INFRARED SPECTRA OF PARTIALLY DEUTERATED CALCIUM SULFATE DIHYDRATE
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Date
1968
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Ohio State University
Abstract
Room and low temperature infrared spectra of thin films of calcium sulfate dihydrate, containing small percentages of hydrated OH and OD in $CaSO_{4}+2D_{2}O$ and $CaSO_{4}\cdot 2H_{2}O$, respectively, have been obtained between 3700 and $2300 cm^{-1}$ Based on probability theory, the two absorptions observed in the OH stretching region of the nearly deuterated hydrate have been assigned to intra- and intermolecularly uncoupled vibrations of the hydrated isotopic species HOD. It will be shown that these uncoupled bands arise from two physically different OH vibrations of a water molecule, which is distorted by its local environment in the crystal, and not from the presence of proton tunnelling in $CaSO_{4}\cdot 2H_{2}O$ as has been previously suggested. The same conclusions apply to the two uncoupled OD(HOD) absorptions observed in the OD stretching region of partially deuterated $CaSO_{4}\cdot 2H_{2}O$. The large observed splitting of the two uncoupled OH (and OD) absorptions indicates that the water molecule is distorted to a greater degree from $C_{2v}$ symmetry than is found in the neutron diffraction study of $CaSO_{4}\cdot2H_{2}O$.
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Author Institution: Department of Chemistry, Temple University of the Commonwealth System of Higher Education