High temperature Raman spectroscopy

In situ high-temperature Raman spectroscopy of melts along the Na2Si205—Na2Ti205 join performed by Mysen and Neuville (1995) has shown that the Raman spectra of Ti-bearing glasses and melts are consistent with Ti(IV) in at least three different structural positions ... 

Gilbert et al. (1975) developed a special cell and furnace design for high temperature Raman spectroscopy, which was later substantially improved by Gilbert and Mateme (1990). The cell is a modified version of the windowless cell used by Young (1964) for UV and visible spectroscopy. The graphite windowless cell is shown in Figure 10.4. The amount of pre-melted solid mixture added to the cell was adjusted so that all the formed liquid has to be retained in the space in between the windows and no melt is... 

P.F. McMillan, B.T. Poe, P.H. Gillet, and B. Reynard, A study of Si02 glass and supercooled liquid to 1950 K via high-temperature Raman spectroscopy. Geochim. Cosmochim. Acta 58, pp. 3653-3664 (1994). 

Pomfret MB, Owrutsky JC, Walker RA (2006) High-temperature Raman spectroscopy of solid oxide fuel cell materials and processes. J Phys Chem B 110(35) 17305-17308... 

High-Temperature and High-Pressure Raman Spectroscopy... 

Abstract Molecular spectroscopy is one of the most important means to characterize the various species in solid, hquid and gaseous elemental sulfur. In this chapter the vibrational, UV-Vis and mass spectra of sulfur molecules with between 2 and 20 atoms are critically reviewed together with the spectra of liquid sulfur and of solid allotropes including polymeric and high-pressure phases. In particular, low temperature Raman spectroscopy is a suitable technique to identify single species in mixtures. In mass spectra cluster cations with up to 56 atoms have been observed but fragmentation processes cause serious difficulties. The UV-Vis spectra of S4 are reassigned. The modern XANES spectroscopy has just started to be applied to sulfur allotropes and other sulfur compounds. 

High-pressure and —temperature Raman spectroscopy was used to study carbonate ions in aqueous solution in the ranges 1-30 GPa and 25-400°C.353 IR and Raman spectra were used to study the pressure-induced phase transition (2.8 GPa) for KHC03.354... 

Raman spectroscopy was used to characterise densely-assembled Ti02 nanorods (diameters 150-200 nm).37 High-temperature Raman spectra of nanocrystalline Ti02 powders (25-1200°C) were used to monitor temperature-dependent effects on the samples.38 The effects of UV irradiation on the structure of sol-gel Ti02 films were followed by IR and Raman spectroscopy.39... 

It is well known that variable-temperature Raman spectroscopy is a useful technique for the investigation of the rotational isomerism of substituted di- or oligosilanes as the frequencies of skeletal modes are usually highly sensitive to the conformation around Si-Si bonds. Energy differences between rotational Isomers can then be determined from variable-temperature spectra by applying van t Hoff s equation ... 

Laser Raman diagnostic teclmiques offer remote, nonintnisive, nonperturbing measurements with high spatial and temporal resolution [158], This is particularly advantageous in the area of combustion chemistry. Physical probes for temperature and concentration measurements can be debatable in many combustion systems, such as furnaces, internal combustors etc., since they may disturb the medium or, even worse, not withstand the hostile enviromnents [159]. Laser Raman techniques are employed since two of the dominant molecules associated with air-fed combustion are O2 and N2. Flomonuclear diatomic molecules unable to have a nuclear coordinate-dependent dipole moment caimot be diagnosed by infrared spectroscopy. Other combustion species include CFl, CO2, FI2O and FI2 [160]. These molecules are probed by Raman spectroscopy to detenuine the temperature profile and species concentration m various combustion processes. 

Chronister E L and Crowell R A 1991 Time-resolved coherent Raman spectroscopy of low-temperature molecular solids in a high-pressure diamond anvil cell Chem. Phys. Lett. 182 27... 

Because Raman spectroscopy requires one only to guide a laser beam to the sample and extract a scattered beam, the technique is easily adaptable to measurements as a function of temperature and pressure. High temperatures can be achieved by using a small furnace built into the sample compartment. Low temperatures, easily to 78 K (liquid nitrogen) and with some diflSculty to 4.2 K (liquid helium), can be achieved with various commercially available cryostats. Chambers suitable for Raman spectroscopy to pressures of a few hundred MPa can be constructed using sapphire windows for the laser and scattered beams. However, Raman spectroscopy is the characterizadon tool of choice in diamond-anvil high-pressure cells, which produce pressures well in excess of 100 GPa. ... 

Pressure-induced phase transitions in the titanium dioxide system provide an understanding of crystal structure and mineral stability in planets interior and thus are of major geophysical interest. Moderate pressures transform either of the three stable polymorphs into the a-Pb02 (columbite)-type structure, while further pressure increase creates the monoclinic baddeleyite-type structure. Recent high-pressure studies indicate that columbite can be formed only within a limited range of pressures/temperatures, although it is a metastable phase that can be preserved unchanged for years after pressure release Combined Raman spectroscopy and X-ray diffraction studies 6-8,10 ave established that rutile transforms to columbite structure at 10 GPa, while anatase and brookite transform to columbite at approximately 4-5 GPa. 

Rahn L. A., Palmer R. E. Studies of nitrogen self-broadening at high temperature with inverse Raman spectroscopy, J. Opt. Soc. Am. B 3, 1164-9 (1986). 

The large energy differences between the global minimum structure of C2v symmetry and the other isomers indicate that equilibrium sulfur vapor will contain only minute amounts of the latter, even at very high temperatures. However, under non-equilibrium conditions as in electrical discharges or by illumination with a laser as in Raman spectroscopy unstable isomers may be formed and detected. 

At least five high-pressure allotropes of sulfur have been observed by Raman spectroscopy up to about 40 GPa the spectra of which differ significantly from those of a-Sg at high pressures photo-induced amorphous sulfur (a-S) [57, 58, 109, 119, 184-186], photo-induced sulfur (p-S) [57, 58, 109, 119, 184, 186-191], rhombohedral Se [58, 109, 137, 184, 186, 188, 191], high-pressure low-temperature sulfur (hplt-S) [137, 184, 192], and polymeric sulfur (S ) [58, 109, 119, 193]. The Raman spectra of two of these d-lotropes, a-S and S, were discussed in the preceding section. The Raman spectra of p-S and hplt-S have only been reported for samples at high-pressure conditions. The structure of both allotropes are imknown. The Raman spectrum of Se at STP conditions is discussed below. 

The species S3 (absorbing at 420 nm) and S4 (absorbing at 530 nm) have been detected by reflection spectra in the condensate but the formation of S4 is unexplained [16]. S3 and SO2 have also been observed by Raman spectroscopy in such samples [15] (the expected S4 Raman line at 678 cm was probably obscured by the SS stretching mode of S2O at 673 cm but a shoulder at the high-frequency side of the S2O line indicates that some S4 may have been present). While the reddish colors turn yellow on warming at about -120 °C, the sulfur radicals could be observed by ESR spectroscopy up to 0 °C [10]. If the condensation of S2O gas is performed very slowly at -196 °C the condensate is almost colorless and turns red only if the temperature is allowed to increase slowly. Hence, it has been suspected that S2O is actually colorless like SO2. 

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