Dah-Chung Shieh

Correlation of framework Raman bands of zeolites with structure

A correlation is developed between the ring sizes and average T-O-T angles present in zeolites, with the prominent oxygen-bending frequency observed in the Raman spectra of these materials. Based on this correlation, predictions are made about the structure of a synthetic, magadiite-type aluminosilicate mineral.

Raman spectroscopic studies of the tetramethylammonium ion in zeolite cages

Abstract The skeletal Raman modes of tetramethylammonium ions are influenced by the size of the zeolite cages in which they are trapped. These changes in the Raman spectra are used to study the role of this cation in the synthesis of the zeolite ZK-4.

Raman Spectral Study of the Composition of Basic Silicate Solutions

Raman spectral data are reported for silicate solutions at varying hydroxide ion concentrations. The gradual change in the spectra is explained as being due to various monomeric, dimeric, cyclic, and polymeric silicate species in solution. Band assignments are made by comparison with the Raman spectra of phosphates and crystalline silicate minerals.

Influence of alkali chlorides on distribution of aqueous base solubilized silicate species

Abstract Monomeric, dimeric, trimeric and tetrameric silicate species were found in alkali (Li, Na, K, Cs) hydroxide solubilized silicates by laser Raman spectroscopy. Alkali chlorides promote condensation of these silicate species in solution. A siliceous precipitate whose Raman spectrum resembled that of alkali disilicate glasses was formed upon addition of LiCl to 1 M silicate solutions. This precipitate could be redissolved and the Raman spectrum indicated that it did so by hydrolysis into smaller silicate species. This study shows that, besides hydroxide ion, alkali cations can be used to control the degree of polymerization of aqueous silicate solutions and that Raman spectroscopy provides a convenient probe to monitor such changes.

Partition Coefficients of Biologically Important Pyrimidines and Purines [1]

Abstract Partition coefficients of sixteen biologically important pyrimidines and purines between an organic phase and water have been determined and the best organic solvents for their extraction have been suggested.