Hydration number Raman

Uchida, T. Hirano, T. Ebinuma, T. Narita, H. Gohara, K. Mae, S. Matsumoto, S. (1999a). Raman spectroscopic determination of hydration number of methane hydrates AIChEJ., 45 (12), 2641-2645. 

Sum measures hydrate composition and hydration number using Raman spectroscopy... 

Structure identification and relative cage occupancies. The hydration number and relative cage occupation for pure components and guests were measured by Sum et al. (1997), Uchida et al. (1999), and Wilson et al. (2002). Raman guest spectra of clathrate hydrates have been measured for the three known hydrate crystal structures si, sll, and sH. Long (1994) previously measured the kinetic phenomena for THF hydrate. Thermodynamic sl/sll structural transitions have been studied for binary hydrate systems (Subramanian et al., 2000 Schicks et al., 2006). 

Infrared and Raman spectroscopy have very wide applications and have proved an important source of information on ion-solvent interactions and hydration numbers. In general, the position of an absorption enables a guess to be made for the hydration numbers, h+ and h-. Since spectroscopic techniques deal with frequencies associated with coordinative bonding between the ion and the solvent, such techniques furnish information about the strength of the ion-solvent interactions in the primary solvation. 

Spectroscopic methods. Hydration numbers have been inferred from comparisons of the characteristics of the absorption and the Raman spectra of lanthanide ions in aqueous solution and in crystalline hydrates of known structure (Freed 1942, Krumholz 1958). For the region of 9/2 transitions in... 

Hydration studies for higher oxidation state actinides are reported for some AnOj salts (UO2 or NpO ) but not for any AnOj systems. The Raman spectra of aqueous uranyl solutions were interpreted to show the presence of six water molecules coordinated in the primary plane perpendicular to the O-U-O axis (Sutton 1952). However, similar hydration numbers have been obtained by methods in which the secondary hydration shell may also contribute to the value. For example, the activity coefficient measurements suggest a hydration number of 7.4 [relative to an assumed hydration number of zero for Cs(I) (Hinton and Amis 1971)]. Similarly, a hydration number of seven has been derived from Gusev s conductivity method (Gusev 1971, 1972,1973). 

Principal component analysis has been used in combination with spectroscopy in other types of multicomponent analyses. For example, compatible and incompatible blends of polyphenzlene oxides and polystyrene were distinguished using Fourier-transform-infrared spectra (59). Raman spectra of sulfuric acid/water mixtures were used in conjunction with principal component analysis to identify different ions, compositions, and hydrates (60). The identity and number of species present in binary and tertiary mixtures of polycycHc aromatic hydrocarbons were deterrnined using fluorescence spectra (61). 

Physical measurements are directly input to the statistical thermodynamics theory. For example three-phase hydrate formation data, and spectroscopic (Raman, NMR, and diffraction) data were used to determine optimum molecular potential parameters (e,o,a) for each guest, which could be used in all cavities. By fitting only a eight pure components, the theory enables predictions of engineering accuracy for an infinite number of mixtures in all regions of the phase diagram. This facility enables a substantial savings in experimental effort. 

With respect to the third assumption, for a number of years, Tanaka has shown that the internal particle partition function of the guest molecules differ significantly in the cages, with restricted rotation and vibration, particularly for those molecules larger than methane. Indeed, some restriction on such motions is the basis, for example, in Raman spectroscopic determination of differing environments of the methane molecule, in the gas, in solution, and in the hydrate cages. ... 

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