed for these experiments.)... 

One of the remarkable demonstrations of the capabilities of ultraviolet Raman spectroscopy to probe extremely thin ferroelectric oxide layers reported so far has been its application for studies of ultrathin BaTi03 films [48]. In order to investigate the size effect on the ferroelectric phase transitions, variable temperature UV Raman spectroscopy was applied to studies of a series of BaTi03 films with layer thicknesses varied from 1.6 to 10 nm (4—25 unit cells). 

The dilferent case studies presented here show how a variable-temperature reflectance spectroelectrochemical cell provides the versatility to carry out studies of UV-Vis electronic spectra, IR spectra, and resonance Raman spectra of inorganic and organic compounds in a multiplicity of different redox states. A key finding is that when rates of intramolecular electron transfer in mixed-valence states approach the ultrafast timescale of IR line-... 

Variable temperature spectroscopy, both IR and Raman, can be achieved either by using a variable temperature cell or chamber in a standard spectrometer or by including a variable temperature stage when using an IR or Raman microscope. Variable temperature cells for FT-IR use DRIFTS... 

Another optical arrangement for Raman mapping has proved to be convenient for a variety of cumbersome surface samples and holders, such as variable temperature or pressure cells. The focused laser spot is scanned over the stationary sample and the spectra recorded in sequence. This method is achieved by a new kind of transfer optics placed between the microscope and the spectrometer, which enables an optimized coupling. The coupling optics consist of a pair of lenses. One lens, optically coupled to the back aperture of the objective, can be moved in two orthogonal directions perpendicular to the laser beam. Thus, this lens can focus the light beam on any point... 

The development of variable temperature />i sim spcclroelcctrochemical techniques has enabled us to probe the electronic characteristics of the frontier orbitals of redox-active materials. The important feature of these methods is that the electrosynihesiscd species is generated inside the cavity of the spectrometer. Thus the electron transfer product, which is usually air and/or moisture sensitive, can be studied directly by the chosen spectroscopic method without the necessity of transporting the unstable solution from the eicctrosynthesis cell to the spectrometer. Most spectroscopic methods can be coupled with electrochemical techniques, for example, infrared, raman, resonance raman, uv/vis, epr have all been reported ... 

Earlier studies [24,25] have shown that in addition to the concentration of organic species, temperature is the most significant variable controlling the kinetics of the citric acid-H20 system. Cody et al. [25] further show that for a given citric acid concentration, the system exhibits a very complex behavior at high P and T. These studies have described the behavior of the system under hydrothermal conditions in detail and have formed the basis for interpretation of these diamond cell experiments. In this study, we have used in-situ Raman... 

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